The role of KMT2A in zebrafish development
Date of Issue2018
School of Biological Sciences
The Histone-lysine N-methyltransferase2A (KMT2A) acts as a global regulator of gene expression. KMT2A is responsible for methylation of lysine 4 of histone 3 (H3K4) on a small subset of genes, including HOX genes. The methylation of H3K4 neutralizes lysine positive charge thus making associated genes available for transcription. Having a general cellular function in histone methylation, KMT2A plays important roles in a variety of different cell processes and embryonic development. In medicine KMT2A is known to form fusions with other genes as a result of chromosomal trans locations. The products of these fusions are known as a major cause of infant acute myeloid and lymphoblastic leukaemia. In spite of these extremely important biological roles, the molecular mechanisms of KMT2A action are poorly understood. A better understanding ofthe action ofKMT2A in embryonic development will help shed light on its basic cell functions and on the molecular mechanisms of the oncogenicity ofKMT2A-fusions. To study the role ofKMT2A in embryonic development, we used morpholino (MO) knock-down and CRISPR-Cas9 knock-out approaches in zebrafish embryos. By phenotypic observation of kmt2a morphants and mutants, we found that downregulation or loss of function of kmt2a cause severe defects in blood circulation, defects in the development of some tissues derived from the neural plate border (NPB) and defects in eye development. We revealed severe perturbations of primitive erythropoiesis and vascularization in kmt2a knock-down embryos and established the position of kmt2a in the genetic hierarchy regulating embryonic erythropoiesis and vasculogenesis. kmt2a downregulation also was shown to affect development ofNPB derivatives (craniofacial cartilages, Rohon-Beard cells, trigeminal ganglia). We also detected transcription factors regulating development NPB and its derivatives neural crest (NC) and Rohon-Beard (RB), the expression of which is affected by kmt2a knock-down. The novel role of kmt2a in the bilateral splitting of forebrain into left and right fields and morphogenesis of optic stalk and optic cup was also shown by downregulation and loss-of-function approaches. The study thus revealed novel roles for kmt2a in zebrafish primitive and definitive hematopoiesis, vasculo- and angiogenesis, NPB, forebrain and eye development and provides multiple avenues by a which deeper understanding of the molecular functions of kmt2a can be further explored.