Shown are representative images of diagnostic histopathology and radiographic studies in patients with telomere-mediated disease (A–D) and 5-ethynyl-2′-deoxyuridine (EdU) incorporation detected in corresponding mouse tissues (E–H). The estimated turnover rate of more than 90% of cells is indicated for each pair of images. (A) Photomicrograph of a bone marrow biopsy showing an acellular marrow replaced by adipose tissue with only remnants of hematopoiesis, taken from an individual with aplastic anemia. Image reproduced with permission from Annual Reviews of Genomics and Human Genetics (31). (B) Histopathology of a duodenal biopsy from a patient with telomere-mediated enteropathy shows profound villous atrophy. Image reproduced with permission from Aging Cell (53). (C) Abdominal CT scan image from a patient with liver cirrhosis, as evidenced by the nodular liver surface, the caudate lobe hypertrophy, and splenomegaly. (D) Lung windows of a chest CT scan from a carrier of the telomerase mutation show classic basilar honeycombing changes pathognomonic for IPF. (E) Flow cytometry plot of EdU incorporation in the bone marrow after a short (2-hour) pulse, showing that nearly one-third of the cells have undergone division. (F) Immunohistochemistry of intestinal section after a EdU pulse (5 days) shows that nearly all enteric epithelial cells are positively labeled (brown). (G) Brown staining shows EdU-labeled hepatocytes after EdU labeling (14 days). (H) Image of terminal bronchiole shows EdU-positive lung epithelial cells (red) identified by the Clara cell antigen (green) after 14 day label.