Genetic excision of the regulatory cardiac troponin I extension in high heart rate mammal clades

Mammalian cardiac troponin I (cTnI) contains a highly conserved N-terminal extension harboring protein kinase A targets (Ser23/24) which are phosphorylated during β-adrenergic stimulation to increase cardiomyocyte relaxation rate. Here, we show that the Ser23/24 encoding exon 3 of TNNI3 was pseudoexonized multiple times in shrews and moles to mimic Ser23/24 phosphorylation without adrenergic stimulation, facilitating the evolution of exceptionally high resting heart rates (~1000 beats min-1). We further reveal alternative exon 3 splicing in distantly related bat families and that both exon 3- and exon 3+ cTnI isoforms are incorporated into cardiac myofibrils. Finally, exon 3 of human TNNI3 is shown to exhibit a relatively low splice strength score, offering an evolutionarily informed strategy to excise this exon to improve diastolic function during heart failure. ### Competing Interest Statement The authors have declared no competing interest.