Escargot Restricts Niche Cell to Stem Cell Conversion in the Drosophila Testis

Abstract

Summary Stem cells reside within specialized microenvironments, or niches, that control many aspects of stem cell behaviour. Somatic hub cells in the Drosophila testis regulate the behaviour of cyst stem cells (CySCs) and germline stem cells (GSCs) and are a primary component of the testis stem cell niche. The shutoff (shof) mutation, characterized by premature loss of GSCs and CySCs, was mapped to a locus encoding the evolutionarily conserved transcription factor Escargot (Esg). Hub cells depleted of Esg acquire CySC characteristics and differentiate as cyst cells, resulting in complete loss of hub cells and eventually, CySCs and GSCs, similar to the shof mutant phenotype. We identified Esg-interacting proteins and demonstrate an interaction between Esg and the co-repressor C-terminal binding protein (CtBP), which was also required for maintenance of hub cell fate. Our results indicate that niche cells can acquire stem cell properties upon removal of a single transcription factor in vivo.

A Drosophila toolkit for defining gene function in spermatogenesis

“…Therefore, G-TRACE provides both a spatial and a temporal readout of the expression of a gene of interest (reviewed in del Valle Rodriguez et al 2012). G-Trace has been successfully utilised in the Drosophila testis to show a change of fate from hub cells to cyst cells upon loss of escargot (Voog et al 2014). As other derivations of GAL4-UAS-and FRTbased technologies are enhanced, applications of newer technologies will be useful for future studies in Drosophila spermatogenesis.…”

“…GFP can be visualized in all mutant clones if it is driven by a ubiquitous GAL4 driver or in only a subset of the mutant cells when using a specific GAL4 driver. This system has proved most useful to study the somatic cell lineage in the testis, with GFP-positive marked CySCs more readily visualized in whole testis tissue than negatively marked cells (Leatherman & Dinardo 2008, Amoyel et al 2014, Voog et al 2014. MARCM also allows for the generation of clonal cells overexpressing a transgene because it combines Flp-FRT with the GAL4-UAS system.…”

Simultaneous control of stemness and differentiation by the transcription factor Escargot in adult stem cells: How can we tease them apart?

“…23,33 Such restricted expression in stem cells across tissues is highly unusual; therefore, we sought to characterize and compare the role of Esg in stem cells from both tissues. Clonal analysis to remove Esg function specifically from CySCs resulted in loss of stem cell fate, differentiation into apparently normal cyst cells, 2 and the generation of morphologically abnormal hub cells. 1 In the posterior midgut, loss of Esg function in ISCs resulted in loss of stem cells and an increased proportion of EE cells.…”

“…In the testis, Esg expression is largely restricted to GSCs, CySCs and hub cells. 2 In the midgut, Esg is specifically expressed in ISCs and EBs and is frequently used as a marker for these cell types. 23,33 Such restricted expression in stem cells across tissues is highly unusual; therefore, we sought to characterize and compare the role of Esg in stem cells from both tissues.…”

“…In order to understand the molecular mechanisms involved in stem cell regulation by Esg, we and others have mapped the genomic binding of Esg by DamID, 4 identified putative protein interactors by co-immunoprecipitation followed by mass spectrometry (IP/MS) 2 and analyzed changes in gene expression by RNAsequencing in vivo 3 or in cultured S2 cells by microarray (S. Sandall and L. Jones, unpublished data). We surmise, however, that the data obtained from each of these screens includes a mixture of targets that are in charge of maintaining stem cells in an undifferentiated state and/or regulating differentiation decisions.…”