A non-collagenous glycoprotein from elastic tissue acts as substratum for growth of cells in vitro

The interaction of human fetal neurons and epidermal cells in vitro

The interaction of autologous human fetal neurons with epidermal cells was studied by culturing fetal dorsal root ganglia (DRG) in the center of a dual chamber system with epidermal explants in the outer chamber. The two chambers were separated by two concentric stainless steel annular rings adherent to the substratum by silicon grease and agarose. Axons from the DRG penetrated the agarose barrier, growing into the exterior chamber by 10 d in vitro (DIV) and extended past sparse peripheral fibroblasts to interact specifically with epidermal cells by 12 to 16 DIV. Scanning electron microscopy (SEM) showed single or multiple neuronal fascicles terminating on epidermal cells with spatular, veillike or bulbous axon termini. Transmission electron microscopy (TEM) showed fine axonal termini between epidermal cells, separated by an intercellular gap. The specificity of axonal targeting for epidermal cells rather than fibroblasts was also demonstrated by infecting the DRG with Herpes simplex virus type-1 (HSV-1). Specific anterograde transport of HSV-1 along axons to keratin-expressing epidermal cells was demonstrated by immunofluorescence and immunoperoxidase staining using monoclonal antibodies to viral glycoprotein D. This model allows the study of the mechanism of the specific interactions between neurons and epidermal cells analogous to those in fetal development and after cutaneous nerve regeneration.

Immunolocalization of a 35K structural glycoprotein to elastin-associated microfibrils

In this study, a rabbit antiserum directed against a 35K glycoprotein (35K-GP), extracted from connective tissue, was used to examine the localisation of this antigen within foetal bovine ligamentum nuchae at stages of development preceding (4th month) and coinciding with (7th month) active elastin biosynthesis. In these tissues the antibody, detected by a colloidal gold conjugate technique, localised specifically to 11-nm fibrils, identified as the microfibrillar component, present both in the form of independent bundles and in association with elastin in the developing elastic fibres. No other connective tissue component was recognised by the antibodies which had been purified by affinity chromatography. The ability of the antibodies to bind to the microfibrils appeared to be dependent on embedding in LR White resin, as colloidal gold binding was greatly reduced in tissue embedded in epoxy resin. These results are discussed with respect to the role that 35K-GP may play in the morphogenesis of the elastic fibre.

Keratinocytes synthesize basal-lamina proteins in culture

On histologic vertical sections of skin, the epidermis is separated from the dermis by an amorphous thin membrane, the basal lamina. Ultrastructurally, the basal lamina is composed of four areas, including the basal-cell plasma membrane and hemidesmosomes, the lamina lucida, the lamina densa, and the sub-lamina densa fibrillar region. In culture, epidermal keratinocytes are able to produce hemidesmosomes, lamina lucida, and lamina densa. There is no evidence that cultured keratinocytes can produce sub-lamina densa fibrils. Biochemically, the lamina lucida contains two major glycoproteins. One, the bullous pemphigoid antigen, is synthesized by epidermal keratinocytes in vitro. These cells also synthesize laminin, the other glycoprotein of lamina lucida. At the interface between lamina lucida and lamina densa there is probably a heparan sulfate proteoglycan. Whether this proteoglycan is produced by keratinocytes in culture is not known, but the possibility can be considered. Lamina densa contains collagen IV, and this collagen is synthesized by keratinocytes in culture. However, cultured keratinocytes may also synthesize collagen types I, III, and V. Type V is associated with the basal lamina, but its exact location is unknown. Types I and III (if they are produced in vivo) would be situated in the sub-basal lamina region. The problem of fibronectin remains unsolved. There is "some" fibronectin in the lamina lucida, but its origin is not clear.