We have characterized for the first time the mouse expression patterns of the three known members of the novel RGM gene family ('Repulsive Axonal Guidance molecules' A, B and C) by in situ hybridization. Both RGM A and B are mostly expressed in central nervous systems while RGM C is exclusively expressed in all striated muscle and in the myocardium. RGM A and B appear at every level of the developing neural axis, where they colocalize to a large extent in the mantle layer, although only RGM A appears in the neuroepithelium, and only RGM B in the peripheral nervous system. During development, both RGM A and B appear also in lung and in limb cartilage, while RGM B has additional expression domains in pancreas. (C) 2003 Elsevier B.V. All rights reserved.