Actin organization, bristle morphology, and viability are affected by actin capping protein mutations in Drosophila.

Abstract

Abstract. Regulation of actin filament length and orientation is important in many actin-based cellular processes. This regulation is postulated to occur through the action of actin-binding proteins. Many actin-binding proteins that modify actin in vitro have been identified, but in many cases, it is not known if this activity is physiologically relevant. Capping protein (CP) is an actin-binding protein that has been demonstrated to control filament length in vitro by binding to the barbed ends and preventing the addition or loss of actin monomers. To examine the in vivo role of CP, we have performed a molecular and genetic characterization of the [3 subunit of capping protein from Drosophila melanogaster. We have identified mutations in the Drosophila [3 subunit--these are the first CP mutations in a multicellular organism, and unlike CP mutations in yeast, they are lethal, causing death during the early larval stage. Adult flies that are heterozygous for a pair of weak alleles have a defect in bristle morphology that is correlated to disorganized actin bundles in developing bristles. Our data demonstrate that CP has an essential function during development, and further suggest that CP is required to regulate actin assembly during the development of specialized structures that depend on actin for their morphology.

DrosophilaIk2, a member of the IκB kinase family, is required for mRNA localization during oogenesis

“…The bristle defects are nearly identical to those caused by mutations in actin-associated 1473 RESEARCH ARTICLE Role of Drosophila ik2 in mRNA localization proteins (Hopmann et al, 1996;Verheyen and Cooley, 1994b), or to bristles that were treated with F-actin-inhibitors (Tilney et al, 2000). Bristles contain a central core of microtubules, but mutations in the dynein heavy chain gene Dhc64C or treatment with drugs that disrupt microtubule dynamics do not cause bristle phenotypes like the thick, branched bristles seen in ik2 mutants (Gepner et al, 1996;Tilney et al, 2000) (data not shown).…”

Dynactin is required to maintain nuclear position within postmitoticDrosophilaphotoreceptor neurons

“…cpb/Df(2L)E.2 animals did not survive to third instar, preventing the classic genetic demonstration that these cpb alleles behaved as strong loss-of-function mutations. Fortunately, we found that the [pYES-β] genomic transgene, which contains the CPB coding region (Hopmann et al, 1996), was able to rescue the lethality of cpb/Df(2L)E.2 animals, but did not rescue the previously described cpb bristle defect (Hopmann et al, 1996). This suggested that [pYES-β] was a partially functional rescue construct that could be used to examine the visual systems of otherwise cpb/Df(2L)E.2 animals.…”

Actin capping protein α maintainsvestigial-expressing cells within theDrosophilawing disc epithelium

“…Loss of cpb displaces actin bundles from the cell membrane in Drosophila bristles by increasing the concentration of non-bundle actin snarls (Hopmann et al, 1996;Frank et al, 2006) and CPs may specify actin filament position in the sarcomere (Schafer et al, 1995). In the Drosophila wing blade epithelium, loss of CPs might disrupt attachment of the actin cytoskeleton to the adherens junctions, breaking the connection between cells and inducing cell extrusion (Fig.…”