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At least 1,333 records · Page 74Linked to original sources
PubMed1997

Soma-germ cell interactions in Caenorhabditis elegans: multiple events of hermaphrodite germline development require the somatic sheath and spermathecal lineages.

Germ cells complete multiple events to form functional oocytes and sperm. In the Caenorhabditis elegans hermaphrodite, germ cells develop in proximity to the somatic gonad sheath and spermathecal cells. We present evidence from cellular laser ablation studies indicating that cells of the somatic sheath and spermathecal lineages play critical roles in four events of hermaphrodite germline development. (1) Cells of the sheath and spermathecal lineage support germline proliferation; ablation of sheath/spermathecal precursor cells reduces mitotic proliferation. (2) These cells also play a role in the exit of germ cells from the pachytene stage of meiotic prophase and/or gamete differentiation; ablation can result in undifferentiated germ cells arrested in pachytene. (3) Proximal sheath and distal spermatheca cells are required for ovulation of the oocyte. During wild-type ovulation, the mature oocyte is expelled from the gonad arm by contraction of the proximal myoepithelial sheath and dilation of the distal spermatheca. Ablation of these cells traps mature oocytes in the gonad arm where they endomitotically replicate their DNA (the Emo phenotype). (4) Cells of the sheath and spermathecal lineage also appear to promote the male germ cell fate since ablation of one sheath/spermathecal precursor cell can feminize the hermaphrodite germ line. These somatic ablation-induced germline phenotypes demonstrate that the somatic gonad is required for multiple events in C. elegans germline development. Further, these results suggest that soma to germline cell-cell interactions in C. elegans are physiological in character (i.e., contraction during ovulation) as well as regulatory.

Animals↗
PubMed1998

Developmental expression of the 84-kDa ODF sperm protein: localization to both the cortex and medulla of outer dense fibers and to the connecting piece.

Outer dense fibers (ODF) are specialized cytoskeletal elements of the mammalian sperm tail which are composed of several prominent proteins. We previously reported the isolation of a cDNA (111-450) encoding a putative 84-kDa ODF protein. Here we demonstrate by independent cDNA isolations and by translational/immunoprecipitation of testicular mRNAs using anti-ODF 84 antibodies that 111-450 cDNA encodes the 84-kDa protein. We then analyzed the testicular expression of the ODF 84 mRNA and protein. Riboprobes generated from the clones recognized four testicular-specific transcripts of 1.6, 2.2, 2.4, and 2.8 kb in both rat and bull of which the immunoprecipitable product of the 2.4-kb mRNA comigrates with ODF 84 protein. Developmental Northerns indicated that the 2.2- and 2.4-kb mRNAs are first transcribed during meiotic prophase while the other two species are first expressed in round spermatids. The levels of all the transcripts steadily increased up to elongated spermatids. Immunocytochemistry revealed that the anti-84 reactive ODF proteins were synthesized and assembled in the cytoplasm of elongated spermatids (steps 9-18) with peak activity occurring in step 16 of spermiogenesis. Immunogold labeling was selective to the assembling ODF and connecting piece of the tail and to granulated bodies of the cytoplasmic lobe. Both the striated collar and capitulum of the connecting piece were immunolabeled as well as the basal plate of the implantation fossa. A combination of pre- and postembedding immunogold labeling provided evidence that the 84-kDa ODF protein is localized to both the cortex and medulla of the ODF in contrast to the sole medullary localization of the major 27-kDa ODF protein. Thus the 84-kDa ODF protein, encoded by the 2.4 transcript, is translationally regulated, packaged after synthesis into granulated bodies, assembled in a proximal to distal direction along the axoneme and may interact by means of leucine zippers specifically with the 27-kDa ODF protein during assembly. Its localization to both the cortex and medulla of the ODF, as opposed to exclusive medullary localization of the 27-kDa ODF protein, and the presence of two leucine zippers, only one of which interacts with the 27-kDa ODF, suggests that it could act as a link between proteins of the two regions of the ODF.

