Biomedical subjects

P Kalab

Publications and source records attributed to P Kalab.

12 recordsLinked to original sources

PubMed2000

Characterization of polo-like kinase 1 during meiotic maturation of the mouse oocyte.

We have characterized plk1 in mouse oocytes during meiotic maturation and after parthenogenetic activation until entry into the first mitotic division. Plk1 protein expression remains unchanged during maturation. However, two different isoforms can be identified by SDS-PAGE. A fast migrating form, present in the germinal vesicle, seems characteristic of interphase. A slower form appears as early as 30 min before germinal vesicle breakdown (GVBD), is maximal at GVBD, and is maintained throughout meiotic maturation. This form gradually disappears after exit from meiosis. The slow form corresponds to a phosphorylation since it disappears after alkaline phosphatase treatment. Plk1 activation, therefore, takes place before GVBD and MAPK activation since plk1 kinase activity correlates with its slow migrating phosphorylated form. However, plk1 phosphorylation is inhibited after treatment with two specific p34(cdc2) inhibitors, roscovitine and butyrolactone, suggesting plk1 involvement in the MPF autoamplification loop. During meiosis plk1 undergoes a cellular redistribution consistent with its putative targets. At the germinal vesicle stage, plk1 is found diffusely distributed in the cytoplasm and enriched in the nucleus and during prometaphase is localized to the spindle poles. At anaphase it relocates to the equatorial plate and is restricted to the postmitotic bridge at telophase. After parthenogenetic activation, plk1 becomes dephosphorylated and its activity drops progressively. Upon entry into the first mitotic M-phase at nuclear envelope breakdown plk1 is phosphorylated and there is an increase in its kinase activity. At the two-cell stage, the fast migrating form with weak kinase activity is present. In this work we show that plk1 is present in mouse oocytes during meiotic maturation and the first mitotic division. The variation of plk1 activity and subcellular localization during this period suggest its implication in the organization and progression of M-phase.

Alkaline Phosphatase↗

PubMed1999

The ran GTPase regulates mitotic spindle assembly.

Ran is an abundant nuclear GTPase with a clear role in nuclear transport during interphase but with roles in mitotic regulation that are less well understood. The nucleotide-binding state of Ran is regulated by a GTPase activating protein, RanGAP1, and by a guanine nucleotide exchange factor, RCC1. Ran also interacts with a guanine nucleotide dissociation inhibitor, RanBP1. RanBP1 has a high affinity for GTP-bound Ran, and it acts as a cofactor for RanGAP1, increasing the rate of GAP-mediated GTP hydrolysis on Ran approximately tenfold. RanBP1 levels oscillate during the cell cycle [4], and increased concentrations of RanBP1 prolong mitosis in mammalian cells and in Xenopus egg extracts (our unpublished observations). We investigated how increased concentrations of RanBP1 disturb mitosis. We found that spindle assembly is dramatically disrupted when exogenous RanBP1 is added to M phase Xenopus egg extracts. We present evidence that the role of Ran in spindle assembly is independent of nuclear transport and is probably mediated through changes in microtubule dynamics.

Animals↗

PubMed1998

The hCSE1/CAS protein is phosphorylated by HeLa extracts and MEK-1: MEK-1 phosphorylation may modulate the intracellular localization of CAS.

hCSE1/CAS (CAS), the human homologue of the yeast chromosome segregation gene CSE1, is a nuclear transport factor that plays a role in proliferation and apoptosis. A MEK-1 phosphorylation sequence in CAS raises the possibility that MEK-phosphorylation regulates the function of CAS. CAS protein from cell extracts shows covalent charge modifications; one of these charge variants contains phosphotyrosine. CAS protein can be captured from cell extracts by immobilized anti-phosphotyrosine antibodies. We have produced recombinant protein fragments containing the N-terminal or central portion of CAS and found that the N-terminal fragment, which contains a putative MEK phosphorylation site, is phosphorylated by the HeLa extracts and MEK-1. Treatment of cells with an inhibitor of MEK-1 phosphorylation in vivo changes the intracellular localization of CAS from predominantly cytoplasmic to nuclear. This suggests that a function of CAS in nuclear transport may be regulated by phosphorylation.

Apoptosis↗

PubMed1998

Interplay between CDC2 kinase and MAP kinase pathway during maturation of mammalian oocytes.

