J. Embryo/, exp. Morph. Vol. 16, 1, pp. 183-95, August 1966
Printed in Great Britain
183
Action of actinomycin and puromycin upon
frog oocyte maturation
By T. A. DETTLAFF 1
From the Institute of Animal Morphology, Academy of Sciences
of the U.S.S.R., Moscow
In amphibians, as well as in other vertebrates, occytes start to mature under
the action of hypophyseal gonadotropic hormones. (In this paper the term
'maturation' implies the transformation into ripe eggs of oocytes that have
finished growing.) In the course of maturation the oocytes themselves and the
follicle cells surrounding them undergo changes; the changes of these two cell
types are not causally connected, their coincidence in time is easily broken in
unfavourable conditions (Wright, 1945; Tchou-Su & Wang Yu-lan, 1958). As
shown earlier (Dettlaff, Nikitina & Stroeva, 1964), hypophyseal gonadotropic
hormones affect amphibian oocytes through the oocyte nucleus, the germinal
vesicle. As a result of their action the nuclear sap of the germinal vesicle acquires
the ability to induce cytoplasmic maturation (the property revealed by Delage
on the oocytes of Asterias glacialis, 1899, 1901, and by Wilson on those of
Cerebratulus lacteus, 1903). It is also well known that the presence of gonadotropin is required for oocyte maturation and ovulation only in the first part of
maturation period (hormone-dependent maturation period). Shortly before
disruption of the germinal vesicle membrane, the maturation processes acquire
inertia and do not need further action of hypophyseal hormones (hormoneindependent maturation period). It is of importance here that the main changes
during maturation (dissolution of the germinal vesicle membrane, changes in
the cytoplasmic properties) occur during the hormone-independent period.
This paper makes an attempt to clarify the nature of processes in the oocyte
during the hormone-dependent period and to elucidate the action of the gonadotropin-changed nuclear sap upon the cytoplasm. With this aim specific inhibitors of RNA and protein synthesis were applied, namely actinomycin D (cf.
Goldberg & Reich, 1964; Georgiev, 1965) and puromycin (cf. Nathans, 1964).
Criteria of the maturation process were used which allowed correlation between
metabolic changes produced by inhibition and the events of maturation.
1
Author's address: Institute of Animal Morphology, Academy of Sciences of U.S.S.R.,
Vavilov Street 12-2, Moscow, V-133, U.S.S.R.
184
T. A. DETTLAFF
MATERIALS AND METHODS
The experiments were carried out on oocytes of Rana temporaria. Females
were caught at their hibernation sites or kept at low temperature until required.
The experiments were performed between December and March. The ovary was
minced and pieces containing one or a few oocytes were separated with forceps
under a low powered microscope and placed in different media. The follicular
membrane was removed from some oocytes. The ability of oocytes from each
female to respond by maturation to hypophyseal hormones, and the presence or
absence of maturation inertia in them at the moment of treatment were compared in at least two control sets. In one, oocytes were kept in Ringer solution
with hypophyses (usually two hypophyses per 25 ml of Ringer), while in the
other oocytes were kept in pure Ringer solution. Oocytes at various stages were
treated with actinomycin D (before being placed into Ringer with hypophyses,
and after different times in it); the action of actinomycin on the oocytes of
females caught in different seasons was also compared. Apart from actinomycin
D, actinomycin 2703 (cf. Bondareva, 1962) was used. The oocytes were placed
into actinomycin solution (5, 10 and 20/*g/lml of Ringer solution) for
30 min, 1 and 2 h and then transferred into Ringer solution with or without
hypophyses. As actinomycin was dissolved in 70° alcohol, the action of
corresponding alcohol grades (0-35° and 0-7°) upon oocyte maturation was
also studied. In order to investigate the effect of puromycin, oocytes at different
stages were placed into Ringer solution with hypophyses and puromycin
(40 /*g/ml of solution) for the whole duration of the experiment, as the action
of puromycin is reversible.