Animals↗
PubMed1998

Calcium and endoplasmic reticulum dynamics during oocyte maturation and fertilization in the marine worm Cerebratulus lacteus.

To monitor calcium and endoplasmic reticulum (ER) dynamics during oocyte maturation and fertilization, oocytes of the marine worm Cerebratulus lacteus were injected with the calcium-sensitive indicator calcium green dextran and/or the ER-specific probe "DiI." Based on time-lapse confocal imaging of such specimens, prophase-arrested immature oocytes failed to develop normally after insemination and typically produced non-wave-like calcium transients that were lower in amplitude and less persistent than the wave-like oscillations observed during fertilizations of mature oocytes. Accordingly, the ER of DiI-loaded immature oocytes lacked an obvious substructure, whereas ER clusters, or "microdomains," began to form in maturing specimens at about the time that these oocytes became competent to undergo normal fertilization-induced calcium dynamics and cleavage. The ER microdomains of mature oocytes typically reached widths of 1-8 micrometer and disappeared approximately 1 h after fertilization, which in turn coincided with the termination of the calcium oscillations. Collectively, these findings indicate: (i) changes in ER structure are temporally correlated with the onset and cessation of the calcium oscillations required for subsequent cleavage, and (ii) such ER reorganizations may play an important role in early development by enabling mature oocytes to generate a normal calcium response.

Animals↗
PubMed1999

MAP kinase, meiosis, and sperm centrosome suppression in Urechis caupo.

Although MAP kinase is an important regulatory enzyme in many somatic cells, almost nothing is known about its functions during meiosis, except in frog and mouse oocytes. We investigated MAPK activation and function in oocytes of the marine worm Urechis caupo that are fertilized at meiotic prophase. Activity was first detected at 4-6 min after fertilization in immunoblots with anti-active MAPK, prior to germinal vesicle breakdown (GVBD). MAPK activation did not require new protein synthesis and was dependent on the increases in both intracellular pH and intracellular Ca(2+) that normally occur during activation. When MAPK activation was inhibited with PD98059 or U0126, GVBD still occurred, but meiosis was abnormal and there was a dramatic premature enlargement of sperm asters, which normally do not appear until second polar body formation. Failure of polar body formation and premature sperm aster enlargement also occurred when MAPK activation was inhibited by an entirely different treatment which involved lowering the pH of external seawater to interrupt the normal cytoplasmic pH increase. Thus, in Urechis, active MAPK appears to be required for (1) normal meiotic divisions and (2) suppressing the paternal centrosome until after the egg completes meiosis, a general phenomenon whose mechanism has been unknown.

Animals↗
PubMed2000

Both nuclear and cytoplasmic components are defective in oocytes of the B6.Y(TIR) sex-reversed female mouse.

In the mammalian gonadal primordium, activation of the Sry gene on the Y chromosome initiates a cascade of genetic events leading to testicular organization whereas its absence results in ovarian differentiation. An exception occurs when the Y chromosome of Mus musculus domesticus from Tirano, Italy (Y(TIR)), is placed on the C57BL/6J (B6) genetic background. The B6.Y(TIR) progeny develop only ovaries or ovotestes despite Sry transcription in fetal life. Consequently, the XY offspring with bilateral ovaries develop into apparently normal females, but their eggs fail to develop after fertilization. Our previous studies have shown that the primary cause of infertility can be attributed to oocytes rather than their surrounding somatic cells in the XY ovary. This study attempted to identify the defects in oocytes from the B6.Y(TIR) female mouse. We examined the developmental potential of embryos from XY and XX females after exchanging their nuclear components by microsurgery following in vitro maturation and fertilization. The results suggest that both nuclear and cytoplasmic components are defective in oocytes from XY females. In the XY fetal ovary, most germ cells entered meiosis and their autosomes appeared to synapse normally while the X and Y chromosomes remained unpaired during meiotic prophase. This lack of X-Y pairing probably caused aneuploidy in some secondary oocytes following in vitro maturation. However, normal numbers of chromosomes in the rest of the secondary oocytes indicate that aneuploidy alone can not explain the nuclear defect in oocytes.

