Meeting Abstract
Jaw-closing muscles of members of Carnivora express unique isoforms of several myofibrillar proteins that are not expressed in most other muscles. It is generally believed that the complement of myofibrillar isoforms in these muscles serves high force generation for capturing live prey and defensive biting. A unique, “masticatory”, isoform of tropomyosin (TM-Mast) was reported to be expressed in cat jaw-closing muscles. The objective of this study was to obtain sequence information for the unique TM-Mast in the domestic dog. Samples of masseter (a jaw-closing muscle), tibialis (comprised predominantly of fast-twitch fibers) and the gastrocnemius (with a high proportion of slow fibers) were obtained from adult dogs. Portions of each sample were prepared for protein electrophoresis, immunoblotting and RNA extraction. TM-specific cDNA was cloned. Sequencing of clones identified cDNA identical to genomic predicted striated muscle TM-α and TM-β isoforms, as well as a novel 284 amino acid TM-δ isoform observed only in the masseter muscle. TM-Mast in dog masseter exhibits a unique electrophoretic mobility on SDS-PAGE gels containing 6 M urea compared to TM in other muscles. To validate that our cloned TM-δ isoform is TM-Mast, the E. coli expressed TM-δ isoform was electrophoresed in the presence of urea. Results demonstrate that TM-δ has the same electrophoretic mobility as the unique TM-Mast that is expressed in dog masseter and has a different mobility from that of muscle TM-α, -β or -γ isoforms. Based upon these findings, we conclude that dog TM-Mast is a product of the TPM4 gene (which encodes the TPM-δ family of proteins) and that the 284 amino acid protein product of this gene represents a novel TM isoform never before observed to be expressed in mammalian striated muscle.
