title: The coevolution of insect muscle TpnT and TpnI gene isoforms.
abstract: In bilaterians, the main regulator of muscle contraction is the troponin (Tpn) complex, comprising three closely interacting subunits (C, T, and I). To understand how evolutionary forces drive molecular change in protein complexes, we have compared the gene structures and expression patterns of Tpn genes in insects. In this class, while TpnC is encoded by multiple genes, TpnT and TpnI are encoded by single genes. Their isoform expression pattern is highly conserved within the Drosophilidae, and single orthologous genes were identified in the sequenced genomes of Drosophila pseudoobscura, Anopheles gambiae, and Apis mellifera. Apis expression patterns also support the equivalence of their exon organization throughout holometabolous insects. All TpnT genes include a previously unidentified indirect flight muscle (IFM)-specific exon (10A) that has evolved an expression pattern similar to that of exon 9 in TpnI. Thus, expression patterns, sequence evolution trends, and structural data indicate that Tpn genes and their isoforms have coevolved, building species- and muscle-specific troponin complexes. Furthermore, a clear case can be made for independent evolution of the IFM-specific isoforms containing alanine/proline-rich sequences. Dipteran genomes contain one tropomyosin gene that encodes one or two high-molecular weight isoforms (TmH) incorporating APPAEGA-rich sequences, specifically expressed in IFM. Corresponding exons do not exist in the Apis tropomyosin gene, but equivalent sequences occur in a high-molecular weight Apis IFM-specific TpnI isoform (TnH). Overall, our approach to comparatively analyze supramolecular complexes reveals coevolutionary trends not only in gene families but in isoforms generated by alternative splicing.
authors.affiliation: Departamento de Bioquímica, Instituto de Investigaciones Biomédicas Alberto Sols UAM-CSIC, Facultad de Medicina, Universidad Autónoma de Madrid, C/Arzobispo Morcillo 4, 28029 Madrid, Spain.
authors.forename: Raúl
authors.initials: R
authors.lastname: Herranz
authors.forename: Jesús
authors.initials: J
authors.lastname: Mateos
authors.forename: José A
authors.initials: JA
authors.lastname: Mas
authors.forename: Elena
authors.initials: E
authors.lastname: García-Zaragoza
authors.forename: Margarita
authors.initials: M
authors.lastname: Cervera
authors.forename: Roberto
authors.initials: R
authors.lastname: Marco
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D016000:Cluster Analysis; D019295:Computational Biology; D019143:Evolution, Molecular; D040461:Gene Components / Q000235:genetics; D015870:Gene Expression; D014644:Genetic Variation; D007313:Insecta / Q000235:genetics*; D008969:Molecular Sequence Data; D009132:Muscles / Q000378:metabolism; D010802:Phylogeny; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D019210:Troponin I / Q000235:genetics*; D020107:Troponin T / Q000235:genetics*
chemical_list: D019210:Troponin I; D020107:Troponin T