Aneuploidy↗
PubMed2001

Interplay between Cdc2 kinase and the c-Mos/MAPK pathway between metaphase I and metaphase II in Xenopus oocytes.

Xenopus oocytes arrested in prophase I resume meiotic division in response to progesterone and arrest at metaphase II. Entry into meiosis I depends on the activation of Cdc2 kinase [M-phase promoting factor (MPF)]. To better understand the role of Cdc2, MPF activity was specifically inhibited by injection of the CDK inhibitor, Cip1. When Cip1 is injected at germinal vesicle breakdown (GVBD) time, Cdc25 and Plx1 are both dephosphorylated and Cdc2 is rephosphorylated on tyrosine. The autoamplification loop characterizing MPF is therefore not only required for MPF generation before GVBD, but also for its stability during the GVBD period. The ubiquitin ligase anaphase-promoting complex/cyclosome (APC/C), responsible for cyclin degradation, is also under the control of Cdc2; therefore, Cdc2 activity itself induces its own inactivation through cyclin degradation, allowing the exit from the first meiotic division. In contrast, cyclin accumulation, responsible for Cdc2 activity increase allowing entry into metaphase II, is independent of Cdc2. The c-Mos/mitogen-activated protein kinase (MAPK) pathway remains active when Cdc2 activity is inhibited at GVBD time. This pathway could be responsible for the sustained cyclin neosynthesis. In contrast, during the metaphase II block, the c-Mos/MAPK pathway depends on Cdc2. Therefore, the metaphase II block depends on a dynamic interplay between MPF and CSF, the c-Mos/MAPK pathway stabilizing cyclin B, whereas in turn, MPF prevents c-Mos degradation.

Animals↗
PubMed2000

Essential functions of DNA topoisomerase I in Drosophila melanogaster.

DNA topoisomerase I (topo I) is an essential enzyme involved in replication, transcription, and recombination. To probe the functions of topo I during Drosophila development, we used top1-deficient flies with heat-shock-inducible top1 transgenes and were able to observe both zygotic and maternal functions of top1. A critical period for the zygotic function is in the late larval and early pupal stages. Topo I is required for larval growth and cell proliferation in imaginal disc tissues. The maternal functions consist of two aspects: oogenesis and early embryogenesis. During oogenesis, topo I is detected in the nuclei of early germ-line cells and follicle cells. The mutant ovary exhibits abnormal proliferation and defective nuclear morphology in these cells. There are extranumeral germ-line cells in individual egg chambers, while the follicle cells are underreplicated. Topo I is also stored maternally in early embryos. It localizes to the nuclei during interphase and prophase, but disperses into the cytoplasm at metaphase. Embryos from the mutant mother frequently show disrupted nuclear divisions with defects in chromosome condensation and segregation. The cytological and genetic analysis of the top1 mutant demonstrates that in Drosophila, topo I plays critical roles in many developmental stages active in cell proliferation.

Animals↗
PubMed2000

A role for cyclin A1 in the activation of MPF and G2-M transition during meiosis of male germ cells in mice.

