An inherited functional circadian clock in zebrafish embryos

Circadian clocks are time-keeping systems found in most organisms. In zebra fish, expression of the clock gene Period3 (Per3) oscillates throughout emb ryogenesis in the central nervous system and the retina. Per3 rhythmic expr ession was free-running and was reset by light but not by the developmental delays caused by Low temperature. The time of fertilization had no effect on Per3 expression. Per3 messenger RNA accumulates rhythmically in oocytes and persists in embryos. Our results establish that the circadian clock fun ctions during early embryogenesis in zebrafish. Inheritance of maternal clo ck gene products suggests a mechanism of phase inheritance through ovogenes is.