D.R. Garrod

Localisation of the protein and glycoprotein components of bovine nasal epithelial desmosomes by immunoelectron microscopy.

Desmosomal proteins (dp1‐4) and glycoproteins (dg1‐3) have been localised within desmosomes of bovine nasal epithelium by immunogold labelling of ultrathin frozen sections. Beginning in the extracellular space and proceeding through the plaque to the tonofilaments, the following localisations were found. Labelling for the 130,000 and 115,000 Mr glycoproteins (dg2 and dg3) was predominantly in the extracellular space, a location consistent with their proposed adhesive function. The glycoproteins of 175,000‐164,000 Mr (dg1) were also found in the extracellular space and in addition had cytoplasmic domains extending throughout the cytoplasmic plaque. The 83,000 Mr protein (dp3) was located along the cytoplasmic face of the membrane and extended into the plaque, whereas an antibody which recognises both the 83,000 Mr protein (dp3) and the 75,000 Mr protein (dp4) gave labelling both in and beyond the plaque. Labelling for the high mol. wt proteins of Mr 250,000 and 215,000 (dp1 and dp2) was largely excluded from the plaque, and was located distally, adjacent to the tonofilaments. Hemidesmosomes could not be labelled with antibodies to dg1‐3 or dp3 and 4, but some labelling was obtained with antibody to dp1 and 2.

Hemidesmosome formation by embryonic chick corneal epithelium in vitro

This study was undertaken in order to determine whether 15-day embryonic chick corneal epithelial cells can form hemidesmosomes when cultured on a variety of substrata. It was found that hemidesmosomes were formed on gelatin films, hydrated collagen gels, lens capsule, scraped corneal stroma, matrix produced by corneal endothelial cells and untreated tissue culture plastic. Hemidesmosomes were found after 5 days in cultures produced from either dissociated epithelial cells or whole epithelial explants. Hemidesmosomes occurred both singly and in groups and their morphology varied between well-defined structures with attachment plaques, sub-basal dense plates and connections to intracellular filamentous networks, and more rudimentary forms. The presence of extracellular material was often associated with the hemidesmosomes, although it was also possible to find hemidesmosomes where this material was absent. This work suggests that, in the embryonic chick cornea, extracellular structures such as anchoring filaments and anchoring fibres often associated with mature hemidesmosomes are not essential for hemidesmosome formation.

Calcium-induced desmosome formation in cultured kidney epithelial cells: differences between MDBK and MDCK cells in their requirements for RNA and protein synthesis

Previous work has shown that cultured keratinocytes do not form desmosomes at low [Ca2+] (less than 0.1 mM) but may be induced to do so by raising [Ca2+] to physiological levels (1.8-2 mM). Here, fluorescent antibody staining with specific anti-desmosomal antibodies and electron microscopy have been used to determine whether Ca2+-induced desmosome formation also occurs in simple epithelial cells. Both Madin-Darby canine and bovine kidney cells (MDCK and MDBK) exhibit Ca2+-induced desmosome formation, but there are significant differences between them. MDCK cells resemble keratinocytes in showing rapid desmosome formation characterized by the simultaneous appearance of four desmosomal antigens at the cell periphery within 15-20 min of raising the [Ca2+]. In contrast MDBK cells take between 7 and 8 h to form desmosomes after Ca2+ switching, and this is characterized by slow appearance of two desmosomal antigens, the 175-164(X 10(3)) Mr glycoprotein and desmoplakin, at the cell periphery. Differences in the pattern of staining for desmosomal antigens between the two cell types in low and high [Ca2+] are described and discussed in relation to desmosome formation and internalization. Triton X-100 extractability of desmosomal antigen staining is also considered. While most is non-extractable, staining for the glycoproteins known as desmocollins is completely extractable from MDCK cells in low [Ca2+], but that which reaches the cell periphery after Ca2+ switching becomes non-extractable. Although neither cell type forms desmosomes in low [Ca2+], both possess zonulae adhaerentes, suggesting a difference in Ca2+ requirement for formation of these two junctions.