Alpha smooth muscle actin distribution in cytoplasm and nuclear invaginations of connective tissue fibroblasts.

Alpha smooth muscle actin (alpha-SMA) was recently shown to be present in mouse subcutaneous tissue fibroblasts in the absence of tissue injury. In this study, we used a combination of immunohistochemistry and correlative confocal scanning laser and electron microscopy to investigate the structural organization of alpha-SMA in relation to the nucleus. Furthermore, we explored colocalization analysis as a method for quantifying the amount of alpha-SMA in close approximation to the nucleic acid marker, 4',6-diamidino-2-phenyl-indole, dihydrochloride. Our findings indicate the presence of alpha-SMA within nuclear invaginations in close proximity to the nuclear membrane, but not in the nucleoplasm. Although the function of these alpha-SMA-rich nuclear invaginations is at present unknown, the morphology of these structures suggests their possible involvement in cellular and nuclear mechanotransduction as well as nuclear transport.