Role of hemocytes in the regeneration of germline stem cells in Drosophila

Cellular regeneration, which relies on extensive restructuring of cytoplasmic materials, is an essential process to restore tissues and organs lost during aging, degenerative diseases and injury. At early stages of Drosophila spermatogenesis, when cellular constituents are intensely remodeled, there are two different populations of stem cells, the somatic stem cells and the germline stem cells (GSCs). GSCs divide by asymmetric division to give rise two distinct daughter cells. One of them will leave the stem cells niche and differentiate into spermatogonial cells (SCs). Both aging and cellular stress can lead to the loss of GSCs. Lost GSCs can be restored by dedifferentiation of SCs into functional GSCs. In other tissues, macrophages provide specific conditions for cellular transformation. Here we examined the potential role of immune surveillance cells called hemocytes during dedifferentiation of SGs into GSCs. We found an elevated number of hemocytes during this dedifferentiation process. Immune depletion of hemocytes decreased the regeneration capacity of germline. We also show that autophagy, which plays a pivotal role in cellular differentiation by eliminating unwanted, superfluous parts of the cytoplasm, becomes upregulated in dedifferentiating SCs upon JAK-STAT signaling emitted by hemocytes. Furthermore, these immune cells regulate expression of Omi/HtrA2, a key regulator of apoptosis in early spermatogenesis. Together, we suggest that hemocytes have important functions in the dedifferentiation process of GSCs.