Andersson et al., 2011

21 Pages·2017·3.76 MB·English

©2017.PublishedbyTheCompanyofBiologistsLtd|Development(2017)144,1743-1763doi:10.1242/dev.148007
REVIEW
The developmental biology of genetic Notch disorders
JanMašekandEmmaR.Andersson*
ABSTRACT ADAMsecretaseandtheγ-secretasecomplex,resultinginreleaseof
the Notch intracellular domain (NICD), which translocates to the
Notch signaling regulates a vast array of crucial developmental
nucleuswhereitactstogetherwithRBPJκandMAMLtoactivate
processes. It is therefore not surprising that mutations in genes
transcription. The process is further fine-tuned by numerous post-
encodingNotchreceptorsorligandsleadtoavarietyofcongenital
translationalmodificationsofbothreceptorsandligands,andviaco-
disordersinhumans.Forexample,lossoffunctionofNotchresultsin
activatorsorinhibitorsthatfunctionateverylevelofthe,deceptively
Adams-Oliver syndrome, Alagille syndrome, spondylocostal
simple,signalingpathway(Anderssonetal.,2011;Bray,2016).
dysostosis and congenital heart disorders, while Notch gain of
Mutations in components of the Notch family are generally
function results in Hajdu-Cheney syndrome, serpentine fibula
constrained by the pathway’s essential developmental functions,
polycystic kidney syndrome, infantile myofibromatosis and lateral
although mutations that confer grave congenital disorders and
meningocelesyndrome.Furthermore,structure-abrogatingmutations
fitness costs have been identified (Table 1). The discovery of
in NOTCH3 result in CADASIL. Here, we discuss these human
congenital diseases related to defective Notch signaling began in
congenitaldisordersinthecontextofknownrolesforNotchsignaling
1996, with the linkage analysis-based discovery of mutations on
during development. Drawing on recent analyses by the exome
chromosome 19, more specifically NOTCH3 mutations, in
aggregation consortium (EXAC) and on recent studies of Notch
individuals diagnosed with CADASIL (cerebral autosomal
signalingin modelorganisms,wefurther highlight additionalNotch
dominant arteriopathy with subcortical infarcts and
receptorsorligandsthatarelikelytobeinvolvedinhumangenetic
leukoencephalopathy)(Jouteletal.,1996).Soonafter,twogroups
diseases.
showedthatJAG1wasthegenewithinchromosome20p12thatwas
KEYWORDS:Adams-Oliversyndrome,Alagille,CADASIL,Notch, responsibleforAlagillesyndrome(Lietal.,1997;Odaetal.,1997).
Development,Genetics Sincethen,severalinheriteddisorderscausedbymutationsinNotch
genes have been identified (Table 1). Prior to these discoveries,
Introduction chromosomal rearrangement of human NOTCH1 and viral
Notchsignalingaroseinmetazoans(Gazaveetal.,2009;Richards integration into murine Notch4 had been shown to induce T-ALL
and Degnan, 2009) and is considered one of the core signaling and mammary tumors, respectively (Ellisen et al., 1991;
pathways that controls embryonic development. Indeed, from Uyttendaele et al., 1996), highlighting a key role for Notch in
sponges and roundworms to mice, Notch signaling controls cancer(reviewedbyNowellandRadtke,2017).
multiple crucial processes during development (Andersson et al., ManyofthecongenitaldiseaseslinkedtotheNotchpathwayare
2011).Importantly,sincethediscoveryofamutantflywithnotched rare, with prevalences of just afew per 100,000, emphasizing just
wings, earning the gene the name Notch (N), over 100 years ago howcrucialNotchsignalingcomponentsaretohumansurvival,but
(Dexter, 1914), and the subsequent identification of the genomic alsopresentingserioushurdlestostudyingtheimpactofthesegenes
region responsible (Morgan, 1917), a wealth of studies – ranging in humans. Fortunately, the generation of knockout mice and the
fromtheelucidationoftheNotchpathway(reviewedbyBray,2016; studyofotheranimalmodelshaveprovidedresearcherswithample
KopanandIlagan,2009),tothegenerationofknockoutsinmodel information regarding Notch gene function, allowing the role of
organisms and the discovery of Notch genes mutated in humans specificNotchcomponentsinhumandevelopmentanddiseasetobe
(Gridley, 2003) – has confirmed an essential role for Notch teased apart. In this Review, we describe Notch-driven human
signalinginhumandevelopment. congenital diseases in light of our current knowledge regarding
DifferentspecieshavedistinctrepertoiresofNotchreceptorsand Notchgenefunctioninanimalmodels.TheNotchpathwayhasbeen
ligands (Fig. 1 and Gazave et al., 2009). Humans, for example, implicatedinthedevelopmentofmostorgans,andacomprehensive
express four Notch receptors (NOTCH1-NOTCH4) and five review of Notch control of embryonic development is not in the
different Notch ligands (JAG1 and JAG2, and DLL1, DLL3 and scope of this Review. Rather, we focus on the developmental
DLL4)(Fig.2),whereasfruitflieshaveonereceptor(Notch)andtwo processes underlying the pathologies manifested in Notch-related
ligands (Delta and Serrate). Pathway activation typically occurs congenital disorders, and discuss future routes of research to
whenamembrane-boundheterodimericsingle-passNotchreceptor discoverwhichunknownpathologiesmaybeNotchrelated.Wealso
interacts with a Notch ligand on a contacting cell (Fig. 3). This discuss recent ‘big data’ analyses of whole-exome and whole-
interaction leads to a series of proteolytic cleavages, mediated by genome sequencing that have revealed the presence or absence of T
N
mutations in Notch components in the human population,
E
confirmingthatspecificNotchcomponentsareessentialtospecies M
KarolinskaInstitutet,Huddinge14183,Sweden.
fitness(Table2)andpresentingexcitingfutureavenuesofresearch.
