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Scientists shine light on how eyes adapt to the dark

NEI researchers discover mechanism that speeds dark adaptation
October 14, 2022
Florescent photo of mouse rod photoreceptor, next to photoreceptor schematic showing cell body, inner and outer segments.

Mouse rod photoreceptor

A basic research study from the National Eye Institute (NEI) explains how the molecule transducin moves within light-sensing rod photoreceptors in mouse retina to help the eye quickly adapt from bright to low light and back. The findings may help explain how neurons in the brain increase or decrease sensitivity to stimuli. The research was published in eNeuro. NEI is part of the National Institutes of Health.

The eye’s light-detecting retina functions at various sensitivity levels. Cone photoreceptors function best in bright light; rod photoreceptors function better in dim light. One mechanism that keeps rod photoreceptors from being over-stimulated in bright light is the movement of a subunit of the G-protein transducin from the rod photoreceptor’s outer segment to its inner segment. This movement prevents the rod photoreceptor from over-reacting to the presence of bright light.

A research team led by Anand Swaroop, Ph.D., senior investigator and chief of NEI’s Neurobiology, Neurodegeneration and Repair Laboratory, and Johan Pahlberg, Ph.D., head of NEI’s Photoreceptor Physiology Group, used mice lacking Frmpd1, a unique protein isoform found in the retina’s rod photoreceptors. Frmpd1 was previously identified in the Swaroop laboratory.  In this study, the researchers found that a second protein, Gpsm2 (G-protein signaling modulator 2), interacts with both the transducin subunit and Frmpd1; this second protein likely helps shuttle the transducin subunit from the outer segment to the inner segment of the rod photoreceptor and back again. Without Frmpd1, the mouse rod photoreceptors adapted to bright light, but did not properly adapt back to darkness. 

“Our results suggest that, alongside passive diffusion of these molecules from one part of the rod photoreceptor to another, there’s active trafficking of transducin that speeds up the rod photoreceptor’s ability to adapt to changes in light,” said Pahlberg. 

“Understanding cellular processes that mediate trafficking of proteins in light and dark, and identifying components associated with the Frmpd1-Gpsm2 complex, could provide novel insights into transduction of visual signals in photoreceptors,” said Swaroop. “We’re interested in seeing if there are changes to this process in the early stages of inherited retinal diseases like retinitis pigmentosa or Leber congenital amaurosis, before photoreceptor loss begins.”


The research was funded by the intramural programs of the National Eye Institute (NEI) Intramural Research Program Grants EY000450 and EY000546 (to A.S.), and NEI / National Institute of Dental and Craniofacial Research/National Institute of Neurological Disorders and Stroke/ Grants 100000072 and 100000065 (to J.P.)

Reference:  Campla CK^, Bocchero U^, Strickland R, Nellissery J, Advani J, Ignatova I, Srivastava D, Aponte AM, Wang Y, Gumerson J, Martemyanov K, Artemyev NO, Pahlberg J*, Swaroop A* (2022). Frmpd1 facilitates trafficking of G-protein transducin and modulates synaptic function in rod photoreceptors of mammalian retina. eneuro:ENEURO.0348-0322.202


Lesley Earl