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 eliminati on. However, use of sensitive techniques like in situ end-labelling pl us (ISEL+) has indicated that the period between the initiation of det ectable fragmentation and cell elimination could be longer (days). To address this possibility, we used a model system of cell death and rep lacement, the murine small intestinal villus. Pulses of 5-bromo-2'-deo xyuridine were used to follow quantitatively cohorts of cells from the ir generation in the crypts to their elimination at the villus tips, r esulting in a temporal 'yard-stick' where position on the villus indic ated time before cell elimination; these data allowed a mathematical d escription of cell movement acid clearance. Combining these data with ISEL+ quantitation, enterocytes were found to commence and maintain DN A fragmentation 2-3 days before elimination, a phenomenon that likely has relevance to studies on apoptosis also in other systems.