P
*Authorforcorrespondence([email protected]) O
Adams-Oliversyndrome:rolesforNOTCH1,DLL4andRBPJk L
J.M.,0000-0003-2904-3808;E.R.A.,0000-0002-8608-625X E
inhumandevelopment V
ThisisanOpenAccessarticledistributedunderthetermsoftheCreativeCommonsAttribution Prior to the 1940s, children born with underdeveloped upper or E
License(http://creativecommons.org/licenses/by/3.0),whichpermitsunrestricteduse, D
distributionandreproductioninanymediumprovidedthattheoriginalworkisproperlyattributed. lowerextremitiesweredefinedashavingcongenitalamputations,a
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REVIEW Development(2017)144,1743-1763doi:10.1242/dev.148007
A B
70 H.sapiens/DLL1
100 H. sapiens/NOTCH2 90 M. musculus/Dll1
47 M. musculus/Notch2
99 G. gallus/Dll1
100 X. tropicalis/Notch2
95 D. rerio/Dla
G. gallus/Notch2
51 97 D. rerio/Dld
53 D. rerio/Notch2
D. rerio/Dll4
D. rerio/Notch3
X. tropicalis/Dll4
X. tropicalis/Notch3 96
99 27 G. gallus/Dll4
76 89 H. sapiens/NOTCH3 70 H. sapiens/DLL4
100 M. musculus/Notch3 93
100 M. musculus/Dll4
80 D. rerio/Notch1b
81 X. tropicalis/Dlc
D. rerio/Notch1a
D. rerio/Dlb
70 100 X. tropicalis/Notch1 7647 D. rerio/Dlc
G. gallus/Notch1
94 H. sapiens/DLL3
64 H. sapiens/NOTCH1 90 100 M. musculus/Dll3
100 M. musculus/Notch1
D. melanogaster/Delta
H. sapiens/NOTCH4
D. melanogaster/Serrate
100 M. musculus/Notch4
100 H. sapiens/JAG2
D. melanogaster/Notch 51
84 M. musculus/Jag2
C. elegans/LIN-12 93 G. gallus/Jag2
100 C. elegans/GLP-1 83 82
X. tropicalis/Jag2
0.20 37 D. rerio/Jag2b
90 89 D. rerio/Jag1a
D. rerio/Jag1b
92 G. gallus/Jag1
X. tropicalis/Jag1
89
H. sapiens/JAG1
51
99 M. musculus/Jag1
C. elegans/APX-1
100 C. elegans/ARG-1
C. elegans/DSL-4
C. elegans/LAG-2
CC. elegans/DSL-2
43 33 C. elegans/DSL-1
91 C. elegans/DSL-7
28 C. elegans/DSL-3
C. elegans/DSL-5
51
58 C. elegans/DSL-6
0.5
Fig.1.TheevolutionofNotchreceptorsandligands.ProteinsequencesofNotchreceptors(A)andligands(B)werealignedusingmultiplesequence
alignmentbyMAFFTL-INS-Ianddefaultparameters(http://www.genome.jp/tools/mafft/).Theevolutionaryhistorywasinferredusingthemaximumlikelihood
methodbasedontheJTTmatrix-basedmodel(Jonesetal.,1992).Thepercentageoftreesinwhichtheassociatedtaxaclusteredtogetherisshownnexttothe
branches.Initialtree(s)fortheheuristicsearchwereobtainedautomaticallybyapplyingneighbor-joinandBioNJalgorithmstoamatrixofpairwisedistances
estimatedusingaJTTmodel,andthenselectingthetopologywithsuperiorloglikelihoodvalue.Thetreesaredrawntoscale,withbranchlengthsmeasuredinthe
numberofsubstitutionspersite.Allpositionscontaininggapsandmissingdatawereeliminated.Therewereatotalof940positionsinthefinaldatasetAand163
inB.EvolutionaryanalyseswereconductedinMEGA7(Kumaretal.,2016).GroupsofvertebratereceptorsandligandsclusteringwithindividualhumanNOTCH
receptorsandJAGGEDandDLLligandsareenclosedinseparatebrackets.Foraccessionnumbers,pleaseseeTableS1.
condition now known as terminal transverse limb deficiencies. congenita)andapartialabsenceofskullbones(Fig.4A).Theskinis
These defects were attributed to amniotic band or umbilical cord most significantly affected in the skull region, though the aplasia
constrictionoftheextremities(amnioticbandsyndrome).In1945, cutiscongenitamayalsoaffecttheskinontheabdomen.Typically,
ClarencePaulOliverandForrestH.Adamsdescribedapatientwith bybirth,theaffectedskinregionresembleshealedbutscarredskin,
anomaliesinthefeetandonehand,andalsoadenudedareaofthe and a skin biopsy reveals absent epidermis, dermal atrophyand a
scalp, with a thinner skull. Most importantly, they showed that lackofskinstructuresandelasticfibers.However,symptomsrange T
N
multiplefamilymembershadsimilarsymptoms,andsuggestedthat from acomplete absence of skin to patches of skin that lack hair.
E
theconditionwashereditary(AdamsandOliver,1945).Sincethen, Similarly,skullsymptomsmayrangefromanabsenceofskulltoa M
the diagnosis, genetics and underlying biology of Adams-Oliver near-normal skull (Lehman et al., 1993). In addition, some P
syndrome,asithascometobeknown,hasbecomemorecomplex. individuals have vascular anomalies, including dilated surface O
blood vessels, which give the skin a marbled appearance (cutis L
E
CharacteristicsandgeneticsofAdams-Oliversyndrome marmoratatelangiectatica),pulmonaryorportalhypertension,and V
Adams-Oliversyndromeisdiagnosedbasedonterminaltransverse retinal hypervascularization; around 23% have congenital heart E
D
limb malformations, an absence of skin (termed aplasia cutis defects.IthasbeensuggestedthatmostsymptomsofAdams-Oliver
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REVIEW Development(2017)144,1743-1763doi:10.1242/dev.148007
A Notch receptors B Notch ligands Fig.2.ThehumanNotchrepertoire.
Proteindomainarrangementofhuman
NOTCH1 TM JAG1 TM Notchreceptors(A)andligands(B).
(2555 aa) NRR (1218 aa) EGF-like StructuresarebasedonInterPro
SP EGF-like repeats ANK PEST repeats proteindomainpredictionandother
LNR HD RAM TAD MNNL DSL vWFCJSD PDZL studies(Ehebaueretal.,2005;
36 SP Lubmanetal.,2005).ANK,ankyrin
16
repeats;DLL,Delta-likeprotein;DSL,
Delta/Serrate/LAG-2domain;EGF,
NOTCH2 JAG2
epidermalgrowthfactor;HD,
(2471 aa) Two isoforms (1238/1200 aa) heterodimerizationdomain;JAG,
jagged;JSD,JaggedSerratedomain;
36 16 LNR,Lin-Notchrepeats;MNNL,Notch
ligandN-terminaldomain;NRR,
NOTCH3
negativeregulatoryregion;PDZL,PDZ
DLL1
(2321 aa) liganddomain[PDZ,postsynaptic
(723 aa) densityprotein(PSD95)];PEST,
34 8 proline(P),glutamicacid(E),serine(S)
andthreonine(T)degradationdomain;
NOTCH4 RAM,Rbp-associatedmolecule
(2003 aa) DLL3 domain;s,cleavagesite;SP,signal
peptide;TAD,transactivationdomain;
Two isoforms
29 TM,transmembranedomain;vWFC,
(618 aa/587 aa) 6 vonWillebrandfactortypeCdomain.
DLL4
(685 aa)
s1s2s3 8
syndromeareduetoimpairedcirculation(Pateletal.,2004;Stittrich 2016). However, in families with either familial Adams-Oliver
etal.,2014;Swartzetal.,1999). syndrome or congenital heart disease, asymptomatic family
Thisraregeneticdisordercanbeautosomaldominant,autosomal members bearing the disease-causing mutations have been
recessiveorcausedbydenovomutations.Theautosomalrecessive reported, demonstrating that penetrance is not 100%. This is
forms are caused by mutations in EOGT, which encodes a similar to Alagille syndrome (discussed below), in which family
componentoftheNotchpathway,orinDOCK6,whichencodesa members sharing the same JAG1 mutations can present with
regulatorofRhoGTPasesignaling(Lehmanetal.,2014;Shaheen differentsymptoms,orevenbeasymptomatic.
