Castor is required for Hedgehog-dependent cell-fate specification and follicle stem cell maintenance in Drosophila oogenesis

Abstract

Asymmetric division of stem cells results in both self-renewal and differentiation of daughters. Understanding the molecules and mechanisms that govern differentiation of specific cell types from adult tissue stem cells is a major challenge in developmental biology and regenerative medicine. Drosophila follicle stem cells (FSCs) represent an excellent model system to study adult stem cell behavior; however, the earliest stages of follicle cell differentiation remain largely mysterious. Here we identify Castor (Cas) as a nuclear protein that is expressed in FSCs and early follicle cell precursors and then is restricted to differentiated polar and stalk cells once egg chambers form. Cas is required for FSC maintenance and polar and stalk cell fate specification. Eyes absent (Eya) is excluded from polar and stalk cells and represses their fate by inhibiting Cas expression. Hedgehog signaling is essential to repress Eya to allow Cas expression in polar and stalk cells. Finally, we show that the complementary patterns of Cas and Eya reveal the gradual differentiation of polar and stalk precursor cells at the earliest stages of their development. Our studies provide a marker for cell fates in this model and insight into the molecular and cellular mechanisms by which FSC progeny diverge into distinct fates. polar cell | polar stalk precursor | germarium

A genome-scale in vivo RNAi analysis of epithelial development in Drosophila identifies new proliferation domains outside of the stem cell niche

“…Recent studies provide evidence that these processes start at the border of the region between 2b and 3 of the germarium ( Fig. 1; Nystul and Spradling, 2010;Chang et al, 2013). Our data indicate, however, a strong upregulation of the two pathways already in region 2a and 2b (Fig.…”

“…Individual egg chambers are connected by six to eight cells that form a 'stalk'. The specification of stalk cells starts in the germarium at the border between region 2b and 3 (Nystul and Spradling, 2010;Chang et al, 2013). This process involves at least two signalling events.…”

A Pak-regulated cell intercalation event leading to a novel radial cell polarity is involved in positioning of the follicle stem cell niche in theDrosophilaovary

“…Recent studies have identified two markers expressed in FSCs and their progeny: follicle cell nuclear antigens and Castor (Cas). Staining ovaries for either of these markers together with anti-FasIII reveals probable FSCs as positive for the marker but negative for FasIII (Chang et al, 2013;Hartman et al, 2013 3D), whereas in Pak mutant germaria, we saw additional, internal LanA accumulation, further evidence for internally positioned FSCs (Fig. 3E).…”

“…Adult ovaries were dissected, fixed and stained as previously described (Verheyen and Cooley, 1994). Primary antibodies used in this study were monoclonal anti-BicD [1B11, Developmental Studies Hybridoma Bank (DSHB); 1:10], mouse monoclonal anti-Hts 1B1 (DSHB; 1:5), mouse monoclonal antiHtsRC (DSHB; 1:20), mouse monoclonal anti-Fasciclin III (FasIII) (7G10, DSHB; 1:100), rabbit anti-GFP (G1544, Sigma; 1:500), rat monoclonal anti-Vasa (DSHB; 1:100), guinea pig anti-TJ (Li et al, 2003;1:5000), rabbit anti-β-galactosidase (ab616, Abcam; 1:2000), rabbit anti-Pak (Harden et al, 1996; 1:1000), rat monoclonal anti-DE-Cadherin (DCAD2, DSHB; 1:50), mouse monoclonal anti-Dlg (DLG1, DSHB; 1:5), mouse monoclonal anti-β-PS integrin (CF.6G11, DSHB; 1:2) and rabbit anti-Castor (Chang et al, 2013;1:500). Secondary antibodies were used at a 1:200 dilution and were conjugated to Cy5, FITC or TRITC.…”

Phosphorylated Groucho delays differentiation in the follicle stem cell lineage by providing a molecular memory of EGFR signaling in the niche

“…Indeed, many epithelial stem cell lineages contain a transit-amplifying phase downstream from the stem cell division that is defined by incomplete differentiation. Both stem cells and transit-amplifying cells share similar morphology, remain mitotically active, and often express an overlapping set of molecular markers (Chang et al, 2013;Itzkovitz et al, 2011;Mascré et al, 2012;Yan et al, 2012). Moreover, epithelial stem cells are regularly lost from the niche and replaced by the daughter of a neighboring stem cell during normal homeostasis (Clayton et al, 2007;de Navascués et al, 2012;Margolis and Spradling, 1995;Snippert et al, 2010), indicating that transit-amplifying cells retain the capacity to re-enter the niche and assume the stem cell fate.…”