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Ivan Anastassov, Felice Dunn; Postnatal development of rod bipolar cell dendrites in mouse retina. Invest. Ophthalmol. Vis. Sci. 201657(12):.
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© 2017 Association for Research in Vision and Ophthalmology.
Rod bipolar cells (RBC) receive glutamate from rods through fine dendritic tips, which contain molecular machinery necessary to convey visual information. Establishment of convergence between rods and RBCs, and localization of synaptic proteins are critical to correct function. However, the development of the fine dendritic trees and the temporal expression patterns of dendritic transduction proteins have not been examined on the level of individual RBCs. Thus, it is unknown how dendritic branches develop the appropriate number of rod contacts.
Retinas were taken from a Grm6-TdTomato transgenic mouse line (Kerschensteiner et al. 2009) at different stages of postnatal development, ranging from P7 to P82. In these animals, tdTomato is expressed under the control of the Grm6 promoter in a subset of ON bipolar cells, allowing for easy morphological identification of RBCs. Isolated retinas were flat-mounted, fixed, and stained with antibodies against pre- and post-synaptic proteins (Ribeye, mGluR6, TRPM1). The tissue was imaged by confocal microscopy and RBC dendrites and somas were masked using Amira. The number of RBC dendritic tips, the expression of post-synaptic proteins within the tips of individual RBCs, and the expression of pre-synaptic markers were examined as a function of age.
At postnatal day (P)7, RBCs in the periphery have immature neurites while centrally located RBCs have ~12 dendritic tips (SD 1.73). mGluR6 staining at P7 is diffuse throughout the soma and processes and does not appear punctate at the tips. At P13-14, neurites in the periphery are gone and the average number of RBC dendritic tips increases to ~24 (SD 7.76); mGluR6 staining starts to appear more punctate in the dendritic tips. At P21-30, dendritic tip number increases to ~31 (SD 5.28; SD 5.94), and mGluR6 expression is limited to the tips of dendritic processes. At P69-70, tip number peaks at ~37 (SD 4.91; SD 2.91) and reaches a plateau. Each dendritic tip contains punctate mGluR6.
The number of dendritic tips increases with age and begins to reach an asymptote after P21. Punctate expression of mGluR6 lags several days behind tip differentiation, which starts at P7. Previous studies show dendritic processes of RBCs invaginating into rod terminals starting at P10, which could coincide with punctate mGluR6 expression in RBC tips. Studies on TRPM1 and Ribeye expression during these developmental stages are ongoing.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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