PMID:16854973

Citation	Reber, A, Lehner, CF and Jacobs, HW (2006) Terminal mitoses require negative regulation of Fzr/Cdh1 by Cyclin A, preventing premature degradation of mitotic cyclins and String/Cdc25. Development 133:3201-11
Abstract	Cyclin A expression is only required for particular cell divisions during Drosophila embryogenesis. In the epidermis, Cyclin A is strictly required for progression through mitosis 16 in cells that become post-mitotic after this division. By contrast, Cyclin A is not absolutely required in epidermal cells that are developmentally programmed for continuation of cell cycle progression after mitosis 16. Our analyses suggest the following explanation for the special Cyclin A requirement during terminal division cycles. Cyclin E is known to be downregulated during terminal division cycles to allow a timely cell cycle exit after the final mitosis. Cyclin E is therefore no longer available before terminal mitoses to prevent premature Fizzy-related/Cdh1 activation. As a consequence, Cyclin A, which can also function as a negative regulator of Fizzy-related/Cdh1, becomes essential to provide this inhibition before terminal mitoses. In the absence of Cyclin A, premature Fizzy-related/Cdh1 activity results in the premature degradation of the Cdk1 activators Cyclin B and Cyclin B3, and apparently of String/Cdc25 phosphatase as well. Without these activators, entry into terminal mitoses is not possible. However, entry into terminal mitoses can be restored by the simultaneous expression of versions of Cyclin B and Cyclin B3 without destruction boxes, along with a Cdk1 mutant that escapes inhibitory phosphorylation on T14 and Y15. Moreover, terminal mitoses are also restored in Cyclin A mutants by either the elimination of Fizzy-related/Cdh1 function or Cyclin E overexpression.
Links	PubMed Online version:10.1242/dev.02488
Keywords	Animals; Cell Cycle Proteins/metabolism; Cyclin A/genetics; Cyclin A/metabolism; Cyclin E/genetics; Cyclin E/metabolism; Cyclins/metabolism; Down-Regulation; Drosophila/cytology; Drosophila/embryology; Drosophila Proteins/metabolism; Embryo, Nonmammalian/metabolism; Embryonic Development/genetics; Epidermis/metabolism; Mitosis/genetics; Mutation; Protein Tyrosine Phosphatases/metabolism
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