Repulsive axon guidance molecule Sema3A inhibits branching morphogenesis of fetal mouse lung

Semaphorin III/collapsin-1 (Sema3A) guides a specific subset of neuronal gr owth cones as a repulsive molecule. In this study, we have investigated a p ossible role of non-neuronal Sema3A in lung morphogenesis. Expression of mR NAs of Sema3A and neuropilin-1 (NP-1), a Sema3A receptor, was detected in f etal and adult lungs. Sema3A-immunoreactive cells were found in airway and alveolar epithelial cells of the fetal and adult lungs. Immunoreactivity fo r NP-1 was seen in fetal and adult alveolar epithelial cells as well as end othelial cells. Immunoreactivity of collapsin response mediator protein CRM P (CRMP-2), an intracellular protein mediating Sema3A signaling, was locali zed in alveolar epithelial cells, nerve tissue and airway neuroendocrine ce lls. The expression of CRMP-2 increased during the fetal, neonate and adult periods, and this pattern paralleled that of NP-1. In a two-day culture of lung explants from fetal mouse lung (E11.5), with exogenous Sema3A at a do se comparable to that which induces growth cone collapse of dorsal root gan glia neurons, the number of terminal buds was reduced in a dose-dependent m anner when compared with control or untreated lung explants. This decrease was not accompanied with any alteration of the bromodeoxyuridine-positive D NA-synthesizing fraction. A soluble NP-1 lacking the transmembrane and intr acellular region, neutralized the inhibitory effect of Sema3A. The fetal lu ng explants from neuropilin-1 homozygous null mice grew normally in vitro r egardless of Sema3A treatment, These results provide evidence that Sema3A i nhibits branching morphogenesis in lung bud organ cultures via NP-I as a re ceptor or a component of a possible multimeric Sema3A receptor complex. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.