Additional Author(s): David Bilder
Published on SDB CoRe: Mar 2 2013
Morphogenesis: Cell Movements; Cell Shape Changes; Cell/Tissue Polarity
The Germline: Oogenesis
Stage of Development: Oogenesis
Have you ever wondered how some eggs get their ellipsoid shape? It turns out that in the fruit fly, Drosophila melanogaster, the developing egg (follicle) begins as a sphere but acquires its ellipsoid shape over time. It's been observed that the follicle rotates around its elongating axis during the early phase of follicle elongation. This rotation is important to lay down oriented extracellular matrix (ECM) fibrils on the surface, in the direction of rotation. These ECM fibrils function as a molecular corset so the follicle is constrained to grow out in one axis but is permitted to grow out in the other. So instead of growing out evenly as a sphere, the fly uses this strategy to grow unevenly from a small sphere to a large ellipsoid!
The scientists who discovered the phenomenon of follicle rotation were able to dissect out live follicles from an adult female fruit fly and keep them alive for many hours. The video here uses transgenic flies that express indy-GFP (green), a cell membrane marker of the outer follicle cells, and Histone 2B-mRFP (red), a marker of cell nuclei. Stage 6 and stage 7 follicles can be seen rotating in opposite directions, whereas the stage 4 and stage 9 follicles on either side of them do not rotate. Fluorescence microscopy was used to acquire a time-lapse video every 5 minutes for 3 hours.
This movie was originally published in: Haigo, S.L., Bilder, D. Global tissue revolutions in a morphogenetic movement controlling elongation. Science, 2011, 331:1071-1074.
Bilder, D., Haigo, S.L. Expanding the morphogenetic repertoire: perspectives from the Drosophila egg. Dev Cell, 2012, 22:12-23.