Loss of smooth muscle myosin heavy chain results in the bladder and stomach developing lesion during foetal development in mice.

Smooth muscle myosin heavy chain (SM-MHC) is exclusively expresses in smooth muscle, which takes part in smooth muscle cell contraction. Here, we used an insertional mutation mouse whose heavy polypeptide 11 (Myh11) gene has been disrupted and no SM-MHC protein has been detected. Compared to the wild-type and SM-MHC+/- mice, the SM-MHC-/- neonates had large round bellies, thin-walled giant bladders, and large stomachs with huge gas bubbles. Most of it died within 10 h and the rest within 20 h after birth. Further analysis of the developing foetuses from 16.5 days postcoitum (dpc) stage to newborn showed no significant (P<0.05) difference in the ratio of Mendelian inheritance and average body weight among SM-MHC+/+ , SM-MHC+/- and SM-MHC-/- mice, whereas the abnormal exterior appearance was observed in each SM-MHC-/- bladders from 16.5 dpc. Histological analysis showed no difference in stomach tissues but evidently thin-walled smooth muscle layer and a giant cavity in bladders of SM-MHC-/- foetuses at various stages from 15.5 dpc to newborn. The results indicated that the defect of SM-MHC lead to the bladder developing lesions initially at 15.5 dpc stage in mouse and also implied that the SM-MHC loss might result in the gas bubbles in stomach. The study should facilitate further detailed analyses of the potential role of SM-MHC in bladder and stomach development.