SEQUENTIAL EXPRESSION AND DIFFERENTIAL LOCALIZATION OF I-FIMBRIN, L-FIMBRIN, AND T-FIMBRIN DURING DIFFERENTIATION OF THE MOUSE INTESTINE AND YOLK-SAC

During the differentiation of the intestine epithelium, three cytoskel etal proteins, villin, fimbrin, and myosin I, are sequentially express ed and localized to the apical membrane. Recently, we found that in th e adult mouse and human, three fimbrin isoforms are expressed in a cel l specific manner. I-fimbrin is expressed by intestine and kidney epit helial cells, L-fimbrin is expressed by leukocytes and many tumors, wh ile T-fimbrin is expressed by various cells and tissues, Because non-i ntestinal isoforms of fimbrin could be expressed early in development, the expression of fimbrin isoforms during days 10.5 to 16.5 of intest ine development was investigated. By immunofluorescence microscopy, T- fimbrin was detected in the early stages of intestinal epithelial cell differentiation until day 14.5 and was localized predominantly at the apical surface. L-fimbrin was also detected during this period but it was localized to the basal surface of the epithelium instead of the a pical surface. By day 16.5 no L or T-fimbrin was detected in the epith elium. I-fimbrin was first detected at day 14.5 and a brush border-lik e apical localization pattern was seen by day 16.5. Unlike the intesti nal cells, the visceral endoderm expressed I, L, and T-fimbrin through out the period examined, with the level of I-fimbrin increasing as tim e progresses. L-fimbrin was more evident at the earlier stage than at the later stage of the development. Collectively, these results sugges t that three fimbrin isoforms play different roles during epithelial c ell differentiation. T- and I-fimbrin expression could be critical for the formation and extension of the microvilli whereas L-fimbrin may p lay a role in controlling cell adhesion. (C) 1995 Wiley-Liss, Inc.