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. 2007 Nov 6;17(21):1871-8.
doi: 10.1016/j.cub.2007.09.062. Epub 2007 Oct 25.

The salvador-warts-hippo pathway is required for epithelial proliferation and axis specification in Drosophila

Carine Meignin  1 , Ines Alvarez-Garcia, Ilan Davis, Isabel M Palacios
Affiliations

The salvador-warts-hippo pathway is required for epithelial proliferation and axis specification in Drosophila

Carine Meignin et al. Curr Biol. .

Abstract

In Drosophila, the body axes are specified during oogenesis through interactions between the germline and the overlying somatic follicle cells [1-5]. A Gurken/TGF-alpha signal from the oocyte to the adjacent follicle cells assigns them a posterior identity [6, 7]. These posterior cells then signal back to the oocyte, thereby inducing the repolarization of the microtubule cytoskeleton, the migration of the oocyte nucleus, and the localization of the axis specifying mRNAs [8-10]. However, little is known about the signaling pathways within or from the follicle cells responsible for these patterning events. We show that the Salvador Warts Hippo (SWH) tumor-suppressor pathway is required in the follicle cells in order to induce their Gurken- and Notch-dependent differentiation and to limit their proliferation. The SWH pathway is also required in the follicle cells to induce axis specification in the oocyte, by inducing the migration of the oocyte nucleus, the reorganization of the cytoskeleton, and the localization of the mRNAs that specify the anterior-posterior and dorsal-ventral axes of the embryo. This work highlights a novel connection between cell proliferation, cell growth, and axis specification in egg chambers.

