H+/DI-TRIPEPTIDE TRANSPORTER (PEPT1) EXPRESSION IN THE RABBIT INTESTINE

In order to examine the intestinal expression of the recently cloned H+/di-tripeptide transporter (PepTI), oligonucleoitide probes were synthesized and their specificity confirmed be Northern blot analysis of rabbit jejunal RNA. In situ, hybridization studies, using these probes, show that PepTI is expressed all along the small intestine and at a very much reduced level in the colon. In contrast, PepTI mRNA was not detected in the stomach, sacculus rotundus or caecum. Microscopic examination of tissue sections showed PepTI expression to be restricted to intestinal epithelium with no detectable expression in the lamina propria, muscularis mucosae, muscularis or serosa. The accumulation of PepTI mRNA along the crypt-villus axis was also investigated. In all regions of the small intestine (in duodenum, jejunum and ileum). PepTI mRNA was undetectable in deeper epithelial cells of the crypts. Expression was first detectable at or near the crypt-villus junction the amount of PepTI mRNA increasing rapidly in the lower villus to a maximum approximately 100-200 mu m from this point. Along the length of the small intestine PepTI mRNA was most abundant in duodenal and jejunal enterocytes, with lower levels in the ileal epithelium. PepTI expression is greatly depressed in the follicle-associated epithelium if the Peyer's patch relative to both interfollicular and adjacent ''normal'' villi. These data are discussed in the context of the known physiological role of PepTI in the gastrointestinal tract.