Capping protein beta is required for actin cytoskeleton organisation and cell migration during Drosophila oogenesis

Abstract

Capping protein (CP) is a well-characterised actin-binding protein important for regulation of actin filament (AF) assembly. CP caps the barbed end of AFs, inhibiting the addition and loss of actin monomers. In Drosophila melanogaster, the gene encoding CP β-subunit is named capping protein beta (cpb; see Hopmann et al. [1996] J Cell Biol 133: 1293-305). The cpb level is reduced in the Drosophila bristle actin cytoskeleton and becomes disorganised with abnormal morphology. A reduced level of the CP protein in ovary results in disruption of oocyte determination, and disturbance of nurse cell (NC) cortical integrity and dumping. We describe novel defects appearing in cpb mutants during oogenesis, in which cpb plays an important role in border and centripetal follicle cell migration, ring canal development and cytoplasmic AF formation. The number of long cytoplasmic AFs was dramatically reduced in cpb hypomorphs and abnormal actin aggregates was seen on the inner side of NC membranes. A hypothesis to explain the formation of abnormal short-cut cytoplasmic AFs and actin aggregates in the cpb mutant NCs was proffered, along with a discussion of the reasons for 'dumpless' phenotype formation in the mutants.

GAGA protein is required for multiple aspects of Drosophila oogenesis and female fertility

“…Some of these genes: chic (Cooley, Verheyen, & Ayers, ), cpb (Ogienko et al, ) , sn (Cant, Knowles, Mooseker, & Cooley, ), sax (Twombly et al, ) are essential for the formation of cytoplasmic actin filaments in nurse cells. Disorders in the expression of genes sn (Cant et al, ) , chic (Cooley et al, ), and tsr (Chen et al, ) lead to impairments in the functioning of egg chamber somatic cells.…”

“…Some of these genes: chic (Cooley, Verheyen, & Ayers, 1992), cpb (Ogienko et al, 2013), sn (Cant, Knowles, Mooseker, & Cooley, 1994),…”

Prostaglandin signaling temporally regulates actin cytoskeletal remodeling during Drosophila oogenesis

“…Ultrastructural analysis of these actin bundles revealed that they are composed of tightly bundled actin filaments that are oriented with their barbed, or growing, ends positioned at or near the nurse cell membranes (Guild et al, 1997). Genetic analyses have revealed that the actin monomerbinding protein, Profilin (Drosophila Chickadee, Chick) (Cooley et al, 1992); the actin bundling proteins, Fascin (Drosophila Singed, Sn) and Villin (Drosophila Quail, Qua) (Mahajan-Miklos and Cooley, 1994b); the actin elongation factor, Enabled (Ena) (Gates et al, 2009); and the actin filament barbed end capping protein, Capping protein (Cp; Drosophila Cpa and Cpb) (Gates et al, 2009;Ogienko et al, 2013), are required for parallel actin bundle formation during S10B. Additionally, the cell adhesion molecule, E-Cadherin (Drosophila Shotgun, Shg) (Oda et al, 1997;Godt and Tepass, 1998;White et al, 1998;Niewiadomska et al, 1999;Huelsmann et al, 2013) and the cell adhesion scaffolding protein/transcription factor, β-Catenin (Drosophila Armadillo, Arm) (Peifer et al, 1993;Cox et al, 1996;Oda et al, 1997;White et al, 1998) are required for actin bundle formation, where they likely play a role in establishing/maintaining appropriate actin bundle orientation (Huelsmann et al, 2013).…”

“…Cp is known to be an important functional antagonist of Ena/VASP-dependent actin filament elongation (Bear et al, 2002;Bear and Gertler, 2009). Additionally, Cp has been shown to play critical roles during Drosophila oogenesis, including oocyte determination (Gates et al, 2009), parallel actin filament bundle formation during S10B (Gates et al, 2009;Ogienko et al, 2013), and border cell migration (Gates et al, 2009;Lucas et al, 2013;Ogienko et al, 2013). With these findings in mind, we asked if reduced Cp could alter follicle sensitivity to COX inhibition.…”

“…Parallel actin filament bundle formation during S10B of Drosophila oogenesis is known to require the activity of numerous actin-binding proteins including Profilin (Cooley et al, 1992), Fascin , Ena (Gates et al, 2009), Cp (Gates et al, 2009;Ogienko et al, 2013), and Villin (Mahajan-Miklos and . However, not all proteins required for parallel actin filament bundle formation during S10B exhibit an interaction in our pharmaco-genetic interaction screen, as reduced levels of Villin (Groen et al, 2012) or Profilin fail to modify follicle sensitivity to COX inhibition (Table 2.1, Figure 2.2, and Appendix A), while reduced levels of Fascin, Ena, and Cp strongly sensitize follicles to the effects of COX inhibition.…”