et al., 2011, 2013; Sukalo et al., 2015a,b), whereas the dominant WhyareNOTCH1mutations,andindeedotherNotchcomponent
formsarecausedbymutationsinNOTCH1,RBPJorDLL4,allof mutations, not 100% penetrant? The linear Notch signaling
which are Notch pathway components, or in ARHGAP31, which pathway, which does not include signal-amplification steps, is
encodes another Rho GTPase regulator (Hassed et al., 2012; Isrie exquisitelydosesensitive.Geneticandenvironmentalfactorsthus
et al., 2014; Meester et al., 2015; Southgate et al., 2011, 2015; likely shift the intrinsic duration or strength of Notch signaling,
Stittrich et al., 2014). In the case of DLL4, it was noted that the alteringmutationtoleranceindifferentindividuals.Indeed,screens
disease-associated mutations are distributed throughout the ligand formodifiersofNotch-dependentphenotypesorsignalingpersein
(Meester et al., 2015; Fig. 4B), and so far no distinct pattern of Drosophila (Go and Artavanis-Tsakonas, 1998; Shalaby et al.,
mutationhasbeenidentified.However,somegenotype-phenotype 2009), mouse (Rubio-Aliaga et al., 2007) and in vitro (Mourikis
correlationsarebeginningtoemerge.Forexample,individualswith et al., 2010) have revealed many candidate modifiers of Notch-
NOTCH1 mutations more often have cardiac defects compared to dependentdisease.Forexample,lossofItch(anegativeregulatorof
individuals with ARHGAP31 or DOCK6 mutations (Southgate Notch signaling) in mice interacts with gain of Notch1 in
etal.,2015).Together,themutationsdiscoveredthusfaraccountfor developing thymocytes to produce autoimmune disease, while
∼50%ofpatients,suggestingthatmoreassociatedgenesarelikely loss of one allele of Dll3 in Notch1 heterozygous mice results in
tobediscovered. axial segmentation defects in 30% of double heterozygous mice
It should be noted that NOTCH1 mutations can also cause an (Loomesetal.,2007a).ThissuggeststhatNotchsignalingstrength,
array of isolated cardiovascular defects, including aortic valve whichcanbemodifiedbytheseinteractions,translatesintoagiven
defects, hypoplastic left heart syndrome and tetralogy of Fallot output.Insupportofthis,ithasbeenshownthat,inthehaemogenic
(Gargetal.,2005;Kerstjens-Frederikseetal.,2016;McBrideetal., endothelium of mice, distinct levels of Notch signal activation in T
N
2008;McKellaretal.,2007;Mohamedetal.,2006).Suchmutations response to Jag1 versus Dll4 create a switch between acquiring a
E
includemissense,nonsenseandtruncationmutations,implyingthat haemogenicversusanarterialendothelialfate(Gama-Nortonetal., M
heterozygouslossofNOTCH1functioncanleadtoeitherAdams- 2015).ItisthuslikelythatmodificationstogenesthatimpactNotch P
Oliver syndrome (Fig. 4C) or congenital heart defects. Further signalingalsoimpactdiseasepresentation. O
supportingtheideathatgivenmutationsmaycauseheartdefectsor L
E
Adams-Oliver syndrome, it has been shown that ARHGAP31 ThebiologyofAdams-Oliversyndrome:insightsfromknockoutmice V
mutations lead to both Adams-Oliver syndrome (Southgate et al., Notch1, Dll4 and Rbpj, or their homologs, are required for the E
D
2011) and congenital heart defects (Kerstjens-Frederikse et al., embryonic development of most animal models (Conlon et al.,
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REVIEW Development(2017)144,1743-1763doi:10.1242/dev.148007
This is in stark contrast to an earlier study in which the use of
anotherTie2-Crestrain(Limbourgetal.,2005)suggestedthatloss
Signal-sending cell ofendothelialNotch1wasthesolecauseofembryonicdeathseenin
Notch ligand null mice; however, it was subsequently noted that the Tie2
promoterusedinthisstrainisalsoactiveinthefemalegermline(de
NCSTN γ-Secretase Langeetal.,2008).
PSEN 1
complex VasculardevelopmentisclearlyabrogatedbylossofNotch1,and
PEN2
these studies in mice beg the question of whether defective
vasculature is the underlying cause of Adams-Oliver syndrome.
Notch receptor APH1
Signal-receiving cell Thishypothesiswassuggestedbeforethefirstcausativegeneswere
identified(Swartzetal.,1999),andhasmorerecentlybeenrefined
tosuggestthatpericytedysfunction,inparticular,isthemaindriver
NICD
ofbothscalpandskulldefects,aswellaslimbdefectsinhumans
(Pateletal.,2004;Stittrichetal.,2014).Infurthersupportofthis,
thetransientsilencingofNotchsignaling(usingdominantnegative
Nucleus Maml)invascularsmoothmusclecell(vSMC)precursorsinhibits
NICD RBPJκ their differentiation and leads to hemorrhages in the head and
MAML interdigital space (Chang et al., 2012). However, mesenchymal
DNA
Notch1andNotch2(Panetal.,2005)areactivatedbyJag2(Jiang
et al., 1998; Sidow et al., 1997) to regulate limb development
through Rbpj, indicating that several Notch-regulated processes
mayacttogethertocontrollimbdevelopment.
Various studies have indicated that Notch1 signaling also has
essential roles in skin development (reviewed by Nowell and
Fig.3.ThecoreNotchpathway.ThecanonicalNotchsignalingpathwayisat
itscoreastraightforwardsignalingmechanisminwhichaNotchligandona Radtke, 2013). Notch1 deletion in murine skin leads to tumors
signal-sendingcellbindstoaheterodimericNotchreceptoronacontacting (Demehri et al., 2009; Nicolas et al., 2003) and atopic dermatitis
signal-receivingcell.BindingleadstocleavageofthereceptorbyADAM (Dumortieret al., 2010), suggesting that individuals with Adams-
secretase(notpictured)andsubsequentcleavagebytheγ-secretase Oliversyndromeshouldbeassessedforriskofskinmalignanciesor
complex,whichiscomposedofnicastrin(NCSTN),presenillinenhancer2
skin conditions, as they may be predisposed to developing skin
(PEN2),presenillin1(PSEN1)andanteriorpharynx1(APH1).Cleavage
conditions. In addition, considering that neonatal silencing of
releasestheNotchintracellulardomain(NICD),whichtranslocatestothe
nucleustoactivatethetranscriptionoftargetgenes,actingtogetherwith Notch1leadstoareducedthymusandblockedT-celldevelopment
recombinationsignalbindingproteinforimmunoglobulinkappaJregion (Radtkeetal.,1999),itisremarkablethatAdams-Oliverpatientsdo
[RBPJκ,alsoknownasCSLforCBF1/Su(h)/LAG-1]andtheco-activator notexperiencethymicinsufficiency.
mastermind-like(MAML). Overall,thephenotypesofmousemodelssuggestthatthevarious
symptomsofAdams-Oliversyndromereflectthedose-sensitiverole
1995; Dexter, 1914; Gale et al., 2004; Oka et al., 1995; Swiatek of the Notch pathway in the development of the vasculature.
etal.,1994),andthesemodelshavebeeninvaluableforelucidating Targeting the developing vasculature may prove difficult
themechanismsdrivingAdams-Oliversyndrome.WhileNOTCH1, therapeutically, and current treatment options typically include
DLL4 and RBPJ mutations cause autosomal dominant disease in surgery to close the scalp or skull, or heart surgery. While many
humans,inmiceonlyDll4mutationresultsinaseverephenotypein currentclinicaltrialsfocusoninhibitionofNotchsignalingthrough
theheterozygousstate(Galeetal.,2004),althoughinthiscaseitis small-molecule inhibitors or antibodies (Andersson and Lendahl,
soseverethatmostheterozygousDll4knockoutmicedieinutero. 2014),therapeuticactivatorsofNotchsignalinghaveprovenmore
Similarly, Dll4 heterozygous-null mice display background- difficult to develop – but may prove beneficial to transiently and
dependentembryoniclethality,withimpairedvascularremodeling preciselyboostvasculardevelopment.
