Study Of Cyclin C During Zebrafish Early Embryo Development

Ontogenesis begins from the fertilized embryo. After the cells proliferation during the embryo cleavage, it enters the stage of blastoderm differentiation, tissue and organ formation. Embryo cells display a synchron cleavage rhythm during the cleavage stage, there is almost no gene transactivation, which is regulate and operated by the mRNAs and protein of oocyte. The futhur development needs the expression of zygotic transactivation. In fish and amphibia, the transition from maternal gene transcription to zygotic transcription happens during the time of midblastula formation, this stage is named by midblastula transition (MBT), at this period, embryo cell cycle composition changes, it is the first time to G1 time appearance, the cell cycle timelimit lengthens and the cell division synchronism loses, the large quantities of zygotic gene transcription starts. The molecular mechanism of this major phase during vertebrate embryonic development is poorly understood.In eukaryotic expression, the cyclin C mRNA and protein achieves the highest level in the early stage of G1, and cyclin C can make yeast mutant which can not produce the G1 time cycle protein (CLNs) restore the growth, This suggest that cyclin C has function to the cell behavior in the G1 time. In addition, cyclin C binds the cyclin-dependent kinase (cdk) cdk3, The cdk3/cyclin C pair is a key regulator of cell cycle re-entry in human cells. In addition, The cdk8/cyclin C pair was discovered in yeast and human cells, which has a role in transcriptional repression. In human cells, cdk8/cyclin C also has phosphorylates cyclin H, parts of TFIIH, repressing cdk7 activity and transcription. Further cdk8/cyclin C also constitutes parts of RNA polymerase II CTD, and phosphorylation of RNA polymerase II CTD is key regulation factor for the begaining of trnscription.Cyclin C has relation with the cell cycle and transcript regulation. And the union of the two aspects is the key point for the well known of midblastula transition (MBT) mechanism. In zebrafish, The spatio-temporal expression of cyclin C and it's role in early embryo development and MBT stage has not been exploited.The cDNA of zebrafish cyclin C is obtained by our lab (GeneBank NO: AY450302), sequence analysis shows zebrafish cyclin C cDNA is conservative to the human orthologue, meanwhile, it is conserved from the DNA level to the protein level,which suggest the importance of cyclin C. Northern bloting and and whole-mount in situ hybridization (WISH) analysis, suggest cyclin C is maternally loaded in embryos and organs of adult fish. It was expressed both maternally and zygotically. Distribution of cyclin C transcripts is ubiquitous during early stages, becoming restricted to the brain and back body. Overexpression of cyclin C can induced malformation of tail and brain; western bloting test show cyclin C is degradated after MBT in the early development of zebrafish embryo. This suggest cyclin C is an important gene in the early embryo development of zebrafish, it take part in the mechanism of early development.