Cryptochromes function as photoreceptors for circadian rhythm entrainment in insects and in plants. Tu et al. provide evidence that cryptochromes may function similarly in vertebrates. The isolated iris sphincter muscle from chicks will constrict strongly and rapidly in light and redilate in the dark in the absence of any extrinsic neural input. The characteristics of the photopigment underlying this activity did not fit the template for an opsin photoreceptor, but instead matched the known absorption spectra for cryptochromes. Antisense knockdown of cryptochromes, but not melanopsin, caused a proportional loss of intrinsic iris photosensitivity.
D. C. Tu, M. L. Batten, K. Palczewski, R. N. Van Gelder, Nonvisual photoreception in the chick iris. Science 306, 129-131 (2004). [Abstract] [Full Text]
