Schering Symposium on Intrinsic and Extrinsic Factors in Early Mammalian Development, Venice, April 20 to 23, 1970

643 Pages·1971·24.864 MB·English

by  Gerhard Raspé (Eds.)

Advances in the Biosciences
Editor: G. Rasp6
Associate Editor: S. Bernhard
Technical Assistance:
H. Schmidt
The Schering Symposia and Workshop Conferences
are conducted and sponsored by
Schering AG, 1 Berlin 65, MullerstraBe 170
A dvances in the Biosciences 6
Schering Symposium
on Intrinsic and Extrinsic Factors
in Early Mammalian Development
Venice, April 20 to 23,1970
Editor: Gerhard Raspe
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ISBN 3 528 076887 (Vieweg)
1971
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Copyright ©1971 by Friedr. Vieweg + Sohn GmbH, Verlag, Braunschweig
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Opening
G. Raspe
Scherlng AG, Berlin, Germany
Ladies and Gentlemen:
I have the pleasure of thanking you for accepting our invitation to participate in this
symposium, and I have also the pleasure of mentioning that we are honoured by the
presence of Dr. Mow, the Director General of the Ministry of Health. This is the
fourth symposium on Advances in Biosciences which Schering AG has sponsored.
Schering SpA accepted for this time the role of host. I should like to express our
thanks to the group in Milan, particularly to my good friend Dr. Giusepp eVita who
made the meeting possible at its new venue.
Now, why Venice? Beautiful cities are aid to enlighten the spirits of people. On the
other hand they are very tempting. This leads to the troublesome process of reflec­
tion whether one is doing the right thing at the right time .I have seen scientists sit­
ting in art galleries reading their scientific programs and others studying gallery
guides in the lecture hall. This place is surrounded by water, a fact which should
ease the decision-making process.
Now, why 'Intrinsic and Extrinsic Factors in Early Mammalian Development'? Our
last symposium dealt with mechanisms involved in conception, and we already
touched upon some of the questions which shall be discussed in the days to come.
Then there was one man from Cambridge. He acted as a one-man program-commit­
tee. He recommended the speakers and arranged their papers. As an introduction I
wanted to tell you something about his curriculum vitae. So I looked into the 4th vo­
lume of the proceedings of these meetings - this is what I found: "Being a bashful
sort of chap I avoid curriculum vitae like the plague. I am a happy research worker
contentedly sitting in traditional Cambridge, currently Reader in Physiology and hav­
ing worked in various universities in Britain and America." Anyway Dr. Edwards
does not need too much of an introduction.
When opening the 1969 symposium, I tried to pinpoint some of the objectives of the
meeting. Let me do a little thinking for two minutes on this. First, despite a large and
ever-increasing number of congresses, symposia, workshops and whatever the neat
terms may be, there seems to be little opportunity for comprehensive presentation of
work done in related fields by workers who are scattered all over the world T.he chair­
men presiding over such meetings are increasingly defensive. Pressure on time forces
them to kill a discussion before it really starts. We do hope that these symposia will
1 Schering 6
2
help to build bridges between related fields. Second, smaller meetings tend to become
closed affairs amongst the established workers who are regarded by the younger
people as 'Mafiosi'. We have always tried to enable a reasonable number of young
people to attend, in particular those who do not have access to travelling funds. Third,
there are fields which seem to be 'over-studied', and others which seem to be 'under­
studied'. The reasons are obviously manifold. Let me cite horn John R. Platt's article
in Science, vol. 154, page 1134: "It is as though we had collective taboos against cer­
tain types of development, like the taboo against the work on contraceptives before
about 1950, or the refusal to consider Buckminster Fuller's geodesic dome buildings
until the army used the principle for radomes, or the reluctance of psychologists and
physiologists to study sleep, before the work of Nathaniel Kleitman and his co-wor­
kers made it respectable. Scientists are not really innovators and neither are industri­
al companies nor government agencies and their research and development teams.
They all shrink like other men from unheard of projects for which there is no prece­
dent, even obvious and important projects, because they are afraid they will be laugh­
ed at, or cut off from support." We do hope that we can put light on some fields
which look like being somewhat understudied.
Just a few words about the program. The program is the most extensive we have had
so far. The sections on the oocyte and the egg and on the metabolism of preimplanta-
tion embryos should give a rather comprehensive picture of these aspects. Section 3
dealing with the placental and fetal physiology will supposedly lead to less complete
pictures, but discussion may augment information. Sections 4, 5 and 6 are even less
completely prepared. So we will rely on the stimuli given by the discussion and the
lectures.
Before stepping away, I have to fulfill a very pleasant task, to announce the winners
of the 1970 Schoeller-Junkmann Award. They are Dr. Rudolf Knuppen from the
Dept. of Biochemical Endocrinology, Institute of Clinical Biochemistry, University
of Bonn; Dr. Hermann Schneider, Scientific Center, University of Kiel; and Dr. Diet-
mar Lommer, First Medical Center, University of Mainz.