Oocytes from thirty-five females were used and each experimental run was
repeated many times. In several experiments the action of puromycin and
actinomycin on oocytes from the same female, and at the same maturation
stages, were tested in parallel.
The state of oocyte maturation was determined by the following criteria:
(1) The cytoplasmic properties of succeeding maturation stages (contractility of
the cortical layer and the internal pressure of the endoplasm); changes in these
were revealed by a small cut in the follicular membranes and the cortical layer
in the animal region of the oocyte. (2) The position, size and extent of dissolution
of the germinal vesicle. In order to check rapidly the germinal vesicle state during
the experiment, oocytes were fixed in boiling water and cut with a razor blade
in a plane including the animal-vegetative axis. For microscopic study the
oocytes were fixed with San Felice, Bouin's fluid and with formalin (1:9).
Sections 7 /i thick were stained by the Heidenhein azan method and with ironhaematoxylin. The percentage of ovulation was taken into account in all the
experiments.
Frog oocyte maturation
185
EXPERIMENTAL RESULTS
A. Changes in the properties of the oocyte cytoplasm {contractility of the
cortical layer and internal pressure of the endoplasm) during maturation
Fig. 1 presents a scheme of the changes in these cytoplasmic properties during
maturation. Column A shows sections through oocytes at four successive,
clearly distinguished stages. Column B depicts the appearance of oocytes at
corresponding stages immediately after a cut in the membrane and cortical
layer; column C, the same oocytes 1-2 h after the cut.
In the oocytes at the initial stage, long before the appearance of maturation
inertia (the top row), the edges of the wound did not close for a long time after
being cut; in other words, the cortical layer did not reveal contractility. The
germinal vesicle might later protrude through the cut after which the edges of
the wound began to close, but still a trace of the cut remained. With maturation
inertia established, or shortly beforehand (the second row), wounds in the cortical layer closed more actively, but a scar still remained. Neither at this, nor at
the earlier stage was endoplasm spontaneously extruded through the cut. By
the stage of germinal vesicle dissolution (the third row) contractility of the cortical layer had greatly increased. Wounds in the oocyte surface layer closed almost
instantly, leaving no trace. If the surface of the oocyte was slightly pressed at
this time, part protruded through the persistent slit in the oocyte membranes.
This kind of response could not be induced at earlier stages when the cortical
layer had not acquired contractility. However, on releasing the pressure the
protrusion was gradually withdrawn and the egg regained its spherical shape.
At the final stage (the bottom row) which follows the preceding one after a short
interval of time oocyte behaviour changes drastically. By this time the internal
pressure of the cytoplasm has greatly increased, and endoplasm is expelled
through cuts in the cortical layer. But several minutes after this cut, as the
internal pressure is somewhat reduced, the edges of the wound closed rapidly,
the site of the cut becoming indiscernible. Yet the pressure of the endoplasm,
although equilibrated for a short time, continues to increase, and pear-shaped
exovates are spontaneously expelled through the slit in the membrane and
gradually detached (cf. the bottom row in Fig. 1). The oocyte cytoplasm
preserves these properties throughout the first maturation division and during
early developmental stages in fertilized eggs. Thus, the first signs of contractility
of the cortical layer were revealed shortly before the inertia period and sharply
increased by the time of germinal vesicle dissolution. Soon after that the internal
pressure of the endoplasm rose sharply.
According to the data of Tchou-Su & Yen Pai-Hu (1950), the water content
of the oocytes also increases at this time. Possibly the increase in internal
pressure is a result of rapid hydration. It is of interest in this connexion that
Holtfreter solution is hypotonic for oocytes with intact germinal vesicles, and
186
T. A. DETTLAFF
Fig. 1. Response of Rana temporaria oocytes at different maturation stages to a cut
in the follicle membrane and the cortical layer: A, oocyte structure at the moment
of the cut; B, oocyte appearance just after the cut; C, appearance of the same
oocytes 1-2 h after the cut. g.v., Germinal vesicle; n.s., nuclear sap; w., the wound
in the cortical layer at the site of the cut; e., endoplasm; e.p., egg protrusion through
the slit in the membranes.
