Drosophila grainyheadgene and its neural stem cell-specific enhancers show epigenetic synchrony in the cells of the central nervous system

Enhancers are the epicentres of tissue-specific gene regulation. In this study, we have used the central nervous system (CNS) specific expression of theDrosophila grainyhead(grh) gene to make a case for deleting the enhancers in a sensitised background of other enhancer deletion, to functionally validate their role in tissue-specific gene regulation. We identified novel enhancers forgrhand subsequently deleted two of them, to establish their collective importance in regulatinggrhexpression in CNS. This showed thatgrhrelies on multiple enhancers for its robust expression in neural stem cells (NSCs), with different combinations of enhancers playing a critical role in regulating its expression in various subset of these cells. We also found that these enhancers and thegrhgene show epigenetic synchrony across the three cell types (NSCs, intermediate progenitors and neurons) of the developing CNS; andgrhis not transcribed in intermediate progenitor cells, which inherits the Grh protein from the NSCs. We propose that this could be a general mechanism for regulating the expression of cell fate determinant protein in intermediate progenitor cells. Lastly, our results underline that enhancer redundancy results in phenotypic robustness ingrhgene expression, which seems to be a consequence of the cumulative activity of multiple enhancers.