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Circulation Research
Year: 2009  |  Volume: 105  |  Issue: 11  |  Page No.: 1102 - 1109

Conditional Ablation of Nonmuscle Myosin II-B Delineates Heart Defects in Adult Mice

X Ma, K Takeda, A Singh, Z. X Yu, P Zerfas, A Blount, C Liu, J. A Towbin, M. D Schneider, R. S Adelstein and Q. Wei    

Abstract:

Rationale: Germline ablation of the cytoskeletal protein nonmuscle myosin II (NMII)-B results in embryonic lethality, with defects in both the brain and heart. Tissue-specific ablation of NMII-B by a Cre recombinase strategy should prevent embryonic lethality and permit study of the function of NMII-B in adult hearts.

Objective: We sought to understand the function of NMII-B in adult mouse hearts and to see whether the brain defects found in germline-ablated mice influence cardiac development.

Methods and Results: We used a loxP/Cre recombinase strategy to specifically ablate NMII-B in the brains or hearts of mice. Mice ablated for NMII-B in neural tissues die between postnatal day 12 and 22 without showing cardiac defects. Mice deficient in NMII-B only in cardiac myocytes (BMHC/BMHC mice) do not show brain defects. However, BMHC/BMHC mice display novel cardiac defects not seen in NMII-B germline-ablated mice. Most of the BMHC/BMHC mice are born with enlarged cardiac myocytes, some of which are multinucleated, reflecting a defect in cytokinesis. Between 6 to 10 months, they develop a cardiomyopathy that includes interstitial fibrosis and infiltration of the myocardium and pericardium with inflammatory cells. Four of 5 BMHC/BMHC hearts develop marked widening of intercalated discs.

Conclusions: By avoiding the embryonic lethality found in germline-ablated mice, we were able to study the function of NMII-B in adult mice and show that absence of NMII-B in cardiac myocytes results in cardiomyopathy in the adult heart. We also define a role for NMII-B in maintaining the integrity of intercalated discs.

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