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PubMed2005

Comprehensive analysis of dynamics of histone H4 acetylation in mitotic barley cells.

Nucleosomal histones are covalently modified at specific amino acid residues. In the case of histone H4, four lysines (K5, K8, K12, and K16) are acetylated. In the current studies, we examined the dynamics of histone H4 acetylation at K8 and K12 in mitotic barley cells using a three-dimensional immunofluorescent method. Based on the results and previous studies on the dynamics of K5 and K16 acetylation, we provide a comprehensive view of the dynamics of H4 acetylation. Interphase nuclei exhibit strong acetylation in the centromeric region at K5, K8 and K12. In the case of K12, strong acetylation at nucleolar organizing regions was observed from prophase to anaphase. The dynamics of K12 were closely related to those of K5. On the other hand, K8 exhibited a pattern of almost uniform acetylation from prophase to telophase and strong acetylation in distal regions of chromosomes at both metaphase and anaphase, which is very similar to the dynamics of K16 acetylation. Thus, it appears that there is pair-wise acetylation of K12 and K5 in the nucleolar organizing regions and of K8 and K16 in the gene-rich regions. Together, these results suggest that pair-wise dynamics of H4 acetylation regulate chromosomal structure and function during the cell cycle.

Acetylation↗
PubMed1990

[Synaptonemal complexes of the A- and B-chromosomes of the spermatocytes from the East Asian mouse Apodemus peninsulae].

The analysis of whole-mount preparations of synaptonemal complexes (SCs) from surface-spread spermatocytes of A. peninsulae (2n = 48A + 1, 2, ... 12 B) had revealed SCs of 23 autosomal bivalents, sex bivalent XY, axial cores and SCs of the B-chromosomes. The intercellular and interindividual variability of the number of B-chromosomes varied from 1 to 12 per cell. The SCs of autosomal bivalents were shown to have a typical structure. The structure and behaviour of SCs of sex bivalent throughout meiotic prophase I appeared to be similar to those observed in other species of this order. Mainly B-univalents and less frequently B-bivalents containing SCs were found to be formed in meiotic prophase I. The full homologues appear to be rarely seen among B-chromosomes of the East-Asiatic mouse. A tendency of forming clusters of B-univalents near the sex bivalent was found, in addition to B-bivalents with lateral elements, having the form of bi- and tri-stranded elements with rare synaptic fragments. Besides this, the SCs of the autosomes of pachytene cells were found to contain structures resembling the recombination nodules.

Animals↗
PubMed1987

Lithium alters mitotic progression in stamen hair cells of Tradescantia in a time-dependent and reversible fashion.

Stamen hair cells of Tradescantia exhibit remarkable precision in the timing of their mitotic events. This precision is altered dramatically with treatment in 50 microM to 1 mM LiCl, an inhibitor of the polyphosphoinositide cycle. Mitotic progression is altered as a function of the time of treatment with LiCl. If cells are treated during late prophase, greater than 80% fail to enter metaphase. Most of the cells that undergo nuclear envelope breakdown become arrested in metaphase. Treatment with LiCl earlier in prophase also results in metaphase arrest. Metaphase arrest can be reversed by the addition of 10 microM myo-inositol or 100 microM CaCl2 to the extracellular medium. The timing of reversal by myo-inositol takes 10 to 14 min while CaCl2 promotes anaphase onset in 2 to 5 min. The difference in kinetics for reversal between these two treatments suggests that myo-inositol addition overrides a biochemical pathway while Ca2+ addition supplants a phosphoinositide-mediated rise in the cation that may be necessary for anaphase onset. Buffer without myo-inositol or CaCl2 is insufficient for reversal. If the cells are treated with LiCl in mid-late-metaphase, at least 5 min prior to the expected time of anaphase onset, sister chromatids split at the normal time, 33 +/- 4 min after nuclear envelope breakdown, but further chromosome separation is arrested. Anaphase chromosome movement can be restored by treatment with either 10 microM myo-inositol or 100 microM CaCl2 in the medium.(ABSTRACT TRUNCATED AT 250 WORDS)

Anaphase↗
PubMed1985

NMR studies of intracellular sodium ions in amphibian oocytes, ovulated eggs, and early embryos.

