Fig. 1.

Tβ4 −/Y hearts display no hypertrophy or fibrosis although cardiomyocytes are slightly smaller. Histological sections of Tβ4 +/Y (A and C) and −/Y (B and D) littermate adult hearts reveal no evidence of hypertrophy; consistent with no significant re-expression of hypertrophy-related foetal genes, β-MHC (Myh7), ANF (Nppa) or BNP (Nppb) (E–G). Quantitative analysis of Tβ4 −/Y myocardium in transverse section revealed a significant reduction of myocyte cross-sectional (I, compared with +/Y, H) and longitudinal area (K, compared with J), with more cells at a reduced size compared with +/Y controls (quantification in L–N). Masson's Trichrome staining revealed no evidence of interstitial or perivascular fibrosis (O–R). Scale bars: 1 mm in A applies also to B; 100 μm in C applies to D; 50 μm in H applies to I, J, K; 200 μm in O applies to P and 25 μm in Q applies to R; n = 6 hearts per genotype, except E–G: n = 9 +/Y; n = 13 −/Y.