Meeting Abstract
P3.92 Tuesday, Jan. 6 Actin polymerization underlies the postprandial lengthening of the pythons microvilli TEW, Whitney Y.*; SECOR, Stephen M.; University of Alabama; University of Alabama wytew@bama.ua.edu
Pythons experience with feeding dramatic upregulation of intestinal function that appears to be explained in part by the unprecedented lengthening of their intestinal microvilli. Within 24 hours after feeding, the microvilli have increased in length by as much as 5-fold. This increase in length and surface area matches the postprandial increase in nutrient transporter and enzyme activities. We hypothesized that an underlying mechanism of microvillus growth is the rapid polymerization of filamentous actin (F-actin), the internal skeleton of the microvilli, from cytoplasmic globular actin (G-actin). To demonstrate the postprandial mobilization of G-actin and the formation of F-actin with microvillus lengthening, we labeled with fluorescent probes both G-actin (DNase 1) and F-actin (phalloidin) of the intestinal epithelium of fasted and fed Burmese pythons. Fasted pythons exhibited a high concentration of cytoplasmic G-actin, whereas for fed pythons, G-actin concentrations were less and F-actin was highly concentrated at the brushborder membrane. To experimentally test the role of actin polymerization in postprandial microvillus growth, we infused either cytochalasin D, an inhibitor of actin polymerization, or DMSO, a control, into the intestinal lumen of digesting pythons. We observed a significant reduction (40-50%) in the length of the microvilli following 24 hours of infusion with cytochalasin D compared to snakes infused with DMSO or those fed without infusion. In addition to being shorter, microvilli exposed to cytochalasin D were irregular in shape and bent. We suspect that feeding triggers the mobilization of G-actin molecules and other cytoskeletal proteins from the cytoplasm to rapidly lengthen the microvilli. Upon the completion of digestion, these steps are apparently reversed to shorten the microvilli.
