Juan A. Larrain, Ph.D.

Research

Our main interest is to study cell-cell signaling during the early development of the vertebrate embryo. We use Xenopus laevis embryos as a model of study. Spemann s Organizer is one of the most classical models of cell-cell signaling regulation during early development.

After an analysis of the amino-acidic sequences of the factors secreted by the Organizer (Chordin, Follistatin, Sonic hedgehog, Cerberus, Noggin, etc) we found that all contain a putative heparin binding domain (HBD), indicating that all these molecules probably interact with Heparan sulphate Proteoglycans (HSPG). Our hypothesis is that HSPG are necessary to establish an extracellular gradient of the different antagonists or growth factors secreted by the Organizer. We propose that this function of HSPG is fundamental for the correct establishment of dorso-ventral patterning of the three germ layers. To understand the role of HSPG in Organizer function we are currently studying their function in the activity of two Spemann s Organizer molecules: Chordin and Sonic Hedgehog (Shh). For these we are studying the effect of point mutations in the putative HBD of Chordin and Shh, we are testing the activity of the mutants by microinjection of synthetic mRNA in Xenopus laevis embryos. We are also trying to identify the specific Chordin and Shh interacting HSPG using affinity columns.

The understanding of the cell-cell signaling pathways that regulate the early development of the vertebrate embryo are each day more important in view of the progress on the isolation of stem cells from embryos and adult tissues. Unraveling the mechanism used by the embryo to determine the different cell fates will provide us with a very valuable information that can be used for the in vitro differentiation of stem cells for therapeutic uses. We would like to apply what we have learned from Spemann s Organizer in the manipulation of pluripotential cells isolated from umbilical cords. This experimental approach will allow us to study the bioethics implications of our research.