Crag Regulates Epithelial Architecture and Polarized Deposition of Basement Membrane Proteins in Drosophila

Howard Hughes Medical Institute, Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA.
Developmental Cell (Impact Factor: 9.71). 04/2008; 14(3):354-64. DOI: 10.1016/j.devcel.2007.12.012
Source: PubMed

ABSTRACT The polarized architecture of epithelia relies on an interplay between the cytoskeleton, the trafficking machinery, and cell-cell and cell-matrix adhesion. Specifically, contact with the basement membrane (BM), an extracellular matrix underlying the basal side of epithelia, is important for cell polarity. However, little is known about how BM proteins themselves achieve a polarized distribution. In a genetic screen in the Drosophila follicular epithelium, we identified mutations in Crag, which encodes a conserved protein with domains implicated in membrane trafficking. Follicle cells mutant for Crag lose epithelial integrity and frequently become invasive. The loss of Crag leads to the anomalous accumulation of BM components on both sides of epithelial cells without directly affecting the distribution of apical or basolateral membrane proteins. This defect is not generally observed in mutants affecting epithelial integrity. We propose that Crag plays a unique role in organizing epithelial architecture by regulating the polarized secretion of BM proteins.

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Available from: Trudi Schüpbach, Sep 26, 2015
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    • "In a genetic mosaic screen designed to identify genes involved in FC patterning, differentiation and morphogenesis during Drosophila oogenesis (Denef et al., 2008; Yan et al., 2009; Yan et al., 2011; Sun et al., 2011; Domanitskaya et al., 2012), two homozygous lethal mutations, FL99 and FT59 were isolated, which fail to complement each other, indicating that they are alleles of the same gene. Using either Slow border cells (Slbo) which labels the border cells, or Cut, a marker for the polar cells, we found that in egg chambers containing FL99 or FT59 whole epithelial homozygous mutant clones, migration of the BCs was severely disrupted . "
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    ABSTRACT: The border cells of Drosophila are a model system for coordinated cell migration. Ecdysone signaling has been shown to act as the timing signal to initiate the migration process. Here we find that mutations in phantom (phm), encoding an enzyme in the ecdysone biosynthesis pathway, block border cell migration when the entire follicular epithelium of an egg chamber is mutant, even when the associated germline cells (nurse cells and oocyte) are wildtype. Conversely, mutant germline cells survive and do not affect border cell migration, as long as the surrounding follicle cells are wildtype. Interestingly, even small patches of wildtype follicle cells in a mosaic epithelium are sufficient to allow the production of above-threshold levels of ecdysone to promote border cell migration. The same phenotype is observed with mutations in shade (shd), encoding the last enzyme in the pathway that converts ecdysone to the active 20-hydroxyecdysone. Administration of high 20-hydroxyecdysone titers in the medium can also rescue the border cell migration phenotype in cultured egg chambers with an entirely phm mutant follicular epithelium. These results indicate that in normal oogenesis, the follicle cell epithelium of each individual egg chamber must supply sufficient ecdysone precursors, leading ultimately to high enough levels of mature 20-hydroxyecdysone to the border cells to initiate their migration. Neither the germline, nor the neighboring egg chambers, nor the surrounding hemolymph appear to provide threshold amounts of 20-hydroxyecdysone to do so. This "egg chamber autonomous" ecdysone synthesis constitutes a useful way to regulate the individual maturation of the asynchronous egg chambers present in the Drosophila ovary.
    Developmental Biology 12/2013; 386(2). DOI:10.1016/j.ydbio.2013.12.013 · 3.55 Impact Factor
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    • "vkg-GFP (CC00791), trol-GFP (CA06698), Sar1-GFP (CA07674), and Sec61a-GFP (CC00735) are from Buszczak et al. (2007). Crag GG43 , FRT19A, and UAS- HA-Crag are from Denef et al. (2008). fat2 N103-2 , FRT80 is from Horne- Badovinac et al. (2012). "
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    ABSTRACT: Basement membranes (BMs) are specialized extracellular matrices that are essential for epithelial structure and morphogenesis. However, little is known about how BM proteins are delivered to the basal cell surface or how this process is regulated during development. Here, we identify a mechanism for polarized BM secretion in the Drosophila follicle cells. BM proteins are synthesized in a basal endoplasmic reticulum (ER) compartment from localized mRNAs and are then exported through Tango1-positive ER exit sites to basal Golgi clusters. Next, Crag targets Rab10 to structures in the basal cytoplasm, where it restricts protein delivery to the basal surface. These events occur during egg chamber elongation, a morphogenetic process that depends on follicle cell planar polarity and BM remodeling. Significantly, Tango1 and Rab10 are also planar polarized at the basal epithelial surface. We propose that the spatial control of BM production along two tissue axes promotes exocytic efficiency, BM remodeling, and organ morphogenesis.
    Developmental Cell 01/2013; 24(2):159-168. DOI:10.1016/j.devcel.2012.12.005 · 9.71 Impact Factor
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    • "Directed mosaics as a method to identify new regulators of egg chamber elongation Since its introduction in 1998, the directed mosaic technique has been used to identify novel genes required for multiple aspects of follicle cell biology (Bilder et al. 2000; Denef et al. 2008; Duffy et al. 1998; Horne- Badovinac and Bilder 2008; Liu and Montell 1999; Lu and Bilder 2005; Sun et al. 2011; Yan et al. 2009, 2011). The first application of this method by Duffy et al. (1998) uncovered one of the first round egg mutants, likely corresponding to the bPS integrin gene myospheroid. "
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    ABSTRACT: The elongation of tissues and organs during embryonic development results from the coordinate polarization of cell behaviors with respect to the elongation axis. Within the Drosophila melanogaster ovary, initially spherical egg chambers lengthen dramatically as they develop to create the elliptical shape of the mature egg. This morphogenesis depends on an unusual form of planar polarity within the egg chamber's outer epithelial cell layer known as the follicle cells. Disruption of follicle cell planar polarity leads to the production of round rather than elongated eggs; however, the molecular mechanisms that control this tissue organization are poorly understood. Starting from a broadly based forward genetic screen, we have isolated 12 new round egg complementation groups, and have identified four of the mutated genes. In mapping the largest complementation group to the fat2 locus, we unexpectedly discovered a high incidence of cryptic fat2 mutations in the backgrounds of publicly available stocks. Three other complementation groups correspond to the genes encoding the cytoplasmic signaling proteins Tricornered (Trc), Furry (Fry), and Misshapen (Msn). Trc and Fry are known members of an NDR kinase signaling pathway, and as a Ste20-like kinase, Msn may function upstream of Trc. We show that all three proteins are required for follicle cell planar polarity at early stages of egg chamber elongation and that Trc shows a planar polarized distribution at the basal follicle cell surface. These results indicate that this new mutant collection is likely to provide novel insight into the molecular mechanisms controlling follicle cell planar polarity and egg chamber elongation.
    G3-Genes Genomes Genetics 03/2012; 2(3):371-8. DOI:10.1534/g3.111.001677 · 3.20 Impact Factor
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