Involvement Of Histone H3Lysine56Acetylation In Cell Cycle Regulation During Development Of Artemia-encysted Embryos

The primitive crustacean, Artemia, possesses two independent reproductive pathways that allow adaptation to different growth conditions. Motile nauplii are released in favourable surroundings. However, when encounting extreme environmental conditions, encysted diapause embryos are produced in which cell division is restricted and the development arrested at gastrulae stage for long periods but without loss of embryonic survival viability. Morevover, this dormancy state of diapause cysts can be terminated after specific environmental stimulii, and then the post-diapause cysts develope into nauplius larvea under suitable conditions. So far, the mechanism underlying cell cycle arrest of Artemia diapause is not clear. This study focused on the roles of histone post-translational modifications and mitosis-related kinases.Histone H3lysine56(H3K56) acetylation was identified in both yeast and human cells recently, and reported to involve in the DNA replication of S phase and DNA damage checkpoint recovery. The steady-state equilibrium of H3K56acetylation is balanced by the opposing catalytic activities of histone acetylase (HAT) and deacetylase (HDAC). In this study, we found that there are no significant differences of the level of total H3K56acetylation during embryonic development of the two distinct reproduction pathways, but the acetylation of H3K56distributed mostly in the soluble fraction and on chromatin in the nauplii and diapause cysts, respectively. After the diapause termination, the H3K56acetylation on chromatin decreased and then remained a constant low level during the post-diapause developmental process, while the soluble H3K56acetylation increased coupling with the cell division resumption. Inhibition of deacetylase both in HeLa cells and Artemia increased the level of H3K56ac on chromatin and induced a cell cycle arrest, which leading an arrest of embryonic development in Artemia.SLK was firstly identified in Xenopus and characterized as the upstream kinase of Plkl to involve the transition from G2to M phase during the oocyte maturation. In our study, we identified another novel member of SLK superfamily, termed ArSLK. The analysis of mRNA level and protein expression revealed that there was no significant vibration of the mRNA level, while the protein level of ArSLK was high in diapause cysts, and relatively low in nauplius larvea. The result of cell fractionation displayed that ArSLK mainly distributed in the nuclei in diapause cysts while transferred into the cytoplasm in nauplius larvea. Based on these results, we speculated that the specifier subcellular localization was correlated with the regulation of Artemia diapause. However, more evidence is needed to prove this hypothesis.