May I now ask Dr. Edwards to give his introduction. Thank you for your kind atten­
tion.
Introduction
R. G. Edwards
Physiological Laboratory, Cambridge, Great Britain
Dr. Raspe, Dr. Mow, Ladies and Gentlemen.
There is very little I can say to add to Dr. Raspe's remarks. We are delighted to come
to Venice to meet with so many of our distinguished collaborators and scientists pre­
sent here today. I believe that the entry of the Schering Symposia into our field is a
wonderful opportunity for us. The early Symposia dealt with steroid biochemistry.
Last year the decision to hold a meeting on conception brough ta whole new group
of people into the range of Schering's interests, and there was an excellent confe­
rence in Berlin. Carryingon that topic to the early embryo was a recognition of the
value of the last meeting to the scientists involved and to Schering.
I am sure I speak on behalf of all of us when I give our deepest thanks t oDr. Raspe
and Dr. Bernhard for their excellent hospitality, for their wonderful organisation,
and for the kindness and courtesy with which they have received us. They could not
have done more to give us an opportunity for a series of discussions on a variety of
topics. I would like to make one other point about this meeting .We are the guests of
an industrial firm which has made excellent contributions to steroid biochemistry,
some leading workers have worked with Schering. We are benefiting from the colla­
boration between Industry and University, which I believe to be an excellent thing,
deserving to be pursued vigorously, and which I sincerely hope will continue with
Schering in the future. I'm sure this is their intention, and I trust they will carry
on their excellent work in this field. Perhaps next year will follow some of the
topics that are not covered in such detail in this symposium. We have plenty of scope
for more and, Dr. Raspe, should you wish to follow this conference with a further
one, we will be delighted to help; I think we would all be delighted to come to
Venice again!
I am not sure why Venice was chosen for this conference,I notice outside the hall
there is a beautiful beach, marvellous sand. I do not know what the temperature of
the water is — perhaps slightly cold for swimming. I hope that the speakers are chal­
lenging and stimulating, because if not there may be a mass exodus towards the beach,
or we may find we have a lot of impromptu sessions in bathing costumes.
4
I believe that introductions should be as brief as possible, and we want to get down
to the hard part of the conference. You will notice from your program that we have
some very young scientists amongst the speakers. One or two speakers are still pre-
doctoral and I hope you will give them a sympathetic ear when they speak before you.
It is always a pleasure to meet the distinguished scientists of the past or of the present
and we are very, very fortunate to-day that we have some of them with us. The first
chairman I am to introduce is one of these — Dr. Buzzati Traverso - and without more
ado I would like to invite him to take the chair and introduce the first session.
Welcoming address
A. A. Buzzati-Traverso
UNESCO, Paris, France
Ladies and gentlemen, I want to say a few words before giving the podium to the first speaker to
express the feeling of uncertainty and of being somewhat out of place here today. As the chairman
of the first session of this symposium I feel somewhat out of place because I can't claim any scienti­
fic eminence in this field. As a matter of fact I can hardly claim even a primary interest in your field
of research since my work has only dealt with straightforward genetics in the past. But I accepted
with pleasure the invitation that Dr. Raspe"sent me, for a number of reasons which I'll explain brief­
ly.
First - for the last few months I don't consider myself a real human being any more, having become
an international 'fonctionnaire' - as they say in Paris. For this reason it's good for me to be brought
back to reality and see that I too was born out of mammalian development.
Second - and I think the only significant point - might be perhaps the following. UNESCO, which
I'm representing here, has been active in the field of science for many, many years; but my feeling
is that there haven't been enough contacts between the scientific community, as a whole and the
Paris offices. I think it my duty, since I carry the responsibility of the sector of science at UNESCO,
to try and do what I can to improve this situation, by trying to attend scientific meetings and there­
by having a chance of meeting old friends and new colleagues, and see if we can be useful in any
way.
We may also examine together the possibility of whether there is any international action that
might be worthwhile taking at any one time in any one field. I wish to remind you that in its early
years UNESCO wasresponsibleforgettingtheCERN(Centre Europe'en de Recherches Nucteaires)
Laboratory started in Geneva, which, as you know, has become one of the leading centres in the
world for nuclear research. Now I do not know whether this might be the time for a similar effort
at an international level in the study of the mammalian egg - this is up to you to say so - but if
this were the case, I'd be delighted to take the message to Paris and do whatever I can to help you
along this line. With this I wish to call on this morning^s first speaker, who I'm sure is going to give
us a very interesting talk. Thank you.
