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First published online September 7, 2007

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Rabs traffic polarity signals to oocyte

Rab GTPases are regulators of membrane trafficking that play many important developmental roles. In this issue of Development, two papers describe their involvement in Drosophila oogenesis. In the first paper, Bogard and colleagues report that Rab11 maintains the balance between self-renewal and differentiation of the germline stem cells (GSCs) of the Drosophila ovary (see p. 3413). Two or three GSCs lie at the anterior of the germarium and are attached by adherens junctions to niche cap cells, which secrete short-range signals that maintain GSC identity. When a GSC divides, one daughter remains attached to the niche cap cells but the other (the cystoblast) is displaced and consequently differentiates, eventually producing a polarized oocyte and 15 nurse cells. Rab11, Bogard and colleagues report, is strongly expressed in GSCs and cystoblasts in discrete dots. These Rab11-positive recycling endosomes are tightly associated with the fusome, a spectrin-rich structure that controls the axis of GSC division by anchoring the mitotic spindle to the anterior cortex of the GSC. The recycling endosomes also contain the adherens junction component E-cadherin, report the researchers. In clonal inactivation experiments, Bogard et al. show that rab11-null GSCs detach from the niche cap cells, contain displaced fusomes and undergo abnormal cell division, all of which leads to GSC loss and early arrest of GSC differentiation. Furthermore, E-cadherin accumulates in reduced amounts on the surface of rab11-null GSCs. The researchers propose, therefore, that Rab11 maintains GSC identity through polarized trafficking of E-cadherin during early oogenesis in Drosophila. In the second paper, Januschke and colleagues reveal that Rab6-mediated protein secretion helps to establish oocyte polarity later during oogenesis (see p. 3419). The researchers show that Rab6 localizes to Golgi and Golgi-derived membranes and interacts with Bicaudal D, a protein involved in oocyte axis determination. Additional experiments indicate that Rab6 function is also required for other aspects of oocyte polarity determination, such as the correct localization of oskar mRNA and of microtubule plus-ends at the posterior of the egg. Together, these two papers establish the importance of Rab-mediated membrane trafficking during oogenesis.

Related articles in Development:

Rab11 maintains connections between germline stem cells and niche cells in the Drosophila ovary

Nicholas Bogard, Lan Lan, Jiang Xu, and Robert S. Cohen
Development 2007 134: 3413-3418. [Abstract] [Full Text]  

Rab6 and the secretory pathway affect oocyte polarity in Drosophila

Jens Januschke, Emmanuelle Nicolas, Julien Compagnon, Etienne Formstecher, Bruno Goud, and Antoine Guichet
Development 2007 134: 3419-3425. [Abstract] [Full Text]  

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Related articles in Development Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Search for Related Content