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Updated: Sep 29, 2026
Functional Cloning Using a Xenopus Oocyte Expression System
Published on: January 30, 2016
Cloning of ribosomal protein S6 kinase cDNA and its involvement in meiotic maturation in Rana dybowskii oocytes
Hyang Min Byun1, Sung Goo Kang, Hae Mook Kang
1Department of Genetic Engineering, Chongju University, Korea.
Abstract:
Several protein kinases are involved in the meiotic maturation of frog oocytes in order to activate the maturation-promoting factor (MPF). Among these kinases, the 90 kDa ribosomal protein S6 kinase (p90Rsk or Rsk) is directly phosphorylated and activated by the mitogen-activated protein kinase (MAPK). During Xenopus oocyte maturation, the activation of Rsk closely parallels that of MAPK. Both enzymes are dephosphorylated when the cytostatic factor (CSF) disappears after fertilization. Therefore, Rsk seems to play an essential role in the activation of MPF. To evaluate it in other frog oocytes, we cloned and characterized Rsk cDNA in Rana dybowskii oocytes. The cloned Rana Rsk cDNA had 2,961 bp of nucleotides, which contained 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 88%) with Xenopus Rsk. It also had two well-conserved kinase domains with specific phosphorylation sites, which are known to be essential for the activation of Rsk. A Northern analysis showed that Rana Rsk mRNA was strongly expressed in ovary tissue, but weakly in other tissue. Rana Rsk protein is expressed with the pTYB1 vector and purified with the IMPACT-CN system. The purified Rana Rsk cross-reacted with Xenopus, a p90Rsk2 antiserum. Therefore, we examined the phosphorylation of Rana Rsk during Rana oocyte maturation. In P4-treated oocytes, Rana Rsk was phosphorylated about 6-9 h, which correlated well with the germinal vesicle breakdown of Rana oocytes. Therefore, it is likely that Rana Rsk plays an important role in the meiotic maturation of seasonal breeding animals.
Insights
The 90 kDa ribosomal protein S6 kinase (Rsk) is crucial for frog oocyte maturation, acting downstream of MAPK to activate MPF. This study characterizes Rana Rsk, confirming its role in meiotic maturation.
Area of Science:
- Cell Biology
- Molecular Biology
- Developmental Biology
Background:
- Meiotic maturation in frog oocytes involves protein kinases activating maturation-promoting factor (MPF).
- Mitogen-activated protein kinase (MAPK) phosphorylates and activates 90 kDa ribosomal protein S6 kinase (p90Rsk or Rsk).
- Rsk activation parallels MAPK activation during Xenopus oocyte maturation and deactivates with cytostatic factor (CSF) disappearance post-fertilization.
Purpose of the Study:
- To clone and characterize Rsk cDNA in Rana dybowskii oocytes.
- To investigate the role of Rana Rsk in meiotic maturation of frog oocytes.
- To confirm the functional conservation of Rsk across different frog species.
Main Methods:
- Cloning and sequencing of Rana Rsk cDNA.
- Bioinformatic analysis of deduced amino acid sequence and homology with Xenopus Rsk.
- Northern blot analysis for tissue-specific mRNA expression.
- Protein expression and purification using pTYB1 vector and IMPACT-CN system.
- Western blot analysis using anti-Xenopus p90Rsk2 antiserum.
- Examination of Rana Rsk phosphorylation during progesterone-induced oocyte maturation.
Main Results:
- Cloned Rana Rsk cDNA (2,961 bp) encoded a 733 amino acid, 83 kDa protein with high homology (88%) to Xenopus Rsk.
- Rana Rsk possesses conserved kinase domains and essential phosphorylation sites for activation.
- Rana Rsk mRNA was predominantly expressed in ovarian tissue.
- Purified Rana Rsk protein cross-reacted with anti-Xenopus p90Rsk2 antiserum.
- Rana Rsk phosphorylation was observed 6-9 hours after progesterone treatment, correlating with germinal vesicle breakdown.
Conclusions:
- Rana Rsk is functionally conserved with Xenopus Rsk and plays a significant role in Rana oocyte meiotic maturation.
- The phosphorylation and activation of Rana Rsk are key events during meiotic maturation.
- Rsk is likely essential for MPF activation in seasonal breeding animals like Rana.
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