Frog oocyte maturation
187
they are rapidly injured by immersion in it, while at the end of maturation period
they can develop in this solution.
These changes in contractility and in internal pressure during maturation by
no means exhaust the processes occurring at this time; they may, nevertheless,
serve as suitable criteria of the changes in the state of the cytoplasm under
different experimental conditions.
\f
3
Fig. 2. Action of actinomycin upon maturation of Rana temporaria oocytes: A,
oocyte structure at the moment of actinomycin treatment; B, oocyte structure by the
end of the experiment, after about 24 h in Ringer solution with hypophyses; C,
appearance of the same oocytes (response to a cut in the cortical layer and in
the membranes). 1, Hormone-dependent period; 2, actinomycin-sensitive period;
3, actinomycin-insensitive period.
B. Action of actinomycin upon oocyte maturation
At different actinomycin concentrations (5, 10 and 20 /tg/ml of Ringer solution) the same result was obtained with oocytes of all females studied; oocytes
treated with actinomycin D lost the ability to respond to hypophyseal hormones
188
T. A. DETTLAFF
by maturation (Fig. 2), while control oocytes in Ringer solution with hypophyses
matured and ovulated. The experimental oocytes remained at the initial stage
and did not ovulate. Actinomycin prevented maturation of oocytes not only at
the initial stage but arrested the maturation process at any time prior to the
appearance of maturation inertia, and in some cases even at its onset. After the
Fig. 3. Action of puromycin upon maturation of Rana temporaria oocytes. A,
Oocyte structure at the beginning of puromycin treatment; B, oocyte structure at the
end of the experiment, after about 24 h in Ringer solution with hypophyses and
puromycin; C, appearance of the same oocytes (response to a cut in the cortical
layer and in the follicle membrane). 1, Hormone-dependent period; 2, puromycinsensitive period.
stage of inertia was reached actinomycin no longer affected maturation, and
oocytes could mature in Ringer solution containing this antibiotic. In such
oocytes the germinal vesicle membrane ruptured, the cortical layer acquired
contractility and the endoplasm underwent hydration.
Frog oocyte maturation
189
It is worth mentioning that cells of the follicular epithelium were sensitive to
actinomycin longer than the oocyte itself. At the beginning of inertia, when
actinomycin treatment did not prevent oocyte maturation, it could still prevent
ovulation. It can be surmised that oocytes and follicle cells respond to gonadotropin at different times.
C. Action of puromycin upon oocyte maturation
Unlike actinomycin, puromycin affected oocyte maturation at the beginning
of the inertia period, when actinomycin no longer exerted an effect (Fig. 3).
Oocytes at the initial stage, or, in spring frogs after the beginning of the action
of gonadotropic hormones but before the onset of maturation inertia, did not
mature in Ringer solution with hypophyses and puromycin. Their germinal
vesicle did not dissolve, no cortical contractility appeared, and endoplasmic
properties remained unaltered.
Oocytes placed into puromycin solution at the beginning of maturation inertia
prior to disruption of the germinal vesicle membrane behaved in the same
manner. Somewhat later oocytes acquired the capacity of disrupting the germinal
vesicle membrane in the presence of puromycin but although their germinal
vesicle dissolved and contractility appeared in the cortical layer, yet the
osmotic properties of the endoplasm remained unchanged. These oocytes were
arrested at the stage reached by normal oocytes at the moment of rupture of the
germinal vesicle membrane: a cut in the cortical layer was rapidly closed without
a trace, while artificially produced egg protrusions could be withdrawn. This
effect of pyromycin upon oocytes was reversible: when returned from Ringer
solution containing puromycin to pure Ringer solution the oocytes acquired
normal internal pressure and formed protrusions spontaneously if their membrane was cut. On the contrary, disruption of the germinal vesicle membrane
was irreversibly blocked by puromycin. Being taken from Ringer solution with
puromycin, and placed into Ringer or Ringer with hypophyses, oocytes did not
mature.
