Absence of Wee1 ensures the meiotic cell cycle in Xenopus oocytes.
Meiotic cells undergo two successive divisions without an intervening S phase. However, the mechanism of S-phase omission between the two meiotic divisions is largely unknown. Here we show that Wee1, a universal mitotic inhibitor, is absent in immature (but not mature) Xenopus oocytes, being down-regulated specifically during oogenesis; this down-regulation is most likely due to a translational repression. Even the modest ectopic expression of Wee1 in immature (meiosis I) oocytes can induce interphase nucleus reformation and DNA replication just after meiosis I. Thus, the presence of Wee1 during meiosis I converts the meiotic cell cycle into a mitotic-like cell cycle having S phase. In contrast, Myt1, a Wee1-related kinase, is present and directly involved in G(2) arrest of immature oocytes, but its ectopic expression has little effect on the meiotic cell cycle. These results strongly indicate that the absence of Wee1 in meiosis I ensures the meiotic cell cycle in Xenopus oocytes. Based on these results and the data published previously in other organisms, we suggest that absence of Wee1 may be a well-conserved mechanism for omitting interphase or S phase between the two meiotic divisions.
Nakajo
N
N
Department of Biology, Graduate School of Science, Kyushu University, Fukuoka 812-8581, Japan.
Yoshitome
S
S
Iwashita
J
J
Iida
M
M
Uto
K
K
Ueno
S
S
Okamoto
K
K
Sagata
N
N
D000818:Animals; D015153:Blotting, Western; D018797:Cell Cycle Proteins; D004261:DNA Replication / Q000502:physiology; D015536:Down-Regulation; D018507:Gene Expression Regulation, Developmental; D008540:Meiosis / Q000502:physiology*; D009687:Nuclear Proteins; D009865:Oocytes / Q000166:cytology; D009866:Oogenesis / Q000502:physiology*; D011418:Prophase / Q000502:physiology; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016196:S Phase / Q000502:physiology; D014981:Xenopus; D029867:Xenopus Proteins
D018797:Cell Cycle Proteins; D009687:Nuclear Proteins; D029867:Xenopus Proteins; C095970:MYT1 kinase, Xenopus; C530005:WEE1 protein, Xenopus; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases