MOLECULAR AND CELLULAR BIOLOGY OF THE SMALL-INTESTINE

The small intestinal epithelium differentiates in a migration-dependen t manner into four different lineages. Each of these cell types produc es characteristic gene products and structures essential for its parti cular function: enterocytes produce brush border hydrolases, goblet ce lls release mucins and trefoil peptides, enteroendocrine cells secrete chromaffins, and Paneth's cells make lysozyme, criptidins, and defens ins. Cell-type specific intestinal gene expression is tightly regulate d along both the crypt-to-villus vertical axis and the cephalocaudal h orizontal axis. The complex mechanisms of this gene regulation include a combination of transcriptional, translational, and posttranslationa l controls, Recent studies have identified and characterized transcrip tion factors regulating intestinal gene expression. Furthermore, a var iety of experimental approaches including the generation of knockout m ice have provided new insights into the function of trefoil peptides.