Keratin type intermediate filaments in sweat gland myoepithelial cells

A study was undertaken to clarify the origin of sweat gland myoepithelial cells using monoclonal antibodies EKH1, EKH4, and AN3. EKH1 recognizes all classes of intermediate filaments. EKH4 and AN3 recognize keratin type intermediate filaments. Since within the skin, only epithelial cells of ectodermal origin contain keratin, EKH4 and AN3 could be used as ectodermal markers within the skin. Sweat gland myoepithelial cells were labeled by all three antibodies. In contrast, arrector pili muscle and vascular smooth muscle were recognized only by EKH1, but not by EKH4 and AN3. This study demonstrated that myoepithelial cells of sweat glands contain keratin type intermediate filaments and suggested their ectodermal origin. On the other hand, arrector pili muscle and vascular smooth muscle did not contain keratin type intermediate filaments, despite their ultrastructural similarity to myoepithelial cells. Electron microscopic studies using human fetal and adult skin revealed that myoepithelial cells are developed from basal cells of the coiled tip of fetal gland and not from mesenchymal cells. In order to determine the time of appearance of myoepithelial cells during fetal development, embryonic and newborn mouse skin was also examined. It was found that sweat gland myoepithelial cells first appear around 20 weeks of gestation in humans and after birth in mice.