A bioinformatic and computational study of myosin phosphatase subunit diversity

Variability in myosin phosphatase (MP) subunits may provide specificity in signaling pathways that regulate muscle tone. We utilized public databases and computational algorithms to investigate the phylogenetic diversity of MP regulatory (PPP1R12A-C) and inhibitory (PPP1R14A-D) subunits. The comparison of exonic coding sequences and expression data confirmed or refuted the existence of isoforms and their tissue-specific expression in different model organisms. The comparison of intronic and exonic sequences identified potential expressional regulatory elements. As examples, smooth muscle MP regulatory subunit (PPP1R12A) is highly conserved through evolution. Its alternative exon E24 is present in fish through mammals with two invariant features: 1) a reading frame shift generating a premature termination codon and 2) a hexanucleotide sequence adjacent to the 3' splice site hypothesized to be a novel suppressor of exon splicing. A characteristic of the striated muscle MP regulatory subunit (PPP1R12B) locus is numerous and phylogenetically variable transcriptional start sites. In fish this locus only codes for the small (M21) subunit, suggesting the primordial function of this gene. Inhibitory subunits show little intragenic variability; their diversity is thought to have arisen by expansion and tissue-specific expression of different gene family members. We demonstrate differences in the regulatory landscape between smooth muscle enriched (PPP1R14A) and more ubiquitously expressed (PPP1R14B) family members and identify deeply conserved intronic sequence and predicted transcriptional cis-regulatory elements. This bioinformatic and computational study has uncovered a number of attributes of MP subunits that supports selection of ideal model organisms and testing of hypotheses regarding their physiological significance and regulated expression.