Molecular Characterization And Functional Analysis Of Cyclin K During The Embryonic Development Of Artemia Parthenogenetica

Artemia is a genus of anostracan crustaceana living in the saline of worldwide. As a strategy to cope with environmental stresses, Artemia has evolved a special reproductive mode in which in addition to giving birth to nauplii by the ovoviviparous pathway, it also releases encysted embryos by the oviparous pathway. Released encysted embryos possess powerful adaptations to extreme environments. They are developmentally arrested at the gastrula stage with a low metabolic rate and complete turnoff of replication, transcription, and translation; however, without loss of embryonic viability for an extremely long period. The intrinsic mechanisms regulating this process are not well understood.Our research identified cyclin K was posttranscriptional regulated in Artemia diapause embryos and this is of great significance in the formation and postdiapause development of encysted embryos. Cyclin K can interact with cyclin dependent kinases (CDKs) to regulate the activity of RNA polymerase Ⅱ (RNAPII) which has an essential role from cell proliferation to embryonic development.In the present study, we analyzed the mRNA and protein expression of Artemia cyclin K in two developmental pathways, and identified cyclin K was posttranscriptional regulated in Artemia diapause embryos. Basing on this, we further tested the phosphorylation of position2serines in the C-terminal domain (CTD) of the largest subunit (Rpbl) of RNAP Ⅱ and the localization of cyclin K and phosphorylated RNAPII. In addition, in vivo knockdown of cyclin K in developing embryos by RNA interference was carried out.Our results represent that the cyclin K protein was down-regulated in the diapause-destined embryo as entering dormancy and reverted to relatively high levels of expression once development resumed, consisting with the fluctuations in phosphorylation of position2serines (Ser2) in the C-terminal domain (CTD) of the largest subunit (Rpb1) of RNA polymerase Ⅱ (RNAP Ⅱ). Interestingly, the cyclin K transcript levels remained constant during this process. In vitro translation data indicated that the template activity of cyclin K mRNA stored in the postdiapause cyst was repressed. In addition, in vivo knockdown of cyclin K in developing embryos by RNA interference eliminated phosphorylation of the CTD Ser2of RNAP Ⅱ and induced apoptosis by inhibiting the extracellular signal-regulated kinase (ERK) survival signaling pathway.Taken together, these findings reveal a role for cyclin K in regulating RNAP Ⅱ activity during diapause embryo development, which involves the post-transcriptional regulation of cyclin K. In addition, a further role was identified for cyclin K in regulating the control of cell survival during embryogenesis through ERK signaling pathways.