Abstract
Pathogenic variants in SF3B4, a component of the U2 snRNP complex important for branchpoint sequence recognition and splicing, are responsible for the acrofacial disorders Nager and Rodriguez Syndrome, also known as SF3B4-related syndromes. Patients exhibit malformations in the head, face, limbs, vertebrae as well as the heart. To uncover the etiology of craniofacial malformations found in SF3B4-related syndromes, mutant mouse lines with homozygous deletion of Sf3b4 in neural crest cells (NCC) were generated. Like in human patients, these embryos had craniofacial and cardiac malformations with variable expressivity and penetrance. The severity and survival of Sf3b4 NCC mutants was modified by the level of Sf3b4 in neighboring non-NCC. RNA sequencing analysis of heads of embryos prior to morphological abnormalities revealed significant changes in expression of genes forming the NCC regulatory network, as well as an increase in exon skipping. Additionally, several key histone modifiers involved in craniofacial and cardiac development showed increased exon skipping. Increased exon skipping was also associated with use of a more proximal branch point, as well as an enrichment in thymidine bases in the 50 bp around the branch points. We propose that decrease in Sf3b4 causes changes in the expression and splicing of transcripts required for proper craniofacial and cardiac development, leading to abnormalities.