Occluding Junctions are Master Regulators of Communication Between Stem Cells and Their Niche

Stem cells are essential for animal development and allow the maintenance and regeneration of tissues.  Stem cells retain the capability to divide and to develop into many types of adult cells throughout the lifetime of an organism.  Stem cell fate and behavior is often governed by signals derived from their local microenvironment, also known as the stem cell niche.  My lab has a longstanding interest in understanding how Cell-Cell junctions help shape stem cell niches and control stem cell behavior.  Our recent work had focused on the role of occluding junctions in regulating communication between the niche and the stem cells.  We study two different stem cell niche systems in Drosophila:  the hub cells in testes and the Posterior Signaling Centre in the lymph gland which is the key site for post embryonic hematopoiesis in flies.  Our work in both systems has identified key roles for modulation of occluding junctions in controlling niche homeostasis and shaping the signaling environment around the niche.  Moreover, in the context of the fly hematopoiesis, we show that occluding junctions are key regulators of the immune response.  Bacterial infection alters occluding junctions around the hemaotopoietic niche which is both necessary and sufficient to induce the immune response.  Taken together our results illustrate that occluding junctions are key regulators of stem cell niches and that this function is likely to be a central feature of many stem cell niches.