Modulation of alpha-actin and alpha-actinin proteins in cardiomyocytes by retinoic acid during development.

Early heart development is known to be sensitive to retinoid concentrations. Although the influence of retinoids on cardiac morphogenesis has been described previously, the effect of retinoids on cardiomyocyte differentiation during development has not been characterized. We quantified the effects of the retinoic acids all-trans RA and 13-cis RA on alpha-actin and alpha-actinin at the subcellular level in cultures of chick embryo cardiomyocytes obtained from Hamburger and Hamilton's (HH) stage 22, 32 and 40 embryos. The retinoids increased the concentration of alpha-actin and alpha-actinin in the cytoplasmic and cytoskeletal fractions of cells at all three stages of development. The effect was greatest in cardiomyocytes treated for 24 h with all-trans RA and in cells from HH22 embryos. The greatest increases in alpha-actin concentration occurred in the cytoskeletal fraction of HH22 cells cultured for 24 h with all-trans or 13-cis RA, whereas the greatest increases in alpha-actinin were found in the cytoplasmic fraction of HH22 cells exposed to retinoids for 24 h. We conclude that retinoic acid plays a role in the reorganization of the pattern of sarcomeric protein expression during cardiomyocyte differentiation.