UC San Diego

Stem cell maintenance is an essential process that is needed to preserve a delicate balance between self-renewal and differentiation. Excess amounts of self-renewal can lead to tumorigenesis, while too little can lead to stem cell depletion. In the male Drosophila gonad, local activation of the JAK/STAT pathway by the ligand unpaired (Upd) is needed to maintain this stem cell self-renewal. Here it is shown that selective ectopic expression of Upd in certain germline cells is sufficient to induce over- proliferation of both early germline and somatic cells. This over-proliferation can be induced through activation of JAK/STAT signaling in germ cells as late as partially differentiated spermatogonia, suggesting that these cells may possess the ability to de-differentiate. Over- expression of the Upd homologue Upd2 also appears to be sufficient to induce over-proliferation, and may actually have a more pronounced effect on somatic cells and disrupt the transition from spermatogonial cysts to spermatocytes. The response of these cells to ectopic JAK/STAT activation can help further our understanding of how stem cell self- renewal is organized, and the ways in which the surrounding somatic cells support this process