Download (Danio rerio) cryptochrome genes

P209
Evolution and functional divergence of zebrafish
(Danio rerio) cryptochrome genes
CH AO LIU1 , JI A HU1, CHUNX I A NG QU1, GUOD ONG HUA NG1, H AN WAN G1
1
Center for Circadian Clocks, Soochow University, Suzhou, Jiangsu, CHINA
Cryptochrome (Cry) genes play important roles in circadian regulation and photoreception . While zebrafish
are known to have six cry genes, their evolutionary relationships and the mechanisms underlying their
functional divergence are not yet fully resolved . Here we aim to elucidate the mechanisms underlying
zebrafish cry evolution and functional divergence . Using phylogenetic and
syntenic analyses, we found that following the two-round vertebrate genome duplication (VGD) and
subsequent gene loss, teleost fish retained three subgroups of cry genes including cry1, cry2 and cry3;
before the third-round teleost genome duplication (TGD), local duplication of cry1 likely occurred in teleost fish,
which generated cry1 .1 and cry1 .2; and following TGD and subsequent gene loss, zebrafish retained cry1
.1a, cry1 .1b, cry1 .2a, cry1 .2b, cry2 and cry3 . In situ hybridization and quantitative real-time PCR showed that
these six cry genes are rhythmically expressed with distinct patterns in a robust manner, suggesting that
these cry genes have evolved divergent functions . In vitro cell transfection assays showed zebrafish possess
two types of Cry proteins, inhibitory Cry (IC) including Cry1 .1a, Cry1 .1b, Cry1 .2a, and Cry1 .2b that are potent
repressors of Clock:Bmal heterodimers-mediated transcription, and non-inhibitory Cry (NIC) including Cry2
nor Cry3 that cannot repress Clock:Bmal heterodimers-mediated transcription . We also found possible
mechanisms underlying non-inhibition of Cry2 and Cry3, i .e ., Cry3 is a cytoplasmic protein, and Cry2 cannot
effectively bind to the Bmal1 protein, even though it can enter inside the nucleus . In addition, Cry1 .1a and Cry1
.2b appear to evolve different nuclear localization signal (NLS) sequences . Taken together, these findings
contribute to the growing body of knowledge of Cry evolution, and set the stage for studying their functions .
*These authors contributed equally to this work
SOCie t y FOR Re Se a RCh On BiOl Og iCa l Rh y th MS
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