DISCUSSION
The experiments described show that actinomycin D and actinomycin 2703
specifically suppress the maturation of frog oocytes during the hormonedependent period. In the period of inertia actinomycin cannot arrest maturation.
This implies that gonadotropins induce in the oocyte nucleus processes blocked
by actinomycin, i.e. the DNA-dependent synthesis of m-RNA specific for
maturation; this is in good agreement with the data obtained by Brown &
Littna (1964) who isolated such a gonadotropin-induced m-RNA from Xenopus
oocytes that had terminated growth.
Thus, gonadotropic hypophyseal hormones affect the process of oocyte
maturation in the same manner as many other hormones affect their target
190
T. A. DETTLAFF
organs (cf. Epifanova, 1964, 1965; Clever, 1964; Davidson, 1965; Zalta &
Beetschen, 1965), by promoting the synthesis of specific m-RNAs.
The data obtained suggest that synthesis of m-RNA proceeding in the
oocyte occurs during the hormone-dependent period, but not during the
hormone-independent period. This agrees with the data of Ficq (1964). She
demonstrated in in vivo experiments an active incorporation of 3H-cytidine and
3
H-uridine into the nuclear sap and the cytoplasm of certain large oocytes that
have terminated growth in mature ovaries of sea urchins and Xenopus, while
other such oocytes showed no radioactivity. It seems that oocytes that incorporated the label had come into contact with 3H-cytidine and 3H-uridine during
the hormone-dependent stage, while those that remained unlabelled had been
exposed to them during the hormone-independent stage. The morphogenetic
function of the nucleus during oocyte maturation thus reveals a periodicity
resembling that discovered by Neyfakh (1959) in embryonic development.
As to puromycin, it suppresses oocyte development at the beginning of the
hormone-independent period and later inhibits some processes. Since puromycin specifically inhibits protein synthesis, the maturation processes suppressed
by it may be directly or indirectly related to the synthesis of some proteins.
The immunochemical investigations of Apekin (1965) on the changes in sturgeon
oocytes after germinal vesicle dissolution point in the same direction.
The treatment with actinomycin or puromycin at different times of maturation
period allows us to analyse the processes of maturation separately.
An experiment on the disintegration of the germinal vesicle membrane on
spring Bufo viridis was described in an earlier paper (Dettlaff et al. 1964). A
small amount of a mixture of karyoplasm and cytoplasm was taken from
oocytes at, or immediately after, the stage of disintegration of the germinal
vesicle membrane. When injected into the cytoplasm of oocytes from another
female that had not reached maturation inertia, this mixture induced rupture of
the germinal vesicle membrane. A mixture of karyoplasm and cytoplasm from
oocytes that had not attained maturation inertia did not have this effect. These
experiments suggested that substances responsible for the rupture of the germinal
vesicle membrane were able to act not only in situ but in the cytoplasm of
another, less mature oocyte; on the other hand, they could be thought to appear
only at the time of rupture of the germinal vesicle membrane.
Our present data support this suggestion. Actinomycin arrests maturation and
prevents disruption of the germinal vesicle membrane at the end of the hormonedependent period, and puromycin at the beginning of inertia. Thus we may
suppose that at the end of the hormone-dependent period gonadotropins induce
DNA-dependent synthesis of specific m-RNAs. After some time protein synthesis
starts, including the synthesis of enzymes participating somehow in the rupture
of the germinal vesicle membrane. The problem concerning the nature and site
of synthesis of the proteins requires special investigation. It is not ruled out,
however, that they are synthesized in the cytoplasm. Experiments performed by
Frog oocyte maturation
191
Skoblina (unpublished observations) show that germinal vesicles isolated from
oocytes that have not acquired inertia increase in volume when placed in Ringer
solution with hypophyses, yet their membranes do not rupture.