Two principal kinases, p34cdc2 kinase and MAP kinase play a pivotal role in maturation of mammalian oocytes. In the porcine and bovine oocytes both kinases are activated around the time of germinal vesicle breakdown (GVBD). Butyrolactone I (BL I), a specific inhibitor of cdk kinases, prevents effectively and reversibly resumption of meiosis in the porcine and bovine oocytes. Neither p34cdc2 kinase nor MAP kinase are activated in oocytes inhibited in the GV stage. The bovine oocytes maintained for 48 h in the medium supplemented with BL I, progress subsequently to metaphase II in 91%, their cumuli expand optimally and after in vitro fertilization they possess two pronuclei. When the cdc2 kinase is blocked in the porcine oocytes by BL I, MAP kinase, activated by okadaic acid treatment, is able to substitute cdc2 kinase and induce GVBD. The histone H1 kinase activity sharply decreases in the metaphase II oocytes treated by BL I and one or two female pronuclei are formed. These data indicate that BL I is a useful tool either for the two step in vitro culture of mammalian oocytes or for their activation in nuclear transfer experiments.

4-Butyrolactone↗

PubMed1998

Regulation of protein tyrosine phosphorylation in boar sperm through a cAMP-dependent pathway.

Changes of protein tyrosine phosphorylation in ejaculated boar sperm incubated in vitro were examined with the use of antiphosphotyrosine antibodies and immunoblotting. The intracellular levels of cAMP were modulated by treatment with various combinations of caffeine, 3-isobutyl-1-methylxanthine (IBMX), and dibutyryl cyclic AMP (dbcAMP), and acrosome reactions (ARs) were induced via treatment with divalent cation ionophore A23187. Proteins of Mr 34, 38, 40, and 44 (p34 ... p44) were strongly phosphorylated on tyrosine residues in freshly prepared sperm samples and at the same level during all subsequent treatments. Incubation of sperm in vitro for various periods of time induced an increase of tyrosine phosphorylation of p20, p93, and p175. The tyrosine phosphorylation of p93, p175, and several other sperm proteins was up-regulated in a concentration-dependent manner following treatment of the sperm with dbcAMP, caffeine, or IBMX alone, or with combinations of caffeine and IBMX, respectively, with dbcAMP; the tyrosine phosphorylation of p20 was not correlated with treatment of sperm with cAMP-elevating reagents. The percentage of sperm cells undergoing spontaneous ARs was not affected by the manipulation of cAMP levels and was not correlated with protein tyrosine phosphorylation. In contrast, the addition of calcium to the incubation media decreased protein tyrosine phosphorylation and elevated percentage of spontaneous ARs. The induction of ARs with A23187 caused a significant decrease of tyrosine phosphorylation of p93, p175, and p220/230, indicating that dephosphorylation on protein tyrosine residues might be associated with calcium influx during physiological ARs as well. Proteins p93 and p175 were effectively solubilized in greater than 9M urea/1% triton and in SDS sample buffer, but to only a small extent in triton, while p20 was virtually completely extractable with triton. In conjunction with the previously reported isolation of active tyrosine kinase sp42 from triton extracts of noncapacitated boar sperm cells (Berruti and Porzio, 1992: Biochim Biophys Acta 1118: 149-154), our results suggest that a cAMP-dependent event is required for tyrosine phosphorylation of triton-insoluble proteins such as p93 and p175. On the other hand, the tyrosine phosphorylation of p20 (and potentially other triton-soluble substrates) might not strictly require such cAMP up-regulation. We discuss the differences in the regulation of cAMP-dependent tyrosine phosphorylation in mouse, human, and boar sperm, and suggest that sensitivity to calcium and distinct basal levels of cyclic nucleotide PDE might correspond to species-specific reproduction strategies in mammals.

Animals↗

PubMed1997

Damaged chromatin does not prevent the exit from metaphase I in fused mouse oocytes.

The presence of checkpoint mechanisms which are able to recognize damaged chromatin and thereafter to prevent exit from metaphase I has been investigated in giant mouse oocytes produced by fusion of a normal metaphase I oocyte with an equivalent oocyte with damaged chromatin. The presence of damaged chromatin did not prevent the onset of anaphase I in both sets of chromatin in the fused cells. Interestingly, fused or unfused cells containing only damaged chromatin failed to enter anaphase and persisted instead in a metaphase-like state. These results demonstrate the fragility of checkpoint controls in mammalian female germ cells.

Animals↗

PubMed1996

Properties and localization of a tyrosine phosphorylated form of hexokinase in mouse sperm.

