Drosophila myosin V is required for larval development and spermatid individualization

Abstract

Class V myosins are multifunctional molecular motors implicated in vesicular traffic, RNA transport, and mechanochemical coupling of the actin and microtubule-based cytoskeletons. To assess the function of the single myosin V gene in Drosophila (MyoV), we have characterized both deletion and truncation alleles. Mutant animals exhibit no detectable defects during embryogenesis but are delayed in larval development; most die prior to 3rd instar. MyoV protein is widely distributed; however, there are no obvious cytological defects in mutant larval tissues where MyoV was normally highly expressed. Of the few adult MyoV mutant escapers, females were fertile but males were not. We examined the expression of MyoV during spermatogenesis. MyoV was associated with membranes, microtubule, and actin structures required for spermatid maturation; MyoV was strongly associated with the sperm nuclei during the maturation of the actin-rich investment cones that package spermatids in individual membranes. In MyoV mutant escaper males, the early stages of spermatogenesis were normal; however, in the later stages, the investment cones stained weakly for actin and their registration was disrupted; no mature sperm were produced. Our results suggest that MyoV contributes to the formation of the actin-based investment cones and acts to coordinate and/or anchor these structures and other components of the individualization complex.

Critical roles of long noncoding RNAs in Drosophila spermatogenesis

“…In regard to sperm individualization, the testes of 19 lncRNA KO mutants, including CR42858 −/− and CR43282 −/− , exhibited defects in coordinated actin cone movement, resulting in poorly aligned or lagging ICs. Similar phenotypes have been reported for the mutants in the genes encoding the testis-specific proteasome subunit Prosα6T, myosin VI, myosin V, and dynein (Hicks et al 1999;Li et al 2004;Mermall et al 2005;Zhong and Belote 2007). It remains to be determined whether these lncRNAs are directly functional in late spermatogenesis or instead play a role in the early spermatogenesis that is only manifest in the late stage.…”

The testis-specific proteasome subunit Prosα6T of D. melanogaster is required for individualization and nuclear maturation during spermatogenesis

“…Although the mechanism of the actin cone movement has not been fully elucidated, it has been proposed that actin polymerization and depolymerization are the driving force (Noguchi and Miller, 2003). Myosin VI seems to be an actin cone structure stabilizer (Noguchi et al, 2006), and myosin V is required for actin cone formation (Mermall et al, 2005). Here, we demonstrate that the ubiquitin-proteasome pathway is also important in IC movement.…”

“…Our observations that in the Pros␣6T 1 mutant, active Dronc disappears from the IC and active Ice is significantly reduced is consistent with this model. The fact that active Ice is not completely eliminated suggests that there might be an additional Dronc-independent pathway for Ice activation, as has been suggested by Huh et al (Huh et al, 2004 (Hicks et al, 1999;Li et al, 2004;Ghosh-Roy et al, 2005;Mermall et al, 2005). The spermatid nuclear bundles in these mutants are also disrupted.…”

Separating from the pack: Molecular mechanisms ofDrosophilaspermatid individualization

“…Although Myosins V and VI are important for this process, motor activity does not seem to power migration of the IC. 23,[27][28][29] The observation that actin polymerization is essential for IC progression suggests that the IC moves by incorporating new actin filaments at the cones, 21,27 and experimental evidence indicates that the rear bundles specifically are involved. 25 Classical genetic studies have identified at least 70 genes that mutate to give individualization phenotypes ( Table 1).…”