Egg ligation alters the Bcd protein gradient and segmentation gene expression in embryos of Drosophila

A concentration gradient of the anterior morphogen Bicoid (Bcd) plays a key role in the specification of cell fates in the early Drosophila embryo. We found that introduction of a membrane barrier across the embryo results in increased levels of Bcd protein on the anterior side of the barrier and decreased levels on the posterior side, consistent with a blockage in the postulated anterior-to-posterior translocation of Bcd protein. The expression patterns of downstream segmentation genes were in large part consistent with their regulation by the Bcd morphogen. However, some aspects of the patterns did not correlate with the altered Bcd distribution, suggesting that other morphogens also regulate the anteroposterior pattern. Our results suggest that axial translocation of morphogens is critical for establishing a well-proportioned body plan.