A common single nucleotide variant in the cytokine receptor-like factor-3 (CRLF3) gene causes neuronal deficits in human and mouse cells
Single nucleotide variants in the general population are common genomic alterations, where the majority are presumed to be silent polymorphisms without known clinical significance. Using human induced pluripotent stem cell (hiPSC) cerebral organoid modeling, we previously discovered that the cytokine receptor-like factor-3 (CRLF3) gene is a major regulator of neuronal maturation in the 1.4 megabase Neurofibromatosis type 1 (NF1) deletion syndrome. Moreover, children with NF1 and the CRLF3L389P variant have greater autism burden, suggesting that this gene might be important for neurologic function. To explore the functional consequences of this variant, we generated CRLF3L389P-mutant hiPSC lines and Crlf3L389P-mutant genetically engineered mice. While this variant does not impair protein stability, brain structure, or mouse behavior, CRLF3L389P-mutant human cerebral organoids and mouse brains exhibit impaired neuronal maturation and dendrite formation. In addition, Crlf3L389P-mutant mouse neurons have reduced dendrite lengths and branching, without any axonal deficits. Moreover, Crlf3L389P-mutant mouse hippocampal neurons have decreased firing rates and amplitudes relative to wild type controls. Taken together, these findings establish the CRLF3L389P variant as functionally deleterious and suggest that it may be a neurodevelopmental disease modifier. Overall design: Crlf3L389P-mutant and WT hippocampi were collected from four 4-week-old mice (4 hippocampi/  2 mice per genotype) and pooled to prepare single-cell isolations for each region.