Abstract. Cadherins and catenins play an important role in cell-cell adhesion. Two of the catenins, [3 and ~/, are members of a group of proteins that contains a repeating amino acid motif originally described for the Drosophila segment polarity gene armadillo. Another member of this group is a 120-kD protein termed p120, originally identified as a substrate of the tyrosine kinase pp60 ~r¢. In this paper, we show that endothelial and epithelial cells express p120 and pl00, a 100-kD, p120-related protein. Peptide sequencing of pl00 establishes it as highly related to p120. p120 and pl00 both appear associated with the cadherin/catenin complex, but independent p120/catenin and pl00/catenin complexes can be isolated. This association is shown by coimmunoprecipitation of cadherins and catenins with an anti-p120/ pl00 antibody, and of pl20/pl00 with cadherin or catenin antibodies. Immunocytochemical analysis with a p120-specific antibody reveals junctional colocalization of p120 and 13-catenin in epithelial cells. Catenins and p120/p100 also colocalize in endothelial and epithelial cells in culture and in tissue sections. The cellular content of p120/p100 and 13-catenin is similar in MDCK cells, but only ~20% of the p120/p100 pool associates with the cadherin/catenin complex. Our data provide further evidence for interactions among the different arm proteins and suggest that p120/p100 may participate in regulating the function of cadherins and, thereby, other processes influenced by cell-cell adhesion.

Brain capillary endothelial cells

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Pericytes are cells of mesodermal origin which are closely associated with the microvasculature. Despite numerous studies little is known about their function. We have studied the relationship between pericytes and the endothelium in rat myocardial capillaries employing ultrastructural and immunogold techniques. 14% of the subendothelial cell membrane is covered by comparatively small pericytic cell processes. About half of these processes are completely embedded in basement membrane material, whereas the remaining half forms closer contacts with the endothelium. These contacts are devoid of anti-laminin immunogold label, a marker for basement membranes. A small fraction of these contacts has been identified as tight junctions resembling those seen between endothelial cells in capillaries of the same tissue. The remaining majority of junctions reveals a cleft of approximately 18 nm between the apposed membranes in which a succession of cleft-spanning structures can often be detected. It was also found that pericytic processes are preferentially located close to interendothelial junctions. We suggest that the high frequency of intimate junctions between pericytes and the endothelium and the preferential localisation near paracellular clefts may have functional significance.

Abstract. Renal coccidiosis was diagnosed in four bats of different species (Pipistrellus pipistrellus, Myotis mystacinus, M. nattereri, and Nyctulus noctula). Multiple white and partly indented foci up to 2 mm in diameter were visible on the renal surface. Histologically, the foci appeared as cystic dilated tubules with proliferated epithelium. Asexual and sexual coccidian stages were seen in the epithelial cells, and the extremely distended tubular lumina were filled with schizonts, free zoites, microgamonts, macrogamonts, and unsporulated oocysts. Because the majority of the renal tissue appeared uninvolved in the disease process at the gross and histologic levels and there was no evidence for uremia in other organs, renal function was probably not impaired. Precise classification of the coccidia was impossible because no sporulated oocysts were available. The parasite morphology and the hitherto unreported cystic dilatation of infected tubules containing all developmental stages differ from renal coccidioses reported previously and therefore suggest an undescribed coccidian species.

The morphology and molecular composition of intercellular adherens junctions have most frequently been described in epithelial cells and the fascia adhaerens of the intercalated disc. A group of cytoplasmic molecules is known to be associated with adherens junctions. The intercellular bond is mediated by cadherins which bridge the cells by homophilic binding. Recently, endothelial cells have also been shown to form intercellular junctions of the adherens-type. However, they are morphologically less distinct and little is known about their molecular components. In this study we report the localization of some adherens junction components in intact microvessels of the blood-brain barrier in the rat. We used antibodies raised against alpha-actinin, vinculin, zyxin, cadherin (antipan-cadherin antibody) and A-CAM (N-cadherin) in immunohistochemical experiments at light and electron microscopical levels. Microvessel walls reacted positively for all antigens throughout postnatal development. All antigens were localised, though not necessarily exclusively, to interendothelial junctions. At the ultrastructural level, pan-cadherin reactivity was present throughout the entire length of the cleft. These results could mean that in blood-brain barrier endothelial cells the complex tight junction is embedded in an adherens junction which occupies the entire length of the cleft.

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