Ras promotes cell survival by antagonizing both JNK and Hid signals in the Drosophila eye

This new function is likely to be mediated through the JNK pathway since the inhibition of JNK signalling can significantly suppress rasKP-induced apoptosis, whereas the removal of hid only weakly suppresses the phenotype. Furthermore, the reduction of JNK signalling together with the expression of the baculovirus caspase inhibitor p35, which blocks Hid activity, strongly suppresses the rasKP cell death. In addition, we find a strong correlation between rasKP-induced apoptosis in the eye disc and the activation of JNK signalling.In the Drosophila eye, Ras may protect cells from apoptosis by inhibiting both JNK and Hid activities. Surprisingly, reducing Ras activity in the wing, however, does not cause apoptosis but rather affects cell and organ size. Thus, in addition to its requirement for cell viability, Ras appears to mediate different biological roles depending on the developmental context and on the level of its expression.Programmed cell death, or apoptosis, is a fundamental physiological process in multicellular organisms. It plays a critical role in normal development where it is required for proper morphogenesis and tissue homeostasis, as well as serving a protective mechanism against extracellular pathogenic agents [1-3]. Apoptosis is also seen in pathological conditions such as when cells are deprived of survival signals. The biochemical pathway involved in apoptosis has been shown to be conserved from lower organisms, such as Drosophila, to mammals. The activation of apoptosis can be elicited by numerous signalling pathways.Drosophila eye development is one of the best models for studying mechanisms of apoptosis [4]. The compound eye is composed of about 800 units called ommatidia. Each ommatidium has eight photoreceptor cells and six supporting cells, all differentiated from epithelial cells in the larval eye imaginal disc [5]. During late pupal development, excess cells that are not recruited for differentiation are removed by apoptosis. Thus, mutation