1. Department of Zoology, Unviersity of Toronto, 25 Harbord Street, Toronto, Ontario M5S 3G5, Canada
2. These authors contributed equally to this work

Correspondence to: Dorothea Godt^1,2 Correspondence and request for materials should be addressed to D.G. (e-mail: Email: dgodt@zoo.utoronto.ca) or U.T.(e-mail: Email: utepass@zoo.utoronto.ca).

Abstract

In a Drosophila follicle the oocyte always occupies a posterior position among a group of sixteen germline cells. Although the importance of this cell arrangement for the subsequent formation of the anterior–posterior axis of the embryo is well documented^{1, 2, 3, 4}, the molecular mechanism responsible for the posterior localization of the oocyte was unknown. Here we show that the homophilic adhesion molecule DE-cadherin^{5, 6, 7} mediates oocyte positioning. During follicle biogenesis, DE-cadherin is expressed in germline (including oocyte) and surrounding follicle cells, with the highest concentration of DE-cadherin being found at the interface between oocyte and posterior follicle cells. Mosaic analysis shows that DE-cadherin is required in both germline and follicle cells for correct oocyte localization, indicating that germline–soma interactions may be involved in this process. By analysing the behaviour of the oocyte in follicles with a chimaeric follicular epithelium, we find that the position of the oocyte is determined by the position of DE-cadherin-expressing follicle cells, to which the oocyte attaches itself selectively. Among the DE-cadherin positive follicle cells, the oocyte preferentially contacts those cells that express higher levels of DE-cadherin. On the basis of these data, we propose that in wild-type follicles the oocyte competes successfully with its sister germline cells for contact to the posterior follicle cells, a sorting process driven by different concentrations of DE-cadherin. This is, to our knowledge, the first in vivo example of a cell-sorting process that depends on differential adhesion mediated by a cadherin.

1. Department of Zoology, Unviersity of Toronto, 25 Harbord Street, Toronto, Ontario M5S 3G5, Canada
2. These authors contributed equally to this work

Correspondence to: Dorothea Godt^1,2 Correspondence and request for materials should be addressed to D.G. (e-mail: Email: dgodt@zoo.utoronto.ca) or U.T.(e-mail: Email: utepass@zoo.utoronto.ca).