Tropomyosin Isoform Diversity in the Cynomolgus Monkey Heart and Skeletal Muscles Compared to Human Tissues.

Old world monkeys separated from the great apes, including the ancestor of humans, about 25 million years ago, but most of the genes in humans and various nonhuman primates are quite similar even though their anatomical appearances are quite different. Like other mammals, primates have four tropomyosin genes (TPM1, TPM2, TPM3, and TPM4) each of which generates a multitude of TPM isoforms via alternative splicing. Only TPM1 produces two sarcomeric isoforms (TPM1 and TPM1), and TPM2, TPM3, and TPM4 each generate one sarcomeric isoform. We have cloned and sequenced TPM1, TPM1, TPM2, TPM3, and TPM4 with RNA from cynomolgus (Cyn) monkey hearts and skeletal muscle. We believe this is the first report of directly cloning and sequencing of these monkey transcripts. In the Cyn monkey heart, the rank order of TPM isoform expression is TPM1 > TPM2 > TPM1 > TPM3 > TPM4. In the Cyn monkey skeletal muscle, the rank order of expression is TPM1 > TPM2 > TPM3 > TPM1 > TPM4. The major differences in the human heart are the increased expression of TPM1, although TPM1 is still the dominant transcript. In the Cyn monkey heart, the only sarcomeric TPM isoform at the protein level is TPM1. This is in contrast to human hearts where TPM1 is the major sarcomeric isoform but a lower quantity of TPM1, TPM2, and TPM3 is also detected at the protein level. These differences of tropomyosin and/or other cardiac protein expression in human and Cyn monkey hearts may reflect the differences in physiological activities in daily life.