Figure 6. Cardiac interstitial Col1a1⁺ cells are rare in Pod1^−/− mouse hearts.

(A–B”) RNA ISH was performed on E18.5 mouse heart sections using a Col1a1 mRNA probe. Col1a1 is expressed in the epicardium of Pod1^+/− (A’,A”) and Pod1^−/− (B’,B”) hearts (arrows). Interstitial Col1a1⁺ cells (arrowheads in A’–B”) are scarce within Pod1^−/− myocardium (B’,B”). Normal Col1a1 expression is observed in mitral valves (MV, arrowheads) of Pod1^+/− (A) and Pod1^−/− (B) hearts. (C,D) Differentiation of Pod1-deficient EPDCs into fibroblasts was analyzed by double IF using anti-βGal (green) and anti-Col1a1 (red) antibodies. In E17.5 Pod1^+/− mice, heterozygous for the Pod1/LacZ locus, βGal⁺ interstitial cells coexpress Col1a1 (yellow, arrowheads and inset). (D) In E17.5 Pod1^−/− hearts, Pod1-deficient βGal⁺ interstitial cells (green) are negative for Col1a1 expression (arrowheads, inset). (E) Total Col1a1-expressing cells within the myocardial interstitium of Pod1^+/− and Pod1^−/− hearts were quantified (as in A–B”). Statistical significance of observed differences between Pod1^+/− controls and Pod1^−/− was determined by Student’s t-test (n=3). #P•0.05.