Zhu Haisun, Sauman Ivo, Yuan Quan, Casselman Amy, Emery-Le Myai, Emery Patrick, Reppert Steven M
Department of Neurobiology, University of Massachusetts Medical School, Worcester, Massachusetts, United States of America.
PLoS Biol. 2008 Jan;6(1):e4. doi: 10.1371/journal.pbio.0060004.
The circadian clock plays a vital role in monarch butterfly (Danaus plexippus) migration by providing the timing component of time-compensated sun compass orientation, a process that is important for successful navigation. We therefore evaluated the monarch clockwork by focusing on the functions of a Drosophila-like cryptochrome (cry), designated cry1, and a vertebrate-like cry, designated cry2, that are both expressed in the butterfly and by placing these genes in the context of other relevant clock genes in vivo. We found that similar temporal patterns of clock gene expression and protein levels occur in the heads, as occur in DpN1 cells, of a monarch cell line that contains a light-driven clock. CRY1 mediates TIMELESS degradation by light in DpN1 cells, and a light-induced TIMELESS decrease occurs in putative clock cells in the pars lateralis (PL) in the brain. Moreover, monarch cry1 transgenes partially rescue both biochemical and behavioral light-input defects in cry(b) mutant Drosophila. CRY2 is the major transcriptional repressor of CLOCK:CYCLE-mediated transcription in DpN1 cells, and endogenous CRY2 potently inhibits transcription without involvement of PERIOD. CRY2 is co-localized with clock proteins in the PL, and there it translocates to the nucleus at the appropriate time for transcriptional repression. We also discovered CRY2-positive neural projections that oscillate in the central complex. The results define a novel, CRY-centric clock mechanism in the monarch in which CRY1 likely functions as a blue-light photoreceptor for entrainment, whereas CRY2 functions within the clockwork as the transcriptional repressor of a negative transcriptional feedback loop. Our data further suggest that CRY2 may have a dual role in the monarch butterfly's brain-as a core clock element and as an output that regulates circadian activity in the central complex, the likely site of the sun compass.
生物钟在黑脉金斑蝶（Danaus plexippus）的迁徙中起着至关重要的作用，它为时间补偿太阳罗盘定向提供时间成分，这一过程对成功导航至关重要。因此，我们通过关注果蝇样隐花色素（cry）（命名为cry1）和脊椎动物样隐花色素（命名为cry2）的功能来评估黑脉金斑蝶的生物钟机制，这两种隐花色素都在蝴蝶中表达，并将这些基因置于体内其他相关生物钟基因的背景下进行研究。我们发现，在含有光驱动生物钟的黑脉金斑蝶细胞系的头部，生物钟基因表达和蛋白质水平的时间模式与DpN1细胞中的相似。CRY1在DpN1细胞中介导光诱导的无时间蛋白降解，并且在大脑外侧叶（PL）的假定生物钟细胞中发生光诱导的无时间蛋白减少。此外，黑脉金斑蝶cry1转基因部分挽救了cry(b)突变果蝇的生化和行为光输入缺陷。CRY2是DpN1细胞中CLOCK:CYCLE介导转录的主要转录抑制因子，内源性CRY2在不涉及周期蛋白的情况下有效抑制转录。CRY2与PL中的生物钟蛋白共定位，并在适当的时间转移到细胞核进行转录抑制。我们还发现了在中央复合体中振荡的CRY2阳性神经投射。这些结果定义了黑脉金斑蝶中一种以CRY为中心的新型生物钟机制，其中CRY1可能作为蓝光光感受器用于生物钟的同步，而CRY2在生物钟机制中作为负转录反馈环的转录抑制因子发挥作用。我们的数据进一步表明，CRY2在黑脉金斑蝶大脑中可能具有双重作用——作为核心生物钟元件以及作为调节中央复合体昼夜活动的输出，中央复合体可能是太阳罗盘的所在位置。
