Drac1 and Crumbs participate in amnioserosa morphogenesis during dorsal closure in Drosophila.
ABSTRACT Dorsal closure of the Drosophila embryo involves morphological changes in two epithelia, the epidermis and the amnioserosa, and is a popular system for studying the regulation of epithelial morphogenesis. We previously implicated the small GTPase Drac1 in the assembly of an actomyosin contractile apparatus, contributing to cell shape change in the epidermis during dorsal closure. We now present evidence that Drac1 and Crumbs, a determinant of epithelial polarity, are involved in setting up an actomyosin contractile apparatus that drives amnioserosa morphogenesis by inducing apical cell constriction. Expression of constitutively active Drac1 causes excessive constriction of amnioserosa cells and contraction of the tissue, whereas expression of dominant-negative Drac1 impairs amnioserosa morphogenesis. These Drac1 transgenes may be acting through their effects on the amnioserosa cytoskeleton, as constitutively active Drac1 causes increased staining for F-actin and myosin, whereas dominant-negative Drac1 reduces F-actin levels. Overexpression of Crumbs causes premature cell constriction in the amnioserosa, and dorsal closure defects are seen in embryos homozygous for hypomorphic crumbs alleles. The ability of constitutively active Drac1 to cause contraction of the amnioserosa is impaired in a crumbs mutant background. We propose that amnioserosa morphogenesis is a useful system for studying the regulation of epithelial morphogenesis by Drac1.
Article: Zebrafish mosaic eyes is a novel FERM protein required for retinal lamination and retinal pigmented epithelial tight junction formation.[show abstract] [hide abstract]
ABSTRACT: Polarization is a common feature of many types of cells, and we are beginning to understand how cells become polarized. The role of cell polarity in development and tissue morphogenesis, however, is much less well understood. Our previous analysis of the mosaic eyes (moe) mutations revealed that moe is required for retinal lamination and also suggested that zebrafish moe function is required in the retinal pigmented epithelium (RPE) for the proper localization of adjacent retinal cell divisions at the apical neuroepithelial surface. To understand the function of moe in the RPE, we cloned the moe locus and show that it encodes a novel FERM (for 4.1 protein, ezrin, radixin, moesin) domain-containing protein. Expression of moe in the eye, kidney, and brain reflects phenotypes found in moe(-) mutants, including RPE and retinal lamination defects, edema, and small or absent brain ventricles. We show that moe function is required for tight junction formation in the RPE. We suggest that moe may be a necessary component of the crumbs pathway that regulates apical cell polarity and also may play a role in photoreceptor morphogenesis.Current Biology 05/2004; 14(8):711-7. · 9.65 Impact Factor
Article: The Sac1 lipid phosphatase regulates cell shape change and the JNK cascade during dorsal closure in Drosophila.[show abstract] [hide abstract]
ABSTRACT: The Sac1 lipid phosphatase dephosphorylates several phosphatidylinositol (PtdIns) phosphates and, in yeast, regulates a diverse range of cellular processes including organization of the actin cytoskeleton and secretion. We have identified mutations in the gene encoding Drosophila Sac1. sac1 mutants die as embryos with defects in dorsal closure (DC). DC involves the migration of the epidermis to close a hole in the dorsal surface of the embryo occupied by the amnioserosa. It requires cell shape change in both the epidermis and amnioserosa and activation of a Jun N-terminal kinase (JNK) MAPK cascade in the leading edge cells of the epidermis . Loss of Sac1 leads to the improper activation of two key events in DC: cell shape change in the amnioserosa and JNK signaling. sac1 interacts genetically with other participants in these two events, and our data suggest that loss of Sac1 leads to upregulation of one or more signals controlling DC. This study is the first report of a role for Sac1 in the development of a multicellular organism.Current Biology 11/2003; 13(21):1882-7. · 9.65 Impact Factor