The Hippo signalling pathway regulates the timing of epithelial cell replacement during Drosophila abdominal morphogenesis.

Developmental apoptosis plays an important role in shaping the organs of developing animals, such as occurs during the development of the adult fly abdomen, in which the apoptosis of larval epidermal cells (LECs) is delicately balanced with the proliferation of the presumptive adult epithelial cells. The signalling pathways involved in the coordinated regulation of these processes are at present poorly understood. Here, we demonstrate a role for the Hippo signalling pathway in regulating the timing of LEC clearance during abdominal development. Downregulating Hippo signalling promotes LEC survival into adulthood, whereas upregulating Hippo signalling induces premature LEC removal from the epithelium. Crucially, this effect was found to be dependent upon Hippo pathway-mediated transcription, with increases in the expression of pro-survival genes and increased nuclear localization of the Hippo effector Yorkie occurring in LECs during early pupal development. These findings demonstrate a role for Hippo signalling in abdominal morphogenesis and highlight a biologically relevant example of the function of this pathway as a regulator of developmental apoptosis.