S7-2.2 Sunday, Jan. 6 Symbiont luminescence entrains daily host-tissue rhythms through direct regulation of a host cryptochrome gene HEATH-HECKMAN, Elizabeth A.C.*; PEYER, Suzanne M.; MCFALL-NGAI, Margaret J.; University of Wisconsin - Madison; University of Wisconsin - Madison; University of Wisconsin - Madison firstname.lastname@example.org
All animals exist in the presence of beneficial microbial symbionts, however the extent to which these microbes control, or are controlled by, host circadian rhythms has not been addressed. We studied the role of bacterial partners in regulating biological rhythms in the symbiosis between the squid Euprymna scolopes and its luminous symbiont Vibrio fischeri. This binary model for the chronic bacterial colonization of animal epithelia is characterized by daily transcriptional rhythms in both partners, as well as by daily rhythms in symbiont luminescence. Two transcripts encoding cryptochromes, blue-light receptors that entrain circadian rhythms in all invertebrates, were identified in the host. We first determined whether these genes, escry1 and escry2, cycle in host tissues. Whereas both cycled in the head with a similar pattern to that found in other animals, escry1 cycles in the symbiont-colonized light organ with an 8-fold up-regulation coincident not with environmental light but with the rhythms of bacterial luminescence. Manipulating the colonization process revealed that escry1 transcription patterns in the light organ were dependent upon the presence of symbionts. Mutants of V. fischeri defective in luminescence (Δlux) failed to induce escry1 expression to wild-type levels, providing evidence that bacterial luminescence entrains host cryptochrome expression. In addition to being the first known characterization of cryptochromes in a mollusc, this study demonstrates that bacterial symbionts have the potential to be active participants in the setting of host biological rhythms. The conservation of both epithelial-bacterial interactions and circadian gene regulation across the metazoa suggests that symbiont-induced circadian rhythms may be widespread.