Cell-cycle transition at G2-M is controlled by MPF (M-phase-promoting factor), a complex consisting of the Cdc2 kinase and a B-type cyclin. We have shown that in mice, targeted disruption of an A-type cyclin gene, cyclin A1, results in a block of spermatogenesis prior to the entry into metaphase I. The meiotic arrest is accompanied by a defect in Cdc2 kinase activation at the G2--M transition, raising the possibility that a cyclin A1-dependent process dictates the activation of MPF. Here we show that like Cdc2, the expression of B-type cyclins is retained in cyclin A1-deficient spermatocytes, while their associated kinases are kept at inactive states. Treatment of arrested germ cells with the protein phosphatase type-1 and -2A inhibitor okadaic acid restores the MPF activity and induces entry into M phase and the formation of normally condensed chromosome bivalents, concomitant with hyperphosphorylation of Cdc25 proteins. Conversely, inhibition of tyrosine phosphatases, including Cdc25s, by vanadate suppresses the okadaic acid-induced metaphase induction. The highest levels of Cdc25A and Cdc25C expression and their subcellular localization during meiotic prophase coincide with that of cyclin A1, and when overexpressed in HeLa cells, cyclin A1 coimmunoprecipitates with Cdc25A. Furthermore, the protein kinase complexes consisting of cyclin A1 and either Cdc2 or Cdk2 phosphorylate both Cdc25A and Cdc25C in vitro. These results suggest that in normal meiotic male germ cells, cyclin A1 participates in the regulation of other protein kinases or phosphatases critical for the G2-M transition. In particular, it may be directly involved in the initial amplification of MPF through the activating phosphorylation on Cdc25 phosphatases.

Animals↗
PubMed2001

Transcriptional activity of the mouse oocyte genome: companion granulosa cells modulate transcription and chromatin remodeling.

Chromatin configuration in the germinal vesicle (GV) undergoes dynamic changes during oocyte growth, yet little is known about the mechanisms regulating chromatin remodeling in mouse oocytes. The hypothesis that companion granulosa cells play a role in modulating chromatin configuration and subsequent transcriptional activity in the oocyte genome was tested. Analysis of transcriptional activity, as determined by Br-UTP incorporation, revealed a similar percentage of transcriptionally active and inactive oocytes present in the large antral follicles of mature females. However, gonadotropin stimulation of follicular development induced an increase in the proportion of transcriptionally inactive oocytes. Interestingly, a similar proportion of stage-matched, oocyte-granulosa cell complexes grown in vitro without gonadotropin stimulation displayed chromatin redistribution around the nucleolus and no transcriptional activity. In contrast, when cultured in the absence of companion granulosa cells, transcriptional activity remained unabated in the majority of denuded GV stage oocytes. Extended prophase arrest in fully grown transcriptionally inactive oocyte-granulosa cell complexes had no effect on the progression of meiosis after in vitro maturation. However, it reduced the competence to complete preimplantation embryo development. These results indicate that chromatin redistribution around the nucleolus is associated with transcriptional repression in the GV of both fully grown in vivo-derived oocytes and cultured oocyte-granulosa cell complexes. Moreover, the results presented here suggest that some aspects of intraovarian control mechanisms were abrogated during culture of oocyte-granulosa cell complexes, resulting in a higher proportion of oocytes with "mature" chromatin. Most importantly, companion granulosa cells played an active role in modulating the transcriptional activity of the oocyte genome.

Animals↗
PubMed2001

Fertilization blocks apoptosis of starfish eggs by inactivation of the MAP kinase pathway.

Fully grown starfish oocytes are arrested at prophase of meiosis I. The hormonal stimulation of 1-methyladenine (1-MA) induces meiosis reinitiation and germinal vesicle breakdown (GVBD). Optimal development occurs when maturing oocytes are fertilized between GVBD and first polar body emission. In the absence of sperm, oocytes complete both meiotic divisions to yield haploid interphase-arrested eggs. We now report that spontaneous and synchronous activation of caspase-3 in starfish eggs occurs 9-12 h after 1-MA stimulation. Then, caspase-dependent membrane blebbing and egg fragmentation occur, indicating that mature eggs undergo apoptosis if not fertilized. Activation of caspase-3 and induction of apoptosis are blocked both by a MEK inhibitor and by emetine treatment which inhibits MEK kinase (Mos) synthesis. Conversely, when recombinant GST-Mos is injected into the emetine-treated eggs, apoptosis is induced. These results indicate that persistent activation of the Mos/MEK/MAP kinase cascade gives the death-activating signal in starfish eggs. Fertilization inactivates the MAP kinase pathway and suppresses apoptosis, followed by normal development.

