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


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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    • "Although the core components of BMs are well conserved and characterized, their mechanism of assembly into mature BM, their diversity, and their origin remain poorly characterized. Current knowledge from flies shows that ColIV originates from diverse sources during development: plasmatocytes in embryos (Bunt et al., 2010; Fessler and Fessler, 1989); fat body in the larvae (Pastor-Pareja and Xu, 2011); and follicle cells in the adult ovary (Denef et al., 2008; Lerner et al., 2013; Medioni and Noselli, 2005). But what remained unclear was the behavior of the newly synthesized ColIV from these sources and whether any specific targeting mechanism existed. "
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    ABSTRACT: The extracellular matrix plays an essential role for stem cell differentiation and niche homeostasis. Yet, the origin and mechanism of assembly of the stem cell niche microenvironment remain poorly characterized. Here, we uncover an association between the niche and blood cells, leading to the formation of the Drosophila ovarian germline stem cell niche basement membrane. We identify a distinct pool of plasmatocytes tightly associated with the developing ovaries from larval stages onward. Expressing tagged collagen IV tissue specifically, we show that the germline stem cell niche basement membrane is produced by these "companion plasmatocytes" in the larval gonad and persists throughout adulthood, including the reproductive period. Eliminating companion plasmatocytes or specifically blocking their collagen IV expression during larval stages results in abnormal adult niches with excess stem cells, a phenotype due to aberrant BMP signaling. Thus, local interactions between the niche and blood cells during gonad development are essential for adult germline stem cell niche microenvironment assembly and homeostasis.
    Full-text · Article · Oct 2015 · Cell Reports
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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.
    Full-text · Article · Dec 2013 · Developmental Biology
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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.
    Preview · Article · Jan 2013 · Developmental Cell
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