Preserved Close Linkage Between the Genes Encoding Troponin I and Troponin T, Reflecting an Evolution of Adapter Proteins Coupling the Ca2+ Signaling of Contractility

Abstract

Ca(2+)-regulated motility is essential to numerous cellular functions, including muscle contraction. Systems with troponin C, myosin light chain, or calmodulin as the Ca(2+) receptor have evolved in striated muscle and other types of cells to transduce the cytoplasm Ca(2+) signals into allosteric conformational changes of contractile proteins. While these Ca(2+) receptors are homologous proteins, their coupling to the responding elements is quite different in various cell types. The Ca(2+) regulatory system in vertebrate striated muscle represents a highly specialized such signal transduction pathway consisting of the troponin complex and tropomyosin associated with the actin filament. To understand the molecular mechanism in the Ca(2+) regulation of muscle contraction and cell motility, we have revealed a preserved ancestral close linkage between the genes encoding two of the troponin subunits, troponin I and troponin T, in the genome of mouse. The data suggest that the troponin I and troponin T genes may have originated from a single locus and evolved in parallel to encode a striated muscle-specific adapter to couple the Ca(2+) receptor, troponin C, to the actin-myosin contractile machinery. This hypothesis views the three troponin subunits as two structure-function domains: the Ca(2+) receptor and the signal transducing adapter. This model may help to further our understanding of the Ca(2+) regulation of muscle contraction and the structure-function relationship of other potential adapter proteins which are converged to constitute the Ca(2+) signal transduction pathways governing nonmuscle cell motility.

Deletion of a Genomic Segment Containing the Cardiac Troponin I Gene Knocks Down Expression of the Slow Troponin T Gene and Impairs Fatigue Tolerance of Diaphragm Muscle

“…We previously detected in ex vivo promoter analysis that the kb Ϫ2.2 to Ϫ5.4 upstream region of the ssTnT gene, which overlaps with the 3Ј region of the cTnI gene, contained major enhancer activity required for high level transcription of the ssTnT gene (6). The present study further demonstrated that deletion of the cTnI gene between the two BamHI sites (Fig.…”

“…The cardiac TnI (cTnI) (TNNI3) and ssTnT genes are very closely linked. Shown in ex vivo promoter analysis, the 5Ј upstream enhancer region of the ssTnT gene overlaps with the structure of the cTnI gene (6). This structural integration of cTnI and ssTnT genes suggested that a previously developed mouse line in which the entire Tnni3 gene was deleted through embryonic stem cell gene targeting (7) would have lost a large portion of the 5Ј-enhancer region of the Tnnt1 gene (Fig.…”

“…Melting curve analysis was performed at the end to verify that there was no significant (6). The targeted deletion of the entire cTnI gene in a cTnI knock-out mouse line (7) had concurrently removed a segment containing 5Ј-enhancer(s) of the ssTnT gene promoter, which would reduce transcriptional activity as indicated by significantly decreased transcriptional activity of the Ϫ2.2 kb promoter construct versus the Ϫ5.4 kb control in previous ex vivo experiments (6). FIGURE 2.…”

Exon Skipping in Cardiac Troponin T of Turkeys with Inherited Dilated Cardiomyopathy

“…Genomic Cloning and Sequencing-Genomic DNA was prepared from the liver of domestic turkey by proteinase K digestion and phenol/ CHCl 3 extraction (39). Two oligonucleotide primers were synthesized for PCR amplification of the segment containing the exon 7 to exon 10 region of the turkey cTnT gene.…”

Characterization of the Mouse Adeno-Associated Virus AAVS1 Ortholog

“…AAVS1 is located 14.9 and 36 kb centromeric to the slow skeletal troponin T (TNNT1) and cardiac troponin I (TNNI3) genes, respectively (12). The mouse Tnni3 and Tnnt1 genes are located on chromosome 7 (13,14), in a region previously shown to be syntenic to the human chromosome 19 region that contains AAVS1 (7). We used the Celera discovery system to search the Celera mouse genome assembly with the mouse Tnni3 and Tnnt1 genes, the AK010836 cDNA, and the human MBS85 genomic sequence.…”