[Show abstract][Hide abstract] ABSTRACT: Adducin is a cytoskeletal protein having regulatory roles that involve actin filaments, functions that are inhibited by phosphorylation of adducin by protein kinase C. Adducin is hyperphosphorylated in nervous system tissue in patients with the neurodegenerative disease amyotrophic lateral sclerosis, and mice lacking β-adducin have impaired synaptic plasticity and learning. We have found that Drosophila adducin, encoded by hu-li tai shao (hts), is localized to the post-synaptic larval neuromuscular junction (NMJ) in a complex with the scaffolding protein Discs large (Dlg), a regulator of synaptic plasticity during growth of the NMJ. hts mutant NMJs are underdeveloped, whereas over-expression of Hts promotes Dlg phosphorylation, delocalizes Dlg away from the NMJ, and causes NMJ overgrowth. Dlg is a component of septate junctions at the lateral membrane of epithelial cells, and we show that Hts regulates Dlg localization in the amnioserosa, an embryonic epithelium, and that embryos doubly mutant for hts and dlg exhibit defects in epithelial morphogenesis. The phosphorylation of Dlg by the kinases PAR-1 and CaMKII has been shown to disrupt Dlg targeting to the NMJ and we present evidence that Hts regulates Dlg targeting to the NMJ in muscle and the lateral membrane of epithelial cells by controlling the protein levels of PAR-1 and CaMKII, and consequently the extent of Dlg phosphorylation.
[Show abstract][Hide abstract] ABSTRACT: The Rho family small GTPases Rho, Rac, and Cdc42 regulate cell shape and motility through the actin cytoskeleton. These proteins cycle between a GTP-bound "on" state and a GDP-bound "off" state and are negatively regulated by GTPase-activating proteins (GAPs), which accelerate the small GTPase's intrinsic hydrolysis of bound GTP to GDP. Drosophila RhoGAP68F is similar to the mammalian protein p50RhoGAP/Cdc42GAP, which exhibits strong GAP activity toward Cdc42. We find that, despite the strong similarities between RhoGAP68F and p50RhoGAP/Cdc42GAP, RhoGAP68F is most effective as a GAP for RhoA. These in vitro data are supported by the in vivo analysis of mutants in RhoGAP68F. We demonstrate through the characterization of two alleles of the RhoGAP68F gene that RhoGAP68F participates in gastrulation of the embryo, a morphogenetic event driven by cell constriction that involves RhoA signaling. We propose that RhoGAP68F functions as a regulator of RhoA signaling during gastrulation.
Development Genes and Evolution 10/2006; 216(9):543-50. DOI:10.1007/s00427-006-0067-6 · 2.18 Impact Factor
[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. DOI:10.1016/j.cub.2003.09.056 · 9.92 Impact Factor
[Show abstract][Hide abstract] 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.