23Na NMR, in combination with an anionic paramagnetic shift reagent dysprosium bis(tripolyphosphate), has been used to study intracellular Na+ in Rana oocytes, ovulated eggs, and early cleavage embryos. The technique allows accurate and simultaneous determination of both extracellular space and intracellular Na+ concentration. In prophase-arrested, follicle-enclosed oocytes, only about 17% of the total oocyte Na+ (approximately 40 mmol/kg of cells) was NMR-visible. Homogenizing oocytes in 0.24 M sucrose did not significantly affect the 23Na resonance. About 30% of the total oocyte Na+ was associated with the yolk platelets isolated at room temperature by differential centrifugation. NMR analysis, however, did not yield a detectable 23Na signal from these intact platelets. Thus, while yolk platelets are rich in Na+, this Na+ does not contribute to the oocyte 23Na NMR signal. Denuded oocytes, obtained by removing the follicular epithelium, gained about 10 mmol of total Na+/kg of cells and exhibited a comparable increase in NMR-visible Na+, suggesting the existence of compartments with varying degree of NMR visibility within the oocyte. Partially relaxed 23Na Fourier transform NMR spectra revealed the existence of at least two major intracellular compartments of NMR-visible Na+ with different magnetic environments and relaxation behavior in denuded oocytes. Since platelet Na+ appears to be NMR-invisible, one of the two observed compartments may be the nucleus. Progesterone action on the amphibian oocyte caused measurable changes in NMR-visible Na+. By ovulation (second metaphase), there is a gain in total egg Na+, and the NMR-visible Na+ is also increased. Following fertilization, however, there is some loss of total cell Na+ but, by the 2-4 cell stage, about 70% of the total Na+ becomes NMR-visible. These results indicate that a sizable fraction of the Na+ in follicle-enclosed, prophase oocyte is sequestered and located in NMR-invisible compartments and that changes in NMR-visible intracellular Na+ occur following hormonal and developmental stimuli.

Animals↗
PubMed1979

Mitotic activity and delay in fixation of tumour tissue. The influence of delay in fixation on mitotic activity of a human osteogenic sarcoma grown in athymic nude mice.

The purpose of the present investigation was to study the effect of delay in fixation on the mitotic activity in tumour tissue. A human osteogenic sarcoma, especially suitable for counting of mitoses, grown in athymic nude mice, was fixed with varying delay and the mitotic, prophase, metaphase and ana-telophase indices were determined. An almost exponential decline of the mitotic index was observed with a reduction to 49.4% and 15.0% after respectively 60 and 180 minutes. The proportional incidence of prophases, metaphases and ana-telophases changed so that a relative accummulation of advanced phases occured during the 180 minutes of observation. It is concluded that delay in fixation of a magnitude, which is not uncommon in routine surgical pathology, may allow the majority of mitoses to terminate, resulting in unreliable assessments of mitotic activity.

Adult↗
PubMed1977

[Ultrastructure of the micronucleus of the infusorian Didinium nasutum during meiosis].

Six stages can be distinguished in the micronuclear first maturation division prophase of D. nasutum. Nucleolus-like structures of fibrillar nature, connected with micronuclear chromosomes seem to develop at the late leptotene. At zygotene-pachytene, the chromosomes condense, forming irregular loops. This coincides with formation of classically structured synaptinemal complexes in the micronuclei. At diplotene-diakinesis, chromosomal bivalents are uniformly scattered throughout the micronucleus. They aggregate into a net equatorial plate in the first division metaphase; chromosomes show prominent kinetochores with attached chromosomal microtubule bundles. The second maturation division starts immediately after the completion of the first division and is morphologically similar to agamic mitosis of the micronuclei of D. nasutum. During the 2th maturation division prophase, the compact chromosomes form a dense group and show no spreading inside the nucleus. They are interspaced by an amorphous material being possibly involved in the formation of spindle microtubules. The telophase spindle of the 2nd division likely as that of the Ist division divides into three parts, the two daughter nuclei and the separation spindle containing a material of depolymerized microtubules. Only one of the 2nd division derivatives enters the third maturation division. A short telophasic third division spindle is perpendicular to the surface of the contact between the conjugants and produces two pronuclei. The envelopes of the daughter micronuclei are formed from parts of the original nuclear envelope surrounding the entire spindle.

Cell Nucleolus↗
PubMed1979

[Characteristics of oogenesis in the chick. I. The extrafollicular period in the development of the oocytes].

