SPIN, A SUBSTRATE IN THE MAP KINASE PATHWAY IN MOUSE OOCYTES

The newly cloned gene Spin encodes a 30-kDa protein, a well-defined ab undant molecule found in mouse oocytes and early embryos. This protein SPIN undergoes metaphase-specific phosphorylation and binds to the sp indle. To understand the role of SPIN in oocyte meiosis, oocytes were treated with drugs that affect the cell cycle by activating or inactiv ating specific kinases. The posttranslational modification of SPIN in the treated oocytes was then investigated by one-and two-dimensional g el electrophoresis. Modification of SPIN is inhibited by treatment wit h 6-dimethyl-aminopurine (DMAP), suggesting that SPIN is phosphorylate d by a serine-threonine kinase. Furthermore, SPIN from cycloheximide-t reated oocytes that lack detectable MAP kinase activity is only partia lly phosphorylated, indicating that SPIN may be phosphorylated by the MOS/MAP kinase pathway. To confirm this observation, SPIN was analyzed in Mos-null mutant mice lacking MAP kinase activity. Normal posttrans lational modification of SPIN did not occur in Mos-null mutant oocytes . In addition, there is reduced association of SPIN with the metaphase I spindle in Mos-null mutant oocytes, as determined by immunohistoche mical analysis. These findings suggest that SPIN is a substrate in the MOS/MAP kinase pathway and further that this phosphorylation of SPIN may be essential for its interaction with the spindle. (C) 1998 Wiley- Liss, Inc.