The proteins mediate adhesion between germ cells and follicle cells in the ovary, so Xie reasoned that they might be involved in anchoring the GSCs to cells at the distal tip of the ovary, called cap cells. Sure enough, DE-cadherin and Armadillo proteins colocalize in narrow strips between the cap cells and the GSCs.
Genetics suggests that this localization reflects function. Within one week of inducing expression of either a deletion mutant or a weak allele of DE-cadherin, over half of the GSCs left their niche, implying that adhesion is required for GSC maintenance. Similar results followed with armadillo.
Based on the work of others, Xie believes that DE-cadherin and Armadillo (or its mammalian homologue β-catenin) function in a similar manner in a number of other stem cell niches. But they may not act alone. Xie and colleagues found that if primordial germ cells—which are destined to become GSCs—lack DE-cadherin, they are far less likely to be recruited into the stem cell niches, but they do occasionally make it there. This means that DE-cadherin is important for the recruitment of GSCs to their niche as well as for their maintenance, but it also implies that additional recruiting mechanisms are at work. ▪