andembryonicgrowthretardation(Duarteetal.,2004;Kochetal.,
2008;Krebs etal.,2004). Dll4knockoutmicegeneratedfrom the AlagilleandHajdu-Cheneysyndromes:rolesforNOTCH2and
few surviving heterozygous mice die by embryonic day (E) 10.5 JAG1indevelopment
exhibiting growth delay, smaller hearts and a failure to undergo Alagille syndrome and Hajdu-Cheney syndrome are autosomal
vascular remodeling (Duarte et al., 2004). These studies, together dominant, multisystem disorders with an extensive overlap of
with various other studies of Notch signaling during vascular affected tissues. Alagille syndrome (also known as Alagille-
development (summarized in Box 1) reveal that dose-sensitive Watson syndrome or arteriohepatic dysplasia) is characterized
Dll4-inducedNotch1signalingisrequiredforarterialdevelopment by defects in the liver, eyes, ears, kidneys, pancreas, heart,
andgrosssurvival. vascular system,faceandskeleton,aswellasbydelayedgrowth
Notch1 homozygous knockout mice are also embryonic lethal (Fig. 5) (Alagille et al., 1975; Watson and Miller, 1973; for a T
N
priortoE11(Conlonetal.,1995;Swiateketal.,1994),andthisis review, see Penton et al., 2012). Individuals with Hajdu-Cheney
E
recapitulated in processing-deficient Notch1 embryos (Huppert syndrome, on the other hand, suffer from osteoporosis and M
etal.,2000)andinRbpj−/−embryos(Okaetal.,1995),indicating progressive focal bone destruction, defective craniofacial P
that canonical Notch1 signaling is required for vascular development, heart defects, hearing deficits and renal cyst O
development and embryonic survival. However, endothelial formation (Cheney, 1965; Hajdu and Kauntze, 1948; for a L
E
deletion of Notch1 using a Tie2-Cre specifically expressed in review,seeCanalisetal.,2014). V
endothelialcellsisfarlesssevereand50%ofthesemicesurvivefor These two syndromes represent two sides of the same coin. E
atleast8weeks,albeitwithvascularanomalies(Alabietal.,2016). AlagillesyndromeiscausedbyhaploinsufficiencyforJAG1(∼94% D
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REVIEW Development(2017)144,1743-1763doi:10.1242/dev.148007
Table1.GeneticdisordersassociatedwithmutationsinNotchreceptorsorligands
Disease Prevalence Gene Inheritance Frequency Notcheffect Symptoms
Adams-Oliversyndrome 0.44:100,000 NOTCH1 AD 23% Lossoffunction Underdevelopedskulland
(Martínez- (Southgate absentorscarredskin
Fríasetal., etal.,2015; (aplasiacutiscongenita)in
1996) Stittrichetal., headregion,terminal
2014)(OMIM transverselimbdefects
616028; (AdamsandOliver,1945).
AOS5) Autosomaldominantforms
RBPJ(Hassed AD <10% arealsocausedby
etal.,2012) mutationofEOGT(AOS4),
(OMIM ageneencodinganO-
614814; GlcNActransferasethat
AOS3) post-translationally
DLL4(Meester AD 10% modifiesNotchreceptors.
etal.,2015) Recessiveformsare
(OMIM causedbyARGHAP31
616589; andDOCK6mutation
AOS6) (Fig.3).
Alagillesyndrome 1-3:100,000 JAG1(Lietal., AD 94%(Warthen Lossoffunction Bileductpaucity,heart
1997;Oda etal.,2006) malformations,
etal.,1997) characteristicfacial
(OMIM features,butterfly
118450; vertebraeandposterior
ALGS1) embryotoxon(Alagille
NOTCH2 AD 2% etal.,1975)(Fig.4).
(McDaniell
etal.,2006)
(OMIM:
ALGS2)
Aorticvalvedisease 1-2:100(twiceas NOTCH1(Garg AD 8-15% Lossoffunction InAOVD,aorticvalveshave
commonin etal.,2005) twoinsteadofthreeleaflets
males (OMIM (bicuspidaorticvalves).
comparedwith 109730; Thiscanbebenignorlead
females) AOVD1) toaorticvalvestenosisor
insufficiency,andinmore
severecasescanleadto
hypoplasticleftheart
syndrome(Emanueletal.,
1978).
Cerebralautosomal- 2-4:100,000 NOTCH3(Joutel AD 100% NOTCH3 Defectsinsmallcerebral
dominantarteriopathy (Bianchietal., etal.,1996) oligomerization, arteriesleadtosubcortical
withsubcorticalinfarcts 2015;Kalimo (OMIM possible infarctsandwhitematter
and etal.,2002; 125310; neomorph damage.Vascular
leukoencephalopathy Razvietal., CADASIL1) dementiainone-thirdof
(CADASIL) 2005) patientsovertheageof60.
Maleshaveincreasedrisk
ofdiseaseprogression.
Smallarteriesinallorgans
areaffected,butsymptoms
areneurologicaland
limitedtothebrain.
Early-onsetarteriopathy Onepatient NOTCH3 AR Unknown Lossoffunction Thepatienthadchildhood-
andcavitating described (Pippucci onsetarteriopathyand
leukoencephalopathy etal.,2015) severecavitating
leukoecephalopathy.
Parentswere
heterozygouscarriers
(fatherhadsome
CADASIL-likesymptoms).
Hajdu-Cheneysyndrome Unknown,few NOTCH2(Isidor AD 92%(Isidor Gainoffunction HJCYS:acro-osteolysis(loss T
andserpentinefibula patients etal.,2011a; etal.,2011a; ofbonetissue)particularly N
polycystickidney described Majewski Majewski inhandsandfeet, E
syndrome etal.,2011; etal.,2011; osteoporosis,craniofacial M
Simpsonetal., Simpson dysmorphology,kidney P
2011)(OMIM: etal.,2011) defectsandtoothloss O
102500; (Cheney,1965;Hajduand L
E
HJCYS) Kauntze,1948).
V
Continued E
D
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Table1.Continued
Disease Prevalence Gene Inheritance Frequency Notcheffect Symptoms
NOTCH2(Gray AD 100%(Isidor SFPKS:skeletaldysplasia
etal.,2012; etal.,2011b; characterizedbyelongated
Isidoretal., Narumietal., serpentinefibulae,with
2011b) 2013;Wang polycystickidneysand
(SFPKS) etal.,2011) dysmorphicfacialfeatures.
(5/5,all
female)
Infantilemyofibromatosis 0.25- NOTCH3 AD 11%[1/9 Gainoffunction Mesenchymeproliferation
andlateralmeningocele 0.67:100,000 (Martignetti (Cheung defectsleadingtobenign
syndrome(alsoknown etal.,2013) etal.,2013; tumorsinskin,muscleand
asLehmansyndrome) (OMIM:IMF2) Martignetti bone.Canalsoleadto
etal.,2013)] tumorsininternalorgans,
thenwithpoorprognosis
(mortalityrate>70%).
Rarelyhereditary,usually
spontaneous.When
geneticitis,moreoften
associatedwithaPDGFRB
mutation(Martignettietal.,
2013).
Unknown,few NOTCH3(Gripp Denovo 100%(6/6,all Distinctivefacialfeatures:
patients etal.,2015) male) elongatedskull,widely
described (OMIM spacedeyes,drooping
130720; eyelids,jawmisalignment
LMNS) (micro-retrognathia),high-
archedpalate,longflat
verticalgroovebetweenthe
baseofthenoseandthe
edgeoftheupperlip,and
low-setears.
Hyperextensibility,
hypotoniaandprotrusions
ofthearachnoidanddura
throughspinalforamina
(characteristiclateral
meningoceles).
