Sex Combs in Motion: Cell Dynamics of the Cellular Processes Involved in the Sex Comb Rotation in Drosophila melanogaster

A sex comb is a male-specific group of bristles located on the first leg in many species of the Drosophilidae family. (Atallah et al, 2009). This row of bristles is a secondary sexual trait, displaying high morphological divergence during evolution. In many Drosophila species, the sex comb undergoes an interesting morphogenetic process, in that this group of bristles rotates during development. This work focuses on studying the cellular dynamics involved in sex comb rotation in Drosophila melanogaster. To do this, I studied the rotation processes in wild type flies, artificially selected lines and mutants such as sex comb distal and bric à brac [PR72]. Change in sex comb length is a common evolutionary modification observed several times during sex comb evolution. To study the phenotypic effect of changing the number of sex comb teeth, I used lines artificially selected for high and low number of sex comb teeth and large effect mutants. Consistent with previous studies, I observed that selection modulates bristle number without disrupting other morphological features while the ectopic sex combs in large effect mutants display several changes. For example, artificial selection is able to uncouple the number of sex comb teeth and the degree of rotation, while the large effect mutant can affect both simultaneously. Then, I studied the cellular processes involved in the rotation of wild type Drosophila melanogaster sex combs during the pupal period. Although sex comb phenotypes in adult legs show little variance, the underlying cellular behaviours show temporal and spatial variation from leg to leg. In order to better understand how the sex comb rotates, I characterized the cellular dynamics of sex combs of different lengths: the mutant bric à brac [PR72] and the artificially selected lines. As a result, I propose three hypothetical models concerning the source of the force of rotation and suggest that a push from the region distal to the sex comb is the model that best explains current data.Ph