Somatic support cells regulate germ cell survival through the Baz/aPKC/Par6 complex.

Local signals and structural support from the surrounding cellular microenvironment play key roles in directing development in both embryonic organs and adult tissues. In Drosophila, male germ cells are intimately associated and co-differentiate with supporting somatic cells. Here, we show that the function of the Baz/aPKC/Par6 apical polarity complex in somatic cyst cells is required stage specifically for survival of the germ cells they enclose. Although spermatogonia enclosed by cyst cells in which the function of the Par complex had been knocked down survived and proliferated, newly formed spermatocytes enclosed by cyst cells lacking Par complex proteins died soon after onset of meiotic prophase. Loss of Par complex function resulted in stage-specific overactivation of the Jun-kinase (JNK) pathway in cyst cells. Knocking down expression of JNK pathway components or the GTPase Rab35 in cyst cells lacking Par complex function rescued the survival of neighboring spermatocytes, suggesting that action of the apical polarity complex ensures germ cell survival by preventing JNK pathway activation, and that the mechanism by which cyst cells lacking Par complex function kill neighboring spermatocytes requires intracellular trafficking in somatic cyst cells.