PARENT SESSION
Oocyte Development

P90^RSK IS DIRECTLY INVOLVED IN OOCYTE MATURATION OF Rana dybowskii.

Kang, Hae Mook¹, Byun, Hyang Min¹, Kang, Sung Goo², ^{1 2}

ABSTRACT- It has been well known that several protein kinases are involved in the meiotic maturation of frog oocytes, finally to activate maturation-promoting factor (MPF). Among these kinases, the 90-kDa ribosomal protein S6 kinase (p90^Rsk, Rsk) is directly phosphorylated and activated by MAPK. During Xenopus oocyte maturation, activation of Rsk closely parallels that MAPK, and both enzymes are dephosphorylated when cytostatic factor (CSF) disappears after fertilization. Thus, Rsk seems to be an essential role in the activation of MPF. To evaluate it in other frog oocytes, we have cloned and characterized Rsk cDNA in Rana dybowskii oocytes. The cloned Rana Rsk cDNA is about 2950 bp of nucleotides, which is consisting of a complete single open-reading frame with ATG codon and polyadenylation signal. The deduced amino acid sequence of Rana Rsk is 733 amino acids with 83 kDa. Rana Rsk shows a high homology (about 90 %)with Xenopus Rsks. It also well conserved the two kinase domains with the specific phosphorylation sites, which is essential for activation of Rsk. Northern analysis is exhibited that Rana Rsk mRNA is strongly expressed in ovary tissue but weakly in other tissues. Rana Rsk protein is expressed with pTYB1 vector and purified with IMPACT-CN system. The purified Rana Rsk is cross-reacted with Xenopus p90^Rsk antiserum. So, we examined the phosphorylation of Rana Rsk during oocyte maturation. In P₄-treated oocytes, Rana Rsk is phosphorylated about 6-9 hr, which is well correlated with the germinal vesicle breakdown of Rana oocytes. Therefore, it is likely that Rana Rsk play an important role in the meiotic maturation of seasonal breeding animals.

KEY WORDS: Ribosomal protein S6 kinase, Oocyte, Maturation, Rana dybowskii