Acquisition of competence to condense metaphase I chromosomes during spermatogenesis.
Little is known about the timing of meiotic prophase events during spermatogenesis in the mouse or how these events are related to cell-cycle progression. This work was designed to test hypotheses about the timing and biochemical correlates of developmental acquisition of competence to condense bivalent pairs of homologous chromosomes held together by chiasmata. The experimental approach takes advantage of the fact that okadaic acid (OA) treatment of pachytene spermatocytes causes precocious entry into metaphase I (MI) of meiosis. Leptotene and zygotene (L/Z) spermatocytes are not competent to respond to OA with condensation of chiasmate bivalent chromosomes. Competence for MI condensation of chiasmate bivalents is acquired by the middle of the pachytene stage of meiotic prophase, several days after homologous chromosomes become fully synapsed. The acquisition of MI competence is paralleled by the accumulation of histone H1t in the nuclei of mid-pachytene spermatocytes. Biochemical differences also exist between the incompetent L/Z spermatocytes and the competent pachytene spermatocytes. Both have the molecular components of metaphase promoting factor, CDC2 and CYCLIN B1; however, the histone H1 kinase activity of metaphase promoting factor of incompetent L/Z spermatocytes is not activated by OA, as it is in competent pachytene spermatocytes. Additionally, the CDC25C protein phosphatase is present in competent pachytene spermatocytes, but not in incompetent L/Z or early pachytene spermatocytes. Both incompetent and competent spermatocytes accumulate MPM-2 phosphoepitopes and phosphorylated histone H3 in response to OA treatment, indicating that presence of these antigens is not sufficient to promote condensation of meiotic chromosomes. These data demonstrate that meiotic competence of spermatocytes is acquired after homologous chromosome pairing is established and is coincident with first appearance of histone H1t and CDC25C protein phosphatase in spermatocytes.
Cobb
J
J
Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee, 37996, USA.
Cargile
B
B
Handel
M A
MA
D000818:Animals; D016203:CDC2 Protein Kinase / Q000378:metabolism; D002453:Cell Cycle / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000378:metabolism; D002467:Cell Nucleus / Q000502:physiology; D002843:Chromatin / Q000502:physiology; D002875:Chromosomes / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D019926:Cyclin B / Q000378:metabolism; D056744:Cyclin B1; D006657:Histones / Q000378:metabolism; D007621:Karyotyping; D008297:Male; D008540:Meiosis; D008677:Metaphase; D051379:Mice; D008813:Mice, Inbred ICR; D019319:Okadaic Acid / Q000494:pharmacology; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D013090:Spermatocytes / Q000166:cytology / Q000502:physiology*; D013091:Spermatogenesis / Q000235:genetics*; D020687:cdc25 Phosphatases
C534700:Ccnb1 protein, mouse; D018797:Cell Cycle Proteins; D002843:Chromatin; D019926:Cyclin B; D056744:Cyclin B1; D006657:Histones; D019319:Okadaic Acid; D011494:Protein Kinases; C102333:histone H1 kinase; D017346:Protein Serine-Threonine Kinases; D016203:CDC2 Protein Kinase; C517010:Cdc25c protein, mouse; D020687:cdc25 Phosphatases