Netrins, axon guidance cues in the CNS, have also been detected in epithelial tissues. In this study, using the embryonic pancreas as a model system, we show that Netrin-1 is expressed in a discrete population of epithelial cells, localizes to basal membranes, and specifically associates with elements of the extracellular matrix. We demonstrate that alpha6beta4 integrin mediates pancreatic epithelial cell adhesion to Netrin-1, whereas recruitment of alpha6beta4 and alpha3beta1 regulate the migration of CK19+/PDX1+ putative pancreatic progenitors on Netrin-1. These results provide evidence for the activation of epithelial cell adhesion and migration by a neural chemoattractant, and identify Netrin-1/integrin interactions as adhesive/guidance cues for epithelial cells.

Collagens have been shown to influence the survival and function of cultured ␤-cells; however, the utilization and function of individual collagen receptors in ␤-cells is largely unknown. The integrin superfamily contains up to five collagen receptors, but we have determined that ␣ 1 ␤ 1 is the primary receptor utilized by both fetal and adult ␤-cells. Cultured ␤-cells adhered to and migrated on collagen type IV (Col-IV), and these responses were mediated almost exclusively by ␣ 1 ␤ 1 . The migration of cultured ␤-cells to Col-IV significantly exceeded that to other matrix components suggesting that this substrate is of unique importance for ␤-cell motility. The interaction of ␣ 1 ␤ 1 with Col-IV also resulted in significant insulin secretion at basal glucose concentrations. A subset of ␤-cells in developing islets was confirmed to express ␣ 1 ␤ 1 , and this expression co-localized with Col-IV in the basal membranes of juxtaposed endothelial cells. Our findings indicate that ␣ 1 ␤ 1 and Col-IV contribute to ␤-cell functions known to be important for islet morphogenesis and glucose homeostasis.

Using human embryonic stem cells (hESCs), we describe a novel method for the rapid derivation and enrichment of cells that are comparable to primordial germ cells (PGCs) and Sertoli cells. The methodology described is based on modest changes to the growth conditions commonly used to expand hESCs and does not require genetic manipulation or complex three-dimensional culture. Remarkably, we have determined that simply reducing the size of cultured ESC colonies and manipulating the number of feeding cycles, results in the rapid emergence of cells that are comparable to migratory PGCs. Importantly, these cells can be monitored and purified on the basis of the expression of the chemokine receptor CXCR4. Under more stringent differentiating conditions these cells mature and upregulate the expression of specific germ cell markers. Importantly, this process is accompanied by the development of Sertoli-like support cells. Such cells normally provide trophic support and immunoprotection to developing germ cells and may have significant clinical utility in the prevention of graft rejection. The putative Sertoli-germ cell cocultures generated in this study may ultimately be developed to study and manipulate interactions and processes involved in human gametogenesis.