Abstract
Purpose :
The retina contains ~120 transcriptionally distinct neuronal subtypes, ~40 of these are retinal ganglion cells (RGCs). However, the functional properties of most RGCs remain unknown, creating a significant gap in our understanding of their role in visual processing. This gap is due in part to a lack of genetic tools that allow for the consistent, reproducible targeting of specific RGC subtypes across experimental modalities. MafBmCherry-2A-Cre selectively labels multiple undefined RGC subtypes. Identifying the dendritic morphology and retinorecipient projection pattern of MafB expressing (MafB+) RGCs will further elucidate their role in visual processing.
Methods :
MafB+ RGCs were sparsely labeled to quantify morphology using a low titer (14 x 10^9 vg/mL) intravitreal injection (IV) of AAV2-CAG-FLEX-EGFP in adult MafB mice. MafB+ RGCs were reconstructed, and morphometric data (area of the neuron, arbor density, arbor complexity, soma size, branch length, and IPL stratification) collected in ImageJ and Imaris. Retinorecipient locations of MafB+ RGCs were identified using a high titer (7×10^12 vg/mL) IV injection of AAV2-CAG-FLEX-EGFP and CTB in adult MafB mice. Injection of both reagents into a WT littermate served as a control. Serial fixed brain sections (100μm) were collected to colocalization between EGFP and CTB. A 4-channel antibody retina stain (SPP1, CALB1, MEIS2, GFP) separated MafB+ RGC subtypes. Retrograde brain injections using AAV2-Retro-CAG-FLEX-EGFP into MafB+ retinorecipient locations, paired with IHC, back-labeled MafB+ RGCs in the retina. Retro-AAV was injected into the somatosensory cortex, a non-visual brain region, as a negative control.
Results :
Early experiments show that sparse viral labeling will allow isolation of the dendritic stratification pattern of single MafB+ RGCs. At least three distinct morphologies have been identified. High titer IV injections show that MafB+ RGCs project to the OPN, dLGN, vLGN and SC. Preliminary data from the retro-AAV injections suggests that multiple MafB+ subtypes project to the same region.
Conclusions :
The MafB line labels novel RGC subtypes with varied morphologies that project to image and non-image forming brain regions. These subtypes are not fully characterized, and further work is underway to identify their light response and intrinsic membrane properties.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.