Insect Cryptochromes: Gene Duplication and Loss Define Diverse Ways to Construct Insect Circadian Clocks

Jan 25, 2007Molecular biology and evolution

Insect light-sensitive proteins: gene gains and losses create different internal clock designs

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Abstract

Insect CRY2 proteins from honeybees and red flour beetles are not light sensitive.

CRY2 proteins from honeybees and bumblebees were found to inhibit transcription without responding to light.
The same was observed for CRY2 in the red flour beetle, indicating a possible divergence in circadian mechanisms among insects.
Phylogenetic analysis suggests that the transcriptional repression function of insect CRY2 evolved from a light-sensitive ancestral gene.
Insects like Apis and Tribolium, which lack CRY1, may use alternative light input pathways for their circadian clocks.

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Cryptochrome (CRY) proteins are components of the central circadian clockwork of metazoans. Phylogenetic analyses show at least 2 rounds of gene duplication at the base of the metazoan radiation, as well as several losses, gave rise to 2 cryptochrome (cry) gene families in insects, a Drosophila-like cry1 gene family and a vertebrate-like cry2 family. Previous studies have shown that insect CRY1 is photosensitive, whereas photo-insensitive CRY2 functions to potently inhibit clock-relevant CLOCK:CYCLE-mediated transcription. Here, we extended the transcriptional repressive function of insect CRY2 to 2 orders--Hymenoptera (the honeybee Apis mellifera and the bumblebee Bombus impatiens) and Coleoptera (the red flour beetle Tribolium castaneum). Importantly, the bee and beetle CRY2 proteins are not light sensitive in culture, in either degradation of protein levels or inhibitory transcriptional response, suggesting novel light input pathways into their circadian clocks as Apis and Tribolium do not have CRY1. By mapping the functional data onto a cryptochrome/6-4 photolyase gene tree, we find that the transcriptional repressive function of insect CRY2 descended from a light-sensitive photolyase-like ancestral gene, probably lacking the ability to repress CLOCK:CYCLE-mediated transcription. These data provide an evolutionary context for proposing novel circadian clock mechanisms in insects.

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Insect Cryptochromes: Gene Duplication and Loss Define Diverse Ways to Construct Insect Circadian Clocks

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