Molecular cloning, expression, and activity of zebrafish semaphorin Z1a

Semaphorins/collapsins are a large family of secreted and cell surface mole cules that are thought to guide growth cones to their targets. Although som e members are clearly repulsive to specific growth cones in vitro, the in v ivo role of many of these molecules in vertebrate embryos is still unclear. As a first step towards clarifying the in vivo role of semaphorins/collaps ins, we analyzed semaZ1a in the simple and well-characterized zebrafish emb ryo. SemaZ1a is a secreted molecule that is highly homologous to Sema III/D /collapsin-1, and it can collapse chick dorsal root ganglion growth cones i n vitro. It is expressed in highly specific patterns within the developing embryo, which suggests that it influences outgrowth by a variety of growth cones including those of the posterior lateral line ganglion. Consistent wi th this hypothesis, the peripherally extending growth cones of posterior la teral line neurons retract and partially collapse during normal outgrowth, (C) 1999 Elsevier Science Inc.