Spondylocostaldysostosis Unknown,few DLL3(Bulman AR 70% Lossoffunction Axialskeletaldisorders,with
(alsoknownasJarcho- patients etal.,2000) (Turnpenny vertebralsegmentation
Levinsyndrome,JLS) described (OMIM etal.,2013) defect,shortenedthorax
277300; andribmisalignment.Can
SCDO1) resultindecreased
numbersofribsand
variableintercostalfusion
(Rimoinetal.,1968).Can
alsobecausedby
mutationsinHES7
(SCDO4),LFNG(SCDO3),
MESP2(SCDO2),TBX6
(SCDO5)andRIPPLY2
(SCDO6).JLSalso
includesspondylothoracic
dyostosis.
AD,autosomaldominant;AR,autosomalrecessive;ARHGAP31,RhoGTPaseactivatingprotein31;DLL,Delta-like;DOCK6,dedicatorofcytokinesis6;EOGT,
EGFdomain-specificO-linkedN-acetylglucosaminetransferase;HES7,HesfamilybHLHtranscriptionfactor7;JAG1,jagged1;LFNG,lunaticfringehomolog
(O-fucosylpeptide3-beta-N-acetylglucosaminyltransferase);MESP2,mesodermposteriorbHLHtranscriptionfactor2;PDGFRB,plateletderivedgrowthfactor
receptorβ;RBPJ,recombinationsignalbindingproteinforimmunoglobulinkappaJregion;TBX6,T-box6;RIPPLY2,ripplytranscriptionalrepressor2.
of cases) (Li et al., 1997; Oda et al., 1997) or by mutations in are likely a reflection of the varied and indispensable roles – as T
NOTCH2 (∼2% of patients) (McDaniell et al., 2006), and is revealedbyvariousinvitrostudiesandknockoutstudiesinanimal N
E
consideredtobeaNotchloss-offunctionphenotype(Fig.6A).By models–ofJag1andNotch2indevelopmentalprocesses. M
contrast,Hajdu-Cheneysyndrome,whichisdrivenbyproductionof P
a stabilized NOTCH2 lacking a functional PEST degradation Notch2andJag1functionintheliver O
domain, is caused by gain-of-function mutations in NOTCH2 Mammalianliverdevelopmentisacomplexprocessthatisregulated L
E
(Fig.6B)(Grayetal.,2012;Hanetal.,2015;Isidoretal.,2011a,b; by multiple signaling pathways, including the Notch pathway. V
Majewskietal.,2011;Simpsonetal.,2011).Aswehighlightbelow, Notch signaling is, in particular, tightly linked with the E
D
thevastnumberoftissuesandorgansaffectedinthesesyndromes development of bile ducts (reviewed by Gordillo et al., 2015). In
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REVIEW Development(2017)144,1743-1763doi:10.1242/dev.148007
Table2.ComponentsoftheNotchpathwayarecrucialforhuman (POGLUT1,alsoknownasRumi),andthatreducedRumilevelsin
development Jag1+/−/Rumi+/− animals rescue the biliary phenotype of Jag1-
deficient animals. Notch2 deficiency leads to bile duct agenesis
Missenseconstraint Loss-of-functionconstraint CNV
Gene (z) (pLI) (z) perinatallyandsecondarybileductformationafterweaning(Falix
etal.,2014),aprocessthatappearstobeNotchindependent(Walter
NOTCH1 4.48 1.00 −0.79
etal.,2014).Asimilarrecoveryoftheliverphenotypewithagehas
NOTCH2 3.78 1.00 nan
NOTCH3 4.79 0.21 0.97 been reported in individuals with Alagille syndrome (Riely et al.,
NOTCH4 2.45 0.00 −0.28 1979), although it is not yet clear which JAG1 or NOTCH2
JAG1 4.05 1.00 0.62 genotypes,ifany,arelinkedtorecovery.
JAG2 2.63 0.99 −1.54
DLL1 2.23 1.00 0.69
RolesforNotch2andJag1inthedevelopmentofsensoryorgans
DLL3 2.62 0.00 0
Individuals with Alagille syndrome exhibit inner ear and eye
DLL4 3.24 0.98 0.93
PSEN1 1.81 1 1.25 defects,highlightingrolesforJag1andNotch2inthedevelopment
PEN2 1.05 0.54 −0.25 of sensory organs. One of the most easily observed hallmarks of
APH1A 2.41 0.13 0.24 Alagille syndrome – posterior embryotoxon (an irregularity of
APH1B −0.86 0 0.88 Schwalbe’sline)–isabenigndefectthatisrelativelycommoninthe
NCSTN 1.39 1 1.48
general population (Emerick et al., 1999; Ozeki et al., 1997).
RBPJK 3.73 1 0.64
MAML1 −0.03 1 0.16 However,itshouldbenotedthatposteriorembryotoxonisdifficult
MAML2 −1.32 1 0.34 tostudyinrodents,whichinsteadmanifesteyedefects,suchasiris
MAML3 0.77 0.33 0.2 abnormalities(Xueetal.,1999).Jag1andNotch2areexpressedin
thedevelopinglensandciliarybody(CB),andNotch2isexpressed
TheExomeAggregationConsortium(EXAC)haveaggregatedand
harmonizedsequencingdatafrom60,706individuals,andestablishedan in the retinal pigmented epithelium (RPE) (Le et al., 2009;
onlineresourceallowinginvestigationofhowcommonorraremutationsin Saravanamuthu et al., 2012). During development, the Jag1-
specificgenesare(http://exac.broadinstitute.org/,version0.3.1).Lossof expressing inner CB interacts with the Notch2-expressing outer
functionwasdefinedasnonsensemutation,spliceacceptorsandsplice CB(derivedfromRPE)toregulateproliferationandBMPsignaling
donors.Foreachgene,EXACpredictshowmanymutationsareexpectedina
during CB morphogenesis (Zhou et al., 2013). It has also been
givengene,andcomparesthiswithhowmanywereactuallyobservedinthe
shownthattheectoderm-specificdeletion(usingAp2a-Cre)ofJag1
sampledpopulations.Fromthis,aconstraintmetriciscalculated(loss-of-
functionconstraint,pLI),where<0.9(nohighlight)istoleranttolossoffunction, results in arrested separation of the lens vesicle from the surface
andvalues>1(gradedfromyellowtored)denoteextremeintolerancetolossof ectodermandanarrestinlensdevelopment(Leetal.,2012).Notch2
function(haploinsufficientgenes).Missenseandcopynumbervariant(CNV) deletioninthelens(viaLens-Cre)alsodisruptslensdifferentiation
constraint(z)aregreaterthan0iffewermutationswerefoundthanexpected, (Saravanamuthuetal.,2012),althoughthisphenotypeissimilarto
andlessthan0ifmoremutationswerediscoveredthanexpected.Twoofthe
the phenotype of the heterozygous Lens Cre-expressing mouse
fourNotchreceptors,andfourofthefiveligandsinhumans,areextremely
strainitself(Doràetal.,2014).
