Abstract: Objective To observe the protein expression, subcelluar localization of activated Pak1 and its relationship with chromosome separation during meiosis in mouse oocytes. Methods Western blot was applied to analyze the expression of activated Pak1 (phosphorylated Pak1 at Ser204, pPak1Ser204) at different stages of meiotic progression in semi-quantitative manner; immunofluorescent staining was employed to detect the sub-cellular localization of pPak1Ser204 and its spatial-temporal correlation with spindle and microtubule organizing centers (MTOC) during oocyte meiosis. Results pPak1Ser204 expression was detected upon germinal vesicle breakdown (GVBD) in mouse oocytes, increased along with the meiotic progression, reaching peak level at metaphase I (MI), which remained up to meiosis II (MII). From pro-metaphase I (pro-MI) to MI and at MII stage, pPak1Ser204was co-localized with MTOC key components, pericentrin and ?-tubulin on spindle poles, pPak1Ser204 was also distributed on chromosomes; During anaphase I (AI) to telophase I (Tel I) progression, pPak1Ser204 was detached from chromosomes and MTOC, and mainly concentrated on the cleavage furrow. Conclusions pPak1Ser204 is expressed upon meiotic resumption in oocytes, it is a MTOC-associated protein, may regulate chromosome separation through participating the formation and maintenance of spindle apparatus.

Key words: pPak1Ser204, oocytes, meiosis, chromosome separation