Originally published as Genetics Published Articles Ahead of Print on August 24, 2007.

Genetics, Vol. 177, 329-345, September 2007, Copyright © 2007
doi:10.1534/genetics.107.076513

Rhythm Defects Caused by Newly Engineered Null Mutations in Drosophila's cryptochrome Gene

Eva Dolezelova¹, David Dolezel^1,2 and Jeffrey C. Hall³

Department of Biology, Brandeis University, Waltham, Massachusetts 02454

³ Corresponding author: Department of Biology, MS-008, Brandeis University, Waltham, MA 02454-9110.
E-mail: hall{at}brandeis.edu

Much of the knowledge about cryptochrome function in Drosophila stems from analyzing the cry^b mutant. Several features of this variant's light responsiveness imply either that CRY^b retains circadian-photoreceptive capacities or that additional CRY-independent light-input routes subserve these processes. Potentially to resolve these issues, we generated cry knock-out mutants (cry⁰'s) by gene replacement. They behaved in an anomalously rhythmic manner in constant light (LL). However, cry⁰ flies frequently exhibited two separate circadian components in LL, not observed in most previous cry^b analyses. Temperature-dependent circadian phenotypes exhibited by cry⁰ flies suggest that CRY is involved in core pacemaking. Further locomotor experiments combined cry⁰ with an externally blinding mutation (norpA^P24), which caused the most severe decrements of circadian photoreception observed so far. cry^b cultures were shown previously to exhibit either aperiodic or rhythmic eclosion in separate studies. We found cry⁰ to eclose in a solidly periodic manner in light:dark cycles or constant darkness. Furthermore, both cry⁰ and cry^b eclosed rhythmically in LL. These findings indicate that the novel cry⁰ type causes more profound defects than does the cry^b mutation, implying that CRY^b retains residual activity. Because some norpA^P24 cry⁰ individuals can resynchronize to novel photic regimes, an as-yet undetermined light-input route exists in Drosophila.

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