Biological clock in total darkness: The Clock/MOP3 circadian system of theblind subterranean mole rat

Blind subterranean mole rats retain a degenerated, subcutaneous, visually b lind but functionally circadian eye involved in photoperiodic perception. H ere we describe the cloning, sequence, and expression of the circadian Cloc k and MON cDNAs of the Spalax ehrenbergi superspecies in Israel. Both genes are relatively conserved, although characterized by a significant number o f amino acid substitutions. The glutamine-rich area of Clock, which is assu med to function in circadian rhythmicity, is expanded in Spalax compared wi th that of humans and mice, and is different in amino acid composition from that of rats. We also show that MOP3 is a bona fide partner of Spalax Cloc k and that the Spalax Clock/MOP3 dinner is less potent than its human count erpart in driving transcription. We suggest that this reduction in transcri ptional activity may be attributed to the Spalax Clock glutamine-rich domai n, which is unique in its amino acid composition compared with other studie d mammalian species. Understanding Clock/MOP3 function could highlight circ adian mechanisms in blind mammals and their unique pattern as a result of a dapting to life underground.