David S. Bailey

Structural and biochemical differentiation of the guinea-pig colon during foetal development.

SummaryWe have studied some aspects of the morphological and biochemical differentiation of the foetal guinea-pig colonic epithelium. At day 40 the epithelium was organised in ridges and appeared pseudo-stratified. Folding of the epithelium, followed by villus formation, occurred between days 45 and 55, and by day 50 mucus-secreting goblet cells appeared at the bases of the colonic villi. By day 55 most epithelial cells, including goblet cells, possessed numerous microvilli which, by day 65, had become organised into well developed brush-borders. Between day 55 and term (day 65–68) mucosal depth increased markedly and the colon attained its final glandular morphology.Biochemical studies showed the specific activities of the microvillar hydrolases to be much lower in the washed colon than in either foetal meconium or small intestine at all times during development. Furthermore, a membrane fraction highly enriched in microvillus hydrolase activities was prepared from foetal colonic meconium using techniques originally devised to isolate the foetal small intestinal microvillus membrane. This meconial subfraction was almost identical in polypeptide composition to the highly-purified foetal small intestinal microvillus membrane. Identification of the colonic microvillus membrane was hampered by the absence of reliable membrane markers. Nevertheless, a fraction 14-fold enriched in aminopeptidase activity was prepared from day 40 foetal colon and its polypeptide composition compared by SDS-PAGE to that of the small intestinal microvillus membrane at the same age.

Comparative Analysis of Adult and Fetal Human Small Intestinal Microvilli

The aim was to study the development of human small intestinal microvillus membranes. We compared the protein patterns of human fetal and adult small intestinal microvillus membranes using the high-resolution technique of sodium dodecyl sulphate-polyacrylamide gel electrophoresis. We also examined the synthesis of brush border membrane proteins from the adult small intestine using small intestinal biopsy organ culture 35S-methionine uptake and subsequent gel electrophoresis. We observed that the fetal and colonic microvillus membranes were similar, but differed in certain respects from adult small intestinal microvillus membranes. The jejunal biopsy organ culture revealed that synthesised brush border membrane proteins could be recognized by gel electrophoresis.

Cell-free synthesis of high-molecular-weight small intestinal polypeptides

An intrinsic membrane glycoprotein, Mr 131 000, is a major developmentally specific component of the neonatal guinea-pig small intestinal microvillar membrane. Such high-molecular-weight proteins are often difficult to translate in vitro. In this study we report a successful strategy for the identification of the primary translation product of this glycoprotein, a high-molecular-weight precursor polypeptide of approximate Mr 225 000.