Inhibition of Mitosis by Frühstart: function of the hydrophobic patch
Zusammenfassung der Projektergebnisse
The mid-blastula transition (MBT) is characteristic for species with large eggs and an initial cleavage stage. MBT serves as a paradigm for a developmental switch defined by concerted changes in gene expression and cell morphology and behaviour. The switch in cell cycle mode from fast alternating S and M phases to a G2 pause is a central and most obvious aspect of MBT. This switch is controlled by mitotic inhibitors that eventually lead to inhibition of the Cdk1-cyclin complex. Multiple pathways act in a redundant manner to ensure a robust switch after always 13 nuclear divisions, such as activation of the DNA checkpoint by zygotic genome activation, degradation of the Cdc25/Twine protein and blocking of cyclin A. Here we isolated and cloned new germ line clone mutations with cell cycle phenotypes during the blastoderm stage. We characterised three of these mutations. X161, a mutation in the 3’untranslated region of the gene encoding the large subunit of the RNA polymerase II leading to a reduced translation, induces a precocious onset of zygotic gene expression. This allowed to establish the functional relationship of zygotic gene expression and cell cycle pause and resolved a long-standing problem that onset of zygotic genome activation leads to checkpoint activation and subsequent cell cycle pause and not that the cell cycle pause is a prerequisite for onset of zygotic transcription. Furthermore, we characterised a mutation in the gene encoding the metabolic enzyme serine hydroxymethyltransferase, that induces a cell cycle arrest already in interphase 12 by activation of the DNA replication stress. A third mutation in the protein phosphatase V (Pp-V) leads to an additional nuclear division cycle and delayed MBT in interphase 15. The failed G2 pause is due to higher steady state levels of the Cdc25/Twine protein but not an impaired destabilization of Twine. To distinguish these two models, we measured steady state levels and decay constant by fluorescence correlation spectrometry of GFP-Twine in wild type and mutant embryos.
Projektbezogene Publikationen (Auswahl)
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Number of nuclear divisions in the Drosophila blastoderm controlled by onset of zygotic transcription. Curr Biol 23 (2013) 133-138
H.-W. Sung, S. Spangenberg, N. Vogt, J. Großhans
