Together, our data indicate that Cdh3-GFP mice selectively label the RGCs that project to the vLGN, IGL, OPN, and mdPPN, the very same non-image-forming
retinorecipient targets that express Cdh6. The limited number of retinorecipient targets innervated by Cdh3-RGCs prompted us to investigate which RGC types express GFP in this mouse line. Cdh3-RGCs represent ∼1% of the total RGC population (mean Cdh3-RGCs per retina = 964.71 ± 57.62 GFP+; n = 14 retinas; 14 mice) (Jeon et al., 1998). Morphological analysis showed that approximately Metformin manufacturer half (∼47%; n = 14/30) of the Cdh3-RGCs had radial, sparse dendritic arbors (Figure 3E), whereas other Cdh3-RGCs (∼53%; n = 16/30) had asymmetric, densely branching dendritic arbors (Figure 3F). Also, many Cdh3-RGCs had dendrites that stratified exclusively in the On sublamina of the inner retina, (e.g., Figure 3C) whereas other Cdh3-RGCs had dendrites stratifying in both the On and Off sublamina (Figures 3J and 3K). Approximately 10% of Cdh3-RGCs also expressed the photopigment melanopsin (Figures 3G–3I). Thus, Cdh3-RGCs are not a random sampling of RGC types, nor do they comprise a single RGC type. Rather, Cdh3-RGCs include a limited number of different RGC types. We next wanted to determine whether Cdh3-RGCs also express Cdh6. We found that Cdh6 mRNA was expressed
by a subset of cells in the early postnatal RGC layer (Figures 3L and 3M), which is in agreement with a previous report Selleck MLN2238 (Honjo et al., 2000). Immunostaining revealed that all Cdh3-RGCs also express Cdh6 protein (Figures 3N–3Q). However, not all Cdh6 immunoreactive cells were Cdh3-RGCs (Figures 3P and 3Q), suggesting that Cdh6-RGCs represent a broader population of RGCs. Consistent with this idea, we obtained brains
from Cdh6-GFP transgenic mice in which GFP is localized to axon terminals by Gap43-EGFP fusion (Inoue et al., 2009). Cdh6-RGCs through heavily target the vLGN, IGL, OPN, and mdPPN, just like Cdh3-RGCs. However, Cdh6-RGCs also projected to the medial terminal nucleus (MTN) and the SC and the MTN itself expressed Cdh6 mRNA (Figure S3). Thus, Cdh3-RGCs selectively innervate Cdh6 expressing retinorecipient targets and Cdh6-RGCs project to those same targets, as well as to additional Cdh6-expressing targets. The most widely held view of cadherin-mediated cell-cell interactions is a homophilic model whereby cells expressing specific cadherin family members preferentially bind to cells expressing the same cadherin or combination of cadherins (Takeichi, 2007). Thus, we hypothesized that Cdh6 is involved in matching the axons of Cdh3/6-RGCs to Cdh6-expressing targets. To address this, we mated Cdh3-GFP transgenic mice to Cdh6 mutant mice (Dahl et al., 2002) to generate Cdh3-GFP::Cdh6+/− and Cdh3-GFP::Cdh6−/− mice.