| Light regulates animal behavior through visual and nonvisual photoreceptive pathways. While vision is governed by the opsins in rod and cone photoreceptors of the mammalian retina, other nonvisual tasks, such as circadian entrainment and masking, appear to be mediated through multiple photoreceptors. Cryptochrome (Cry) is a blue-light photoreceptor present in the mammalian retina which is also an integral part of the circadian clock mechanism and functions alongside melanopsin and classical opsins to transmit light information to the brain, as assayed by both behavioral assays and molecular gene induction by light in the brain. Specifically, in this study, several mouse models have been used to explore the contribution of cryptochrome and opsins to circadian regulation and other nonvisual irradiance detection tasks, and include retinal degeneration (rd) mice, cryptochrome knockout mice (cry1−/−cry2−/ −), plasma retinol binding protein knockout mice ( rbp−/−), and combinations thereof. I have found that cryptochromes and opsins both contribute to molecular gene induction in the SCN through photoreception in the retina, and that only in the absence of both do animals become totally unresponsive to light. In addition, the action spectrum of circadian gene photoinduction in a non-retinal-derived embryonic cell line from zebrafish supports cryptochrome as the primary photoreceptor governing this response. The evidence to date indicates that both cryptochrome and opsin are sufficient but neither is essential for nonvisual photoresponses in mammals. |
