Conditional Ablation of Nonmuscle Myosin II-B Delineates Heart Defects in Adult Mice
- Xuefei Ma
- Kazuyo Takeda
- Aman Singh
- Zu-Xi Yu
- Patricia Zerfas
- Anthony Blount
- Chengyu Liu
- Jeffrey A. Towbin
- Michael D. Schneider
- Robert S. Adelstein
- Qize Wei
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 (BαMHC/BαMHC mice) do not show brain defects. However, BαMHC/BαMHC mice display novel cardiac defects not seen in NMII-B germline-ablated mice. Most of the BαMHC/BαMHC 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 BαMHC/BαMHC 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.