An increase in internal pressure of the endoplasm occurred after the passage
of the nuclear sap to the cytoplasm and was suppressed by puromycin. Therefore, it was somehow related to, or coincided with, protein synthesis in the
cytoplasm. A similar relation between the hormone-induced hydration of the
cytoplasm and protein synthesis was revealed earlier by Mueller, Gorski &
Aizawa (1961) in the cells of the rat uterine mucosa: uptake of water by the
uterine mucosa cells was induced by oestradiol and blocked by puromycin.
Changes in the cortical layer and the appearance of its contractility are
important in maturation and at early stages of embryonic development. The
appearance of contractility in the cortical layer precedes changes in endoplasmic
properties, and thus protects the oocyte from possible disruption resulting from
an increase in internal pressure.
Slight contractility in the cortical layer can be found prior to the onset of
maturation inertia; contractility sharply increases as the nuclear sap passes into
the cytoplasm. However, in oocytes maturing in natural conditions, all the
processes develop slower than in those artificially stimulated, and a stage is
revealed during which the germinal vesicle can be removed while the cortical
layer acquires considerable contractility in its absence. Thus the substances
formed in the germinal vesicle which participate in the development of contractility in the cortical layer, begin to enter the cytoplasm before visible disruption
of the germinal vesicle membrane.
The appearance of contractility in the cortical layer is blocked by actinomycin
and is, therefore, related to the synthesis of m-RNA. However, the initial stages
of processes leading to the appearance of contractility are also blocked by
puromycin. In oocytes placed in Ringer solution with puromycin at the appearance of inertia the germinal vesicle membrane does not rupture and no signs
of contractility can be found in the cortical layer. Only after the onset of maturation inertia, when puromycin no longer blocks germinal vesicle membrane
rupture, is it without effect on the cortical layer, whose contractility increases
both in pure Ringer solution and in the presence of actinomycin or puromycin.
It seems that at this time contractility is no longer dependent upon protein
synthesis. The changes in the cortical layer differ in this respect from those in
the endoplasm, the latter being puromycin-sensitive throughout and thus related
somehow to protein synthesis.
The data obtained may be summarized in the following tentative scheme
(Fig. 4). Gonadotropic hypophyseal hormones promote the DNA-dependent
synthesis of different RNAs both in the germinal vesicle and in the nuclei of
follicle cells. In the germinal vesicle m-RNAs are synthesized to specify the
synthesis of proteins, including those participating in rupture of the germinal
vesicle membrane, endoplasmic proteins, and those involved in the development
192
T. A. DETTLAFF
of contractility in the cortical layer, M-RNAs and proteins concerned in the
process of ovulation are synthesized in the follicle cells.
Certainly this picture will become much more complicated when other
phenomena are also taken into account, e.g. the appearance of cytasters and
Ovulation
Germinal vesicle
membrane
disintegration
Contractility
of the cortical
layer
Change in osmotic
properties of the
endoplasm
Fig. 4. Oocyte changes in the course of maturation (a tentative scheme): 1, actinomycin-sensitive processes; 2, puromycin-sensitive processes (dotted line shows the
suppposed part of the process).; 3, processes insensitive to both actinomycin and
puromycin. /., Follicle cells; f.n., follicle cell nucleus.
globules of hydrophilous colloids in the cytoplasm after the passage of the
nuclear sap into it, as well as the ability of the cortical iayer to show cortical
reaction and to conduct activation impulse.
