Circadian Control at the Post-Transcriptional Level: the Gonyaulax story

Woody Hastings (October 25, 2010)

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Several different circadian rhythms, as well as an annual rhythm, have been studied in the marine dinoflagellate Gonyaulax polyedra (now Lingulodinium polyedrum), many features of which may be grist for modeling mills, whatever they may be. The rhythm of bioluminescence provides an easy "hand" for the automation of its measurement in vivo, and the luciferase and luciferin responsible serve as unambiguous biochemical correlates. This presentation will present highlights of several of its features, starting the subject of the title: post transcriptional control of circadian protein expression. The term "temperature compensation" was introduced in this system to replace "temperature independence" used earlier, based on the observation that the rhythm has a Q10 less than 1. Rhythmicity is lost at low temperatures and bright light (also observed in other systems) but reverts simply upon the return to permissive conditions, with the phase always determined by the time at which permissive conditions were restored. As first reported in humans, different rhythms may have different periods under some conditions - still not well defined in any system. And different rhythms have characteristically different phase angle relationships, but these can be altered by conditions. Might circadian phase be affected by a humoral factor(s)? This is of continuing interest in the mammalian SCN, where dozens of peptides have recently been reported; a unicell might be a favorable system to investigate the possibility. And do models for circadian systems have applicability to infra- ultradian rhythms? A circannual rhythm in Gonyaulax may be a good challenge for elucidating mechanisms. These and other aspects of circadian rhythms in Gonyaulax will be presented for discussion.