Both JNK and apoptosis pathways regulate growth and terminalia rotation during Drosophila genital disc development.

Apoptosis is necessary for the regulation of growth during development, but the precise details of this regulation have not been completely characterized. In this study, we used the Drosophila genital disc as a model to analyze the contribution of apoptosis to growth regulation. We studied the expression or activity of several elements of the apoptotic death pathway such as Drosophila inhibitor of apoptosis1, caspases, the apoptotic genes reaper (rpr) and head involution defective, as well as elements of the Jun-NH2-terminal kinase (JNK) pathway. We found that the JNK pathway is active in a dynamic, asymmetric and genitalia-specific manner. Apoptosis, as measured in terms of the expression of a variety of apoptotic molecules, occurs in a JNK-dependent and -independent manner and was detected among engrailed (en) expressing cells. JNK regulation of apoptotic genes is necessary to control growth in both sexes and rotation in males; this regulatory role is necessary to execute en(+) cell death and to activate expression of rpr in these cells. rpr is up-regulated at antero-posterior borders, and this expression appears to be of particular importance in the control of growth, since the balance between cell proliferation and death in those regions appears to depend on the equilibrium between pro- and anti-apoptotic factors at a cellular level.