Translational control of an intestinal microvillar enzyme

The rates of biosynthesis of adult and foetal pig small-intestinal aminopeptidase N (EC 3.4.11.2) were compared to determine at which level the expression of the microvillar enzyme is developmentally controlled. In organ-cultured explants, the rate of biosynthesis of foetal aminopeptidase N is only about 3% of the adult rate. The small amount synthesized occurs in a high-mannose-glycosylated, membrane-bound, form that is processed to the mature, complex-glycosylated, form at a markedly slower rate than that of the adult enzyme. Extracts of total RNA from adult and foetal intestine contained comparable amounts of aminopeptidase N mRNA, encoding gel-electrophoretically identical primary translation products. Together, these data indicate that the expression of aminopeptidase N is controlled at a translational level.

Immunolocalization of keratan sulphate in the human embryonic cornea and other human foetal organs

An antibody raised against keratan sulphate was used to localize keratan sulphate in the human embryonic cornea and other human foetal organs. It was found that keratan sulphate was present in the corneal endothelium, as well as in the corneal stroma. In contrast, no keratan sulphate could be demonstrated in the corneal epithelium or in any posterior parts of the human foetal eye. Human corneal stromal cells grown in monolayers in tissue culture lost their capacity to bind this antibody. This suggests that explantation in vitro decreases or alters the expression of keratan sulphate in this cell type. Keratan sulphate was found to be present in abundant quantities in human embryonic cartilage and to a lesser extent in placenta. In contrast, keratan sulphate could not be detected in the foetal intestine, liver, suprarenal glands, the umbilical cord or in the foetal yolk sack.