The Jak-STAT Target Chinmo Prevents Sex Transformation of Adult Stem Cells in the Drosophila Testis Niche

Local signals maintain adult stem cells in many tissues. Whether the sexual identity of adult stem cells must also be maintained was not known. In the adult Drosophila testis niche, local Jak-STAT signaling promotes somatic cyst stem cell (CySC) renewal through several effectors, including the putative transcription factor Chronologically inappropriate morphogenesis (Chinmo). Here, we find that Chinmo also prevents feminization of CySCs. Chinmo promotes expression of the canonical male sex determination factor DoublesexM (Dsx(M)) within CySCs and their progeny, and ectopic expression of DsxM in the CySC lineage partially rescues the chinmo sex transformation phenotype, placing Chinmo upstream of Dsx(M). The Dsx homolog DMRT1 prevents the male-to-female conversion of differentiated somatic cells in the adult mammalian testis, but its regulation is not well understood. Our work indicates that sex maintenance occurs in adult somatic stem cells and that this highly conserved process is governed by effectors of niche signals

A Flagellar Polycystin-2 Homolog Required for Male Fertility in Drosophila

AbstractA common inherited cause of renal failure, autosomal dominant polycystic kidney disease results from mutations in either of two genes, PKD1 and PKD2, which encode polycystin-1 and polycystin-2, respectively [1]. Polycystin-2 has distant homology to TRP cation channels [2] and associates directly with polycystin-1 [3, 4]. The normal functions of polycystins are poorly understood, although recent studies indicate that they are concentrated in the primary cilia of a variety of cell types [5–8]. In this report we identified a polycystin-2 homolog in Drosophila melanogaster; this homolog localized to the distal tip of the sperm flagella. A targeted mutation in this gene, almost there (amo), caused nearly complete male sterility. The amo males produced and transferred normal amounts of motile sperm to females, but mutant sperm failed to enter the female sperm storage organs, a prerequisite for fertilization. The finding that Amo functions in sperm flagella supports a common and evolutionarily conserved role for polycystin-2 proteins in both motile and nonmotile axonemal-containing structures

Jak-STAT regulation of male germline stem cell establishment during Drosophila embryogenesis

Germline stem cells (GSCs) in Drosophila are descendants of primordial germ cells (PGCs) specified during embryogenesis. The precise timing of GSC establishment in the testis has not been determined, nor is it known whether mechanisms that control GSC maintenance in the adult are involved in GSC establishment. Here, we determine that PGCs in the developing male gonad first become GSCs at the embryo to larval transition. This coincides with formation of the embryonic hub; the critical signaling center that regulates adult GSC behavior within the stem cell microenvironment (niche). We find that the Jak-STAT signaling pathway is activated in a subset of PGCs that associate with the newly-formed embryonic hub. These PGCs express GSC markers and function like GSCs, while PGCs that do not associate with the hub begin to differentiate. In the absence of Jak-STAT activation, PGCs adjacent to the hub fail to exhibit the characteristics of GSCs, while ectopic activation of the Jak-STAT pathway prevents differentiation. These findings show that stem cell formation is closely linked to development of the stem cell niche, and suggest that Jak-STAT signaling is required for initial establishment of the GSC population in developing testes. (C) 2009 Elsevier Inc. All rights reserved

Conversion of Quiescent Niche Cells to Somatic Stem Cells Causes Ectopic Niche Formation in the Drosophila Testis

Adult stem cells reside in specialized regulatory microenvironments, or niches, where local signals ensure stem cell maintenance. The Drosophila testis contains a well-characterized niche wherein signals from postmitotic hub cells promote maintenance of adjacent germline stem cells and somatic cyst stem cells (CySCs). Hub cells were considered to be terminally differentiated; here, we show that they can give rise to CySCs. Genetic ablation of CySCs triggers hub cells to transiently exit quiescence, delaminate from the hub, and convert into functional CySCs. Ectopic Cyclin D-Cdk4 expression in hub cells is also sufficient to trigger their conversion into CySCs. In both cases, this conversion causes the formation of multiple ectopic niches over time. Therefore, our work provides a model for understanding how oncogenic mutations in quiescent niche cells could promote loss of quiescence, changes in cell fate, and aberrant niche expansion

The phosphorylation state of β-catenin affects CySC maintenance in the <i>Drosophila</i> testis.

a<p>Testes with CySC clones = testes with GFP⁺, Zfh-1⁺ cells/total testes scored (percentage).</p>b<p>P value vs Robo2 RNAi with Arm overexpression.</p><p>** = P value<.01.</p><p>*** = P value<.001.</p><p>The phosphorylation state of β-catenin affects CySC maintenance in the <i>Drosophila</i> testis.</p

Ecad overexpression or Abl knockdown partially rescues loss of Robo2 mutant CySC clones.

a<p>Testes with CySC clones = testes with GFP⁺, Zfh-1⁺ cells/total testes scored (percentage).</p>b<p>Testes with >50% marked CySCs = testis where GFP⁺, Zfh-1⁺ cells>GFP⁻, Zfh-1⁺ cells/total testes scores (percentage).</p>c+e<p>Wild type clones expressing Ecad or Abl-RNAi = wild type MARCM Frt 40A flies driving (c) Ecad or (e) Abl-RNAi specifically in induced clones.</p>d+f<p>Robo2¹ clones expressing Ecad or Abl-RNAi = Robo2¹ MARCM flies driving (c) Ecad or (e) Abl-RNAi specifically in induced clones.</p>g<p>P value compared to Robo2¹ clones.</p>h<p>P value compared to wild type clones.</p><p>ND = Not Determined, ACI = After Clone Induction,</p><p>* = P value<.05,</p><p>** = P value<.01.</p><p>Ecad overexpression or Abl knockdown partially rescues loss of Robo2 mutant CySC clones.</p