Functional Study Of TET In Early Hematopoietic Development Of Zebrafish

DNA cytosine methylation is one of the most important epigenetic modifications and plays essential roles in a variety of cellular processes. DNA methylation is generally considered to be a relatively stable epigenetic modification. However, emerging evidences prove that DNA methylation can be removed by passive or active pattern, in which active demethylation draw great attention especially. The identification of enzymes that involves in demethylation has been the subject of intense research. Recently, the discovery that TET dioxygenase mediates conversion of5mC to5hmC provides a novel avenue for the research of active DNA demethylation. In this study, we mainly focus on the functions and mechanisms of TET in early hematopoietic development of zebrafish, and preliminarily discuss the role of TET in regulation of IL-2expression during immune response.In part one, three TET homologs were identified in zebrafish. Bioinformatics study further demonstrated that these homologs share conserved structural domains with their mammalian counterparts. Expression analysis showed that TETs express in the stage of hematopoiesis, and that TET2and TET3express in the critical hematopoietic region of zebrafish embryos. The deletion of TET2inhibited erythropoiesis by suppressing the expression of hematopoietic genes. Further investigation displayed that TET2-upregulated lineage-specific genes and erythropoiesis are closely associated with the occurrence of5hmC and demethylation in the intermediate CpG promoters(ICPs). In addition, we found that TET2not only functions on the formation of erythroid progenitors but also on the differentiation of erythroid progenitors. In part two, IL-2gene of zebrafish was firstly identified and analyzed by bioinformatics. Functional study showed that IL-2is up-regulated in PMA stimulated lymphocytes accompanied by increasing of TETs expression. Moreover, a transcriptional memory was observed in second immune stimulation which displayed that IL-2was up-regulated faster and stronger in restimulated lymphocytes than the first one. We speculated that TET-mediated5hmC participates in IL-2expression regulation by "intermediate status" or "terminal status"pattern. In conclusion, our study demonstrated that TET2plays an essential role in erythropoiesis by regulating lineage-specific genes via DNA oxidative demethylation in zebrafish model. This report is anticipated to broaden current information on hematopoiesis and pathogenesis of related diseases such as MDS. In addition, we provided hypothesis about the potential functions and mechanisms of TET-mediated5hmC in regulation of immune factors and immune response.