cDNA cloning and distribution of the Xenopus follistatin-related protein

Recently, several proteins which have a follistatin module have been isolated. One of them, the follistatin-related protein (FRP), is encoded by TSC-36 (TGF-beta-stimulated clone 36) in mouse, originally isolated as a cDNA clone up-regulated by TGF-beta1 in mouse osteogenic MC3T3E1 cells. To determine the physiological role of FRP in early Xenopus embryonic development, we cloned the Xenopus FRP (xFRP) cDNA. The resulting cDNA clone was a secreted glycoprotein consisting of 299 amino acid residues with about 70% similarity to the mammalian and avian FRPs. Northern blotting analysis revealed that xFRP gene expression started at stage 10, the onset of gastrulation, gradually increased during the blastula and neurula stages and was sustained through the tail-bud stage. Whole-mount in situ hybridization analysis showed the localization of xFRP mRNAs in the Spemann organizer, notochord, neural floor plate, hypochord and somite. The similarities with the pattern of expression of Xenopus follistatin mRNA suggests that xFRP may play a role in neuralization.