Abstract
Purpose :
Daylight vision is mediated by cone photoreceptors in vertebrates. The synapse between cone photoreceptors and bipolar cells is functionally and anatomically complex and critical for normal visual function. ON cone bipolar cell dendrites make invaginating synapses and OFF cone bipolar cell dendrites make flat synapses with cone pedicles, however, the mechanism of whole synaptic assembly is not completely understood. Here we report a leucine-rich repeat (LRR) protein, LRFN2 that is expressed selectively at cone pedicles and involved in modulation of cone synaptic function.
Methods :
Using an unbiased proteomic approach we identified LRFN2 as a candidate synaptic organizer protein in mouse retina, and generated a Lrfn2-/- mouse line using zinc finger nucleases. Immunohistochemistry was performed in retinal sections to localize protein expression. Biochemical interaction studies were performed in HEK293T cells expressing both LRFN2 and TRPM1. We characterized retinal function of Lrfn2-/- mice using electroretinogram (ERG) recordings.
Results :
We show that LRFN2 expression is co-localized with PNA staining at the cone pedicles. We confirmed interaction between LRFN2 and TRPM1 in a heterologous system. In the absence of LRFN2, the synaptic markers: LRIT3, ELFN2, mGluR6, TRPM1 and GPR179 are properly localized. Similarly, LRFN2 expression and localization is not dependent on these synaptic proteins. Functional analysis showed a reduction in the amplitude of the photopic b-wave of the ERG in Lrfn2-/- mice.
Conclusions :
Our data show that LRFN2 likely interacts with TRPM1 and is expressed exclusively at the cone pedicles. Further, its absence compromises normal synaptic transmission between cones and ON cone bipolar cells.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.