Structure and transcription of the singed locus of Drosophila melanogaster.

Abstract

Developmental and genetic studies of the singed gene of Drosophila melanogaster indicate that the gene has a role in somatic cells during the formation of adult bristles and hairs, and in the female germline during oogenesis. During metamorphosis a single 3.6-kilobase (kb) RNA is made, and this RNA is also present in adults and early embryos. Early embryos and adult females have additional 3.3- and 3.0-kb RNAs. The RNAs differ only in the length of the 3' untranslated region and a single gene product of 57 kilodaltons is predicted. Analysis of RNA from females lacking ovaries suggests that the 3.3- and 3.0-kb RNAs are made only in ovaries. The absence of the 3.3- and 3.0-kb RNAs in pupae and the time course of their appearance in adult females after eclosion suggests that transcription of singed in the ovary is from middle to late stages of oogenesis. Analysis of RNA in embryos from the reciprocal crosses between wild type and singed-3 showed that all three RNAs are maternally inherited with very little zygotic transcription in embryos. The mutation singed-3 appears to separate the two requirements for singed function as it has an extreme effect upon bristle development, but does not obviously affect oogenesis. In singed-3, there is a deletion at the 5' end of the gene, but the coding region is intact. Transcription in singed-3 is from a cryptic promoter in the upstream flanking sequences which is sufficiently active during oogenesis for fertility, but less active than the wild-type promoter during metamorphosis. The role of the single singed gene product may be in the asymmetric organization and/or movement of cytoplasmic components.

Actin Filament Cables in Drosophila Nurse Cells Are Composed of Modules That Slide Passively Past One Another during Dumping

“…Western and immunofluorescence analyses showed that the singed protein is absent from the nurse cells (Cant et al, 1994). Since the molecular defect of this mutation is unknown (Paterson and O'Hare, 1991), tiny amounts of the protein, beneath the limit of detection by these techniques, could be present in these cells. The phenotype described by Cant et al (1994) was a severe reduction in cytoplasmic actin bundles, but the ring canals and subcortical actin appeared to be like the wild type.…”

Drosophila singed, a fascin homolog, is required for actin bundle formation during oogenesis and bristle extension.

“…Some of the sites of mutation for these alleles have been described (Paterson and O'Hare, 1991;Roiha et al, 1988). Transcription of singed in singed 3 uses a cryptic prometer and starts 200-bp closer to the o/fE promoter; the developmental profile of the cryptic promoter allows adequate expression during oogenesis but not bristle formation (Paterson and O'Hare, 1991). cn;ry 5°6 flies were used as the wild type control.…”

“…In sterile singed mutants, singed ~ and singed36% the 57-kD protein was absent or nearly absent. Three transcripts are generated from the singed locus that differ only in the 3'-untranslated region and encode the same 57-kD protein (Paterson and O'Hare, 1991). The absence of protein in severe, sterile singed alleles suggested that all transcripts are affected.…”

“…The reduction in actin filament bundles in singed bristles and the failure of nurse cell cytoplasm transport in egg chambers of sterile singed females both suggest that the singed protein may interact with the actin-hased cytoskeleton. The cloning of the singed gene revealed an open reading frame of 1,536 nucleotides encoding a 57-kD protein, but the protein function remained elusive (Paterson and O'Hare, 1991). Recently, the gene encoding echinoderm fascin was cloned and found to have 35% peptlde identity and 67% peptide similarity with the singed gene (Bryan et al, 1993).…”

Cloning and Expression of a Murine Fascin Homolog from Mouse Brain

“…Recent cloning of fascin cDNAs from Strongylocentrotus purpuratus demonstrated that fascins are widely distributed throughout the animal kingdom (Bryan et al, 1993). Sequence comparison showed that echinoid fascin is homologous to the product of the Drosophila singed gene (Paterson and O'Hare, 1991), which is important in both mechanosensory bristle development and oogenesis. Overton showed that developing bristles contain a central core of mi-* The costs of publication of this article were defrayed in part by the payment of page charges.…”