The early stages of oogenesis in the chick were studied by means of light cytochemistry and autoradiography. The oocytes devoided of follicular epithelium are located in the ovarian cortex in groups of 8, 16 or 32 cells. Within the bounds of the group they develop synchronously until the beginning of formation of the follicular epithelium around each oocyte. By 15 days of postembryonic development all oocytes in the ovarian cortex enter the diplotene stage of meiotic prophase. The formation of follicles is completed by 22 days. The morphological descriptions are given for the oocyte nuclei at the preleptotene, leptotene, zygotene, pachytene and early diplotene stages of meiotic prophase. The nucleolus appears at the early diplotene stage and is characterized by extremely weak synthetic activity. It is specially stressed that the nucleolus forms not in alloocytes and that the population of germ cells in the chick ovary is heterogenous by this character. The beginning of RNA synthesis in the oocyte nucleus is timed to the early diplotene stage. The data are obtained on DNA synthesis in the nuclei of preleptotene and leptotene oocytes not related to the amplification of ribosomal genes.

Animals↗
PubMed1977

Differentiation by colchicine and vincristine sulphate of regenerative hepatocellular mitosis and tumour-associated hepatocellular mitosis.

Colchicine and vincristine sulphate differentiate sharply between hepatocyte mitosis associated with the Ehrlich ascites tumour, and regenerative (post-CCl4 necrosis) hepatocyte mitosis. In the former case there is a gross depression of prophase index and a marked lowering of the overall mitotic index. In the latter, although a degree of prophase depression is evident, this is insufficient to prevent an overall substantial elevation of mitotic index due to accumulation at metaphase. Very low doses of colchicine claimed to be effective in stathmokinesis of hepatocytes under influence of hepatomitogenic tumour brei and tumour extracts, produced no discernible effect on the mitotic pattern of hepatocytes in Ehrlich ascites tumour-bearing mice nor in post-CCl4 regenerating livers. The results are discussed in the context of known features of tumour-associated hepatocellular mitosis.

Animals↗
PubMed1983

Blocking of the cell division by stress-inducing electrical stimulation. A study in rat oral epithelium.

The purpose of the present study was to localize in the cell cycle, the site of the stress-induced blockage of cells entering the mitotic phase, and to estimate the length of time this block is effective. A total of 140 rats were subjected to electrical stimulation applied by a live metal grill in the bottom of their cages. Forty animals left undisturbed in the cages were used as controls. At various intervals after the start of electrical stimulation, groups of animals were killed and histologic sections were prepared of the palatal mucosa. The number of prophases, metaphases, and ana/telophases was counted in the epithelium in three sections of each animal. Electrical stimulation for 1 min resulted in a blocking of the entrance of cells into mitosis, followed by a transient increase in the number of mitotic figures to a level much higher than that of the controls. Electrical stimulation for 10 min resulted in the maintenance of the blocking effect for approximately 45 min. By renewed electrical stimulation the period of blockage was extended for a further 35 min. In each experiment the number of prophases decreased immediately after the start of electrical stimulation, indicating that the site of the blockage of the entrance of cells into mitosis is located near the G2/M transition.

Anaphase↗
PubMed1982

The genesis of paired cisternae during the mitotic cycle.

Paired cisternae, which are conspicuous in mitotically active cells, are two or more flattened, membrane-bound saccules stacked in parallel arrays. The origin, development, and fate of paired cisternae during the cell cycle were studied in a poorly differentiated carcinoma of the eyelid. Early in the mitotic cycle, multiple membrane-bound, ovoid vesicles separated by interconnecting septa formed at the nuclear-cytoplasmic interface coincident with the disappearance of the nuclear envelope. These vesicles became progressively flattened and elongated to form paired cisternae, and by late prophase, had migrated to the cell periphery. During early anaphase, intimate association of paired cisternae with condensing chromosomes was observed. During late anaphase and telophase, distension of the cisternae resulted in vesicles similar to those observed in prophase cells. An apparent coalescence of these distended vesicles around the aggregated chromatin of daughter cells resulted in newly formed nuclear envelopes. Paired cisternae appear to be specialized nuclear membrane-derived structures that are fundamental in the generation of nuclear membranes of daughter cells. An infrequently observed variant of paired cisternae, subsurface confronting cisternae, is briefly described.

Aged↗
PubMed1997

Apoptotic condensations in M-phase cells.

