Anchor filament bundles in embryonic skin: Origin and termination

Abstract

AbstractDuring development and maturation of skin and its derivatives, bundles of extracellular filamentous elements appear, which traverse a cross section of dorsal skin from deep mesenchyme to the basal lamina of the dermo‐epidermal junction. Observations on freshly fixed tissue and on pieces of skin grown in culture for three to five days, especially in areas where the presence of anchor filaments could be predicted, indicate that the filaments most likely originate from fibroblasts which are usually located in a stratified layer of the deeper mesenchyme. The distal end, or termination, appears to be the basal lamina into which the anchor filament blends and is dispersed.The anchor bundles are composed of long thin filaments in close aggregation and they demonstrate cross‐striations separated by approximately 400 Å in the midportions, and up to 600 Å near their origin and termination. The diameters of the bundles average approximately 0.33 μ at their thickest part. However, at or near their origin, they measure 0.2 μ or less in diameter.The analogy of the filaments to a growing tree is suggested in that, the roots, or origins of the filaments are thin, tortuous and in many cases widely separated. In certain areas they converge into one main trunk which tapers toward their termination in the basal lamina. The observations also suggest that some bundles may have several roots or rootlets, while others have only one or two.Although collagen is often seen close to the bundles, the data indicate that the latter are distinct from, and not derived from collagen.