Wnts encode secreted signals that regulate growth and cellular differentiation of various stem cells during embryonic development. No useful systems are available to express the Wnts in their biologically active form and to maintain the stem cells undifferentiated in vitro. We will develop efficient recombinant production applicable to any given Wnt. The biological activity of the produced Wnts will be tested in vitro with cellular readout systems and in early Xenopus embryo. The consortium members have identified that Wnts are important maintenance factors of stem cells in many different organ system. The Wnts, their receptors and signal transduction components will be screened in these systems. The biological activity of the recombinant Wnts will be tested in their capacity to keep the cells pluripotent in vitro and if they play a role in driving cells to specific cell lineages.