Analysis of Transforming Growth Factor (ss) Family Cleavage Products Secreted Into the Blastocoele of Xenopus laevis Embryos

The two arms of the Transforming Growth Factor (sic) (Tgf(sic)) superfamily, represented by Tgf(sic)/Nodal or Bone morphogenetic protein (Bmp) ligands, respectively, play essential roles in embryonic development and adult homeostasis. Members of the Tgf(sic) family are made as inactive precursors that dimerize and fold within the endoplasmic reticulum. The precursor is subsequently cleaved into ligand and prodomain fragments. Although only the dimeric ligand can engage Tgf(sic) receptors and activate downstream signaling, there is growing recognition that the prodomain moiety contributes to ligand activity. This article describes a protocol that can be used to identify cleavage products generated during activation of Tgf(sic) precursor proteins. RNA encoding Tgf(sic) precursors are first microinjected into X. laevis embryos. The following day, cleavage products are collected from the blastocoele of gastrula stage embryos and analyzed on Western blots. This protocol can be completed relatively quickly, does not require expensive reagents and provides a source of concentrated Tgf(sic) cleavage products under physiologic conditions.