intoleranttolossoffunction.ItisnoteworthythatNOTCH3isrelatively
Jag1 and Notch2 also regulate inner ear development. Deafness
unconstrainedwhenitcomestolossoffunctionmutations,buthighly
constrainedwhenitcomestomissensemutations,inlinewithourcurrent and impaired balance have been identified in fourethylnitrosourea
understandingofCADASIL.Similarly,γ-secretasecomponentsand (ENU)-induced Jag1 mutant mouse strains: Slalom (Tsai et al.,
transcriptionfactorcomplexcomponentsarelargelyintoleranttolossof 2001),Headturner(Kiernanetal.,2001),Ozzy(Vrijensetal.,2006)
function.APH1,anteriorpharynx1;DLL,delta-like;JAG,jagged;MAML, and Nodder (Hansson et al., 2010). These phenotypes are caused
mastermindlike;nan,notanumber(datainsufficient);NCSTN,nicastrin;PEN,
whenJag1-dependentNotchsignalingfailstodefinethepresumptive
presenilinenhancer;PSEN,presenilin;RBPJ,recombinationsignalbinding
sensory epithelium of the ear and maintain an appropriate ratio of
proteinforimmunoglobulinkappaJregion.
proliferationbetweenpopulationsofhaircellsandsupportingcells,
via Hes1-dependent expression of p27kip (Brooker et al., 2006;
mice, the initiation of Jag1 expression in the portal vein Kiernan et al., 2006; Murata et al., 2009; Pan et al., 2010).
mesenchyme (PVM) marks the onset of bile duct development Conversely, expression of Notch1ICD (Notch1 intracellular
aroundE12.5(Hofmannetal.,2010;Zongetal.,2009).Here,Jag1 domain) in the developing otic vesicle causes ectopic formation
interactswithNotch2inadjacentbiliaryepithelialcellstoinducethe ofsensoryandsupportivecellsinthecochleaandvestibule(Pan
expressionofHes1,Hnf1βandSox9,whichfurtherregulateductal et al., 2010), offering a possible explanation for the hearing
plateformationandintrahepaticbileductmorphogenesis(Antoniou deficits found in Hajdu-Cheney patients (Isidor et al., 2011a).
etal.,2009;Geisleretal.,2008;Kodamaetal.,2004;Zongetal., Sensory organ development shows similar dose-sensitivity to
2009).Jag1isrequiredspecificallyinthePVMandnotintheportal other Notch-regulated processes, wherein a carefully titrated,
vein endothelium (Hofmann et al., 2010) nor in biliary epithelial moderate reduction of Notch signaling activity mediated by the
cells(Loomesetal.,2007b),whereitisneverthelessalsoexpressed. glycosyltransferaseslunaticfringe(Lfng)andmanicfringe(Mfng)
Compound heterozygous Jag1 and Notch2 hypomorphic mice creates a border between the prosensory primordium of the
mimic several features of Alagille syndrome, including jaundice, cochleardomainandtheKölliker’sorgan.Thisoccurspriortothe T
N
growth retardation, disrupted differentiation of intrahepatic bile fate decision of the first differentiating inner hair cells and their
E
ducts, and heart, eye and kidney defects (McCright et al., 2002). associatedsupportingcells,affirmingthesensitivityofthisorgan M
Interestingly, similar to other Jag1 phenotypes (Kiernan et al., to even very mild changes in Notch signaling intensity (Basch P
2007), the biliary phenotype is highly background dependent, as et al., 2016). It is also worth noting that truncated posterior O
backcrossing of Jag1+/− into a C57BL/6J background results in semicircularcanalsandmissingampullaeareobservedinJag1del1/+ L
E
defects similar to those observed in Jag1/Notch2 double andFoxg1Cre+/−;Jag1fl/+heterozygousmice(Kiernanetal.,2006), V
heterozygotes (Thakurdas et al., 2016). This study also revealed andthattheseverityofthevestibularphenotypeinJag1del1/+mice E
D
thatJag1stabilityisnegativelyregulatedbyO-glucosyltransferase1 dependsongeneticbackground.
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REVIEW Development(2017)144,1743-1763doi:10.1242/dev.148007
A Adams-Oliver syndrome hallmarks Fig.4.Adams-Oliversyndrome.(A)Thehallmarksof
Adams-Oliversyndromeincludeabsentorscarredskin,
Thin skull Absent or scarred skin usuallyoccurringinthescalpregion,withanunderlyingthin
Terminal transverse limb defects
skull,andterminaltransverselimbdefects.Terminal
transverselimbdefectscanresembleamputations,and
Syndactyly Absent digit Fused toes Missing toes
patientsmayalsohavesyndactyly.Adams-Oliversyndrome
canbecausedbymutationsinDLL4(B)orinNOTCH1(C),
aswellasinRBPJ,EOGT,ARHGAP31orDOCK6(not
pictured).DLL4mutationsappearmorerandomly
distributedintheligand,evenincludingtwotruncation
mutationsoftheC-terminaldomain.NOTCH1mutationsare
mostoftenmissensemutationsincysteines,especiallyin
EGFrepeat11,inparticularintheligand-bindingdomain.
However,truncationmutations,splicesitesandentire
deletionsarealsoinvolvedinAdams-Oliversyndrome.
B DLL4 mutations Mutationsknowntohaveincompletepenetranceareingray.
Asterisksindicatestop;fsisframeshift.NOTCH1andDLL4
F195L C390R/C390Y structuresarebasedonInterProproteindomainprediction
A121P R186C P267T C455W Q554* andotherstudies(Ehebaueretal.,2005;Lubmanetal.,
R558* 2005).ANK,ankyrinrepeats;DSL,Delta/Serrate/LAG-2
8 EGF-like domain;EGF,epidermalgrowthfactor;fs,frameshift;HD,
SP MNNL DSL repeats heterodimerizationdomain;LNR,Lin-Notchrepeats;MNNL,
NotchligandN-terminaldomain;NRR,negativeregulatory
EGF-like region;PEST,proline(P),glutamicacid(E),serine(S)and
repeats
TM threonine(T)degradationdomain;RAM,Rbp-associated
moleculedomain;SP,signalpeptide;TAD,transactivation
C NOTCH1 mutations
domain;TM,transmembranedomain.
NRR TM
10 20 30 LNR HD
SP 36 EGF-like repeats
RAM ANKTAD PEST
P407R C4Y5565Y0* C1374R M1580Ifs*30 S2017Tfs*9
E1555*
C449R D1989N
R448Q EGF11 C1496Y
C429R A1740S
Notch2andJag1functionduringkidneydevelopment experiments.Itshouldalsobenotedthat,althoughMETcanoccur
Kidney development is tightly regulated by Notch signaling and, without Notch signaling (Cheng et al., 2007; Chung et al., 2016),
althoughitisnotadiagnosticcriteria,manyindividualswithAlagille NotchsignalingcanreplacetheWnt/β-cateninpathwayduringMET
syndromesufferfromseriouskidneyproblems(Kamathetal.,2013). (Boyleetal.,2011),anditsactivityinmedialandproximalsegments,
During kidney development, Notch2 is first expressed in the which is promoted by BMP signaling, is mutually exclusive, with
brancheduretericbudandthesurroundingcapmesenchyme,while highlevelsofWnt/β-cateninsignaling(Lindströmetal.,2015).
Jag1expressionarises,togetherwithNotch2andNotch1expression, WhilethestudiesdescribedabovehighlightkeyrolesforNotch2
inepithelialvesicles(theaggregatesderivedfromcapmesenchyme andJag1inkidneydevelopment,itisnotclearhowspecifichuman
via mesenchymal-to-epithelial transition – MET). These vesicles mutationsassociatedwiththesesyndromesleadtokidneydefects.For
transformthroughthestagesofcomma-shapedbodiesandS-shaped example, no kidney phenotype was described in the Hajdu-Cheney
bodiesintofullydevelopednephronsinwhichJag1isfoundinthe syndrome mouse model harboring the Notch2Q2319X mutation
glomerularendothelium,andbothNotch1andNotch2arefoundin (Canalisetal.,2016).Nonetheless,severalresultsillustratethathigh
glomerular epithelial cells (extensively reviewed by Kamath et al., levelsofNotchsignalingnegativelyimpactonkidneydevelopment.
