Dissecting the direct downstream targets of Hand2 during zebrafish cardiac development

Abstract

Defects in the development of the heart lead to Congenital Heart Diseases (CHD), making it important to study the developmental mechanisms and signaling pathways. Hand2 is one of the transcription factors that is found to be important in cardiac development. Hand2 is a basic helix-loop-helix (bHLH) transcription factor that is expressed in the lateral plate mesoderm (LPM) starting at the completion of gastrulation, and is expressed in the LPM of zebrafish, chick, frog, and mouse embryos. Its function is essential for many processes including precardiac cell differentiation into clmc2 expressing myocardial precursors; it is important for the generation of vmhc expressing ventricular cells; for maintenance of myocardial tbx5 expression and formation of the midline heart tube. Hand2 is also important for the early transition of the cardiogenic LPM, and in hand2 mutants the progenitor cells residing in the anterior LPM fail to generate differentiated cardiomyocytes. Here, in this study we focused on generating a zebrafish transgenic line with an HA epitope tag inserted into the endogenous Hand2 protein to determine the downstream targets of Hand2 using ChIP sequencing. We also looked at two possible downstream targets of Hand2, which are pdgfra and timp2a, and performed functional studies on both genes in the endocardium and myocardium.