Egfr signaling controls the size of the stem cell precursor pool in the Drosophila ovary

Abstract

In many animals, germline progenitors are kept undifferentiated to give rise to germline stem cells (GSCs), enabling continuous production of gametes throughout animal life. In the Drosophila ovary, GSCs arise from a subset of primordial germ cells (PGCs) that stay undifferentiated even after gametogenesis has started. How a certain population of PGCs is protected against differentiation, and the significance of its regulatory mechanisms on GSC establishment remain elusive. Here we show that epidermal growth factor receptor (Egfr) signaling in somatic stromal intermingled cells (ICs), activated by its ligand produced in germ cells, controls the size of the PGC pool at the onset of gametogenesis. Egfr signaling in ICs limits the number of cells that express the heparan sulfate proteoglycan Dally, which is required for the movement and stability of the locally-produced stromal morphogen, Decapentaplegic (Dpp, a BMP2/4 homologue). Dpp is received by PGCs and maintains them in an undifferentiated state. Altering Egfr signaling levels changes the size of the PGC pool and affects the number of GSCs established during development. While excess GSC formation is compensated by the adult stage, insufficient GSC formation can lead to adult ovarioles that completely lack GSCs, suggesting that ensuring an absolute size of the PGC pool is crucial for the GSC system.

Adipocyte amino acid sensing controls adult germline stem cell number via the amino acid response pathway and independently of Target of Rapamycin signaling in Drosophila

“…Tissues were incubated overnight at 4°C in the following primary antibodies diluted in blocking solution: rabbit anti-GFP (Torrey Pines; 1:2500, TP401); mouse monoclonal anti-Hts (1B1) (DSHB; 1:10); mouse anti-α-spectrin (3A9) (DSHB; 1:50); mouse monoclonal anti-Lamin C (LC28.26) (DSHB; 1:100); rat monoclonal anti-E-cadherin (DCAD2) (DSHB; 1:100); and rabbit anti-pMad (Smad3) (Epitomics; 1:100, #1880). [This particular Smad3 antibody is widely used in Drosophila to detect pMad specifically (Hayashi et al, 2009;Ables and Drummond-Barbosa, 2010;Issigonis and Matunis, 2012;Matsuoka et al, 2013;Ma et al, 2014;Sulkowski et al, 2014).] Tissues were washed in PBT, and incubated for 2 h at room temperature in 1:200 Alexa Fluor 488-or 568-conjugated secondary antibodies (Molecular Probes).…”

Sonication-facilitated Immunofluorescence Staining of Late-stage Embryonic and Larval <em>Drosophila</em> Tissues <em>In Situ</em>

“…Multiple ovarioles arise from a single embryonic gonad comprised of PGCs and SGPs. By mid-L3, SGPs give rise to TF precursors at the ovary anterior, while germ cells localize to the ovary posterior and associate with SGP-derived intermingled cells (ICs) [19][20][21][22] . By late-L3, TF cells differentiate and organize into the stacks found in the adult stem cell niche, GSCs and cap cells are established, and germ-line cyst differentiation is observed 19,20,23 .…”

gone early, a Novel Germline Factor, Ensures the Proper Size of the Stem Cell Precursor Pool in the Drosophila Ovary

“…This difference in PGC behavior along the anterior–posterior axis of the ovary likely results from a locally produced diffusible morphogen, Decapentaplegic (Dpp, a BMP2/4 homologue). This factor is produced by the anterior somatic cells [7], and is received by the anteriorly located PGCs, protecting them from gametogenesis by repressing the transcription of a differentiation gene, bag of marbles ( bam ). By contrast, posterior PGCs fail to receive Dpp, and therefore permit bam expression and initiate differentiation [7]–[10].…”

“…This factor is produced by the anterior somatic cells [7], and is received by the anteriorly located PGCs, protecting them from gametogenesis by repressing the transcription of a differentiation gene, bag of marbles ( bam ). By contrast, posterior PGCs fail to receive Dpp, and therefore permit bam expression and initiate differentiation [7]–[10]. At the white pupal stage (WP), when GSC niche formation is complete (as evidenced by the appearance of cap cells), some of the anterior PGCs are accommodated in this niche and start asymmetric division as GSCs (Figure 1A) [1], [4], [6].…”

“…Thus, it is the shape of the Dpp signaling gradient that determines the size of the GSC precursor pool by protecting PGCs from the global differentiation signal ecdysone. Artificially induced excess PGC differentiation at the onset of gametogenesis results in a decrease or absence of GSCs in the adult GSC niche, underscoring the importance of regulation of PGC pool size [7], [11].…”