Distinct and cooperative roles of mammalian Vg1 homologs GDF1 and GDF3 during early embryonic development

Vgl, a member of the TGF-beta superfamily of ligands, has been implicated in the induction of mesoderm, formation of primitive streak, and leftright patterning in Xenopus and chick embryos. In mice, GDF1 and GDF3 - two TGF-beta superfamily ligands that share high sequence identity with Vgl - have been shown to independently mimic distinct aspects of Vgl's functions. However, the extent to which the developmental processes controlled by GDFI and GDF3 and the underlying signaling mechanisms are evolutionarily conserved remains unclear. Here we show that phylogenetic and genomic analyses indicate that Gdf] is the true Vg1 ortholog in mammals. In addition, and similar to GDFI, we find that GDF3 signaling can be mediated by the type I receptor ALK4, type 11 receptors ActRIIA and ActRIIB, and the co-receptor Cripto to activate Smaddependent reporter genes. When expressed in heterologous cells, the native forms of either GDF I or GDF3 were incapable of inducing downstream signaling. This could be circumvented by using chimeric constructs carrying heterologous prodomains, or by co-expression with the Furin proprotein convertase, indicating poor processing of the native GDFI and GDF3 precursors. Unexpectedly, co-expression withNodal - another TGF-beta superfamily ligand involved in mesoderm formation - could also expose the activities of native GDFI and GDF3, suggesting a potentially novel mode of cooperation between these ligands. Functional complementarity between GDFI and GDF3 during embryonic development was investigated by analyzing genetic interactions between their corresponding genes. This analysis showed that Gdf1(-/-);Gdf3(-/-) compound mutants are more severely affected than either Gdfl_ (_) or Gdf3(-/-) single mutants, with defects in the formation of anterior visceral endoderm and mesoderm that recapitulate VgI loss of function, suggesting that GDFI and GDF3 together represent the functional mammalian homologs of Vgl. (c) 2007 Elsevier Inc. All rights reserved.