BACKGROUND: Apoptosis is a morphologically distinctive form of programmed cell death/cell suicide in which genomic DNA degradation/fragmentation and variegated dense chromatin aggregates are characteristic hallmarks that have never been demonstrated in mitotic cells. Perceptions of mutual exclusivity between apoptosis and mitosis imply that M-phase cells cannot be apoptotic. However, in the present study we show apoptotic morphologies in M-phase cells after an acute oxidative stress and endonuclease digestion. METHODS: Degradation of genomic DNA in human Chang liver cells (American Type Culture Collection, ATCC CCL13) was demonstrated by flow cytometric cell-by-cell evaluation of (a) propidium iodide intercalative binding to DNA and (b) terminal deoxynucleotidyl transferase (TdT)-mediated 3'OH nick end labeling (TUNEL) of fragmented DNA. Oxidative stress was imposed by a 30-min prepulse with 200 microM vanadyl(4), which produces hydroxyl free radicals (OH*), the most reactive of the free radical species. Oxidative stress in the cells was demonstrated by evaluating glutathione-S-transferase (GST)-mediated monochlorobimane-glutathione adduct fluorescence for glutathione content, the main reducing agent of a cell, and methylene blue redox metachromasia, which is a deep color when oxidized and colorless when reduced. Cells with DNA fragmentation were highlighted by TUNEL. Apoptotic morphologies were visualized by staining with Giemsa and neutral red dyes and by DNA-propidium iodide binding to chromatin. Direct endonuclease induction of apoptotic morphologies in permeabilized M-phase cells was produced by 1 hr incubation (37 degrees C) with 16 units/ml of micrococcal nuclease. RESULTS: The genomic DNA of proliferative cells, namely in G2/M phase of the cell cycle, was degraded by vanadyl(4) prepulsing and by micrococcal nuclease digestion, concomitantly with DNA fragmentation shown by TUNEL. Cytological profiles showed GSH depletion and M-phase cells with particularly high oxidative reactivity indicated by methylene blue redox metachromasia. DNA fragmentation in M-phase cells was highlighted by TUNEL. Characteristic apoptotic condensations, ranging from single-ball condensations to "pulverized" aggregates of a mitotic catastrophe, buddings, and "apoptotic bodies," were found in prophase, metaphase, anaphase, and telophase mitotic cells. The observed separation of condensed chromatin aggregates from the main chromosome mass in prophase and metaphase cells could explain micronuclei, linking it with apoptosis. Direct endonuclease digestion readily produced apoptotic morphologies in interphase and in M-phase cells. CONCLUSION: Apoptotic morphologies in M-phase cells can be induced indirectly via oxidative stress or directly via endonuclease activity, which has long been established as a pervading hallmark of apoptosis.

Apoptosis↗
PubMed1998

Changes in the rate of RNA synthesis during the cell cycle.

BACKGROUND: Although the rate of RNA synthesis is known to drop at mitosis, the recent identification of 11 stages in the cell cycle (El-Alfy et al., 1994) makes it possible to measure the rate of this synthesis at each one of the stages and thus find out how it varies throughout the cell cycle. METHODS: Mice were injected intravenously with the RNA precursor, 3H-uridine; the duodenum was fixed 5-15 minutes later for embedment in Epon, and the duodenal crypts were cut in semithin serial sections for study of the rapidly dividing crypt columnar cells. Using Feulgen-stained sections, each cell nucleus was assigned to one of the 11 stages described in the cell cycle, and the same nucleus was identified in the next serial section that had been processed for radioautography, so that the overlying silver grains were enumerated. The count was taken as an index of the rate of RNA synthesis by this nucleus. RESULTS: Starting from stage I of the cell cycle (the period defined by the presence of a minimal amount of chromatin during which the S phase begins) and up to stage IV (when the S phase ends and the G2 phase begins), all or nearly all nuclei are synthesizing RNA with the rate peaking at stage III. During stages V to VIII (the period comprising the mitotic steps), the percentage of RNA-synthesizing nuclei decreases to over half at stage V (prophase), -10% at stages VIa (prometaphase) and VIb (metaphase) and none at stages VII (anaphase) and VIII (telophase). During stages IX-XI (which correspond to the G1 phase), the percentage rises sharply at stage XI to reach up to 100% at stages X and XI. Finally, on the average, 35% of nuclear silver grains are over the nucleolus (presumably representing ribosomal RNA precursors), whereas 65% are over the nucleoplasm (presumably representing mainly heterogeneous RNA precursors). CONCLUSIONS: Cells synthesize RNA during the interphase, but at a variable rate with a peak in S. The synthesis proceeds in a majority of the cells at prophase, but only in a few of them at prometaphase and metaphase, and in none at anaphase and telophase.