Mouse sperm possess a phosphotyrosine-containing hexokinase type 1 (HK1) that is associated with the plasma membrane fraction of these cells (Kalab et al., 1994; J. Biol Chem 269:3810-3817). This apparent plasma membrane association appears unique, since somatic HK1 is normally cytoplasmic or bound to the outer mitochondrial membrane via contact sites with a voltage-dependent anion channel (porin) through a porin-binding domain. In male germ cells, three cDNA clones have been described that encode unique HK1 isoforms (HK1-sa, HK1-sb, HK1-sc) that do not contain porin binding domains (Mori et al., 1993: Biol Reprod 49:191-203). This suggests that these proteins might not be localized to the outer mitochondrial membrane and could have alternative functions in germ cells and/or sperm. We demonstrate in the mouse that male germ cells and sperm could potentially express four HK1 isoforms (HK1-sa, HK1-sb, HK1-sc, and the somatic HK1). At the protein level, at least one of the HK1 isoforms becomes phosphorylated on tyrosine residues during spermatogenesis. Treatment of sperm membrane fractions to dissociate the phosphotyrosine-containing HK1 (pY-mHK1) yields results demonstrating that pY-mHK1 has properties of an integral membrane protein. Indirect immunofluorescence using a monoclonal antibody to HK1 demonstrates specific staining both in the head and tail regions of sperm. Surface biotinylation of intact sperm followed by precipitation with either polyclonal HK1 antiserum or with avidin-Sepharose suggests that pY-mHK1 possesses an extracellular domain. These results suggest that mouse sperm contain at least one HK1 isoform that is present on the sperm head, has an extracellular domain, and behaves as an integral membrane protein.

Animals↗

PubMed1996

Activation of p90rsk during meiotic maturation and first mitosis in mouse oocytes and eggs: MAP kinase-independent and -dependent activation.

Mitogen-activated protein kinases (MAPK) become activated during the meiotic maturation of oocytes from many species; however, their molecular targets remain unknown. This led us to characterize the activation of the ribosomal subunit S6 kinase of Mr 82 X 10(3) - 92 X 10(3) (p90rsk; a major substrate of MAPK in somatic cells) in maturing mouse oocytes and during the first cell cycle of the mouse embryo. We assessed the phosphorylation state of p90rsk by examining the electrophoretic mobility shifts on immunoblots and measured the kinase activity of immunoprecipitated p90rsk on a S6-derived peptide. Germinal vesicle stage (GV) oocytes contained a doublet of Mr 82 x 10(3) and 84 x 10(3) with a low S6 peptide kinase activity (12% of the maximum level found in metaphase II oocytes). A band of Mr 86 x 10(3) was first observed 30 minutes after GV breakdown (GVBD) and became prominent within 2 to 3 hours. MAPK was not phosphorylated 1 hour after GVBD, when the p90rsk-specific S6 kinase activity reached 37 % of the M II level. 2 hours after GVBD, MAPK became phosphorylated and p90rsk kinase activity reached 86% of the maximum level. The p90rsk band of Mr 88 x 10(3), present in mature M II oocytes when S6 peptide kinase activity is maximum, appeared when MAPK phosphorylation was nearly complete (2.5 hours after GVBD). In activated eggs, the dephosphorylation of p90rsk to Mr 86 X 10(3) starts about 1 hour after the onset of pronuclei formation and continues very slowly until the beginning of mitosis, when the doublet of Mr 82 X 10(3) and 84 X 10(3) reappears. A role for a M-phase activated kinase (like p34cdc2) in p90rsk activation was suggested by the reappearance of the Mr 86 X 10(3) band during first mitosis and in 1-cell embryos arrested in M phase by nocodazole. The requirement of MAPK for the full activation of p90rsk during meiosis was demonstrated by the absence of the fully active Mr 88 X 10(3) band in maturing c-mos -/- oocytes, where MAPK is not activated. The inhibition of kinase activity in activated eggs by 6-DMAP after second polar body extrusion provided evidence that both MAPK- and p90rsk-specific phosphatases are activated at approximately the same time prior to pronuclei formation.

Animals↗

PubMed1994

p95, the major phosphotyrosine-containing protein in mouse spermatozoa, is a hexokinase with unique properties.

