In the vertebrate circadian feedback loop, CLOCK:BMAL heterodimers induce the 
expression of Cry genes. The CRY proteins in turn inhibit CLOCK:BMAL-mediated 
transcription closing the negative feedback loop. Four CRYs, which all inhibit 
CLOCK:BMAL-mediated transcription, exist in zebrafish. Although these zebrafish 
Crys (zCry1a, 1b, 2a, and 2b) show a circadian pattern of expression, previous 
studies have indicated that the circadian oscillation of zCry1a could be 
CLOCK:BMAL-independent. Here we show that abrogation of CLOCK:BMAL-dependent 
transcription in zebrafish cells by the dominant negative zCLOCK3-DeltaC does 
not affect the circadian oscillation of zCry1a. Moreover, we provide several 
lines of evidence indicating that the extracellular signal-regulated kinase 
(ERK) signaling cascade modulates the circadian expression of zCry1a gene in 
constant darkness. Taken together, our data strongly support the notion that 
circadian oscillation of zCry1a is CLOCK:BMAL-independent and further indicate 
that mechanisms involving non-canonical clock genes could contribute to the 
circadian expression of zCry1a gene in a cell autonomous manner.