Immunological localization of glycoprotein 330, low density lipoprotein receptor related protein and 39 kDa receptor associated protein in embryonic mouse tissues.

In this study we have immunologically examined the expression of the structurally and functionally related receptors, LRP and gp330, and their associated 39 kDa protein (RAP) in tissues of the embryonic mouse. One aim was to determine whether these proteins were coordinantly expressed. The data reveals that gp330 is expressed on the apical surfaces of many specialized absorptive epithelia most prominently, choroid plexus, ependyma, metanephric tubules, ear, thyroid, pericardium, and intestine. LRP was detected in all epithelia expressing gp330 with the exception of the epicardium and metanephric tubule epithelium. However, the subcellular pattern of LRP deposition in polarized epithelium was distinct from the apical pattern of gp330, perhaps indicating that LRP was either sequestered intracellularly or distributed basolaterally. The pattern of LRP expression in tissues of the mouse embryo was however much wider than that of gp330. Prominent expression of LRP was observed in skin, myocardium, mesenchyme, liver, pancreas, and marginal regions of the brain. In the developing liver, LRP was not detected in day 10.5 but was detected in megacaryocyte-like cells of 12.5 day and in hepatocytes of 14.5 day embryonic liver. RAP was observed to be coexpressed with either or both of the receptors but its subcellular pattern of distribution coincided with that of LRP. The coexpression of gp330 and LRP in epithelial cells and the observation that gp330 staining was always localized apically while LRP was distributed basolaterally or sequestered intracellularly suggests that these receptors have distinct functions in polarized epithelial cells.