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Thymosin beta 4 is dispensable for murine cardiac development and function.

ABSTRACT: Thymosin beta 4 (T?4) is a 43-amino acid factor encoded by an X-linked gene. Recent studies have suggested that T?4 is a key factor in cardiac development, growth, disease, epicardial integrity, and blood vessel formation. Cardiac-specific short hairpin (sh)RNA knockdown of t?4 has been reported to result in embryonic lethality at E14.5-16.5, with severe cardiac and angiogenic defects. However, this shRNA t?4-knockdown model did not completely abrogate T?4 expression. To completely ablate T?4 and to rule out the possibility of off-target effects associated with shRNA gene silencing, further studies of global or cardiac-specific knockouts are critical.We examined the role of T?4 in developing and adult heart through global and cardiac specific t?4-knockout mouse models.Global t?4-knockout mice were born at mendelian ratios and exhibited normal heart and blood vessel formation. Furthermore, in adult global t?4-knockout mice, cardiac function, capillary density, expression of key cardiac fetal and angiogenic genes, epicardial marker expression, and extracellular matrix deposition were indistinguishable from that of controls. Tissue-specific t?4-deficient mice, generated by crossing t?4-floxed mice to Nkx2.5-Cre and ?MHC-Cre, were also found to have no phenotype.We conclude that T?4 is dispensable for embryonic viability, heart development, coronary vessel development, and adult myocardial function.

SUBMITTER: Banerjee I

PROVIDER: S-EPMC3739283 | biostudies-literature | 2012 Feb

REPOSITORIES: biostudies-literature

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Thymosin beta 4 is dispensable for murine cardiac development and function.

Banerjee Indroneal I Zhang Jianlin J Moore-Morris Thomas T Lange Stephan S Shen Tao T Dalton Nancy D ND Gu Yusu Y Peterson Kirk L KL Evans Sylvia M SM Chen Ju J

Circulation research 20111208 3

<h4>Rationale</h4>Thymosin beta 4 (Tβ4) is a 43-amino acid factor encoded by an X-linked gene. Recent studies have suggested that Tβ4 is a key factor in cardiac development, growth, disease, epicardial integrity, and blood vessel formation. Cardiac-specific short hairpin (sh)RNA knockdown of tβ4 has been reported to result in embryonic lethality at E14.5-16.5, with severe cardiac and angiogenic defects. However, this shRNA tβ4-knockdown model did not completely abrogate Tβ4 expression. To comple ...[more]

PMID: 22158707

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Project description:BackgroundPhosphatidylinositol phosphates (PIPs) are low-abundance phospholipids that participate in a range of cellular processes, including cell migration and membrane traffic. PIP levels and subcellular distribution are regulated by a series of lipid kinases and phosphatases. In skeletal muscle, PIPs and their enzymatic regulators serve critically important functions exemplified by mutations of the PIP phosphatase MTM1 in myotubular myopathy (MTM), a severe muscle disease characterized by impaired muscle structure and abnormal excitation-contraction coupling. FIG4 functions as a PIP phosphatase that participates in both the synthesis and breakdown of phosphatidylinositol 3,5-bisphosphate (PI(3,5)P2). Mutation of FIG4 results in a severe neurodegenerative disorder in mice and a progressive peripheral polyneuropathy in humans. The effect of FIG4 mutation on skeletal muscle has yet to be examined.MethodsHerein we characterize the impact of FIG4 on skeletal muscle development and function using the spontaneously occurring mouse mutant pale tremor (plt), a mouse line with a loss of function mutation in Fig4.ResultsIn plt mice, we characterized abnormalities in skeletal muscle, including reduced muscle size and specific force generation. We also uncovered ultrastructural abnormalities and increased programmed cell death. Conversely, we detected no structural or functional abnormalities to suggest impairment of excitation-contraction coupling, a process previously shown to be influenced by PI(3,5)P2 levels. Conditional rescue of Fig4 mutation in neurons prevented overt muscle weakness and the development of obvious muscle abnormalities, suggesting that the changes observed in the plt mice were primarily related to denervation of skeletal muscle. On the basis of the ability of reduced FIG4 levels to rescue aspects of Mtmr2-dependent neuropathy, we evaluated the effect of Fig4 haploinsufficiency on the myopathy of Mtm1-knockout mice. Male mice with a compound Fig4+/-/Mtm1-/Y genotype displayed no improvements in muscle histology, muscle size or overall survival, indicating that FIG4 reduction does not ameliorate the Mtm1-knockout phenotype.ConclusionsOverall, these data indicate that loss of Fig4 impairs skeletal muscle function but does not significantly affect its structural development.

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Thymosin beta 4 is dispensable for murine cardiac development and function.

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Thymosin beta 4 is dispensable for murine cardiac development and function.

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