It has been shown that maturation is a result of the gonadotropin-induced
DNA-dependent synthesis of m-RNAs specific for the process. Therefore maturation involves a gonadotropin-induced activation of certain genes. It is interest-
Frog oocyte maturation
193
ing that the activation of genes in maturation is closely connected with the
specific influence of external conditions favourable for reproduction. These
conditions stimulate hypophyseal cells through the organs of sense and thalamic
nuclei and promote a discharge of gonadotropic hormones into the blood; the
hormones, in their turn, activate corresponding genes in the germinal vesicles
and in the nuclei of follicle cells.
During rupture of the germinal vesicle membrane nuclear DNA undergoes
spiralization, the chromosomes pass to the cytoplasm where they undertake two
maturation divisions and a series of synchronous cleavage divisions following
fertilization. Only later does the mitotic cycle have a genuine interphase and the
DNA again reach the state when it might be able to respond to gonadotropic
hormones. However, as shown previously (Dettlaff et al. 1964), after germinal
vesicle removal and replacement by transplanted nuclei from blastulae, oocytes
do not mature in Ringer solution with hypophyses. Presumably the termination
of the hormone-independent period of oogenesis sees the genes responding to
gonadotropic hormones switched off. Yet this is not the only explanation
possible, so that the problem needs further investigation.
SUMMARY
1. An attempt is made to study the action of gonadotropic hypophyseal
hormones upon the maturation of oocytes of Rana temporaria and to clarify the
action of the nuclear sap changed under the effect of gonadotropins upon the
cytoplasmic maturation. The metabolic inhibitors, actinomycin D, actinomycin 2703 and puromycin were used in the experiments. Rupture of the germinal
vesicle membrane, the appearance of contractility in the cortical layer of the
oocyte cytoplasm, and changes in internal pressure of the endoplasm were
chosen as the criteria of maturation. Ovulation was also considered.
2. Actinomycin D and actinomycin 2703 suppressed both maturation and
ovulation of oocytes throughout the hormone-dependent period, but did not
affect these processes after the onset of maturation inertia.
3. The data obtained and those found in the literature allowed the conclusion
to be drawn that gonadotropic hypophyseal hormones stimulate oocyte maturation and ovulation through the induction of the synthesis of m-RNAs specific
for the maturation process in the nuclei of both oocytes and follicle cells.
4. Puromycin suppressed oocyte maturation at the beginning of the hormoneindependent period and inhibited some processes later. It is suggested that the
processes suppressed by puromycin are directly or indirectly associated with
protein synthesis.
5. By treating oocytes with actinomycin or puromycin at different times
during maturation, actinomycin- and puromycin-sensitive links were revealed
in several processes contributing to maturation.
6. Disruption of the germinal vesicle membrane was suppressed by actino13
J E E M l6
194
T. A. DETTLAFF
mycin until the very end of the hormone-dependent period. Puromycin blocked
it at the beginning of the inertia period.
7. A sharp increase in contractility of the cortical layer coincided with disruption of the germinal vesicle membrane; at this stage it was not blocked by
either actinomycin or puromycin.
8. An increase in internal pressure of the endoplasm occurred shortly after
rupture of the germinal vesicle membrane and the appearance of contractility in
the cortical layer. The presence of actinomycin did not prevent this event, while
the presence of puromycin suppressed it reversibly.
PE3I0ME
1. B HacTOflmeH pa6oTe c^ejiaHa nontiTKa H3yniTb cnoco6
ropMOHOB rnno$H3a Ha nepexofl OOITHTOB Rana temporaria
K
H BblflCHHTb fteftCTBHe H3MeHeHH0r0 nOfl BJIHHHIieM TOHaflOTpOnHHOB
coKa Ha co3peBaHHe u,HTonjia3Mii. B pa6oTe npHMeHHJiH HHrnSiiTopBi
MeTa60JIH3Ma
aKTMHOMHHHH J[, aKTHHOMHIJHH 2703 H nypOMHI^HH. B KanecTBe KpjrrepiieB co3peBaHHH HHToruiasMH Hcnojit3OBajiH: pa3pynieHHe
OSOJIO^KH 3apoji;BiiHeBoro ny3LipbKa, noHBjieHne coKpaTHMOCTH KopTHKajitHoro
CJIOH i^HTonjia3MH ooi^HTa H H3MeHeHne BHyTpeHHero aaBJieHira 3Hflonjia3Mti.
