Myofilament proteins in the synchronous flight muscles of Manduca sexta show both similarities and differences to Drosophila melanogaster

Abstract

Insect flight muscles have been classified as either synchronous or asynchronous based on the coupling between excitation and contraction. In the moth Manduca sexta, the flight muscles are synchronous and do not display stretch activation, which is a property of asynchronous muscles. We annotated the M. sexta genes encoding the major myofibrillar proteins and analyzed their isoform pattern and expression. Comparison with the homologous genes in Drosophila melanogaster indicates both difference and similarities. For proteins such as myosin heavy chain, tropomyosin, and troponin I the availability and number of potential variants generated by alternative spicing is mostly conserved between the two insects. The exon usage associated with flight muscles indicates that some exon sets are similarly used in the two insects, whereas others diverge. For actin the number of individual genes is different and there is no evidence for a flight muscle specific isoform. In contrast for troponin C, the number of genes is similar, as well as the isoform composition in flight muscles despite the different calcium regulation. Both troponin I and tropomyosin can include COOH-terminal hydrophobic extensions similar to tropomyosinH and troponinH found in D. melanogaster and the honeybee respectively.