Cytochrome c-d regulates developmental apoptosis in the Drosophila retina

The role of cytochrome c ( Cyt c) in caspase activation has largely been established from mammalian cell- culture studies, but much remains to be learned about its physiological relevance in situ. The role of Cyt c in invertebrates has been subject to considerable controversy. The Drosophila genome contains distinct cyt c genes: cyt c-p and cyt c-d. Loss of cyt c- p function causes embryonic lethality owing to a requirement of the gene for mitochondrial respiration. By contrast, cyt c- d mutants are viable but male sterile. Here, we show that cyt c- d regulates developmental apoptosis in the pupal eye. cyt c- d mutant retinas show a profound delay in the apoptosis of superfluous interommatidial cells and perimeter ommatidial cells. Furthermore, there is no apoptosis in mutant retinal tissues for the Drosophila homologues of apoptotic protease- activating factor 1 ( Ark) and caspase 9 ( Dronc). In addition, we found that cyt c- d - as with ark and dronc - regulates scutellar bristle number, which is known to depend on caspase activity. Collectively, our results indicate a role of Cyt c in caspase regulation of Drosophila somatic cells.