Differential regional and subcellular localization patterns of afadin splice variants in the mouse central nervous system.

AF6/afadin is an F-actin scaffold protein that plays essential roles in the organization of cell-cell junctions of polarized epithelia. Afadin comprises two major isoforms produced by alternative splicing - a longer isoform l-afadin, having the F-actin-binding domain, and a shorter isoform s-afadin, harboring the amino acid sequences unique to the isoform but lacking the F-actin-binding domain. We recently identified functional differences between l- and s-afadin isoforms in the regulation of axon branching in primary cultured cortical neurons; the former potentiates and the latter blocks axon branching. Previous biochemical reports indicate differences in tissue and cell-type distributions of isoforms, and it was shown that l-afadin is ubiquitously expressed in various tissues and cell-types, while s-afadin is predominantly expressed in neuronal tissues and cultured neurons. However, the spatial expression pattern of s-afadin across neuronal tissues or within neurons has not been revealed because no antibody specific for s-afadin is yet available. In this study, we report the generation and characterization of an antibody that specifically distinguishes s-afadin from l-afadin, and its application to investigate the expression profile of s-afadin in primary cultured neurons and tissue cryosections of adult mouse brain and retina. We describe differential regional and subcellular localization patterns of l- and s-afadin isoforms in the mouse central nervous system.