Onset of apoptotic DNA fragmentation can precede cell elimination by days in the small intestinal villus

DNA fragmentation is a hallmark of apoptosis, and has been viewed as a short-lived process (< hour) that immediately precedes cell elimination. However, use of sensitive techniques like in situ end-labelling plus (ISEL+) has indicated that the period between the initiation of detectable fragmentation and cell elimination could be longer (days). To address this possibility, we used a model system of cell death and replacement, the murine small intestinal villus. Pulses of 5-bromo-2'-deoxyuridine were used to follow quantitatively cohorts of cells from their generation in the crypts to their elimination at the villus tips, resulting in a temporal 'yard-stick' where position on the villus indicated time before cell elimination; these data allowed a mathematical description of cell movement acid clearance. Combining these data with ISEL+ quantitation, enterocytes were found to commence and maintain DNA fragmentation 2-3 days before elimination, a phenomenon that likely has relevance to studies on apoptosis also in other systems.