Ignacio Provencio, Ph.D.

Contact Information

Research Interests

Blind mice lacking rod and cone photoreceptors can still regulate their circadian rhythms by light, suggesting that the photoreceptors responsible for this light-mediated regulation of the circadian system are not the well-studied rods and cones involved in vision. However, the spectral sensitivity of the mouse circadian system resembles the absorption profile of retinaldehyde-based photopigments, similar to those found in rods and cones. Melanopsin is a novel retinaldehyde-based photopigment that we initially discovered in the dermal melanophores of Xenopus laevis. The murine homolog is found exclusively in the eye, and its expression is restricted to less than 2% of retinal ganglion cells. These cells are intrinsically photosensitive and possess long, overlapping, melanopsin-rich dendrites that form a "photoreceptive net" lining the inner layer of the retina. Around 80% of the retinal ganglion cells that project to the hypothalamic suprachiasmatic nucleus, the site of the primary circadian pacemaker, contain melanopsin. Taken together, these data suggest that melanopsin retinal ganglion cells may play a role in the photic regulation of mammalian circadian rhythms.

Photoreceptive net of retinal ganglion cells in a flat-mounted mouse retina labeled with an antibody against melanopsin.         (Courtesy of Dr. Ana Castrucci)

Wheel running activity records of a wild-type mouse and a mouse lacking rods, cones, and melanopsin. Top: Representative double plotted activity record of a wild-type mouse under entraining conditions of 12 hr white light (800 lux) and 12 hr darkness (grey box). Bottom: Representative double plotted activity records of a mouse lacking rods, cones, and melanopsin under identical entraining conditions. While wild-type mice consolidate their activity to the dark phase and the time of activity onset is coincident with the light to dark transition, the mice lacking rods, cones, and melaopsin continue to free run with an intrinsic period length of less than 24hr. (Adapted from Supplementary Data from Panda S, Provencio I, Tu DC, Pires SS, Rollag MD, Castrucci AM, Pletcher MT, Sato TK, Wiltshire T, Andahazy M, Kay SA, Van Gelder RN, Hogenesch JB: Melanopsin is required for non-image-forming photic responses in blind mice. Science. 2003:301-525.)

To test this possibility, we, in collaboration with colleagues at The Scripps Research Institute and the Genomics Institute of the Novartis Research Foundation, have generated melanopsin-null mice. These mice show dramatic deficiencies in their capacity to phase shift circadian locomotor rhythms, indicating a central role for melanopsin as a circadian photopigment. Perhaps the most surprising aspect of these "knock out" studies is that disrupting both copies of the melanopsin gene does not completely abolish light induced circadian phase shifting; some capacity for phase shifting remains. The photoreceptors mediating this residual sensitivity are likely to be the rods or the cones.

To test this possibility, we crossed melanopsin-null mice with visually blind mice lacking rods and cones. The progeny of this cross that were rodless, coneless, and melanopsin-null were incapable of photoentrainment, even at high irradiances of ambient light. Importantly, the complete loss of photic responses in melanopsin-null mice lacking rods and cones demonstrates that no additional photopigments, such as cryptochromes, are required for non-visual photic signaling. Thus, it appears that multiple photoreceptor systems subserve non-visual photoreception, a phenomenon observed across phylogeny.

Representative Publications

1. Tu, D.C., Zhang, D., Demas, J., Slutsky, E.B., Provencio, I., Holy, T.E., & Van Gelder, R.N. (2005) Physiologic diversity and development of intrinsically photosensitive retinal ganglion cells. Neuron, 48, 987-999.
   
   

2. Kumbalasiri, T., & Provencio, I. (2005) Melanopsin and other novel mammalian opsins. Experimental Eye Research, 81, 368-375.

3. Isoldi, M.C., Rollag, M.D., Castrucci, A.M., & Provencio, I. (2005) Rhabdomeric phototransduction initiated by the vertebrate photopigment melanopsin. Proceedings of the National Academy of Sciences, U.S.A., 102, 1217-1221.

4. Qiu, X., Kumbalasiri, T., Carlson, S.M., Wong, K.Y., Krishna, V., Provencio, I., & Berson D.M. (2005) Induction of photosensitivity by heterologous expression of melanopsin. Nature, 433, 745-749.

5. Panda, S.*, Provencio, I.*, Tu, D.C.*, Pires, S.S., Rollag, M.D., Castrucci, A.M., Pletcher, M.T., Sato, T.K., Wiltshire, T., Andahazy, M., Kay, S.A., Van Gelder, R.N., & Hogenesch, J.B. (2003) Melanopsin is required for non-image forming photic responses in blind mice. Science, 301, 525-527, (*equally contributing authors)

6. Panda, S., Sato, T.K., Castrucci, A.M., Rollag, M.D., DeGrip, W.J., Hogenesch, J.B., Provencio, I.*, & Kay, S.A.* (2002) Melanopsin (Opn4) requirement for normal light induced circadian phase shifting. Science, 298, 2213-2216. (*co-corresponding authors)

7. Provencio, I., Rollag, M.D., & Castrucci, A.M. (2002) Photoreceptive net in the mammalian retina. Nature, 415, 493.

8. Provencio, I., Rodriguez, I.R., Jiang, G., Hayes, W.P., Moreira, E.F., & Rollag, M.D. (2000) A novel human opsin in the inner retina. Journal of Neuroscience, 20, 600-605.

9. Provencio, I., Jiang, G., De Grip, W. J., Hayes, W. P., & Rollag, M. D. (1998). Melanopsin: an opsin in melanophores, brain, and eye. Proceedings of the National Academy of Sciences, U.S.A., 95, 340-345.