Animals↗
PubMed1998

Histone H3 phosphorylation and expression of cyclins A and B1 measured in individual cells during their progression through G2 and mitosis.

Phosphorylation of histone H3 (H3) on Ser-10 correlates with chromatin condensation at mitosis. A new monoclonal antibody (anti-H3-P) was developed that recognizes phosphorylated H3 (H3-P). This antibody was used in multiparameter flow cytometric analysis to relate H3 phosphorylation in individual human leukemic cells to the cells' position in the cycle as well as their expression of cyclins A and B1. Mitotic cells, from prophase to telophase, reacted with anti-H3-P; the binding of the antibody to chromatin of interphase cells was several times weaker. Cell growth in the presence of staurosporine, an inhibitor of the kinase(s) that phosphorylate H3, abolished the cells' reactivity with the antibody. The reactivity also was abolished by incubation of permeabilized mitotic cells with alkaline phosphatase. These data indicate that, within permeabilized cells, the antibody is indeed specific for H3-P and does not detect the unphosphorylated epitope. All cells reacting with anti-H3-P, with the exception of prophase and early prometaphase, were cyclin A negative; the expression of cyclin B1 in these cells was threefold higher than in G2 cells. The analysis of phosphorylation of H3 in individual cells when combined with multiparameter analysis of their cycle position and expression of other proteins offers new possibilities to study molecular mechanisms associated with the G2 to M transition and chromatin condensation. It also offers an assay to screen in vivo inhibitors of kinase(s) or phosphatase(s) involved in H3 phosphorylation or dephosphorylation, and it provides a valuable marker to identify mitotic cells by cytometry.

Alkaline Phosphatase↗
PubMed1996

Sak 57, an intermediate filament keratin present in intercellular bridges of rat primary spermatocytes.

We have previously reported the purification of Sak 57 (for spermatogenic cell/sperm-associated keratin of molecular mass 57 kDa) from outer dense fibers of rat sperm tails. Internal protein sequence analysis of Sak 57 revealed 70-100% homology to the 1A and 2A regions of the alpha-helical rod domain of human, mouse, and rat keratins. A multiple antigen peptide was synthesized using the KQYEDIAQK sequence corresponding to the 2A region and a polyclonal antibody was produced in rabbit to detect Sak 57. During spermiogenesis, Sak 57 associates with the microtubular manchette before becoming a component of para-axonemal keratin structures of the developing tail. We now report that during late meiotic prophase, intercellular bridges linking late pachytene-diplotene spermatocytes display a distinct ribbon containing a Sak 57/beta-tubulin complex, separated by a nonimmunoreactive midzone. Indirect immunofluorescence demonstrates that the ribbon is the final stage of a three-step developmental sequence: (1) a spindlelike arrangement radiating from equidistant spherical centers in early pachytene spermatocytes, (2) an ectoplasmic shell-like framework in mid-to-late pachytene spermatocytes, and (3) a Sak 57/beta-tubulin-containing ribbon found in intercellular bridges linking adjacent late pachytene-diplotene spermatocytes. Shear forces causing a breakdown of one of the conjoined spermatocytes do not disrupt the cytoskeletal ribbon. Results of this work, together with previous observations during spermiogenesis, show that Sak 57 associates with cytoplasmic microtubules in a timely fashion. Upon completion of late meiotic prophase, the Sak 57/microtubule complex behaves as an intercellular ligament and contributes to both the strength of intercellular bridges and the cohesiveness of members of a spermatocyte lineage.

Actin Cytoskeleton↗
PubMed1991

The Golgi apparatus of rat pachytene spermatocytes during spermatogenesis.

