Abstract
To guard genome integrity, response mechanisms coordinately execute the G2/M checkpoint in responding to stress. p38 MAPK is activated to prolong the G2 phase for completion of damage repair. Tlk activity is required for DNA repair, chromosome segregation and G2 recovery. However, the involvement of Tlk in G2 recovery differs from previous findings that Tlk overexpression delays the G2/M transition. To clarify this difference, genetic interaction experiments were performed using the second mitotic wave as model system. The results indicate that Tlk overexpression prolongs the G2 phase through p38 MAPK activation, independent of Tlk kinase activity. The results of co-immunoprecipitation, database search and RNAi screening suggest that eEF1α1 and Hsc70-5 links Tlk to Tak1. Reduced gene activities of Tlk, Hsc70-5, eEF1α1 and/or Tak1 couldn’t prolong the G2 phase induced by heat shock, indicating that these proteins work together to elevate p38 MAPK activity. In contrast, a high level of wild type Tlk decreases phosphorylated p38 MAPK levels. Thus, the difference is explained by a dual function of Tlk. When under stress, inactive Tlk increases p38 MAPK activity to prolong the G2 phase, and then activated Tlk modulates activities of p38 MAPK and Asf1 to promote G2 recovery afterwards.
Highlights
Accumulated information indicates that genome instability is related to age-related diseases, such as neurodegeneration, metabolic disorders and carcinogenesis, etc[1]
In eye disc behind the morphogenetic furrow (MF) with Tlk overexpression, the S phase progression was not affected as seen by the bromodeoxyuridine labeling (Supplementary Fig. S1), while the G2 phase was prolonged as evidenced by the significantly widened distribution of CycA by immunostaining (Fig. 1a)
We showed widened distribution of CycA, indicating that Tlk overexpression prolongs the G2 phase
Summary
Accumulated information indicates that genome instability is related to age-related diseases, such as neurodegeneration, metabolic disorders and carcinogenesis, etc[1]. Tlk[1] and Tlk[2], are identified and their kinase activities are maximally activated by DNA damage during the S phase[16,17]. These two kinases participate in chromosomal segregation[17]. Chromosomal missegregation is observed in embryos lacking Tlk activity[12,18], indicating that Tlk activity is required for maintaining genome integrity As mentioned above, both Tlk[1] and Tlk[2] activities promote the G2 recovery from the G2 arrest induced by DNA damage[3,5]. To clarify the role of Tlk in the G2/M transition, we mainly performed genetic interaction experiments using the second mitotic wave (SMW) in Drosophila eye disc as a model system[22]
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