ABSTRACT
The Xenopus Vgl gene encodes a maternal mRNA that is localized to the vegetal hemisphere of both oocytes and embryos and encodes a protein related to the TGF-β family of small secreted growth factors. We have raised antibodies to recombinant Vgl protein and used them to show that Vgl protein is first detected in stage IV oocytes and reaches maximal levels in stage VI oocytes and eggs. During embryogenesis, Vgl protein is synthesized until the gastrula stage. The embryonically synthesized Vgl protein is present only in vegetal cells of an early blastula. We find that Vgl protein is glycosylated and associated with membranes in the early embryo. Our results also suggest that a small proportion of the full-length Vgl protein is cleaved to give a small peptide of Mr= —17×103. These results support the proposal that the Vgl protein is an endogenous growth-factor-like molecule involved in mesoderm induction within the amphibian embryo.
