Hindsight controls border cell migration, Armadillo expression and polar cell fate in the ovary

MARIANA MELANI; DENISE J. MONTELL

Huston, Texas, USA

Conferencia; 2006 Drosophila Research Conference; 2006

Connections between cells forming an epithelium must fulfill a two-fold role. They must be stable enough to give strength and resilience to the tissue but also, have to be dynamic and capable of fast remodeling to allow changes in shape and growth in response to developmental cues. In the ovary, each egg chamber is composed of 16 germ line-derived cell surrounded by a follicle cell epithelium. As the egg chamber develops, the epithelial cells not only undergo dramatic changes in shape but also, a group of 6 to 8 cells (border cells) delaminate from the epithelium and migrate through the germline towards the oocyte. This process cannot be viewed as a typical epithelial to mesenchymal transition since the border cell cluster maintains epithelial characteristics through out migration. Hindsight (HNT) is a transcription factor required to maintain epithelial integrity during several morphological changes that occur during embryo development. We found that hnt is expressed in the follicle cell epithelium, including the border cells, but not the polar and stalk cells. hnt is required for border cell migration and for the epithelial morphological changes that are associated with egg chamber growth. Adherens junction proteins such as Armadillo are enriched in hnt mutant clones. Overexpression of hnt in the border cells also leads to border cell migration defects, but in this case Arm is decreased and the cluster loses integrity. These results indicate that HNT might be required to maintain appropriate levels of adherens junctions allowing epithelial integrity and plasticity at the same time. We also found that hnt is a target of Eyes absent (EYA). HNT expression is undetectable in eya mutant clones, and eya misexpression leads to HNT upregulation. Misexpression of hnt in the polar cells, which recruit the border cells, leads to a variety of phenotypes including loss of polar cells and fused egg chambers, suggesting that hnt is one essential target of EYA in repressing polar cell fate.