Acquisition of Competence to Condense Metaphase I Chromosomes during Spermatogenesis

Abstract

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.

Mutation of Eif4g3, encoding a eukaryotic translation initiation factor, causes male infertility and meiotic arrest of mouse spermatocytes

“…1G,H). To determine whether spermatogenesis became arrested in repro8 mutants before or after the mid-pachytene stage of meiotic prophase, we assessed the presence of histone H1t, a midpachynema marker (Cobb et al, 1999a;Drabent et al, 1993;Inselman et al, 2003). Histone H1t was detected in nuclei of repro8 mutant spermatocytes (see Fig.…”

“…5A, CDC2A kinase activity at P14 in Eif4g3 repro8 mutant spermatocytes was dramatically reduced compared with wild-type spermatocytes. Furthermore, unlike wild-type P18 spermatocytes, P18 spermatocytes from Eif4g3 repro8 mutants did not form fully condensed metaphase I chromosomes after treatment in vitro with the phosphatase inhibitor okadaic acid, an experimental test of the competence of the intracellular machinery for mediating the G2/MI transition (Cobb et al, 1999a) (Fig. 5B).…”

Reproductive Isolation in Hybrid Mice Due to Spermatogenesis Defects at Three Meiotic Stages

“…Scale bars: 200 mm. replaces somatic H1 on chromatin at mid-pachytene and thus serves as a marker of mid-to-late pachytene spermatocytes (Moens 1995;Cobb et al 1999). In most early pachytene spermatocytes in B6-ChrX MSM males, SYCP3 signals were observed as thick fibers as observed in control males, but B6-ChrX MSM spermatocytes also frequently exhibited aggregation of SYCP3 ( Figure 3A).…”

PCNA Protein Expression during Spermatogenesis of the Japanese Eel (Anguilla japonica)

“…Recently, Cobb et al (1999) have demonstrated that the meiotic competence of spermatocytes is acquired after homologous chromosome pairing is established, being coincident with the appearance of testis-specific histone H1t and CDC25C protein phosphatase in spermatocytes. It is thus likely that protein dephosphorylation plays a key role in the control of the meiotic competence of spermatocytes.…”