Abstract
Purpose :
Ciliated sensory neurons like hair cells and olfactory cells display their distinct cellular mosaics whose establishment requires the heterophilic interaction between nectins, a family of immunoglobulin-like cell adhesion molecules. For the mosaic formation of another type of ciliated sensory neurons, cone photoreceptors, the mechanism remains unknown. We hypothesised that nectins might also be involved in the formation of cone mosaic.
Methods :
Adult zebrafish retina shows a crystalline-like cone mosaic consisting of four cone types (Red,Green,Blue, and UV cones). This highly regular pattern serves as a good model for screening genes that might participate in the formation of cone mosaic. Using CRISPR/Cas9, we managed to knock out candidate genes and generated corresponding homozygous mutants carrying transgenic reporter genes that indicate the identity of cones. Retina flat mount were made for imaging. Voroinoi diagram-derived regularity indexes were used for quantitative analysis, checking if the absence of the candidate could lead to a disrupted cone mosaic.
Results :
Public ScRNA-seq data revealed the expression of nectin1a and nectin3b in cones and their supporting cells Müller glia, respectively. Confirmed by in situ hybridization, it’s likely that heterophilic interaction between nectin1a and nectin3b, mimicking the scenario in hair cells’ patterning, might guide cones to create their pattern. Frame-shift mutation was introduced into the extracellular domain of both candidates whose homozygous mutants were expected to express no functional protein of nectin1a or nectin3b. Unfortunately, retina flat mount of both nectin1a and nectin3b mutants (3-week postfertilization) showed no obvious disrupted cone mosaic compared to that of their heterozygous siblings. There’s no other phenotype detected. Mutants turned out to be normal and were able to give birth to the next generation.
Conclusions :
Unlike the mosaic formation of hair cells and olfactory cells, the cone mosaic formation might not require the interaction between nectins. However, it is possible that other nectins, such as nectin1b and nectin3a, might get upregulated in the mutant to compensate for the loss of their paralogs. Future study is needed to address this point by introducing double mutants.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.