The world's fastest muscles reveal a surprising evolutionary history, challenging long-held assumptions about muscle function across vertebrates. A recent study led by James Pease at The Ohio State University (OSU) has uncovered a complex story of muscle evolution, highlighting the distinct molecular machinery that underpins muscle contraction in different animal groups.
The research team, including Dr. Christina Harvey from High Point University (HPU), analyzed genomic data from 1,201 myosins across 119 species, spanning 500 million years of history. Their findings overturned the conventional belief that all vertebrates rely on the same molecular mechanism for muscle contraction. Instead, they discovered that each major group of vertebrates has evolved its own unique set of core skeletal muscle myosins, tailored to their specific needs and environments.
This discovery led to the identification of at least 50 new subfamilies of myosin genes, in addition to the 15 already recognized. The team's analysis revealed that genes are copied and lost over time, resulting in each lineage holding a unique set of 'cards' from a shared genetic deck. This process has led to the diversification of myosin molecules, each with specific roles and functions.
One fascinating example is the western diamondback rattlesnake, where different myosins power the head, midsection, and tail muscles. The rattle muscle, in particular, relies on a previously undiscovered myosin, accounting for up to 91% of the muscle's gene expression. This specialization is also evident in superfast muscles used for echolocation, courtship wing-snaps, and rattling, where no single 'extreme' myosin is responsible for all functions.
The study emphasizes that speed is a trait that has been reinvented multiple times across different lineages, each finding its own solution through distinct molecular parts. The key to this diversity lies in two small surface loops of the myosin protein, which vary significantly between species. One loop influences the speed of chemical fuel processing, while the other determines the tightness of the grip between myosin and actin.
The researchers are cautious about attributing specific adaptive reasons for these variations, as adaptation is difficult to prove. However, they suggest that the diversity of molecular subtypes is essential for survival, as the absence of such diversity would likely result in only one type of myosin. This implies that evolution has preserved vital functions while allowing for changes in the molecular components that enable them.
The study's findings, published in the journal Proceedings of the Royal Society B, offer a deeper understanding of muscle evolution and the intricate relationship between molecular processes and animal physiology. As we continue to explore the complexities of muscle function, we gain valuable insights into the remarkable diversity of life on Earth.
