Our results point to a number of genes worthy of follow-up, and we sought an assay that was rapid and amenable to over- and under-expression. Manipulation of zebrafish embryos fits these requirements, especially for evaluation of anatomical phenotypes of early development, such as head and brain size (or area). Perturbing expression of one or more genes in zebrafish has been used to identify genes contributing to neuropsychiatric disorders33–35. Therefore, we asked whether suppression or overexpression of the corresponding gene within each of the five SCZ risk loci could identify key proteins that regulate brain development. To evaluate the four genes up-regulated by risk alleles in the GWAS loci, we injected 200pg of human capped mRNA encoding TSNARE1, CNTN4, SNAP91, or CLCN3 in 1–8 cell stage embryos (N = 60 per experiment, at least two biological replicates performed). At 3 days post-fertilization (dpf), we assessed the area of the head that contains the forebrain and midbrain structures (Fig. 3A, B). Relative to control embryos, overexpression of TSNARE1 or CNTN4 resulted in a significant decrease in head size, 9.5% (P < 0.001)
