Overexpression of jumu induces melanotic nodules by activating Toll signaling in Drosophila.

Melanotic nodules are commonly assumed to be caused by an abnormal immune response. Several hematopoietic mutants and signaling pathways, including the Toll, JAK/STAT, Ras and JNK pathways, can cause melanotic nodules to develop when specifically activated in hemocytes. Here, we used the UAS-Gal4 system to overexpress jumeaux (jumu) in the fly immune response system. Jumeaux (Jumu) is a new member of the winged-helix/forkhead (WH/FKH) gene family of transcription factors, which plays an important role in the growth and morphogenesis of Drosophila and participates in the proliferation and differentiation of hemocytes. Overexpressing jumu in both hemocytes and the fat body generated many melanotic nodules in larvae and adult flies. The nodules observed in the fat body were surrounded by large numbers of blood cells through a process that appeared similar to foreign body encapsulation. This phenomenon is caused by Toll pathway activation and leads to blood cells deposited in the fat body. In addition, we also report the dissociation of fat cells and the abnormal proliferation and differentiation of blood cells. These results suggest a Jumu-mediated crosstalk between hematopoiesis and the fat body, especially during the Toll-dependent formation of melanotic nodules.