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Figures

Figure 1
Figure 1
The SWH Pathway, except Ft, Is Required for Germline Axis Specification (A–F) warts (wts) is required in the follicle cells (FCs) to localize gurken (grk), oskar (osk), and bicoid (bcd) mRNAs in the oocyte. (A)–(C) show that in wild-type stage 9–10 oocytes, grk mRNA is localized to the dorso-anterior corner (A), whereas osk (B) and bcd (C) mRNAs localize to the posterior and anterior pole, respectively. (D)–(F) show that in egg chambers with wts mutant FC clones, the mRNAs are mislocalized: grk mRNA is found at the posterior (D); osk mRNA is found at the center (E), and bcd mRNA is found at the anterior and posterior poles (F). Mutant clones are scored by the lack of Myc staining (green), mRNAs are shown in red, and nuclei are stained with DAPI in blue. In (A)–(M), mutant clones are indicated by the absence of GFP (green), unless stated otherwise. (G and H) hippo (hpo) is required in the FCs to organize the microtubule cytoskeleton in the oocyte. (G) shows that in wild-type oocytes, the microtubules (MTs) are organized in an anterior-to-posterior gradient, as can been seen by TauGFP (white). (H) shows that in egg chambers with hpo mutant FCs, this gradient is lost and the MTs are distributed diffusely all over the oocyte cytoplasm. Mutant cells are marked by the absence of GFP (white). (I and J) wts is not required to translate grk mRNA. (I) shows that in wild-type stage 9 oocytes, grk mRNA is localized to and translated at the dorsoanterior corner of the oocyte. (J) shows that in egg chambers with wts mutant FC clones, grk mRNA is mislocalized to the posterior pole (as shown in [D]), but the RNA is translated, and Grk protein is detected at that pole (J). Grk protein is labeled in white (left panel) and red (right panel), and nuclei are stained with DAPI in blue. (K–N) hippo and expanded (ex), but not fat (ft), are required in the follicle cells to induce polarization of the oocyte. (K) shows that in wild-type stage 9 oocytes, the oocyte nucleus is positioned at the dorsoanterior corner. (L) and (M) show that in egg chambers with hpo (L) and ex (M) mutant FC clones, the oocyte nucleus does not migrate to the dorsoanterior corner and is found instead at the posterior pole. (N) shows that in egg chambers with ft FC clones, both the oocyte nucleus and Staufen (red) are properly localized at the dorsoanterior and posterior pole, respectively. ft mutant cells are marked by the presence of GFP. As shown in (K)–(M), actin is stained with phalloidin (Red). White asterisks mark the oocyte nucleus. (O) Overexpression of yki in the posterior FCs causes the mislocalization of Staufen (red) and the nucleus in the oocyte. UASyki overexpressing cells are marked by the presence of GFP. The image is overexposed so that all the cells expressing GFP (white and green in left and right panels, respectively) could be visualized. The white asterisk marks the oocyte nucleus.
Figure 2
Figure 2
The SWH Pathway Is Required in the Posterior FCs to Induce Oocyte Polarity and in the Anterior and Posterior FCs to Control Proliferation (A–D) The SWH pathway is required in the posterior FCs to induce oocyte polarity. As shown in (A), wild-type posterior FCs in an otherwise hpo mutant epithelium induce the migration of the oocyte nucleus to the dorsoanterior (DA) corner. In (B), hippo (hpo) germline clones show no defects in the localization of the oocyte nucleus, which is found at the DA corner of the oocyte. In (C), a hpo mutant clone at the posterior in an otherwise wild-type epithelium shows defects in the positioning of the oocyte nucleus. The polar cells (stained by Fasciclin III in red, arrow) are wild-type. (D) shows the localization of the oocyte nucleus and Staufen (GFPStau, white) in an egg chamber with a partial warts (wts) posterior FC clone. In this case, Stau is localized in the oocyte region that faces the wild-type FCs. Clones are visualized by the absence of GFP (white). The oocyte nuclei are marked with an asterisk, and actin is stained by phalloidin (red) in (A), (B), and (D). In (A)–(O), clones are marked by the absence of GFP (green), unless stated otherwise. (E–J) The SWH pathway is required in the anterior and posterior FCs to control proliferation. As shown in (E)–(G), wild-type FCs form a cuboidal monolayered epithelium (E), whereas hpo mutant anterior and posterior FCs form an epithelium with two or more layers (F and G). Cells are stained with FasIII (red), which accumulates at the apical lateral side of the membranes in wild-type (E) but not in hpo FCs (F). (H) and (I) show that in wild-type egg chambers, mitotic cells (labeled by phosphohistone 3 [PH3] in red) are detected at early stages ([H], arrow), but never at stage 9, whereas hpo FC clones show cells in mitosis at the posterior of stage 9 egg chambers ([I], arrow). As shown in (J), mitotic cells are also detected in FC clones overexpressing yki (PH3 in red). Clones are marked by the presence of GFP. The image is overexposed so that all the cells expressing GFP (green) could be visualized. (K–L) hpo controls mitotic-spindle orientation in the follicle cells. (K) shows that in wild-type FCs, the mitotic spindle orientates parallel to the surface of the cells. However, in hpo mutant FCs the mitotic spindle is orientated perpendicular to the surface of the cells, as shown in (L). Microtubules are in red, and phosphohistone 3, PH3, are in blue. (M–O) Localization of apical and basolateral markers in hippo and warts mutant cells. (M) shows wild-type localization of nPKC at the apical side (blue) and Dlg at the lateral side (red) of the follicle cells. (N) shows that in hpo FC clones that form a monolayer, nPKC and Dlg are properly localized. However, nPKC and Dlg are often mislocalized in mutant cells that form extra layers, as shown in (O). In these cases, nPKC is always apical in the cells that are in contact with the oocyte but never in the cells that do not contact the germline or the basement membrane ([O], arrow).
Figure 3
Figure 3
hippo and warts Regulate Posterior Follicle Cell Differentiation (A and B) hippo (hpo) is required for the downregulation of Fasciclin III (FasIII). (A) shows that in stage 9 wild-type egg chambers, FasIII is strongly expressed in the polar cells and weakly localizes to the apical lateral membrane in the posterior FCs. In (B), hpo FC clones show both overexpression of FasIII at the posterior follicle cells and redistribution of the protein to the basolateral membrane. In (A)–(F), cells with aberrant expression of FasIII, Eya, and Hnt are marked with a dotted line. In all panels, mutant clones are marked by the absence of GFP (green); expression of FasIII, Eya, Hnt, E(spl)mb7-lacZ, DG and pntLacZ are shown in white or red, and nuclei are stained with DAPI in blue. (C and D) warts (wts) is required for the down-regulation of Eyes absent (Eya). Staining of Eya in stage 9 wild-type (C) and wts (D) egg chambers is shown. wts FC clones show overexpression of Eya in the posterior follicle cells. (E and F) hpo is required for the Notch-dependent expression of Hindsight (Hnt) in the posterior FCs. (E) shows that in wild-type egg chambers, Hnt is expressed in all FCs upon activation of Notch at stage 6 of oogenesis. However, Hnt expression is not activated in hpo posterior FCs, as shown in (F). (G and H) hpo is required for the expression of Enhancer of split [E(spl)mb7-lacZ] in the posterior FCs. As shown in (G), wild-type egg chambers express E(spl)mb7-lacZ in all FCs. (H) shows that in hpo FC clones, the expression is weakly reduced. The hpoJM1 allele was used in this experiment. (I and J) hpo is not required for the Gurken-dependent expression of Dystroglycan (DG). (I) shows that in wild-type egg chambers, DG is expressed in an anterior-to-posterior gradient. (J) shows that this gradient of DG is also present in hpo FC clones. (K and L) hpo is required for the Gurken-dependent expression of pointed (pnt). (K) shows wild-type expression of pointed-LacZ line pnt99812. (L) shows that in hpo FC clones, the expression of the pointed-LacZ line pnt99812 is affected, and cannot be detected in posterior mutant cells. Nuclei are stained with DAPI in blue.
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References

    1. Lopez-Schier H. The polarisation of the anteroposterior axis in Drosophila. Bioessays. 2003;25:781–791. - PubMed
    1. Ruohola H, Bremer KA, Baker D, Swedlow JR, Jan LY, Jan YN. Role of neurogenic genes in establishment of follicle cell fate and oocyte polarity during oogenesis in Drosophila. Cell. 1991;66:433–449. - PubMed
    1. Gonzalez-Reyes A, St Johnston D. Patterning of the follicle cell epithelium along the anterior-posterior axis during Drosophila oogenesis. Development. 1998;125:2837–2846. - PubMed
    1. Deng WM, Bownes M. Patterning and morphogenesis of the follicle cell epithelium during Drosophila oogenesis. Int. J. Dev. Biol. 1998;42:541–552. - PubMed
    1. Sapir A, Schweitzer R, Shilo BZ. Sequential activation of the EGF receptor pathway during Drosophila oogenesis establishes the dorsoventral axis. Development. 1998;125:191–200. - PubMed

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