Cellular and molecular mechanisms of intestinal elongation in mammals: the long and short of it

The gastrointestinal tract carries out essential functions for the organism, including the digestion and absorption of nutrients. The cells lining the lumen of the gut tube derive from the endoderm, one of the three germ layers formed during gastrulation. The length of the intestinal tract determines its digestive and absorptive capacity, and so the intestine expands several times the length of the whole body to ensure an adequate absorptive area to meet nutritional demands. However, the endoderm starts out as a small sheet of cells spanning less than the whole length of the head-fold embryo. In order to achieve its final shape and size, the cells in the endoderm undergo extensive growth and profound morphogenetic changes, which are governed by embryonic signaling pathways and transcription factors. This review, based on mouse development, summarizes our current knowledge of the cellular and molecular mechanisms underlying the morphogenetic changes that participate in shaping the mature intestinal tract in vertebrates.