Molecular and physiological effects of alpha-tropomyosin ablation in the mouse.
Tropomyosin (TM) is an integral component of the thin filament in muscle fibers and is involved in regulating actin-myosin interactions. TM is encoded by a family of four alternatively spliced genes that display highly conserved nucleotide and amino acid sequences. To assess the functional and developmental significance of alpha-TM, the murine alpha-TM gene was disrupted by homologous recombination. Homozygous alpha-TM null mice are embryonic lethal, dying between 8 and 11.5 days post coitum. Mice that are heterozygous for alpha-TM are viable and reproduce normally. Heterozygous knockout mouse hearts show a 50% reduction in cardiac muscle alpha-TM mRNA, with no compensatory increase in transcript levels by striated muscle beta-TM or TM-30 isoforms. Surprisingly, this reduction in alpha-TM mRNA levels in heterozygous mice is not reflected at the protein level, where normal amounts of striated muscle alpha-TM protein are produced and integrated in the myofibril. Quantification of alpha-TM mRNA bound in polysomal fractions reveals that both wild-type and heterozygous knockout animals have similar levels. These data suggest that a change in steady-state level of alpha-TM mRNA does not affect the relative amount of mRNA translated and amount of protein synthesized. Physiological analyses of myocardial and myofilament function show no differences between heterozygous alpha-TM mice and control mice. The present study suggests that translational regulation plays a major role in the control of TM expression.
Rethinasamy
P
P
Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinatti Medical Center, OH 45267-0524, USA.
Muthuchamy
M
M
Hewett
T
T
Boivin
G
G
Wolska
B M
BM
Evans
C
C
Solaro
R J
RJ
Wieczorek
D F
DF
D000818:Animals; D017353:Gene Deletion; D005796:Genes / Q000235:genetics; D006579:Heterozygote; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D016297:Mutagenesis, Site-Directed / Q000235:genetics; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D014335:Tropomyosin / Q000235:genetics* / Q000502:physiology*
D012333:RNA, Messenger; D014335:Tropomyosin