Actin filament crosslinking, bundling and molecular motor proteins are necessary for the assembly of epithelial projections such as microvilli, stereocilia, hairs, and bristles. Mutations in such proteins cause defects in the shape, structure, and function of these actin - based protrusions. One protein necessary for stereocilia formation, Myosin VIIA, is an actin - based motor protein conserved throughout phylogeny. In Drosophila melanogaster, severe mutations in the MyoVIIA homolog crinkled (ck) are “semi - lethal” with only a very small percentage of flies surviving to adulthood. Such survivors show morphological defects related to actin bundling in hairs and bristles. To better understand ck/MyoVIIA’s function in bundled - actin structures, we used dominant female sterile approaches to analyze the loss of maternal and zygotic (M/Z) ck/MyoVIIA in the morphogenesis of denticles, small actin - based projections on the ventral epidermis of Drosophila embryos. M/Z ck mutants displayed severe defects in denticle morphology – actin filaments initiated in the correct location, but failed to elongate and bundle to form normal projections. Using deletion mutant constructs, we demonstrated that both of the C - terminal MyTH4 and FERM domains are necessary for proper denticle formation. Furthermore, we show that ck/MyoVIIA interacts genetically with dusky - like (dyl), a member of the ZPD family of proteins that links the extracellular matrix to the plasma membrane, and when mutated also disrupts normal denticle formation. Loss of either protein alone does not alter the localization of the other; however, loss of the two proteins together dramatically enhances the defects in denticle shape observed when either protein alone was absent. Our data indicate that ck/MyoVIIA plays a key role in the formation and/or organization of actin filament bundles, which drive proper shape of cellular projections.

肌动蛋白丝交联、成束和分子运动蛋白对于微绒毛、静纤毛、毛发和鬃毛等上皮突起的组装是必需的。此类蛋白质的突变会导致这些基于肌动蛋白的突起的形状、结构和功能缺陷。静纤毛形成所必需的一种蛋白质，肌球蛋白VIIA，是一种在整个系统发育过程中保守的基于肌动蛋白的运动蛋白。在果蝇中， MyoVIIA 同系物crinkled ( ck ) 的严重突变是“半致命的”，只有极少数果蝇能存活到成年。这些幸存者表现出与毛发和刚毛中肌动蛋白成束相关的形态缺陷。为了更好地了解ck /MyoVIIA 在束状肌动蛋白结构中的功能，我们使用显性雌性不育方法来分析母体和合子 (M/Z) ck/ MyoVIIA 在小齿形态发生中的损失，腹侧表皮上基于小肌动蛋白的投影果蝇胚胎。M/Z ck突变体在齿状形态上表现出严重的缺陷——肌动蛋白丝在正确的位置起始，但未能伸长和成束以形成正常的突起。使用缺失突变体构建体，我们证明了 C 端 MyTH4 和 FERM 结构域对于正确的小齿形成是必需的。此外，我们还发现ck /MyoVIIA 与dusky-like (dyl)存在遗传相互作用，dusky-like (dyl) 是 ZPD 蛋白家族的成员，将细胞外基质与质膜连接起来，当突变时也会破坏正常的小齿形成。单独丢失任何一种蛋白质都不会改变另一种蛋白质的定位。然而，当两种蛋白质单独缺失时，两种蛋白质一起缺失会显着增强观察到的小齿形状缺陷。我们的数据表明ck /MyoVIIA 在肌动蛋白丝束的形成和/或组织中起着关键作用，肌动蛋白丝束驱动细胞投射的正确形状。