MOLECULAR AND CELLULAR BIOLOGY OF THE SMALL-INTESTINE

The growth and differentiation of the intestinal epithelium is a parad igm for the development of mature columnar cells from undifferentiated precursors. Little is known about growth regulation, although evidenc e for circulating hormones, and paracrine growth factors are becoming more plentiful. The transcriptional events leading to the production o f lineage-specific markers appear to be mediated by tissue-specific nu clear factors, often induced along the differentiation pathway. Molecu lar analysis of intestine-specific gene products help further our unde rstanding of the functions for such proteins as trefoil peptides, muci ns, laminins, and brush-border hydrolases. To understand which process es during gut morphogenesis and programmed cell growth represent key r egulatory steps, molecular genetic systems are being considered to hel p identify and characterize the specific genes involved.