Actins↗
PubMed1993

Mitotic segregation of the nucleolar ribosomal RNA in Physarum polycephalum.

In the naturally synchronous mitosis of the syncytial plasmodium of Physarum polycephalum, the nucleolus disintegrates in prophase, releasing a large amount of ribosomal RNA. Using biotinylated rDNA probes, we studied by high-resolution in situ hybridization the behavior of this nucleolar RNA throughout mitosis. Our results demonstrate that this rRNA is stable and maintained within the mitotic nucleus mainly, but not exclusively, associated with fibrillar nucleolar remnants. The distribution of these rRNA molecules on both sides of the cleavage plane in telophase is indicative of a precise mechanism of mitotic partition of the nucleolar components, supporting our recent findings concerning the rDNA minichromosomes (Puvion-Dutilleul and Pierron, 1992, Exp. Cell Res. 203, 354-364). Taking advantage of the stability of this RNA component in mitosis, we unambiguously demonstrate that the nucleolar remnants are the precursors of the prenucleolar bodies appearing in the newly divided nuclei which, by fusion, reconstitute a single nucleolus. Our data exemplify the persistence of the nucleolar rRNA in mitosis and demonstrate that in Physarum, following its disintegration, the nucleolus is segregated and inherited.

Animals↗
PubMed1994

Nitric oxide synthase localization in cultured cerebrovascular endothelium during mitosis.

Nitric oxide synthase (NOS) is present in cultured endothelial cells of cerebrovascular origin in a unique membrane-bound subcellular distribution. The enzyme can be detected by its ability to reduce nitro blue tetrazolium to an insoluble dense blue formazan precipitate. In resting cells, enzyme is located adjacent to the nuclear membrane in a single focus with very faint staining in the cytoplasm. During the various stages of cell division, however, NOS becomes redistributed in a pattern which appears similar to that of the Golgi complex. Enzyme is found concentrated near the spindle during early prophase and metaphase. During anaphase and telophase, NOS appears to also spread into the cytoplasm for redistribution into the daughter cells.

Amino Acid Oxidoreductases↗
PubMed1995

Tyrosine phosphorylation of p34cdc2 is regulated by protein phosphatase 2A in growing immature Xenopus oocytes.

Growing stage IV Xenopus oocytes are unresponsive to progesterone treatment. They contain a store of preMPF composed of tyrosine phosphorylated p34cdc2 and cyclin B2. The endogenous store of preMPF cannot be recruited by cdc25 protein phosphatase or cyclin protein microinjections. This is in contrast with full-grown stage VI oocytes where microinjections of these proteins are known to activate the autoamplification of MPF. When cyclins are microinjected into stage IV oocytes, they associate with endogenous free p34cdc2 and the illegitimate complexes undergo phosphorylation on tyrosine 15. High doses of human cyclin A allow, however, part of the neoformed complexes to be activated as an histone-H1 kinase; this partial activation of p34cdc2 is sufficient to induce germinal vesicle breakdown in these small oocytes. Co-injections of cyclin A or cyclin B together with okadaic acid (10 microM in the microinjection solution), an inhibitor of protein phosphatase 2A (PP2A), lead to the full activation of neoformed p34cdc2/cyclin complexes. These results indicate that small oocytes possess an active tyrosine kinase that inactivates new p34cdc2/cyclin complexes. Inhibition of PP2A by okadaic acid prevents this inactivation reaction and conversely allows the illegitimate complex to be activated. Neither the activating phosphorylation on threonine 161 nor the inactivating phosphorylation on tyrosine 15 take place in stage IV enucleated oocytes. Altogether, our results show that the accumulation of inactive p34cdc2/cyclin B2 during the long-lasting prophase of the oocyte is positively controlled by PP2A through the tyrosine phosphorylation of p34cdc2.

Animals↗
PubMed1995

Effect of nordidemnin on the cell cycle of sea urchin embryos. Role in synthesis and phosphorylation of proteins and in polyphosphoinositide turnover in mitosis progression.