A morphological and immunocytochemical study of the Golgi apparatus in pachytene spermatocytes was performed in an effort to correlate the structure and function of this organelle during meiotic prophase. In stages I-III of the cycle, the Golgi complex of pachytene spermatocytes is a flattened discoid, 0.5-1 microns in diameter, composed of vesicles interspersed with classically described Golgi cisternae. During subsequent maturation of pachytene spermatocytes (stages IV-XIII), the size of the Golgi complex increases significantly, attaining a size of 2-3 microns. However, unlike pachytene spermatocytes of stages I-III, the majority of the Golgi complex of more mature spermatocytes is characterized by an abundance of distinct stacks of cisternae interspersed with numerous vesicles and tubules. The composition of the Golgi complex was also studied by using two monoclonal antibodies that recognize either the cis or the trans Golgi cisternae, respectively, and employing biotin-streptavidin-peroxidase immunocytochemistry in 5 micron frozen sections of testes. Immunodetection of the distinct cisternae revealed that the increase in size of the Golgi complex during maturation of pachytene spermatocytes was due predominantly to an accumulation of trans Golgi; the amount of cis Golgi remained unchanged. The morphological data presented in this study are consistent with an heightened secretory activity of pachytene spermatocytes during their maturation. In addition, the increase in size of the Golgi apparatus during the extensive prophase of pachytene spermatocytes may suggest that the mechanism employed by germ cells to partition the Golgi complex during the first division of meiosis varies significantly from that of somatic cells undergoing mitosis.

Animals↗
PubMed2001

How do meiotic chromosomes meet their homologous partners?: lessons from fission yeast.

Homologous chromosome pairing is required for proper chromosome segregation and recombination during meiosis. The mechanism by which a pair of homologous chromosomes contact each other to establish pairing is not fully understood. When pairing occurs during meiotic prophase in the fission yeast, Schizosaccharomyces pombe, the nucleus oscillates between the cell poles and telomeres remain clustered at the leading edge of the moving nucleus. These meiosis-specific activities produce movements of telomere-bundled chromosomes. Several lines of evidence suggest that these movements facilitate homologous chromosome pairing by aligning homologous chromosomes and promoting contact between homologous regions. Since telomere clustering and nuclear or chromosome movements in meiotic prophase have been observed in a wide range of eukaryotic organisms, it is suggested that telomere-mediated chromosome movements are general activities that facilitate homologous chromosome pairing.

Animals↗
PubMed1994

The chromosome periphery during mitosis.

A complex structure, visible by electron microscopy, surrounds each chromosome during mitosis. The organization of this structure is distinct from that of the chromosomes and the cytoplasm. It forms a perichromosomal layer that can be isolated together with the chromosomes. This layer covers the chromosomes except in centromeric regions. The perichromosomal layer includes nuclear and nucleolar proteins as well as ribonucleoproteins (RNPs). The list of proteins and RNAs identified includes nuclear matrix proteins (perichromin, peripherin), nucleolar proteins (perichro-monucleolin, Ki-67 antigen, B23 protein, fibrillarin, p103, p52), ribosomal proteins (S1) and snRNAs (U3 RNAs). Only limited information is available about how and when the perichromosomal layer is formed. During early prophase, the proteins extend from the nucleoli towards the periphery of the nucleus. Thin cordon-like structures reach the nuclear envelope delimiting areas in which chromosomes condense. At telophase, the proteins are associated with the part of the chromosomes remaining condensed and accumulate in newly formed nucleoli in regions where chromatin is already decondensed. The perichromosomal layer contains several different classes of proteins and RNPs and it has been attributed various roles: (1) in chromosome organization, (2) as a barrier around the chromosomes, (3) involvement in compartmentation of the cells in prophase and telophase and (4) a binding site for chromosomal passenger proteins necessary to the early process of nuclear assembly.

Animals↗
PubMed1997

Synthesis and function of Mos: the control switch of vertebrate oocyte meiosis.

One distinguishing feature of vertebrate oocyte meiosis is its discontinuity; oocytes are released from their prophase I arrest, usually by hormonal stimulation, only to again halt at metaphase II, where they await fertilization. The product of the c-mos proto-oncogene, Mos, is a key regulator of this maturation process. Mos is a serine-threonine kinase that activates and/or stabilizes maturation-promoting factor (MPF), the master cell cycle switch, through a pathway that involves the mitogen-activated protein kinase (MAPK) cascade. Oocytes arrested at prophase I lack detectable levels of Mos, which must be synthesized from a pool of maternal mRNAs for proper maturation. While Mos is necessary throughout maturation in Xenopus, it seems to be required only for meiosis II in the mouse. The translational activation of c-mos mRNA at specific times during meiosis requires cytoplasmic polyadenylation. Cis- and trans-acting factors for polyadenylation are, therefore, essential elements of maturation.

Animals↗