Mouse sperm contain a major phosphotyrosine-containing protein of M(r) 95,000 (nonreducing conditions) which has been implicated as a sperm membrane receptor for the egg zona pellucida glycoprotein, ZP3 (Leyton, L., and Saling, P. (1989) Cell 57, 1123-1130; Leyton, L., LeGuen, P., Bunch, D., and Saling, P. (1992) Proc. Natl. Acad. Sci. U. S. A. 89, 11692-11695). This protein was purified and subjected to limited tryptic digestion and subsequent amino acid analysis. Three sequenced peptides revealed 100% amino acid identity to a mouse hepatoma hexokinase (Arora, K. K., Fanciulli, M., and Pederson, P. L. (1990) J. Biol. Chem. 265, 6481-6488). The purified protein, which migrated at M(r) 116,000 under reducing conditions (p95/116), reacted with an antiserum to the purified rat brain hexokinase, type 1, and comigrated on sodium dodecyl sulfate-polyacrylamide gel electrophoresis with the purified rat brain enzyme under both nonreducing and reducing conditions. Unlike p95/116, the rat brain enzyme was not a phosphotyrosine-containing protein. The p95/116 protein could be immunoprecipitated with the hexokinase antiserum or an O-phosphotyrosine antibody. Limited tryptic digestion of the purified p95/116 and the rat brain enzyme generated subsets of identical peptides which reacted with the hexokinase antiserum. However, p95/116 also contained phosphotyrosine-containing peptides that were not present in the rat brain hexokinase. When different mouse tissues were probed with the hexokinase antiserum all tissues, with the exception of liver, contained immunoreactive protein. In contrast, only sperm and testis possessed a phosphotyrosine-containing form of hexokinase. These data suggest that the germ cell component of the testis possesses a unique tyrosine-phosphorylated form of hexokinase.

Amino Acid Sequence↗

PubMed1994

Rapid, nonradioactive, and quantitative method to analyze zona pellucida modifications in single mouse eggs.

A rapid, nonradioactive method to monitor the ZP2 to ZP2f conversion in the zona pellucida of single mouse eggs has been developed. This assay is based on the chemiluminescent detection of biotinylated ZP2 and ZP2f following electrophoresis under reducing conditions and electrophoretic transfer to Immobilon P. This method is about 10 times faster and detects similar extents of ZP2 to ZP2f conversion following A23187-induced egg activation, when compared to the commonly used radioiodination procedures.

Animals↗

PubMed1993

Modifications of the mouse zona pellucida during oocyte maturation: inhibitory effects of follicular fluid, fetuin, and alpha 2HS-glycoprotein.

Mouse oocyte maturation in vivo or in vitro is accompanied by a precocious release of cortical granules. When oocytes are matured in vitro in the absence of serum, cortical granule exocytosis results in modifications of the zona pellucida (ZP) that are known to constitute the zona pellucida block to polyspermy. Fetuin, a glycoprotein found in newborn calf serum, can inhibit these maturation-associated changes in the zona pellucida. In this report we demonstrate that the human fetuin homologue, alpha 2-HS-glycoprotein, is present in human follicular fluid. Human follicular fluid, or purified human alpha 2-HS-glycoprotein, inhibits the maturation-associated conversion of mouse ZP2 to ZP2f in a concentration-dependent manner. Although the concentration of alpha 2HS-glycoprotein in human follicular fluid is high enough to account for the inhibitory effect of human follicular fluid on this maturation-associated conversion, human follicular fluid immunodepleted of alpha 2HS-glycoprotein retains its full inhibitory activity. Thus, other inhibitory molecules are likely to be present in follicular fluid and contribute to the inhibition of the maturation-associated conversion of ZP2.

Animals↗

PubMed1991

Modifications of the mouse zona pellucida during oocyte maturation and egg activation: effects of newborn calf serum and fetuin.

A precocious but limited loss of cortical granules (CG) occurs during mouse oocyte maturation both in vivo and in vitro. Although CG loss during maturation in vivo is not associated with changes in the zona pellucida (ZP), a maturation-associated conversion of ZP2 to ZP2f occurs during oocyte maturation in vitro in serum-free medium. We now demonstrate that a maturation-associated change of ZP3 to ZP3f, as assessed by a reduction in sperm binding, also occurs during maturation in vitro in serum-free medium, and that both newborn calf serum (NCS) and fetuin, each of which inhibits the ZP2 conversion, also inhibit the ZP3 conversion. The concentration-dependence of the NCS- and fetuin-mediated inhibition of the ZP2 conversion, coupled with the concentration of fetuin present in NCS, is consistent with fetuin being the component present in NCS that is primarily responsible for this inhibition. Although NCS can inhibit the ZP modifications that occur during oocyte maturation in vitro, ionophore treatment of eggs, which results in an extensive release of CGs over a short period of time, overcomes the inhibitory effect of NCS on the ZP2 conversion. Results of these studies suggest a potential regulatory function of serum-derived components in the formation of a fertilizable egg.

Animals↗