Mouse Lines with Cre-Mediated Recombination in Retinal Amacrine Cells

Mouse lines with Cre-mediated recombination in retinal ACs. Three mouse lines with Cre recombinase expression driven by different promoters were crossed to the Ai9 Cre-sensitive reporter line. Retinas were harvested >p21, processed and sectioned to reveal Cre history via TdTomato (red) expression. Cell nuclei were labeled with DAPI (blue). A, Retina of the Tac1::IRES-cre mouse has Cre history in a subset of ACs and cells in the GCL that stratify in three distinct depths of the IPL. B, The Camk2a-cre mouse line labeled a small number of ACs. C, Scx-cre line showed recombination in a subset of ACs, as well as sparsely in the other three retinal cell types generated postnatally [rod (PR), BP, and Mueller glial (MG) cells, indicated with arrows]. Cre recombination was also observed in a small number of cells in the GCL. White scale bars: 50 μm.

ACs and a small number of RGCs Cre expression history form three unique bands in the IPL of the Tac1::IRES-cre mouse. A, Cre expression history in the Tac1::IRES-cre mouse could be observed in a subset of ACs and a small number of potential RGCs (Brn3a+ yellow cells in the RGC layer). The presence of red only cells in the RGC layer indicates Tac1-Cre expression history in displaced ACs. B, The distinct stratification pattern of tdTom+ processes in the IPL supports a few morphologically distinct types of ACs being labeled in the Tac1-Cre line. There were no ChAT+ Tac1-Cre cells (the apparently yellow cell in B’’ is because of superposition of 2 cells). The ChAT bands were highly complementary to the Tac1 bands in the IPL. C, D, A majority of the ACs with a Tac1-Cre history were GABAergic, not glycinergic. E, Tac1-Cre cells were not TH-positive. White scale bars: 50 μm.

Global reporter expression in Tac1::IRES-cre and Camk2a-cre mouse lines. A, While the majority of cells marked with a Tac1-Cre expression history were ACs, occasional clusters of Mueller glia were observed in cross-sections of the retina, in addition to AC and RGC subtypes. B, B’, Upon closer inspection, multiple tdTom+ Mueller glia (yellow arrow) and a few BPCs (white arrow) were visible (40×). Amongst the Cre-lines we have tested for retinal expression history, the Tac1::IRES-cre line was the only one with these clusters of different cell types (including Mueller glia) in a few locations, and there was a lack of them elsewhere in the retinal cross-sections. C, C’, Sparse tdTom+ ACs were present in the Camk2a-cre reporter mouse retina and there was a lack of labeling in other cell types. White scale bars: 50 μm.

Camk2a-cre line fate maps to an AC type with unique morphology. A, B, Camk2a-cre AC did not express ChAT or calbindin (no yellow cells). However, the ChAT and calbindin bands collectively revealed that the medium sized dendritic arbors of the Camk2a-cre AC stratified mostly between levels 2 and 4, and excluded layers 1 and 5. C, The ACs labeled by Camk2a-Cre expression history were glycinergic (Glyt1+, tdTom+ yellow cells). D, Unique morphology of the AC marked by the Camk2a-Cre line could be visualized more clearly by the delivery of a Cre-dependent fluorescent plasmid into the subretinal space of mouse pups. Although the AC arbor appears uniformly bushy at a first glance with the TdTomato reporter, it seemed to have three distinct layers of stratification in the IPL, corresponding roughly to layers 2, 3, and 4. White scale bars: 50 μm.