Circadian Clock-Specific Roles for the Light Response Protein WHITE COLLAR-2

Abstract

To understand the role of white collar-2 in the Neurospora circadian clock, we examined alleles ofwc-2 thought to encode partially functional proteins. We found that wc-2 allele ER24 contained a conservative mutation in the zinc finger. This mutation results in reduced levels of circadian rhythm-critical clock gene products, frq mRNA and FRQ protein, and in a lengthened period of the circadian clock. In addition, this mutation altered a second canonical property of the clock, temperature compensation: as temperature increased, period length decreased substantially. This temperature compensation defect correlated with a temperature-dependent increase in overall FRQ protein levels, with the relative increase being greater in wc-2(ER24) than in wild type, while overall frq mRNA levels were largely unaltered by temperature. We suggest that this temperature-dependent increase in FRQ levels partially rescues the lowered levels of FRQ resulting from the wc-2 (ER24) defect, yielding a shorter period at higher temperatures. Thus, normal activity of the essential clock component WC-2, a positive regulator offrq, is critical for establishing period length and temperature compensation in this circadian system.

ACKNOWLEDGMENTS

We thank members of our laboratory for thoughtful discussions. We are especially grateful to Allan Froehlich, Hildur Colot, and Minou Nowrousian for experimental help and to anonymous reviewers for constructive suggestions on earlier drafts of the manuscript.

This work was supported by grants from the National Institutes of Health (GM 34985 and MH01186 to J.C.D., MH44651 to J.C.D. and J.J.L.), the National Science Foundation (MCB-0084509 to J.J.L.), and the Norris Cotton Cancer Center core grant at Dartmouth Medical School.