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Cell Biology International (2002) 26, 193–201 (Printed in Great Britain)

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DEFINITIVE EXPRESSION OF C-MOS IN LATE MEIOTIC PROPHASE LEADS TO PHOSPHORYLATION OF A 34KDA PROTEIN IN CULTURED RAT SPERMATOCYTES

Yosinobu Nagao^f1

Division of Clinical Science, Medical Research Institute, and Department of Biochemistry, Kanazawa Medical University, Uchinada, Ishikawa, 920-0293, Japan

Abstract

To investigate the role of c-mos in rat spermatogenesis, expression of c-mos, MAP kinase kinase (MAPKK), MAP kinase (MAPK), cdc2 and protein kinase A (PKA) by spermatogenic cell culture of 14 day-old rats was examined. MAPKK and PKA expressions were constitutive, whereas the expression of MAPK and cdc2 in spermatogonia initially decreased, but later increased on meiotic maturation of spermatocytes. c-mos expression was definitive of late meiotic prophase. c-mos immunoprecipitates prepared from the c-mos-enriched fraction (pI9.0–9.6) could form complex(es) in the cultured spermatogenic cell lysates.In vitro phosphorylation of the c-mos immune complexes revealed a 34 kDa protein that was phosphorylated at serine and threonine residues as a target of the c-mos signal. Its pI value was 4.4–4.5, and cdc2 was not detected, making it different from cdc2 (p34). These results suggest that the phosphorylation of the 34kDa protein by the c-mos signal may play a crucial role in the meiotic division of rat spermatocytes.

Key words: spermatogenesis, c-mos, MAP kinase kinase, MAP kinase, cdc2, protein kinase A.

^f1To whom correspondence should be addressed: Fax: +81-076-286-8291. E-mail: y-nag@kanazawa-med.ac.jp

Received 3 April 2001; accepted 12 September 2001