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Open Biol 2016 Aug 01;68:. doi: 10.1098/rsob.150187.
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Nodal signalling in Xenopus: the role of Xnr5 in left/right asymmetry and heart development.

Tadjuidje E , Kofron M , Mir A , Wylie C , Heasman J , Cha SW .

Nodal class TGF-β signalling molecules play essential roles in establishing the vertebrate body plan. In all vertebrates, nodal family members have specific waves of expression required for tissue specification and axis formation. In Xenopus laevis, six nodal genes are expressed before gastrulation, raising the question of whether they have specific roles or act redundantly with each other. Here, we examine the role of Xnr5. We find it acts at the late blastula stage as a mesoderm inducer and repressor of ectodermal gene expression, a role it shares with Vg1. However, unlike Vg1, Xnr5 depletion reduces the expression of the nodal family member xnr1 at the gastrula stage. It is also required for left/right laterality by controlling the expression of the laterality genes xnr1, antivin (lefty) and pitx2 at the tailbud stage. In Xnr5-depleted embryos, the heart field is established normally, but symmetrical reduction in Xnr5 levels causes a severely stunted midline heart, first evidenced by a reduction in cardiac troponin mRNA levels, while left-sided reduction leads to randomization of the left/right axis. This work identifies Xnr5 as the earliest step in the signalling pathway establishing normal heart laterality in Xenopus.

PubMed ID: 27488374
PMC ID: PMC5008007
Article link: Open Biol
Grant support: [+]

Species referenced: Xenopus laevis
Genes referenced: fgf3 fgf8 foxi1 foxi2 gdf1 lefty mapk1 meis3 msgn1 nodal nodal1 nodal5.2 nodal5.4 odc1 pitx2 smad2 tbxt tek vegfa
Morpholinos: nodal5.4 MO1

Article Images: [+] show captions
References [+] :
Ang, A gene network establishing polarity in the early mouse embryo. 2004, Pubmed