Nordidemnin (NorD) is a cyclic depsipeptide isolated from a Caribbean tunicate. This drug is thought to affect cell proliferation by acting on protein, RNA, and DNA syntheses. We studied the ability of NorD to arrest sea urchin embryos at the prophase stage. We tested whether NorD could alter the synthesis and phosphorylation of proteins as well as polyphosphoinositide (PPI) metabolism, as the activation of these processes is necessary for progression through the cell cycle. The dose-response effect on protein synthesis and cell cleavage suggests that NorD acts in the same way as emetine, a well-known protein synthesis inhibitor. We observed that treatment of eggs with emetine or NorD, even at concentrations that inhibited DNA and protein synthesis as well as phosphorylation of proteins, led to modifications in the incorporation of 32P into phosphatidylinositol phosphate and phosphatidylinositol bisphosphate without any alteration in the chemical amounts of these lipids. However, fluctuations in the PPI messenger system that occur during the cell cycle were maintained in the presence of either drug. We suggest that proteins and PPI are linked in an intricate network to control mitosis and cellular proliferation.

Animals↗
PubMed1995

Components of the nucleolar processing complex (Pre-rRNA, fibrillarin, and nucleolin) colocalize during mitosis and are incorporated to daughter cell nucleoli.

We have traced in onion root cells the mitotic course of rRNA, of the RNA synthesized in the G2 period of the preceding interphase, and of the nucleolar proteins fibrillarin and nucleolin. The rRNA was detected by ultrastructural in situ hybridization with a rDNA probe capable of hybridizing mature rRNAs and also the intermediate forms of pre-rRNA processing. The RNA synthesized in the preceding G2 (which, according to classical data, is mostly rRNA) was revealed by autoradiography on synchronous cells labeled in G2 by tritiated uridine. Fibrillarin was detected by immunofluorescence in both mammalian and onion cells; the results in the latter cells were compared with those obtained after AgNOR staining. Electron microscopical immunocytochemistry was used to detect fibrillarin and nucleolin in onion cells. In all cases, following nucleolar dispersion in prophase, the signal was detected in the chromosome periphery during metaphase and anaphase, in irregular fibrillar masses located between chromosomes in ana-telophase, in prenucleolar bodies during telophase, and in the newly formed nucleoli, after nucleologenesis. Moreover, as expected, ribosomes appeared labeled after in situ hybridization, but a dispersed cytoplasmic labeling was observed in all experiments, mainly during metaphase and anaphase. These results demonstrate that nucleolar components involved in pre-rRNA processing, including rRNA itself, probably in an incompletely processed form, are transferred from the parental to the daughter cell nucleoli by means of transient structures, such as the perichromosomal sheath and prenucleolar bodies. Since these macromolecular components are assembled in the interphase nucleolus, forming the RNP processing complex, their colocalization during mitosis in the same transient structures strongly suggests that at least a subset of these complexes does not disaggregate during cell division, but remains assembled and becomes incorporated to the new nucleolus. Therefore, ribosome biogenesis restarts not only after mitosis at the level of transcription, but also at the intermediate levels of pre-rRNA processing.

Allium↗
PubMed1995

Cell-cycle-regulated localization of tyrosine and threonine phosphoepitopes at the kinetochores of mitotic chromosomes.

