DNER and NFIA are expressed by developing and mature AII amacrine cells in the mouse retina
Understanding the mechanisms underlying AII amacrine cell development requires knowledge of the molecular players expressed by these cells at different ages. Many proteins have been identified to be expressed by mature AII amacrine cells, including calretinin, parvalbumin, Dab1, and Prox1 (Wässle, Grünert, & Röhrenbeck, 1993; Massey & Mills, 1999; Rice & Curran, 2000; Dyer, Livesey, Cepko, & Oliver, 2003). Only a few proteins, however, have been shown to be important for developing AII amacrine cells, such as DSCAML1 and NeuroD2, both implicated in the growth of AII neurites (Fuerst et al., 2009; Cherry et al., 2011). The present study has sought to identify other novel proteins that are expressed by developing and mature AII amacrine cells, by taking advantage of recent advances in molecular profiling, particularly in single cell RNA‐sequencing, that have begun to differentiate the subtleties that exist between different cell types through their transcriptome‐wide molecular signatures (Kay, Chu, & Sanes, 2012; Siegert et al., 2012; Macosko et al., 2015; Shekhar et al., 2016). These gene expression profiles offer a comprehensive look into the proteins that must be critical for the development and function of specific cell types in the retina, including the AII amacrine cell.
In this study, we have used recently published expression profiles of retinal cell types to identify genes that may have roles critical for the development of AII amacrine cells. We found two genes, Delta/Notch‐like EGF repeat containing (Dner) and nuclear factor I/A (Nfia), that are highly expressed in these cells, both in development and adulthood. We subsequently validated the expression of their protein products using immunofluorescent techniques, and determined that probing for both proteins conjointly is a reliable method for identifying the population of AII amacrine cells. As both genes are known to play a role in neural development outside the retina, they are prime candidates for understanding the mechanisms that underlie the development of the AII amacrine cell.