Impact of intragenic NRXN1 deletions on early cortical development
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Background
Deletions in NRXN1 are strongly associated with neurodevelopmental and psychiatric conditions. While exonic deletions are well-studied, intragenic deletions, particularly in intron 5, are less understood and generally consider benign. Recent studies show exonic deletions impact isoform diversity during neurodevelopment, affecting neurogenesis and neuronal function. However, whether intragenic deletions impact isoform expression and neurodevelopment remains underexplored.
Methods
We used hiPSCs from typically developing individuals (control) and those with NRXN1 intron 5 deletions to study neurodevelopment. HiPSCs were differentiated towards a cortical fate, with NRXN1 isoform expression, molecular differences, and neuronal morphology examined.
Results
We observed distinct NRXN1 isoform expression dynamics during early neurodevelopment, with two expression peaks post-neuronal induction and NRXN1β being most highly expressed. Both NRXN1 deletion and control lines showed similar acquisition of regional and cell fate identity, but significant differences in NRXN1 isoform expression were observed between deletion and control lines, and between deletion lines. RNA sequencing revealed genotype-dependent alterations, particularly in pathways related to synaptic function and neuronal morphology. Consistent with these findings, NRXN1 deletion lines exhibited altered dendrite outgrowth, with variations between deletion lines.
Conclusions
Our results indicate a potential role for intron 5 in controlling NRXN1 isoform expression during neurodevelopment. Alterations in gene expression profiles, correlated with morphological changes, suggest a role for NRXN1 isoforms in shaping dendritic morphology. Molecular and cellular differences observed between lines with identical intronic deletions suggest that additional factors, such as genetic background or biological sex, may also play an important role in these phenotypes. Collectively, these findings indicate that NRXN1 intronic deletions are not benign, influencing isoform expression, cellular phenotypes, and neurodevelopment.
