IngentaConnect Coordinated Regulation of M Phase Exit and S Phase Entry by the C...

Authors: Iwabuchi M.¹; Ohsumi K.²; Yamamoto T.M.²; Kishimoto T.^{1, 2}

Source: Developmental Biology, Volume 243, Number 1, March 2002 , pp. 34-43(10)

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Abstract:

In the early embryonic cell cycle, exit from M phase is immediately followed by entry into S phase without an intervening gap phase. To understand the regulatory mechanisms for the cell cycle transition from M to S phase, we examined dependence on Cdc2 inactivation of cell-cycle events occurring during the M-S transition period, using Xenopus egg extracts in which the extent of Cdc2 inactivation at M phase exit was quantitatively controlled. The result demonstrated that MCM binding to and the initiation of DNA replication of nuclear chromatin occurred depending on the decrease of Cdc2 activity to critical levels. Similarly, we found that Cdc2 inhibitory phosphorylation and cyclin B degradation were turned on and off, respectively, depending on the decrease in Cdc2 activity. However, their sensitivity to Cdc2 activity was different, with the turning-on of Cdc2 inhibitory phosphorylation occurring at higher Cdc2 activity levels than the turning-off of cyclin B degradation. This means that, when cyclin B degradation ceases at M phase exit, Cdc2 inhibitory phosphorylation is necessarily activated. In the presence of constitutive synthesis of cyclin B, this condition favors the occurrence of the Cdc2 inactivation period after M phase exit, thereby ensuring progression through S phase. Thus, M phase exit and S phase entry are coordinately regulated by the Cdc2 activity level in the early embryonic cell cycle. ©2002 Elsevier Science (USA).

Keywords: Cdc2; early embryonic cell cycles; Cdc2 inhibitory phosphorylation; S phase entry; Xenopus

Language: English

Document Type: Research article

Affiliations: 1: CREST Research Project 2: CREST Research Project, Laboratory of Cell and Developmental Biology, Tokyo Institute of Technology, Nagatsuta 4259, Midoriku, Yokohama, 226-8501, Japan

Coordinated Regulation of M Phase Exit and S Phase Entry by the Cdc2 Activity Level in the Early Embryonic Cell Cycle