Polycomb group gene E(z) prevents germline-to-soma conversion in Drosophila adult testes. Suk Ho Eun, Xin Chen. Dept Biol, Johns Hopkins Univ, Baltimore, MD.

   In many metazoans, germ cells are separated from somatic lineages early in development. However, little is known about the mechanisms that maintain germline versus somatic cell fate throughout life. Here we show that a key Polycomb group (PcG) component, Enhancer of Zeste [E(z)] H3K27me3-specific methyltransferase, is required to maintain germ cell identity in Drosophila adult testes. We find excessive early-stage somatic gonadal cells in E(z) mutant testes, which originate from both over-proliferative cyst stem cells and a potential germline-to-soma cell fate conversion. Lineage-specific markers reveal cells with both somatic and germline identities in E(z) mutant testes, suggesting an intermediate state between germline and somatic lineages. Using complementary lineage-tracing experiments in E(z) mutant testes, we demonstrate that some excessive early-stage somatic gonadal cells are derived from early-stage germ cells, including germline stem cells. Furthermore, we find that knocking down E(z) specifically in somatic cells causes this germline-to-soma conversion. Thus, our results demonstrate that one role of the somatic gonad is to maintain germline identity. Because mammalian male germ cells have a unique reprogramming potential, our discoveries will bring new insight to the application of germ cells in stem-cell-based regenerative medicine.