Cryptochromes Define a Novel Circadian Clock Mechanism in Monarch Butterflies That May Underlie Sun Compass Navigation

Abstract

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 cryb 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.

Functional circadian clock genes are essential for the overwintering diapause of the Northern house mosquito,Culex pipiens

“…In addition to these core circadian components, Zhu et al (Zhu et al, 2005) discovered that the monarch butterfly, Danaus plexippus, possesses another circadian protein, CRYPTOCHROME2 (CRY2), which is highly homologous to mammalian CRY and is absent in Drosophilia. Yuan et al (Yuan et al, 2007) demonstrated that CRY2 proteins isolated from the monarch butterfly, the malaria mosquito, the honey bee and the flour beetle are light insensitive, and instead repress CLK:CYC-mediated transcription of per in Drosophila Schneider 2 cells.…”

A Flavin Binding Cryptochrome Photoreceptor Responds to Both Blue and Red Light in Chlamydomonas reinhardtii

“…This difference is of interest with regard to the clock system because plant CRYs, such as the ones from Arabidopsis (CRY1 and CRY2), and the animal type I CRYs, such as the one from Drosophila, mediate the input of blue light into clock function (Somers et al, 1998;Stanewsky et al, 1998;Harmer, 2009). On the other hand, animal type II CRYs, represented by mammalian CRYs or monarch butterfly (Danaus plexippus) CRY2, are part of the circadian oscillator (Etchegaray et al, 2003;Zhu et al, 2008). However, not all CRYs are clock-related components.…”

Identification of medaka magnetoreceptor and cryptochromes

“…This implies the diverse roles of magr and cry. Unlike cry, which has already been reported to have other important functions such as circadian rhythm resetting and photosensitivity (Zhu et al, 2008;Chaves et al, 2011), the potential function of magr is to be explored. Since magr is the homologue of bacterial iron-sulfur cluster assembly Isca1, which is evolutionarily highly conserved and found in prokaryotic and eukaryotic organisms for the biogenesis of iron-sulfur cluster across species (Zheng et al, 1998;Schwartz et al, 2001;Vinella et al, 2009), it is predictable that magr may also have similar roles.…”