Targeted Ablation of the Murine α-Tropomyosin Gene

Abstract

We created a mouse that lacks a functional alpha-tropomyosin gene using gene targeting in embryonic stem cells and blastocyst-mediated transgenesis. Homozygous alpha-tropomyosin "knockout" mice die between embryonic day 9.5 and 13.5 and lack alpha-tropomyosin mRNA. Heterozygous alpha-tropomyosin knockout mice have approximately 50% as much cardiac alpha-tropomyosin mRNA as wild-type littermates but similar alpha-tropomyosin protein levels. Cardiac gross morphology, histology, and function (assessed by working heart preparations) of heterozygous alpha-tropomyosin knockout and wild-type mice were indistinguishable. Mechanical performance of skinned papillary muscle strips derived from mutant and wild-type hearts also revealed no differences. We conclude that haploinsufficiency of the alpha-tropomyosin gene produces little or no change in cardiac function or structure, whereas total alpha-tropomyosin deficiency is incompatible with life. These findings imply that in heterozygotes there is a regulatory mechanism that maintains the level of myofibrillar tropomyosin despite the reduction in alpha-tropomyosin mRNA.

Lamin A/C haploinsufficiency causes dilated cardiomyopathy and apoptosis-triggered cardiac conduction system disease

“…Reduced lamin A/C protein levels in heterozygous mutant mouse hearts were surprising, since mutations that create null alleles in structural proteins (e.g., cardiac troponin T, α tropomyosin) often do not alter cardiac structural protein levels [36,37]. However, as part of the inner nuclear membrane, lamin A/C possesses additional properties such as interaction with transcription factors [3], distinct from other structural proteins.…”

Tropomyosin and Troponin Are Required for Ovarian Contraction in theCaenorhabditis elegansReproductive System

“…In both muscle and nonmuscle cells, TM stabilizes actin filaments by protecting them from disassembly (Cooper, 2002). Null or severe lossof-function mutations of a TM gene are lethal in yeast (Balasubramanian et al, 1992;Drees et al, 1995), mice (Blanchard et al, 1997;Rethinasamy et al, 1998), and C. elegans (Williams and Waterston, 1994;Anyanful et al, 2001). Thus, TM is an important regulator of actin-dependent processes in a variety of cells.…”

Tropomyosin is required for cardiac morphogenesis, myofibril assembly, and formation of adherens junctions in the developing mouse embryo

“…1A) (Blanchard et al, 1997;Rethinasamy et al, 1998). The αTM1 +/− adults were phenotypically normal, with wild-type αTM1 protein levels in muscles and myofibrillar fractions despite a 50% reduction in αTM1 mRNA (Blanchard et al, 1997;Rethinasamy et al, 1998).…”

“…1A) (Blanchard et al, 1997;Rethinasamy et al, 1998). The αTM1 +/− adults were phenotypically normal, with wild-type αTM1 protein levels in muscles and myofibrillar fractions despite a 50% reduction in αTM1 mRNA (Blanchard et al, 1997;Rethinasamy et al, 1998). In contrast, the αTM1 −/− mice were reported to be embryonic lethal sometime between E8 and E11.5 days of gestation, due to unknown causes (Blanchard et al, 1997;Rethinasamy et al, 1998).…”