Embryonic expression and extracellular secretion of Xenopus slit

The slit genes have recently been found to encode proteins with a conserved chemorepulsive activity for axons in invertebrates and vertebrates. We hav e determined the expression pattern of a slit gene in Xenopus embryos. In t he neural tube, slit is expressed at the ventral and dorsal midlines, and t he motor neurons. slit is also expressed in a changing pattern in the retin a. The full-length Xenopus Slit protein is secreted extracellularly, wherea s its receptor Roundabout can not be secreted. Using a myc-tagged secreted Slit protein, we confirmed the binding of Slit to Roundabout expressed on t he cell surface. These results confirm Slit-Roundabout interactions and the biochemical prop erties of Slit and Roundabout proteins, and further support the idea that S lit may guide axon projections in multiple regions of the embryo. (C) 2000 IBRO. Published by Elsevier Science Ltd.