Clint L. Makino, Ph.D.

Associate Professor of Ophthalmology

Massachusetts Eye & Ear Infirmary
Ophthalmology
243 Charles St
Boston, MA 02114
Telephone: 617-573-4462
Fax: 617- 573-4290
Email: cmakino@meei.harvard.edu
Lab website: The Makino Lab

Retinal photoreceptors capture light and transform it into a neural signal. Retinal rods approach the pinnacle of sensitivity; they detect single photons. But such extreme sensitivity is only useful when photons are scarce. To maintain a capacity for signaling in bright light, rods must adjust their sensitivity as a function of the ambient light. We are interested in the molecular mechanisms conferring high sensitivity to dark adapted cells and those underlying light adaptation. By recording the electrical activity of single rods from transgenic mice in which expression of a gene has been blocked or reduced, we have begun to identify key proteins whose concentrations affect the timing and amplification of the photoresponse. For example, hemizygous knockout of rhodopsin was shown by microspectrophotometry to result in a 50% reduction in the expression of the visual pigment rhodopsin. Sensitivity was lowered because photon catch declined. However, expression of fewer rhodopsins relieved molecular crowding, increased the rates of chemical reaction subsequent to photon absorption and accelerated the kinetics of the photoresponse. We further showed that the collision rate between rhodopsin and transducin limited the rising phase while another molecular collision rate limited the falling phase.

Photoreceptors are vulnerable to degenerations resulting from naturally occurring mutations in proteins involved in phototransduction. The degenerations lead to permanent blindness because lost photoreceptors are not replaced. We are exploring the signaling defects cause by these mutations in transgenic mice, in an effort to understand the link between alterations in phototransduction and retinal disease.

References:

Isayama T, Chen Y, Kono M, DeGrip WJ, Ma J-X, Crouch RK, Makino C L (2006). Differences in the pharmacological activation of visual opsins. Visual Neuroscience 26: 899-908.
Isayama T, Alexeev D, Makino CL, Washington I, Nakanishi K, Turro, NJ (2006). An accessory chromophore in red vision. Nature 443: 649.
He Q, Alexeev D, Estevez ME, McCabe SL, Calvert PD, Ong DE, Cornwal, MC, Zimmerman AL, Makino CL (2006). Cyclic nucleotide-gated ion channels in rod photoreceptors are protected from retinoid inhibition. Journal of General Physiology 128: 473-485.
Bush RA, Makino CL. Recovering shapes the photoresponse of retinal rods. In Koch K-W, Philippov P, eds. (2006) Neuronal Calcium Sensors. Nova Science.
Yang J, Pawlyk, B, Wen X-H, Adamian M, Soloviev M, Michaud N, Zhao Y, Sandberg MA, Makino CL, Li T. (2007) Mpp4 is required for proper localization of plasma membrane calcium ATPases and maintenance of calcium homeostatis at the rod photoreceptor synaptic terminals. Human Molecular Genetics 16:1017-1029.
Makino CL, Peshenko IV, Wen X-H, Olshevskaya EV, Barrett R, Dizhoor, AM. (2008) A role for GCAP2 in regulating the photoresponse: Guanylyl cyclase activation and rod electrophysiology in GUCA1B knockout mice. Journal of Biological Chemistry 283:29135-29143.
Wen, X.-H., Shen, L., Brush, R. S., Michaud, N., Al-Ubaidi, M. R., Gurevich, V. V., Hamm, H. E., Lem, J., DiBenedetto, E., Anderson, R. E. and Makino, C.L. (2009) Over-expression of rhodopsin alters the structure and photoresponse of rod photoreceptors. Biophysical Journal 96: 939-950.

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