Lcg is a light-inducible and clock-controlled gene expressed in the chicken pineal gland

The circadian clock is an autonomous biological clock that is entrainable to environmental 24-h cycles by receiving time cues such as light. Generally, light given at early and late subjective night, respectively, delays and advances the phase of the circadian oscillator. We previously searched for the chicken pineal genes that are induced by light in a phase-dependent manner. The present study undertook cDNA cloning and characterization of a gene whose expression was remarkably up-regulated by light at late subjective night. The mRNA level of this gene exhibited robust diurnal change in the pineal gland, with a peak in the early (subjective) day under light-dark cycles and constant dark condition, and hence it was designated Lcg (Light-inducible and Clock-controlled Gene). Chicken Lcg encodes a coiled-coil protein composed of 560 amino acid residues. Among chicken tissues, the pineal gland and the retina exhibited relatively high expression levels of LCG. LCG was colocalized with gamma-tubulin, a centrosomal protein, when expressed in COS7 cells, and LCG is the first example of a clock-related molecule being accumulated at the centrosome. Coimmunoprecipitation of LCG with gamma-tubulin in the chicken pineal lysate suggests a link between the circadian oscillator and the centrosomal function.