SPATIOTEMPORAL REGULATION OF HEART DEVELOPMENT IN THE DROSOPHILA EMBRYO

Abstract

The commitment to cardiac cell fates occurs during early stages of mesoderm patterning and is spatiotemporally regulated by inputs from several conserved signalling pathways. The uniform spreading of the mesoderm over the ectoderm is the earliest of all the processes that guide heart formation in the embryo and is crucial for proper fate specification. Heartless (Htl), a Fibroblast Growth Factor Receptor (FGFR) expressed in the mesoderm has a crucial role at both early and later stages of heart development. Though these roles are independent of each other, synergy between them is essential for proper morphogenesis of the heart. However, the dynamics of Htl action are poorly understood after the initial phases of mesoderm spreading. To delineate the effects of conditional Htl activation on embryo development, specifically heart formation, I developed an optogenetic tool termed Opto-Htl, that enables us to activate the FGFR pathway in selective spatial and temporal domains. I found that Htl signalling dosage has an effect on the specification of Tinman (Tin) positive heart cells and Opto-Htl activation favours the specification of these cardioblasts and eliminates other dorsal muscles. Opto-Htl also allows fine tuning of these phenotypic responses making it a powerful tool to dissect the role of Htl during the mesoderm specification stages. Given the crucial role of Tin in specification and diversification of heart and visceral muscles, I have also developed tools to study its expression dynamics and effects of conditional activation / repression. The Tin live reporter has powerful potential to be used in conjunction with other transcription reporters to study the linearity / non-linearity between expression dynamics of different heart specific genes. I further attempted to develop a tool for optogenetic control of Tin-dependent transcription, which would allow dissection of its role during different stages of cardiac fate specification. Overall, I have developed new tools for understanding the dynamics of heart specification and morphogenesis in Drosophila. Given the high conservation of key cardiac genes, these have the potential to impact our understanding of heart development in other organisms.