Actin bundles play different role in shaping scale as compare to bristle in mosquito Aedes aegypti.

Abstract

Insect epithelial cells contain cellular extensions such as bristles, hairs and scales. It has been suggested that these cellular extensions are homologous structures that differ in morphology and function. These cellular extensions contain actin bundles that dictate their cellular morphology; bristle and hair are cylindrical in shape, while scales are wider and flattened. While the organization, function and identity of the major actin bundling protein in bristles and hairs is known, this information in scales is unknown. In this study, we characterized the development of scales and the role of actin bundles in the mosquito, Aedes aegypti. We show that scales undergo drastic morphological changes during development, from cylindrical shape to flat shape with longer membrane invagination. Scale actin bundle distribution changes during development, from symmetrical organization of actin bundles located throughout the bristle membrane, to asymmetrical organization of the actin bundles. By chemically inhibiting actin polymerization and by knocking-out the forked gene in the mosquito (Ae-Forked; a known actin bundling protein), by CRISPR-Cas9 gene editing, we showed that actin bundles are required for shaping bristle, hair and scale morphology. We demonstrated that actin bundles and Ae-Forked are required for bristle elongation, but not that of scales. In scales, actin bundles are required for width formation. Our results reveal a differential requirement of actin bundles in shaping mosquito scales compared to bristles.