The Drosophila synaptotagmin-like protein bitesize is required for growth and has mRNA localization sequences within its open reading frame

Abstract

The vertebrate synaptotagmin-like protein granuphilin binds to the vesicle-trafficking proteins Rab27a and Munc18 and can modulate exocytosis of insulin-containing secretory granules in pancreatic beta cell lines. Here, we report the molecular and genetic characterization of bitesize, a granuphilin homolog and the only Drosophila synaptotagmin-like protein. Mutations that affect bitesize have reduced cell size and number, resulting in smaller animals that develop slowly. We also show that at least two classes of bitesize transcripts are localized to the apical plasma membrane in polarized epithelial cells. Whereas most cis-acting mRNA localization sequences map to 3 untranslated regions, bitesize contains a 2.2-kb sequence within its ORF that is necessary and sufficient for apical localization. Thus, we have found that bitesize is a metazoan example of a transcript for which all identifiable mRNA localization sequences are contained within the protein-coding region.

Developmental control of nuclear morphogenesis and anchoring bycharleston, identified in a functional genomic screen ofDrosophilacellularisation

“…RNAi against CG14858/bitesize (btsz), a gene also implicated in growth control (Serano and Rubin, 2003), produces a fully penetrant arrest of gastrulation in that the epithelium no longer elongates along the anteroposterior axis (see Fig. S3 in the supplementary material).…”

Ezrin, Radixin and Moesin: Minor Molecule with Major Impact: A Review

“…Few studies suggested that bitesize interaction with Moesin is specific to the early stages of epithelial morphogenesis, or that it has redundancy with other, currently unknown proteins. [38] Similarly, although some Moesin-mutant imaginal epithelial cells lose cell integrity and polarity, many remain integrated into the epithelial layer [36] , suggesting that ERMs are not absolutely required for adherens junction stability in established epithelia.…”

A Targeted Gain-of-Function Screen Identifies Genes Affecting Salivary Gland Morphogenesis/Tubulogenesis in Drosophila

“…Its mRNA is expressed in the salivary glands and also in other epithelial tissues, with a strong apical enrichment (Serano and Rubin 2003). Btsz has recently been shown to control the organization of actin at adherens junctions in early embryos, although it might be dispensable in adult fly epithelia (Pilot et al 2006).…”

“…Recruitment of Btsz in early embryos to the apical junctional region is not dependent on E-Cadherin but on phosphatidylinositol-(4,5)-bisphosphate (PIP 2 ) and Par-3/Bazooka, a protein of the Par-3/Par-6/aPKC apical complex (Pilot et al 2006). Two mutant btsz alleles have been described: btsz K13-4 that deletes a portion of the N terminus of some Btsz protein isoforms and btsz J5-2 that introduces a stop codon due to a frameshift in the N-terminal portion of btsz (Serano and Rubin 2003). Expression driven by fkhGal4 from the EP element identified in our screen, EP(3)3567, should lead to production of an antisense RNA in most of the btsz coding sequence and thus could downregulate endogenous btsz mRNA levels (see scheme in Figure 7A and supplemental Figure 2).…”

“…The disruption of the epidermis and the failure of the proper apical localization of Crumbs is to some extent reminiscent of the phenotypes observed in egl mutant embryos. As btsz mRNA is another RNA that is localized apically in various epithelial cells (and the localization signal has been identified; Serano and Rubin 2003), one could speculate that its localization could also be dependent on Egl and BicD, thus explaining some overlap in the phenotypes.…”