Recent findings in the cell and molecular biology of the small intestine

PURPOSE OF REVIEW: Recently published research exploring new aspects of the molecular and cell biology of the small intestine is reviewed. RECENT FINDINGS: The importance has become apparent of several paracrine and autocrine signaling pathways that regulate stem cell proliferation in the crypts and differentiation on the villus. These growth factor systems include: the Wnt pathway, with molecules such as Dickkopf, APC, beta-catenin and SOX9; the Hedgehog system; and members of the TGF-beta family such as bone morphogenetic proteins. Transcription factors activating the expression of genes in the intestine include CDX1, CDX2 and HNF1alpha and their actions are increasingly well characterized. Important findings are being made relating to the Toll-like receptors, which have a major role in innate immunity and intestinal homeostasis. SUMMARY: Many new discoveries using increasingly sophisticated techniques have demonstrated the complexity of the cellular and molecular interactions in the intestinal mucosa.