LRIT3 is essential to localize TRPM1 to the dendritic tips of depolarizing bipolar cells and may play a role in cone synapse formation

• Published in: The European journal of neuroscience 2015-08, Vol.42 (3), p.1966-1975
• Main Authors: Neuillé, Marion, Morgans, Catherine W., Cao, Yan, Orhan, Elise, Michiels, Christelle, Sahel, José-Alain, Audo, Isabelle, Duvoisin, Robert M., Martemyanov, Kirill A., Zeitz, Christina
• Format: Article
• Language: English
• Subjects: Animals; Antibodies; complete CSNB; Dendrites - metabolism; Female; immunolocalization studies; knock-out mice; Life Sciences; Male; Membrane Proteins - immunology; Membrane Proteins - metabolism; mGluR6; Mice; Neurobiology; Neurons and Cognition; Protein Transport; Rabbits; Receptors, Metabotropic Glutamate - metabolism; retina; Retinal Bipolar Cells - metabolism; Retinal Cone Photoreceptor Cells - metabolism; Synapses - metabolism; TRPM Cation Channels - metabolism
• ISSN: 0953-816X; 1460-9568
• DOI: 10.1111/ejn.12959

Mutations in LRIT3 lead to complete congenital stationary night blindness (cCSNB). The exact role of LRIT3 in ON‐bipolar cell signaling cascade remains to be elucidated. Recently, we have characterized a novel mouse model lacking Lrit3 [no b‐wave 6, (Lrit3nob6/nob6)], which displays similar abnormalities to patients with cCSNB with LRIT3 mutations. Here we compare the localization of components of the ON‐bipolar cell signaling cascade in wild‐type and Lrit3nob6/nob6 retinal sections by immunofluorescence confocal microscopy. An anti‐LRIT3 antibody was generated. Immunofluorescent staining of LRIT3 in wild‐type mice revealed a specific punctate labeling in the outer plexiform layer (OPL), which was absent in Lrit3nob6/nob6 mice. LRIT3 did not co‐localize with ribeye or calbindin but co‐localized with mGluR6. TRPM1 staining was severely decreased at the dendritic tips of all depolarizing bipolar cells in Lrit3nob6/nob6 mice. mGluR6, GPR179, RGS7, RGS11 and Gβ5 immunofluorescence was absent at the dendritic tips of cone ON‐bipolar cells in Lrit3nob6/nob6 mice, while it was present at the dendritic tips of rod bipolar cells. Furthermore, peanut agglutinin (PNA) labeling was severely reduced in the OPL in Lrit3nob6/nob6 mice. This study confirmed the localization of LRIT3 at the dendritic tips of depolarizing bipolar cells in mouse retina and demonstrated the dependence of TRPM1 localization on the presence of LRIT3. As tested components of the ON‐bipolar cell signaling cascade and PNA revealed disrupted localization, an additional function of LRIT3 in cone synapse formation is suggested. These results point to a possibly different regulation of the mGluR6 signaling cascade between rod and cone ON‐bipolar cells. The focus of this work was to elucidate the role of LRIT3, a protein implicated in complete congenital stationary night blindness (cCSNB), by using the no b‐wave 6 cCSNB mouse model (Lrit3nob6/nob6), lacking Lrit3. We showed that LRIT3 is localized at the dendritic tips of ON‐bipolar cells in mouse retina, that LRIT3 is essential for the correct localization of TRPM1 at the dendritic tips of ON‐bipolar cells and that other components of the cascade reveal disrupted localization at the dendritic tips of cone, but not rod, ON‐bipolar cells, suggesting an additional role of LRIT3 in cone synapse formation.