A-F). Fibronectin immunoreactivity in sections of heart from WT (+/+) neonate (A), WT adult (C), WT old (E), SPARC-null (-/-) neonate (B), SPARC-null adult (D), and SPARC-null old (F) mice. G-L). Fibronectin immunoreactivity in fibrin gels populated with WT (+/+) neonate (G), WT adult (H), WT old (I), SPARC-null (-/-) neonate (J), SPARC-null adult (K), or SPARC-null old (L) fibroblasts. Size bar in A = 50 µms; each panel is of equal magnification. M). Quantification of fluorescent intensity for fibronectin immunostain in fibrin gels. WT neonate fibroblasts demonstrated significantly increased levels of fibronectin immunoreactivity versus the other conditions. * p< 0.02 by one-way ANOVA analysis.