2013;Kopanetal.,2014).Consistentwiththeseexpressionpatterns, Forexample,constitutivelyactiveNotch1ICD(Chengetal.,2007)or
itwasshownthatmicehaploinsufficientforNotch2andlackingone Notch2ICD(Fujimuraetal.,2010)inthemetanephricmesenchyme
allele of Jag1 exhibit defective glomerulogenesis (McCright et al., (Six2-GFP::Cre) drive pathological kidney development. While
2001),whilethecapmesenchyme-specificdepletionofNotch2,but overexpression of Notch1ICD drives single ureteric bud formation,
not Notch1, blocks the development of podocytes and proximal accompanied by excessive proximal tubule transformation into
tubulespriortoS-shapedbodyformation,resultinginearlypostnatal podocytes and distal tubules (at the expense of mesenchymal
lethality(Chengetal.,2007).Intriguingly,bothNotch1andNotch2 progenitor differentiation) (Cheng et al., 2007), an over-abundance T
N
areactivatedbyeitherJag1orDll1(Liuetal.,2013),sothisunequal of Notch2ICD upregulates Wnt4 expression at E11.5, causing
E
requirement for Notch1 and Notch2 signaling during renal premature tubule differentiation and depletion of nephron M
developmentisprobablycausedbydifferencesintheirextracellular progenitorsbyE14.5,followedbyformationofnumerouscystsand P
domainsorinteractionwiththeLfng,orboth.Indeed,Lfngenhances generaldeteriorationofthekidney(Fujimuraetal.,2010). O
Notch2-mediatedsignalingtoagreaterextentthanNotch1-mediated L
E
signaling, and thus may be a key factor in allowing it to reach the Notch2andJag1inthepancreas V
thresholdrequiredforinductionofproximalstructureformation(Liu Impaired pancreatic function in Alagille syndrome was generally E
D
et al., 2013). However this remains to be tested in genetic consideredcommon(Rovneretal.,2002),andpancreatitishasalso
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REVIEW Development(2017)144,1743-1763doi:10.1242/dev.148007
observed in individuals with Alagille syndrome (Bauer et al.,
Box1.TheNotchpathwayandvasculardevelopment 2010), it has been shown that the development of several
compartments of the heart is dependent on the balanced
Notch1/4+ endothelial cells activitiesofJag1andNotch2.
Dll1+ AblationofJag1expressionintheendocardiumleadstooutflow
phalanx cells Jag1+
stalk cell tract (OFT)defects,aorticvalvehyperplasticity,tetralogyofFallot
and valve calcification, recapitulating the spectrum of cardiac
pathologies often present in Alagille syndrome (Hofmann et al.,
Dll4+ tip cell
2012; MacGrogan et al., 2016). These phenotypes are, at least
Vascular smooth muscle cells Pericytes
(they wrap around the blood vessel) partially, linked to cardiac neural crest (CNC) cells, a highly
Notch1/2/3+ Jag1+ mural cells migratorycellpopulationthatoriginatesfromtheneuralplateborder
Notch signalingcontrolsmostaspectsofvasculardevelopment,from (Jiang et al., 2000). CNC-specific deletion (using Pax3-Cre) of
vasculogenesis and angiogenesis to arterial identity and mural cell either Jag1 (Manderfield et al., 2012) or Notch2 (Varadkar et al.,
attachment, identity and maintenance. For example, during sprouting 2008)revealedthattheyarenotrequiredforCNCmigrationperse,
angiogenesis, Dll4+ endothelial tip cells extend numerous filopodia butthatJag1isakeyinducerofCNC-derivedvSMCdifferentiation.
sproutingforwardswhiletrailingJag1+stalkcellsproliferatetoformthe
Notch2-mediated signaling, meanwhile, maintains vSMC
vesseltrunk.Vascularendothelialgrowthfactor(VEGF)upregulatesDll4
proliferation around the aortic arch arteries and OFT (Varadkar
in tip cells, which activate Notch1 on adjacent stalkendothelial cells,
et al., 2008). Impaired Jag1 and Notch2 signaling also results in
downregulatingVEGFreceptor2/3(VEGFR2/3)andsuppressingthetip
cell phenotype in these trailing cells. Accordingly, Dll4 and Jag1 ventricular septation defects, aortic arch patterning defects and
mutations lead to blood vessel architectural defects, in both mouse pulmonary artery stenosis, all of which are conditions present in
modelsandhumandisease.Notchsignalingisalsoimportantinmural individuals with Alagille syndrome (Manderfield et al., 2012;
cells:Notch3+muralcells,suchasvascularsmoothmusclecellsand Varadkaretal.,2008).Anotherexplanationforthecongenitalheart
pericytes,arerecruitedtomaturingbloodvesselsinaprocessthatis
disease found in Hajdu-Cheney patients (Crifasi et al., 1997) is
dependent on endothelial Jag1. In line with this, loss of Jag1 in the
provided by the role of Notch2 in the formation of trabecular
endotheliumordefectiveNotch3inmuralcellsleadstodefectivemural
cellcoverageofarteriesandcapillaries;inhumansthisresultsin,for myocardium:underphysiologicalconditions,Notch2activitymust
example,thevasculardementiasyndromeCADASIL. be suppressed by Numb and Numbl to balance the formation of
compact versus trabecular myocardium, and its overabundance
causeshypertrabeculation,non-compactationandseptationdefects
been associated with Alagille syndrome (Devriendt et al., 1996). (Yang et al., 2012). Further studies are required to explain how
However, this view was recently revised after a different Notch2 achieves these roles, when the developing myocardium is
methodology showed imbalance in pancreatic function in only devoidofNotch2mRNAexpression(D’Amatoetal.,2016b).
two out of 42 individuals with Alagille syndrome (Kamath et al.,
2012).Nevertheless,itisknownthatNotch2andJag1playessential Notch2andJag1functionduringskeletaldevelopment
rolesduringmurinepancreasdevelopment,potentiallyexplainingthe Notchsignalingalsoplaysanimportantroleindevelopingskeleton
pancreasdefectsobservedinsomepatients.Notchsignalingcontrols and,inlinewiththis,skeletaldefectsareasharedfeatureofAlagille
both the primary (occurring at E8.5-E12.0 of mouse gestation) and Hajdu-Cheney syndromes (reviewed by Zanotti and Canalis,
(Ahnfelt-Rønne et al., 2012; Jensen et al., 2000) and secondary 2016), as well as other congenital Notch disorders (e.g.
