Functional Study Of Demethylase KDM3A During Neural Development In Xenopus Laevis

Determination and differentiation of nervous system is a complicated process during embryonic development.It has been found that many signaling pathways and transcription factors are involved in nervous system development.bHLH transcription factors as a well-known family of proneural genes play a critical role in neural development.Substantial evidence has indicated that Neurog2 and Ascl1 initiate different genetic pathways for neuronal specification and differentiation;however,the molecular mechanisms underlying the differenttransactivities between Neurog2 and Ascl1 have not been fully understood.Epigenetic modification of histones can change the state and strength of gene expression without changing the sequence of genes.More and more evidence shows that histone modification plays a significant role in various stages during embryonic development.In this dissertation,we use Xenopus laevis as a model to study neuronal development.We find that the histone H3 lysine 9 demethylase KDM3 A is expressed in central nervous system.KDM3 A act as a co-activator of Ngnr1,the Xenopus orthologue of Neurog2.KDM3 A depletion diminishes the ability of Ngnr1 to initiate neuronal gene expression.By contrast,KDM3 A is dispensable for Ascl1 to activate tubb2 b.During the primary neurogenesis in Xenopus laevis,we find that KDM3 A depletion does not affect neural induction or the expression of Ngnr1,instead,causes a loss of primary neurons.Biochemical analyses uncover that Ngnr1 via its C-terminal domain interacts with KDM3 A.ChIP-qPCR analyses reveal that Ngnr1 removes the repressive H3K9me2 marks from neuronal gene loci depending on KDM3 A.KDM3A is also required for the establishment of active histone marks such as H3K4me3 and H3K27 ac during Ngnr1-promoted neuronal gene activation.Interestingly,we find evidence that the inability of Ascl1 to transactivate neurod1 is at least in part due to its incapability of recruiting KDM3 A.Moreover we demonstrate that KDM3 A is necessary for Ngnr1 to access its target sites at neuronal gene loci.In summary,we have provided evidence that Ngnr1 transactivate neuronal genes through recruitment of KDM3 A,and the different activities of Ngnr1 and Ascl1 in initiating neuronal development can be at least in part accounted for by their differential requirement of KDM3 A.