Germband extension (GBE) in the early <i>Drosophila </i>embryo provides a simple system in which to study convergence and extension, a type of tissue remodelling common in development. During GBE the embryonic trunk (“germband”) extends in the anterior-posterior (AP) axis, and narrows in the dorso-ventral (DV) axis. I have quantitatively analysed cell and tissue behaviours during GBE. Our collaborators have developed novel algorithms to measure the continuous impact of cell intercalation and cell shape change on tissue deformation. Here I apply these algorithms to describe the behaviours contributing to GBE. I find that wild type embryos not only undergo cell intercalation, but also cell shape change which accounts for up to 50% of the extension rate during the fast phase of GBE. I find that this cell shape change is elevated in AP patterning mutants that have a defect in cell intercalation, and that this elevation accounts for the initial rapid pulse of extension in these mutants. Regional analysis of these cell behaviours in wild type and AP patterning mutants indicate that cell intercalation is regionally autonomous, but that cell shape change is controlled at a more global level. An external force may be present during early GBE, stretching cells in the AP axis if they fail to intercalate properly. Additionally, I have examined the impact that other morphogenetic movements of gastrulation have on GBE. Mutant analysis shows that the ventral furrow affects the rate but not overall extent of tissue deformation, while the posterior midgut invagination appears to be required only for correct displacement of the tissue as it deforms, and not for tissue deformation itself, at least during early GBE. Thus, the amount of tissue extension, the rate at which it occurs, and the tissue displacement by which it is accommodated are separable phenomena.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:597164 |
| Date | January 2009 |
| Creators | Butler, L. C. |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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