ABSTRACT
Cell competition is a cell selection process that arises in growing tissues as a result of interactions between cells of different fitness. This behavior is also observed in Myc super-competition, where healthy wild type cells in growing wing discs of Drosophila are outcompeted by nearby cells that express higher levels of the Myc oncogene. Most work on Myc super-competition has examined it in mixed populations of male and female larvae. However, as physiological and genetic differences between Drosophila males and females could affect the competitive behavior of cells, we have investigated whether sex differences affect the process. Here we show that both male and female wing disc cells are subject to Myc super-competition. Female disc cells appear to be more sensitive to competitive elimination than male cells, potentially due to differences in baseline cellular Myc levels between the sexes. We also report sexual dimorphism of cell size and number between male and female growing wing discs that is independent of competition; wing discs and wing pouches from females are larger than males' due to larger cell size and cell number. We suggest that separately examining male and female tissues in cell competition assays could enhance our understanding of the effects of sex-specific pathways on cell and super-competition.
ABSTRACT
The mariner (myo7aa-/- ) mutant is a zebrafish model for Usher syndrome type 1 (USH1). To further characterize hair cell synaptic elements in myo7aa-/- mutants, we focused on the ribbon synapse and evaluated ultrastructure, number and distribution of immunolabeled ribbons, and postsynaptic densities. By transmission electron microscopy, we determined that myo7aa-/- zebrafish have fewer glutamatergic vesicles tethered to ribbon synapses, yet maintain a comparable ribbon area. In myo7aa-/- hair cells, immunolocalization of Ctbp2 showed fewer ribbon-containing cells in total and an altered distribution of Ctbp2 puncta compared to wild-type hair cells. myo7aa-/- mutants have fewer postsynaptic densities - as assessed by MAGUK immunolabeling - compared to wild-type zebrafish. We quantified the circular swimming behavior of myo7aa-/- mutant fish and measured a greater turning angle (absolute smooth orientation). It has previously been shown that L-type voltage-gated calcium channels are necessary for ribbon localization and occurrence of postsynaptic density; thus, we hypothesized and observed that L-type voltage-gated calcium channel agonists change behavioral and synaptic phenotypes in myo7aa-/- mutants in a drug-specific manner. Our results indicate that treatment with L-type voltage-gated calcium channel agonists alter hair cell synaptic elements and improve behavioral phenotypes of myo7aa-/- mutants. Our data support that L-type voltage-gated calcium channel agonists induce morphological changes at the ribbon synapse - in both the number of tethered vesicles and regarding the distribution of Ctbp2 puncta - shift swimming behavior and improve acoustic startle response.
