The Hox gene Abd-B controls stem cell niche function in the Drosophila testis. Fani Papagiannouli¹, Lisa Schardt², Nati Ha¹, Janina-Jacqueline Ander¹, Ingrid Lohmann¹. 1) Developmental Biology, Centre for Organismal Studies (COS), Heidelberg, Germany; 2) Deutsches Krebsforschungszentrum (DKFZ), Heidelberg, Germany.

   Stem cells reside in a specialized microenvironment, called the stem cell niche, which provides essential signals controlling stem cell behavior. Proper niche architecture is a key for normal stem cell function, yet only few upstream regulators are known. Here we report that the Hox transcription factor Abd-B controls niche positioning and integrity in the Drosophila testis by regulating integrin and actin localization in the neighboring somatic cyst cells. Loss of Abd-B results in centrosome misorientation in germline stem cells (GSCs) and reduced GSC divisions, leading to a dramatic reduction of pre-meiotic stages in adult testes, a hallmark of aging. Genetic dissection revealed that non-cell-autonomous organization of the stem cell niche downstream of Abd-B is mediated by diverse mechanisms, including the Boss-Sev pathway, linking integrin to the extracellular matrix and actin filaments. In order to systematically elucidate the network and hierarchy of events related to Abd-B function in the Drosophila testis, we aimed at identifying direct Abd-B target sites within the Drosophila genome using the in vivo binding-site profiling technique DamID (DNA adenine methyltransferase identification). Our data show for the first time that Abd-B provides positional cues upstream of integrin to maintain niche architecture and localization, ensure proper niche and GSC function, and prevent premature aging.