Investigating the Etiology of Craniofacial and Cardiac Malformations in a Mouse Model of SF3B4-Related Syndromes

Pathogenic variants in SF3B4 are responsible for the acrofacial disorders Nager and Rodriguez Syndrome, also known as SF3B4-related Syndromes, associated with 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 neighbouring non NCC. RNA sequencing analysis of heads of embryos prior to morphological abnormalities showed significant changes in expression of genes forming the NCC regulatory network, as well an increase in exon skipping. We identified several key transcription factors and histone modifiers involved in craniofacial and cardiac development with 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 50bp 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.