Genetics of photoreceptor development and function in zebrafish.

The vertebrate photoreceptor is a cell of unique morphology and function. It is an exquisite light detector, both sensitive and adaptable. Several unusual morphological features facilitate photoreceptor function. Signal detection is accomplished by a specialized apical structure, the outer segment. There, the capture of light produces fluctuations in cell membrane potential, which are then transmitted to the downstream circuitry of the retina via a rare type of synaptic junction, the ribbon synapse. The development, maintenance and function of the vertebrate photoreceptor cell have been studied mainly in four model organisms, ranging from an amphibian to man. A teleost fish, the zebrafish, is an important recent addition to this group. Genetic screens in zebrafish have identified an impressive collection of photoreceptor cell mutants, including the absence or malformation of specific morphological features as well as functional abnormalities. These mutant strains are currently studied using both molecular and embryological tools and provide important insights into photoreceptor biology.