Photoreceptor cells (PRCs) are a highly specialized type of neurons present in the retina, which are responsible for phototransduction. Vertebrate PRCs can be divided into rods, specialized for night vision, and cones, responsible for daylight and colour vision. In zebrafish, there are 4 different types of cones: green, red, blue and UV. Mature PRCs are polarized cells, with the apical surface subdivided into the outer and the inner segment and they arise from columnar epithelial progenitor cells.
PRCs have a highly specialized structure, which is essential for their function. Several studies have focused on the role of different proteins in PRC development and phototransduction. However, a detailed characterization of the morphological changes from the precursor stage to its functional form is lacking.
In this study, we aim to characterize the maturation of the apical surface of PRCs in zebrafish. We are performing a time course of the formation of the inner and outer segments and the connecting cilium using protein markers expressed in specific regions. We are also measuring cell volumes and cell lengths every four hours from the appearance of the PRC precursors to the matured stages using reporter lines specific for the red and UV sensitive PRCs.
We used Crb2a and Crb2b for labeling the inner segment. We found that in PRC precursors Crb2a localizes in the apical membrane of the cells, changing it’s location to the sub-apical region of the incipient inner segment during the maturation process. Crb2b is also present in the sub-apical region of PRCs but it only starts being expressed when the inner segment is forming.
With this detailed characterization we aim to have a better understanding of the maturation process of the apical surface of PRCs. As a next step, we intend to use these methods to investigate the role of candidate proteins in PRC maturation.