Vg1 is an essential signaling molecule inXenopusdevelopment

Abstract

Xenopus Vg1, a transforming growth factor ␤ (Tgf␤) family member, was one of the first maternally localized mRNAs identified in vertebrates. Its restriction to the vegetal pole of the egg made it the ideal candidate to be the mesoderm-inducing signal released by vegetal cells, but its function in vivo has never been resolved. We show that Vg1 is essential for Xenopus embryonic development, and is required for mesoderm induction and for the expression of several key Bmp antagonists. Although the original Vg1 transcript does not rescue Vg1-depleted embryos, we report that a second allele is effective. This work resolves the mystery of Vg1 function, and shows it to be an essential maternal regulator of embryonic patterning.

Activin/Nodal signalling before implantation: setting the stage for embryo patterning

“…Consistent with this view, the expression of a reporter transgene for the autoregulatory Smad2/3-dependent Nodal enhancer ASE, called ASE-YFP, was found to be maintained up to embryonic day (E)4.5 in Nodal 2/2 embryos [23]. In other animal models, there is broad evidence of another TGF-b family member acting upstream of early Nodal expression [58][59][60][61][62]. Vg1 in Xenopus is the prototype of a maternally deposited TGF-b-related ligand that is required to form the organizer and the mesoderm [58], and Vg1-related molecules of maternal origin identified in zebrafish and in sea-urchin appear to have similar properties [59][60][61].…”

“…In other animal models, there is broad evidence of another TGF-b family member acting upstream of early Nodal expression [58][59][60][61][62]. Vg1 in Xenopus is the prototype of a maternally deposited TGF-b-related ligand that is required to form the organizer and the mesoderm [58], and Vg1-related molecules of maternal origin identified in zebrafish and in sea-urchin appear to have similar properties [59][60][61]. Gdf1 and Gdf3 in the mouse are the two factors identified as Vg-1-related, however, as we saw, indications are that it is as Nodal partner and BMP antagonist that they are playing a role in the regulation of Activin/Nodal signalling and Nodal expression, not as inducers.…”

T-cell internal antigen 1 counteracts somatic RNA degradation during early Xenopus embryogenesis

“…Although the LE of gdf1 mRNA does not mediate somatic degradation (Koebernick et al, 2010), gdf1 transcript levels decrease during MZT (Birsoy et al, 2006;Table S1-S4). Thus, gdf1 mRNA might contain miR target sites outside of the LE, or gdf1 mRNA is degraded by other mechanism than miR-mediated decay, which endogenous Tia1 seems to counteract.…”

Forming and Interpreting Gradients in the Early Xenopus Embryo

“…These molecules fell into two classes. The first comprised members of the transforming growth factor type b (TGF-b) family, including activin (Albano et al 1990;Asashima et al 1990;Smith et al 1990), Vg1 (Weeks and Melton 1987;Birsoy et al 2006), derrière (Sun et al 1999), and the Xenopus nodal-related proteins Xnr1, -2, -4, -5, and -6 (Jones et al 1995;Joseph and Melton 1997;Takahashi et al 2000). The second included members of the fibroblast growth factor family, such as FGF2 (Kimelman and Kirschner 1987;Slack et al 1987) and FGF4 (Isaacs et al 1992).…”