Prpf8N1531S homozygous mutant mouse embryos have multiple defects in cardiac development and show aberrant splicing of the cardiac transcription factor Tead1

Mutations in the spliceosomal gene PRPF8 are associated with a range of human diseases. Studies in mouse and zebrafish suggest that Prpf8 also has a developmental function. Here, using a Prpf8 mutant mouse line isolated from a chemical induced mutagenesis screen, we uncover a previously unrecognised and essential role for Prpf8 in heart development, consistent with the embryonic lethality observed in Prpf8N1531S homozygous mutants. Prpf8N1531S mutant embryos display severe defects in ventricular trabeculation and compact zone formation, accompanied by increased cardiomyocyte proliferation specifically in the compact zone. Mutant embryonic hearts also exhibit disrupted cellular organisation, altered cytoskeletal architecture and changes in extracellular matrix protein expression. Notably, these cardiac abnormalities were exacerbated in embryos exhibiting cardiac looping defects. Transcriptomic analysis identified multiple aberrantly spliced transcripts in Prpf8N1531S mutant embryos, among which the cardiac transcription factor Tead1 was selected as a key functional candidate due to it known role in cardiac ventricle wall developemnt. Tead1 mis-splicing generated an in-frame, lower molecular weight protein isoform, associated with reduced overall TEAD1 expression. The Tead1 mis-spliced isoform showed altered nuclear localisation and dysregulation of TEAD1-dependent gene network important for heart development, including known cardiac sarcomeric genes. In addition, we observed reduced levels of the intracellular domain of the NOTCH1 receptor (NICD1), indicating impaired Notch signalling.. These findings suggest that impaired TEAD1-dependent transcription and Notch signalling contribute to abnormal cardiac trabeculation and compact zone development, highlighting a critical role for Prpf8 in maintaining proper heart development through the regulation of cardiac transcription factor expression and associated signalling networks. This study offers new mechanistic insights into congenital heart diseases linked to spliceosomal gene mutations.