Advances in the Biosciences 6
Electron Microscopy of the Primary and Secondary Oocyte
T. G. Baker
Hormone Laboratory, Department of Obstetrics and Gynaecology, University of Edinburgh,
Edinburgh, Great Britain
Summary: It has hitherto been suggested that the oocyte contributes little to its own growth, or
to that of the follicle which surrounds it. The purpose of the present communication is to present
a series of observations which show that the oocyte at the diplotene stage or meiotic prophase is
not 'resting' but is an actively synthesising cell.
The granulosa cells produce protein some of which probably contributes to the growth of oocyte,
while the remainder is used in the synthesis of the zona pellucida. Evidence is presented, however,
that at least some of the mucopolysaccharide of the zona may be produced by the egg itself.
The number of cytoplasmic organelles in the oocyte increases during the growth phase. Some of
the organelles are produced de novo while others are produced from the nuclear envelope by a
process of blebbing.
The chromosomes in the follicular oocyte produce large quantities of ribonucleoprotein. Some
of the latter enters cytoplasmic organelles via the nuclear blebs and acts as informational RNA.
A proportion of the RNP seems to be stored in the cytoplasm and some circumstantial evidence
suggests that this acts as the organizer of early embryonic development.
Introduction
The mammalian oocyte is derived exclusively from the primordial germ cells of the
early embryo. These first appear in the yolk-sac stalk and migrate to the presumptive
gonads by amoeboid movements in mesenteries, or via the blood stream {Baker [5]).
During fetal life the germ cells undergo repeated mitotic divisions and subsequently
pass through the early stages of meiotic prophase (leptotene to pachytene), such that
by shortly after birth, all the oocytes have entered a prolonged period of arrested
development (diplotene or dictyate stage; see below). The egg enlarges in size during
meiotic prophase and continues to grow during follicular development {Baker [3, 4];
Sauramo [47]). Although part of the growth of the oocyte consists in an enlargement
of the nucleus, by far the greatest contribution derives from an increase in the number
and distribution of cytoplasmic organelles.
At the onset of the diplotene phase the oocyte is enclosed in a primordial follicle
consisting of an incomplete or complete layer of flattened granulosa cells, which sub­
sequently become cuboidal in form. These small follicles make up some 90% of the
total population of oocytes in the mature ovary {Green, Mandl and Zuckerman [28]).
Manuscript received: 9 March 1970
8 T. G. Baker
During each reproductive cycle, in response to secretion of gonadotrophin by the
pituitary gland, a crop of primordial follicles is stimulated to grow by mitotic division
of its granulosa cells. The follicle becomes firstly two layered, then three, four and so
on, until a multilayered structure is formed. Subsequently an antrum forms in the
Graafian follicle which, following secretion of LH by the pituitary gland, undergoes
pre-ovulatory changes (affecting mainly the egg) and then ovulates (seeMauleon [35]).
The duration of the post-diplotene period of meiosis in oocytes varies between species
(Edwards [20, 21]).
The duration of follicular growth is not known for most mammalian species, but in
the mouse the interval from the primordial follicle stage to the time of ovulation takes
about 4-5 reproductive cycles (ca. 16 days;Peters and Levy [41]). This growth does
not proceed uniformly however, since Pedersen [40] has shown by autoradiographic
studies using tritiated thymidine that the medium sized follicles persist for a relatively
long time.
Clearly the diplotene stage of meiosis is important in the life of the oocyte since it
occupies a prolonged period and involves the greater part of the growth of the cell.
If one assumes that puberty in girls normally occurs at about age 13 years and the
menopause during the late 40's, then the oocyte at diplotene persists for 13-50 years
before a viable ovulation {Baker [5]).
Hitherto, it has been assumed that the oocyte at diplotene is at a true 'resting' stage
contributing little to its own growth or to that of the follicle which surrounds it. This
view was mainly based on histochemical observations with the light microscope
(e. g. Seshacher and Bagga [48];Jacoby [33]). With the advent of improved techniques
for electron microscopy and autoradiography this view is becoming less tenable. The
purpose of the present report is to describe the results of a series of studies on
mammalian oocytes which show that the period of arrested development is not a
'resting' stage; the oocyte undergoes profound changes which are responsible at least
in part for its growth and maturation.
The observations described in this paper are based on an examination of thin sections
of ovarian fragments removed at surgery or autopsy, from fetal and adult rats, cows,
monkeys and humans. The materials and methods used are similar to those described
in our earlier papers (Baker and Franchi [6-9]).
The role of the granulosa cells
The contribution of the follicular (granulosa) cells in oogenesis has been a matter of
some controversy (see Norrevang [36]). The cells are clearly important in providing a
vehicle for ovulation of the secondary oocyte and for the synthesis of steroid
hormones, but these processes do not apparently involve the egg. The follicle is
dependent on the oocyte for its survival, however, since atresia of the oocyte is