Expression of ileal Na+-dependent bile acids transporter gene in transposed ileum of rat small intestine

In the present paper, we examined whether a luminal environment such as an anatomical location and a luminal contents play a positional signal maintai ning a site specific expression of ileal sodium-dependent bile acid transpo rter (ISBT) gene in a rat small intestine. For this purpose, we surgically exchanged a position of an terminal ileum to a upper jejunum and the expres sion of ISBT gene in the transposed intestinal segments was examined by usi ng Xenopus laevis oocytes functional expression system. Poly (A)(+) RNA was prepared from duodenum, mid-jejunum or distal-ileum of normal rat intestin e and microinjected into Xenopus laevis oocytes. The oocytes injected poly (A)(+) RNA from ileum but not from duodenum or jejunum showed a significant taurocholate uptake activity in the presence of Na+, indicating that ISBT gene was functionally expressed in the oocytes. On the 10th day after surge ry when adaptive hyperplasia reached a plateau, poly(A)(+) RNA was prepared from the respective segments and injected into the oocytes. The result ind icated that ISBT gene expressed only ileum but not jejunum regardless their original or transposed position. Thus, it seems likely that the expression of ISBT gene is rather regulated by a tissue specific fashion in adult rat intestine and is not affected by the luminal environment. (C) 1999 Elsevie r Science Inc.