Loss of zebrafish ctnnd2b results in disorganised forebrain neuron clusters

Delta catenin (CTNND2) is an adhesive junction associated protein belonging to the family of p120ct catenins. It is located on the short arm of chromosome 5, a region deleted in Cri-du-chat syndrome. Heterozygous loss of CTNND2 function has been linked to autism, schizophrenia, and mild intellectual disability with or without dyslexia-like learning difficulties. To date, most functional studies have focused on homozygous loss of the gene, contradictory to the dominant effect of loss of a single allele observed in neurodevelopmental disorders. Here we show that heterozygous loss of ctnnd2b results in a disorganisation and imbalance of neuronal subtypes in forebrain specific regions. Using the zebrafish model, we show that CRISPR/Cas9-induced loss of ctnnd2b but not ctnnd2a results in an increase in isl1-expressing cells and a local reduction of GABA expressing neurons in the optic recess region of the embryonic zebrafish forebrain. Using time-lapse analysis, we found that the disorganised distribution of is1l-expressing forebrain neurons was not due to migration defects, but rather an increase in the number of isl1-GFP neurons in the optic recess region. Upon closer analysis, these neurons appear disorganised and show an altered morphology and orientation. Overall this data suggests that ctnnd2 may affect the differentiation cascade of neuronal subtypes in specific regions of the vertebrate brain.