Identification, characterization, and expression of a novel alpha-tropomyosin isoform in cardiac tissues in developing chicken.
Tropomyosins are present in various muscle (skeletal, cardiac, and smooth) and non-muscle cells with different isoforms characteristic of specific cell types. We describe here a novel smooth/striated chimeric isoform that was expressed in developing chick heart in addition to the classically described TM-4 type. This novel alpha-Tm tropomyosin isoform, designated as alpha-Tm-2, contains exon 2a (in place of exon 2b). The known striated muscle isoform (alpha-Tm-1) was also expressed in embryonic hearts along with the striated muscle isoform of TM-4. In adult heart, TM-4 was expressed, however, expression of both alpha-Tm-1 and alpha-Tm-2 isoforms was drastically reduced or downregulated. Interestingly, we were unable to detect the expression of alpha-Tm-2 in embryonic and adult skeletal muscle, however, the alpha-Tm-1 isoform is expressed in embryonic and adult skeletal muscle. Examination of other possible isoforms of the alpha-TM gene, i.e., alpha-smooth muscle tropomyosin (alpha-Sm), alpha-Fibroblast-1 (alpha-F1), and alpha-Fibroblast-2 (alpha-F2) revealed expression in embryonic hearts and a significant reduction of each of these isoforms in adult heart. In order to elucidate the role of the newly discovered tropomyosin isoform in chicken, we ectopically expressed the GFP fusion protein of alpha-Tm-1 and alpha-Tm-2 separately into cardiomyocytes isolated from neonatal rats. Each isoform was incorporated into organized myofibrils. Our results suggest that the alpha-TM gene may undergo both positive and negative transcriptional control in chicken hearts during development.
Zajdel
Robert W
RW
Department of Cell and Developmental Biology, Syracuse, New York, USA.
Denz
Christopher R
CR
Lee
Sung
S
Dube
Syamalima
S
Ehler
Elisabeth
E
Perriard
Evylene
E
Perriard
Jean-Claude
JC
Dube
Dipak K
DK
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002642:Chick Embryo; D002645:Chickens; D018613:Microscopy, Confocal; D008969:Molecular Sequence Data; D009206:Myocardium / Q000378:metabolism*; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D014162:Transfection; D014335:Tropomyosin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D011993:Recombinant Fusion Proteins; D014335:Tropomyosin