Mice expressing the autism-associated neuroligin-3 R451C variant exhibit increased mucus density and altered distributions of intestinal microbiota.

The intestinal mucus layer protects the host from invading pathogens and is essential for maintaining a healthy mucosal microbial community. Alterations in the mucus layer and composition of mucus-residing microbiota in people diagnosed with autism may contribute to dysbiosis and gastrointestinal dysfunction. Although microbial dysbiosis based on sequencing data is frequently reported in autism, spatial profiling of microbes adjacent to the mucosa is needed to identify changes in bacterial subtypes in close contact with host tissues. Here, we analysed the spatial distribution of the mucin-2 protein using immunofluorescence as well as total bacteria, Bacteroidetes, Firmicutes phyla, and Akkermansia muciniphila using fluorescent in situ hybridization in mice expressing the autism-associated R451C variant in the Neuroligin-3 gene. We show that the Neuroligin-3 R451C variant increases mucus density adjacent to the distal ileal epithelium in mice. The relative density of total bacteria, Firmicutes, and A. muciniphila was increased whereas the density of Bacteroidetes was decreased closer to the epithelium in Neuroligin-3R451C mice. In summary, the autism-associated R451C variant in the Neuroligin-3 gene increases mucus density adjacent to the epithelium and alters microbial spatial distribution in the mouse distal ileum.