We have detected novel phosphotyrosine epitopes at the kinetochores of mitotic chromosomes in rat kangaroo PtK1 and mouse P388D1 tissue culture cells. Immunofluorescence labeling of detergent-resistant cytoskeletons reveals that these phosphotyrosine epitopes are tightly bound at the centrosomes and kinetochores of mitotic cells. These phosphoepitopes are found at the kinetochores during only prophase and prometaphase. Inclusion of a mixture of phosphatase inhibitors in the cell extraction procedure was necessary to preserve these previously undetected phosphotyrosine epitopes. The use of the phosphatase inhibitor mixture also improved the detection of the centrosome and kinetochore antigens recognized by the monoclonal antibody MPM-2. The MPM-2 antibody labels a subset of phosphothreonine-containing antigens found primarily during M phase. Ultrastructural immunolabeling studies indicated that both the phosphotyrosine and the MPM-2 phosphoepitopes were contained in both the outer and the inner dense plaques of the kinetochore. We developed large-scale chromosome isolation procedures designed to maintain chromosome protein phosphorylation. Immunoblot analysis revealed that the phosphotyrosine and MPM-2 antibodies recognized a number of chromosomal proteins, some of which were concentrated in the chromosome scaffold fraction prepared by nuclease digestion and salt extraction of whole chromosomes. The strictly regulated appearance of the phosphotyrosine and MPM-2 epitopes at the kinetochores of chromosomes during various stages of mitosis suggests that these phosphoepitopes may be involved in signal transduction pathways controlling kinetochore assembly and function during mitosis.

Animals↗
PubMed1996

Nuclear localization of nucleoside diphosphate kinase type B (nm23-H2) in cultured cells.

Nucleoside diphosphate (NDP) kinases are metabolic enzymes found ubiquitously in cells. Recently, two known human isoforms of NDP kinase (A and B), identical to the protein products of the genes nm23-H1 and nm23-H2, respectively, have been implicated in cancer metastasis and transcriptional regulation. To date, NDP kinase has been studied extensively in tissue sections and its cellular localization was described as being cytoplasmic. However, the recently discovered role of the nm23-H2 gene product in transcriptional activation of the c-myc proto-oncogene also suggests a nuclear localization of the protein. In this study, we used isoform-specific antibodies against NDPK-B to examine the subcellular localization of the nm23-H2 gene product. The cytoplasmic fluorescence is intense and homogeneous with pronounced labeling in the centromere region. The distribution of NDPK-B in interphase nuclei exhibits a pattern of numerous uniformly dispersed fine dots with reduced staining of the nucleoli. To further characterize the nuclear localization of NDPK-B, in situ sequential extraction of nuclear components was performed. Brief exposure to Triton X-100 and subsequent treatment with RNase A do not change the nuclear staining pattern of NDPK-B. In contrast, treatment of Triton X-100-permeabilized nuclei with DNase I results in a significant loss of fluorescence. In mitotic prophase cells, the protein segregates from forming chromosomes and reappears in newly formed daughter nuclei after cell division. Taken together, the results indicate an association of NDPK-B with chromatin in interphase nuclei, supporting its proposed role in transcription.

Animals↗
PubMed1996

Change of karyoskeleton during mammalian spermatogenesis: expression pattern of nuclear lamin C2 and its regulation.

Nuclear lamins are a multigene family of major karyoskeletal proteins. The expression pattern of members of the lamin family has been shown to be developmentally regulated. Of particular interest have been the findings that mammalian spermatogenic cells express two small lamin isoforms (B3 and C2) which are shorter splicing variants of their somatic counterparts (the lamins B2 and C, respectively). Although lamins B3 and C2 appear to be specific for the germ line, the expression pattern and localization of these proteins is not known. In the present study, we present evidence that during rat spermatogenesis lamin C2 is selectively expressed in spermatocytes, i.e., the cells undergoing meiosis. As in the case of other members of the family, lamin C2 was detected at the nuclear periphery. Northern blotting and in situ hybridization indicate that meiotic expression of lamin C2 is regulated at the transcriptional level. This is in contrast to the situation during amphibian oogenesis, where lamin expression is largely posttrascriptionally regulated. Interestingly, the expression pattern of lamin C2 temporally coincides with that of structural protein components of another meiosis-specific karyoskeletal structure, the synaptonemal complex (SC). Taken together, we conclude that pairing and recombination of homologous chromosomes during meiotic prophase is accompanied by significant changes in the organization of the karyoskeleton which are accomplished by the expression of stage-specific proteins.

Amino Acid Sequence↗