Nok plays an essential role in maintaining the integrity of the outer nuclear layer in the zebrafish retina

Proper visual function of the vertebrate retina requires the maintenance of the integrity of the retinal outer nuclear layer (ONL), which is often affected in many blinding human retinal diseases. While the structural integrity of the ONL has long been considered to be maintained primarily through the outer limiting membrane (OLM), we have little knowledge on the development and maintenance of the OLM itself. Here, by analyzing the adhering properties of photoreceptors in zebrafish N-cad and nok mutants, we demonstrated for the first time that the nok gene is essential for the establishment and/or maintenance of the OLM. In addition, our results imply the possibility that Nok, Crumbs, and their associated proteins may constitute a type of photoreceptor-photoreceptor junctional complex that has not be described before. Thus, our study provides novel insights into the mechanisms by which the integrity of the ONL is maintained in the vertebrate retina.