LRRTM4 Is a Member of the Transsynaptic Complex Between Rod Photoreceptors and Bipolar Cells

Authors

Melina A Agosto
Theodore G Wensel

Publication Date

1-1-2021

Journal

The Journal of Comparative Neurology

DOI

10.1002/cne.24944

PMID

32390181

PMCID

PMC7652719

PubMedCentral® Posted Date

1-1-2022

PubMedCentral® Full Text Version

Post-print

Published Open-Access

yes

Keywords

Animals, COS Cells, Chlorocebus aethiops, HEK293 Cells, Humans, Membrane Proteins, Mice, Mice, Inbred C57BL, Nerve Tissue Proteins, Retinal Bipolar Cells, Retinal Rod Photoreceptor Cells, Synapses, rod bipolar cell, rod photoreceptor, synaptic adhesion molecule, LRRTM4, pikachurin, RRID: CVCL_0045, RRID: IMSR_CRL: 22, RRID:Addgene_59313, RRID:Addgene_18817, RRID:Addgene_18817, RRID:AB_2138196, RRID:AB_2284227, RRID:AB_2336642

Abstract

Leucine rich repeat transmembrane (LRRTM) proteins are synaptic adhesion molecules with roles in synapse formation and signaling. LRRTM4 transcripts were previously shown to be enriched in rod bipolar cells (BCs), secondary neurons of the retina that form synapses with rod photoreceptors. Using two different antibodies, LRRTM4 was found to reside primarily at rod BC dendritic tips, where it colocalized with the transduction channel protein, TRPM1. LRRTM4 was not detected at dendritic tips of ON-cone BCs. Following somatic knockout of LRRTM4 in BCs by subretinal injection and electroporation of CRISPR/Cas9, LRRTM4 was abolished or reduced in the dendritic tips of transfected cells. Knockout cells had a normal complement of TRPM1 at their dendritic tips, while GPR179 accumulation was partially reduced. In experiments with heterologously expressed protein, the extracellular domain of LRRTM4 was found to engage in heparan-sulfate dependent binding with pikachurin. These results implicate LRRTM4 in the GPR179-pikachurin-dystroglycan transsynaptic complex at rod synapses.