(occurringatE13.0-E16.0)(Murtaughetal.,2003;Shihetal.,2012) spondylocostal dysostosis; see below). The systemic deletion of
wavesofpancreaticprogenitordifferentiationthatgiverisetofullset Jag1 or Notch2 did not reveal any somite-related phenotype that
of endocrine (α-, β-, δ-, ε- and PP-cells), acinar and duct cells would suggest their involvement in the early events of bone
(Li et al., 2016; for a review, see Afelik and Jensen, 2013). Jag1 formation(Hamadaetal.,1999;Xueetal.,1999).However,Jag1
regulates pancreas development through inhibition of Dll1-Notch andNotch2intheskeletogenicmesenchymenegativelyregulatethe
signaling duringembryonicstagesandthroughactivationofNotch differentiation of mesenchymal progenitors into osteoblasts, both
signalingduringpostnatalstages(Golsonetal.,2009a).Conditional in vitro and in adolescent mice, and their ablation leads to
deletion of pancreatic epithelial Jag1 (using Pdx1-Cre) leads to progressive bone loss in adult mice (Hilton et al., 2008; Nobta
defectiveductalformation,fibrosisandchronicpancreatitis(Golson etal.,2005;Youngstrometal.,2016).Importantly,Jag1deletionin
etal.,2009b),whileconditionalcompounddeletionofNotch1and mesenchymal progenitors causes expansion of the cortical bone,
Notch2leadstosurprisinglymildeffectsonpancreaticepithelialcell while diminishing trabecular bone mass, suggesting opposing
proliferation (Nakhai et al., 2008), although it is possible that the effects of Jag1 signaling on cortical versus trabecular osteoblasts
phenotypeisrescuedbyNotch3(Apelqvistetal.,1999). (Youngstrometal.,2016).Thisimbalanceleadstospinedefectsand
the formation of butterfly vertebrae, a characteristic feature of
Notch2andJag1functioninheartdevelopment Alagillesyndrome(Emericketal.,1999;Youngstrometal.,2016).
Heart development requires concerted induction, proliferation, Furthermore, both clinical and genome-wide association studies
differentiation, migration and complex morphogenesis events, indicate a positive correlation between mutations in JAG1 and T
N
includingtubeformationandlooping(forareview,seeSedmera, decreased bone mineral density and osteoporotic fractures (Bales
E
2011). Jag1 and Notch2 are both expressed from early stages of etal.,2010;Kungetal.,2010).Theformationofcraniofacialbone, M
theformationoftheheart,and–togetherwithothercomponentsof which arises from intramembranous ossification of neural crest P
theNotchpathway(summarizedinBoxes2and3;forreviews,see (NC)-derived mesenchyme, also requires Jag1: its deletion in NC O
D’Amato et al., 2016a; Luxán et al., 2016) – regulate several cells disrupts mesenchymal differentiation and leads to abrogated L
E
crucial steps of cardiac development. Although it is still unclear mineralizationanddeformitiesofthecraniofacialskeleton,another V
howtolinkdiscreteJAG1mutations,whichhavevariableeffects feature shared by individuals with Alagille and Hajdu-Cheney E
on JAG1 trafficking and activity, to the range of cardiac defects syndromes(Hilletal.,2014;Humphreysetal.,2012). D
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REVIEW Development(2017)144,1743-1763doi:10.1242/dev.148007
A Alagille syndrome – diagnostic criteria B Alagille syndrome – associated symptoms
Posterior Characteristic
embryotoxon facial features
DelaGyerod wgrtohw th
delay
Butterfly
PS vertebrae
OA
Heart
defects VVasacsuclaur laanro amnaoliems aanlides
bleeds in brain, carotid
aartenrdy abnled eadorsta in body
and brain
VSD
Intrahepatic bile
duct paucity
CV DyDspylsasptliac skitdicn eys
kidneys
PT
PT
PV
HA
BD
Fig.5.HallmarksofAlagillesyndrome.(A)Alagillesyndromeisdiagnosedbasedonthepresenceoffivehallmarksofdisease:(1)characteristicfacialfeatures,
includingaprominentforehead,pointedchinanddeep-seteyes;(2)aneyedefectknownasposteriorembryotoxon;(3)heartdefectsrangingfrompulmonary
stenosistotetralogyofFallot;(4)vertebraldefects,suchasbutterflyvertebrae;and(5)jaundice/cholestasisduetointrahepaticbileductpaucity.(B)Inadditionto
thediagnostichallmarks,50-90%ofpatientsaregrowthdelayed(Alagilleetal.,1975;Emericketal.,1999),40%ofpatientsexperiencerenalsymptoms(Kamath
etal.,2013),and10-25%ofpatientshavevascularstructuralanomaliesandbleeds(Emericketal.,1999;Kamathetal.,2004).BD,bileduct;CV,centralvein;HA,
hepaticartery;OA,overridingaorta;PS,pulmonarystenosis;PT,portaltriad;PV,portalvein;VSD,ventricularseptationdefect.
Recently, gain of function Notch2 mice bearing a Q2319X etal.,2012).Morerecently,ithasbeenproposedthattheperivascular
mutation were shown to exhibit enhanced osteoclastogenesis, coverage of newly formed vessels by vSMCs and pericytes is
resulting in cancellous and cortical bone osteopenia and increased facilitated by Jag1-induced expression of integrin αvβ3, which
bone resorption (Canalis et al., 2016). This phenotype is strikingly providesbindingtoabasementmembrane-specificvonWillebrand
different from the phenotypes observed in odontoblast- and factor protein (Scheppke et al., 2012). In adulthood, Jag1 instead
osteocyte-specificNotch1ICDgain-of-functionmice(Canalisetal., acts downstream of Dll4/Notch1 signaling to promote maturation
2013). This variation might be caused by differences between of vSMCs after injury through P27kip1-mediated repression of
constitutiveandCre-dependentapproaches,differentlevelsofNotch proliferation(Boucheretal.,2013;Pedrosaetal.,2015).
activation,orunknownfactorsextrinsictoskeletogenicmesenchyme Jag1alsoregulatessproutingduringangiogenesis;bothgain-and
thatareresponsiblefortheHajdu-Cheneysyndromephenotype. loss-of-function experiments in endothelial cells show that Jag1
promotesthesproutingofnewtipcellsduringretinalangiogenesis
RolesforNotch2andJag1inthevasculature (Highetal.,2008;forreview,seeBeneditoandHellström,2013).
Components of the Notch pathway regulate several aspects of Interestingly,balancedsproutingisachievedbyDll4-induced‘high’
vasculardevelopment,fromvasculargrowthandendothelialtipand Notch signaling and suppression of sprouting, via inhibition of
stalkcellselectiontovSMCdevelopment(seeBox1).Thesystemic VEGFR signaling in tip cells, which is antagonized in stalk
knockout of Jag1 is embryonic lethal in mice at ∼E11.5 due to endothelial cells exhibiting Jag1-mediated ‘low’ Notch signaling
defects in angiogenesis of the embryonic and yolk sac vasculature (Beneditoetal.,2009;Pedrosaetal.,2015).Althoughthesevarious
(Kiernan et al., 2007; Xue et al., 1999). Likewise, homozygous aspects of Jag1 and Notch2 signaling have not yet been linked to
Notch2 knockout mice die at ∼E10.5, displaying widespread Alagille or Hajdu-Cheney syndromes, they may contribute to the T
N
apoptosis (Hamada et al., 1999; McCright et al., 2006). The severity of these conditions, and the likelihood of vascular
E
endothelial-specific deletion (via Tie1- or Tie2-Cre) of Jag1 accidents, including ruptured aneurysms and bleeding (Kamath M
phenocopies systemic Jag1 deletion, revealing that a lack of Jag1 etal.,2004). P
signaling from the vascular endothelium likely causes the O
differentiation defects, loss of vSMCs and severe disruption of DoprimarilyvasculardefectscauseAlagillepathologies? L
E
angiogenesisobservedinJag1mutants(Beneditoetal.,2009;High Several pathologies in Alagille and Hajdu-Cheney syndromes V
etal.,2008).AsimilarlossofvSMCsisobservedinembryoswith appeartohavetheirrootsindefectivedevelopmentofvasculature. E
D
homozygous hypomorphic Notch2 (McCright et al., 2001; Wang As mentioned previously, Jag1 expressed in the portal vein
1752