A two-step Notch-dependant mechanism controls the selection of the polar cell pair inDrosophilaoogenesis

Abstract

SUMMARYOrganisers control the patterning and growth of many tissues and organs. Correctly regulating the size of these organisers is crucial for proper differentiation to occur. Organiser activity in the epithelium of the Drosophila ovarian follicle resides in a pair of cells called polar cells. It is known that these two cells are selected from a cluster of equivalent cells. However, the mechanisms responsible for this selection are still unclear. Here, we present evidence that the selection of the two cells is not random but, by contrast, depends on an atypical two-step Notch-dependant mechanism. We show that this sequential process begins when one cell becomes refractory to Notch activation and is selected as the initial polar cell. This cell then produces a Delta signal that induces a high level of Notch activation in one other cell within the cluster. This Notch activity prevents elimination by apoptosis, allowing its selection as the second polar cell. Therefore, the mechanism used to select precisely two cells from among an equivalence group involves an inductive Delta signal that originates from one cell, itself unable to respond to Notch activation, and results in one other cell being selected to adopt the same fate. Given its properties, this two-step Notch-dependent mechanism represents a novel aspect of Notch action.

Cooperative functions of the two F-BAR proteins Cip4 and Nostrin in regulating E-cadherin in epithelial morphogenesis

“…The formation of compound egg chambers results from a defective encapsulation in the germarium, a phenotype that has not yet been described for many mutants. Most mutations that have been reported of so far, either affect gene functions directly through the regulation of cell division or control of follicle cell differentiation through Notch/Delta signaling (Grammont and Irvine, 2001;López-Schier and St Johnston, 2001;Vachias et al, 2010). However, multicyst egg chambers in nost;;cip4 double mutants display neither defects in cell division nor in the differentiation of follicle cells.…”

JAK/STAT autocontrol of ligand-producing cell number through apoptosis

“…The UAS-Upd line was obtained from Martin Zeidler (Zeidler et al, 1999;Beccari et al, 2002). Two Notch transcriptional reporters were used, GbeSu(H)m8-lacZ and E(spl)m-lacZ (Kramatschek and Campos-Ortega, 1994;Cooper et al, 2000;Furriols and Bray, 2001;Vachias et al, 2010). All crosses for Gal4-induced RNAi and reporter expression were performed at 25°C until eclosion and newly-eclosed adult females were placed at 29°C until dissection 5 or 9 days later.…”

“…S1I). Recently, it was reported that selection of the two surviving PCs requires high Notch activation in one of the two cells and an as-yet-unknown Notch-independent mechanism for the second cell (Vachias et al, 2010). Intriguingly, expression of both Notch and Stat reporters is dynamic in PC clusters and PC survival and death fates are associated with respective activation of the Notch and JAK/STAT pathways (Vachias et al, 2010; Fig.…”

“…Although there have been great advances in understanding the molecular mechanisms that lead to caspase activation and consequent apoptosis, how the cell death machinery is activated in vivo during development is still poorly understood. Drosophila ovarian polar cells (PCs) have emerged as an exquisite and relatively simple model to unravel the mechanisms by which apoptosis is induced in a physiological context during development (Besse and Pret, 2003;Vachias et al, 2010;Khammari et al, 2011). PCs are specialised somatic cells located at each extremity, anterior and posterior, of maturing ovarian follicles, where they are embedded within the monolayered follicular epithelium (Fig.…”

CoREST acts as a positive regulator of Notch signaling in the follicle cells ofDrosophila melanogaster

“…The role of Notch in lateral inhibition during neurogenesis has been extensively studied; it restricts neural cell fates in the embryo, and leads to restriction of sensory-organ formation and induction of boundary formation in the wing discs (Micchelli and Blair, 1999;Portin, 2002;Cau and Blader, 2009). Notch activity is also required for many aspects of oogenesis, such as the establishment of egg chamber polarity, polar cell formation, control of follicle cell (FC) proliferation, differentiation, cell fate specification and morphogenesis (Deng et al, 2001;Grammont and Irvine, 2001;Lopez-Schier and St Johnston, 2001;Horne-Badovinac and Bilder, 2005;Grammont, 2007;Shyu et al, 2009;Klusza and Deng, 2011;Vachias et al, 2010). The Drosophila FCs are somatically derived epithelial cells that form a monolayer covering the germline cells during oogenesis.…”