| Widespread use of zebrafish (Danio rerio) in genetic analysis of embryonic development has led to rapid advances in the technology required to generate, map, and clone mutant genes. In order to identify genes involved in the generation and regulation of vertebrate circadian rhythmicity, we have initiated a screen for dominant mutations that affect the circadian periodicity of larval zebrafish locomotor behavior. In screens totaling ∼1,300 individuals, we recovered two period mutants. The P34 mutant, one of the first mutants recovered, is homozygous viable and has a semi-dominant, short-period phenotype. This mutation also shortens the periods of melatonin production rhythms measured from cultured pineals, indicating that the mutant gene product affects circadian rhythmicity at the cellular or tissue level, as well as at the behavioral level. Using the pineal culture system, I assayed for temperature compensation and light entrainment deficits in the mutant. I found that this mutation alters temperature compensation, but not phase shifting to light. I have mapped the P34 mutation to zebrafish linkage group/chromosome 7 using microsatellite markers. I assayed several candidate genes for the mutation determining their map positions, sequences, and/or expression patterns. One of these genes, the zebrafish period1 gene, is the only known putative clock gene that maps near the mutation. However, I did not find any difference in any of these genes' sequences or expression patterns that was specific to the mutants, suggesting that the P34 mutation may be in a novel circadian clock gene. |
