May be involved in regulating somitogenesis. First detected in stage X-XI blastoderms in the posterior epiblast. At stage 4, detected in the ectoderm around the primitive streak and in later stages, expressed exclusively within the mesoderm of the segmental plate. Expression continues here beyond trunk and tail bud formation and disappears by stage 26-28. By FGF-4, activin and retinoic acid.