Numerous genes expressed by intestinal epithelial cells are developmentally regulated, and the influence that adaptive (AI) and passive (PI) immunity have in controlling their expression has not been evaluated. In this study, we tested the hypothesis that both PI and AI influenced enterocyte gene expression by developing a breeding scheme that used T and B cell-deficient recombination-activating gene (RAG) mice. RNA was isolated from the liver and proximal/distal small intestine at various ages, and the steady-state levels of six different transcripts were evaluated by RNase protection assay. In wild-type (WT) pups, all transcripts [Fc receptor of the neonate (FcRn), polymeric IgA receptor (pIgR), GLUT5, lactase-phlorizin hydrolase (lactase), apical sodium-dependent bile acid transporter (ASBT), and Na+/glucose cotransporter (SGLT1)] studied were developmentally regulated at the time of weaning, and all transcripts except ASBT had the highest levels of expression in the proximal small intestine. In WT suckling pups reared in the absence of PI, pIgR mRNA levels were increased 100% during the early phase of development. In mice lacking AI, the expression of pIgR and lactase were significantly attenuated, whereas FcRn and GLUT5 levels were higher compared with WT mice. Finally, in the absence of both passive and active immunity, expression levels of pIgR and lactase were significantly lower than similarly aged WT mice. In summary, we report that the adaptive and passive immune status of mice influences steady-state mRNA levels of several important, developmentally regulated enterocyte genes during the suckling and weaning periods of life.

The polymeric Ig receptor ( pIgR) is a critical component of the mucosal immune system and is expressed in largest amounts in the small intestine. In this study, we describe the initial characterization of the core promoter region of this gene. Expression of chimeric promoter-reporter constructs was supported in Caco-2 and HT-29 cells, and DNase I footprint analysis revealed a large protein complex within the core promoter region. Site-directed mutagenesis experiments determined that elements within this region serve to either augment or repress basal activity of the human pIgR promoter. Band shift assays of overlapping oligonucleotides within the core promoter identified eight distinct complexes; the abundance of most complexes was enhanced in post-confluent cells. In summary, we report the characterization of the human pIgR promoter and the essential role that eight different nuclear complexes have in controlling basal expression of this gene in Caco-2 cells.