Cell cycle reentry from the late S phase: implications from stem cell formation in the moss Physcomitrella patens
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Differentiated cells are in a non-dividing, quiescent state, but some differentiated cells can reenter the cell cycle in response to appropriate stimuli. Quiescent cells are generally arrested at the G0/G1 phase, reenter the cell cycle, and progress to the S phase to replicate their genomic DNA. On the other hand, some types of cells are arrested at the different phase and reenter the cell cycle from there. In the moss Physcomitrella patens, the differentiated leaf cells of gametophores formed in the haploid generation contain approximately 2C DNA content, and DNA synthesis is necessary for reentry into the cell cycle, which is suggested to be arrested at late S phase. Here we review various cell-division reactivation processes in which cells reenter the cell cycle from the late S phase, and discuss possible mechanisms of such unusual cell cycle reentries with special emphasis on Physcomitrella.
KeywordsCell cycle DNA synthesis Physcomitrella Wounding
We thank Drs. Y. Tamada and I. Imai for critical reading of the manuscript, and Liechi Zhang for providing photographs of an excised leaf. This work was partially supported by the Japan Science and Technology Agency ERATO Program and the Ministry of Education, Culture, Sports, Science and Technology (No. 25291067 to M. H. and M. I.).
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