Deborah Gumucio, Ph.D., Professor, Department of Cell and Developmental Biology, University of Michigan Medical School

In this image of a newborn mouse intestine, the pink color stains dividing cells that lie at the base of finger-like projections called villi. The intestine is remarkable in that its entire surface is replaced every 4-5 days. Cells are "born" within the pink band of cells (some of which are stem cells) and differentiate as they migrate up the villi. Once at the tips of the villi, the cells die and are sloughed into the lumen. An average adult human sheds about 70kg of intestinal cells per year. Here, the nuclei of all cells are stained blue while green marks a subset of the differentiated cells. Because of the rapid and constant turnover of cells and the highly ordered direction of cell migration, the intestine is an important model for the study of tissue stem cells.