YHHTHBaJIH TaK?Ke OByjIHI];HK) OOITHTOB.
2. AKTHHOMHD;HH JJ, H aKTHHOMHu;HH 2703 noflaBJifliOT co3peBaHne oouiHTOB
H HX OByjiHn;HK) B JIIO6OH MOMeHT ropMOHO3aBHCHMoro nepnofla, HO He BJIHHIOT
Ha 9TH npoijeccti nocjie HacTynjieHHH HHepn;HH co3peBaHHH.
3. 3 a H H L i e > nojiyieHHBie B HacTOHmeii paSoTe H npHBOAHMBie B jiHTepaType,
no3BOJiflK)T 3aKjnoHHTb, ^TO roHa«OTponHtie ropMOHH rHno(|)H3a CTHMyjinpyiOT
oou;HTa H OByjiHUHio nyTeM HH^;yKii,HH B n ^ p a x oounTa H (|>OJIJIHJieTOK cneu;H^)HiHLix ,o;jiH npou;ecca C03peBaHHH — M - P H K .
4. E[ypoMHii;HH noflaBJineT co3peBaHne OOHHTOB B Hanajie ropMOHOHe3aBHCHMoro nepnofla H BHKJiiOHaeT ^acTb npon;eccoB nosaHee. MO?KHO npeflnojiaraTB, HTO nponeccLi, noAaBJineMBie nypoMnu;HHOM, npHMO HJIH KOCBGHHO
CBH3aHbI C CHHTe3OM 6eJIKOB.
5. I l p n noMomn B03ji;eHCTHBfl aKTHH0MHn;HH0M H nypoMHUHHOM B pa3Hbie
MOMeHTH nepHOfta C03peBaHHH BHHBJieHBI aKTHH0MHI],HH0- H nypOMHITHHOHyBCTBHTejitHHe 3BeHBH B pa3Hbix npoijeccax, npHBOflflmiHX K co3peBaHHio
OOII;HTOB.
6. Pa3pynieHHe O6OJIOHKH 3apoAtimeBoro
ny3BipbKa noflaBJineTCH
aKTH-
HOMHII;HHOM B JIIOSOH MOMGHT ropMOHO3aBHCHMoro nepnofla BnjiOTb AO caMoro
ero KOHu;a. IlypoMHii;HH noAaBJineT pa3pymeHHe OSOAOHKH 3apoAbimeBoro
ny3HpbKa B H a i a a e nepnoAa HHepu,HH.
7. Pe3Koe yBejiHieHne coKpaTHMOCTH KopTHKajibHoro CJIOH coBnanaeT c
pa3pymeHHeM OSOJIOHKH 3apoAbinieBoro ny3bipbKa; Ha 8T0ii CTa^HH OHO He
SjIOKHpyeTCH HH aKTHH0MHI];HH0M, HH nypOMHU,HHOM.
8. floBbinieHHe BHyTpeHHero AaBJieHHH 9H,n;onjia3Mbi HacTynaeT BCKope
nocjie pa3pynieHHH OSOJIOHKH sapoflbinieBoro ny3HpbKa H noHBJieHHH coKpaTHMOCTH B KOpTHKaJIbHOM CJIOe. IlpHCyTCTBHe aKTHHOMIIITHHa He BJIHfleT Ha 9TOT
n p o n e c c , Tor^a KaK nypoMHrj;HH ero oSpaTHMO
Cordial thanks are due to Mrs L. A. Nikitina for her friendly assistance and to Drs J. G.
Schmerling, A. A. Neyfakh and T. B. Eisenstadt for their valuable advice.
Frog oocyte maturation
195
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APEKIN,
(Manuscript received 31 January 1966)
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