Balancing act: investigating the coordinated mechanics of germband and amnioserosa in Drosophila morphogenesis

Abstract

In the series of morphogenetic events that are required for Drosophila development, some of the most dramatic are those that involve the coordinated movement of the germband and amnioserosa, two epithelia that remain contiguous through the first thirteen hours of morphogenesis until the amnioserosa’s death. The importance of the amnioserosa in ensuring the germband’s proper shape and position has been established, but its exact role as a signaling source and force generator and the balance between amnioserosal and germband forces are not fully understood. Pursuing this question from the germband side of the balance, a new angle-measurement method has yielded information from germband cell edges about the tensions and stresses acting during germband retraction. These results show that the amnioserosa pulls on the germband to produce cell and segment elongation, while the germband cell-edge tensions are polarized to resist elongation, acting in the same direction that they do during the preceding stage of germband extension. The degree of force anisotropy varies in different germband segments, indicating that a more detailed analysis of the entire germband is required to understand the amnioserosa-germband force balance. Other avenues of research support vertical germband polarization and the general picture of the amnioserosa as an essential player in morphogenesis, exerting forces on the germband that are instrumental in proper development.