Induction of the mammalian node requires Arkadia function in the extraembryonic lineages

Abstract

The early mammalian embryo is patterned by signals emanating from extraembryonic and embryonic signalling centres, most notably the anterior visceral endoderm (AVE) and the node, respectively. The AVE is responsible for anterior development, whereas further axis specification depends on the node, the equivalent of Spemann's organizer. Formation of the node, at the anterior primitive streak, depends on expression of the transcription factor HNF3beta (ref. 4). However, both the source and the nature of the signals responsible for inducing the node have been unknown. Here we describe a recessive lethal mutation, arkadia, generated using gene-trap mutagenesis. Mutant embryos establish an AVE but fail to maintain anterior embryonic structures and lack a node. The mutation has disrupted the Arkadia gene, which encodes a putative intracellular protein containing a RING domain. Arkadia is essential for HNF3beta expression in the anterior primitive streak. Analysis with chimaeras, however, shows that Arkadia functions within extraembryonic tissues, revealing that these are required to induce the node. Furthermore, our experiments show that Arkadia interacts genetically with the transforming growth factor (TGF)beta-like factor Nodal, implying that Nodal mediates the function of Arkadia in node induction.

The Wnt co-receptors Lrp5 and Lrp6 are essential for gastrulation in mice

“…As Cer1 and Leftb are Nodal antagonists, and Drap1 is probably a transcriptional corepressor for Nodal, these defects appear to be a consequence of increased levels of Nodal signaling. In support of this idea, mutant embryos with the loss-of-function of two Nodal signaling modulators, Foxh1 and arkadia (Rnf111 -Mouse Genome Informatics), fail to establish an anterior primitive streak/node and its derivatives (Hoodless et al, 2001;Yamamoto et al, 2001;Episkopou et al, 2001). Finally, either conditional loss-of-function of Smad2, a Nodal effector, in the epiblast or decreased Nodal signals in the primitive streak results in a specific loss of the ADE and prechordal mesoderm (Vincent et al, 2003).…”

The SMAD2/3 corepressor SNON maintains pluripotency through selective repression of mesendodermal genes in human ES cells

“…Genetic evidence in mice favors a role for Arkadia because Arkadia-null mutant embryos succumb to severe gastrulation defects due to impaired Nodal/Smad2/3 signaling (Episkopou et al 2001;Mavrakis et al 2007). One interpretation of this phenotype is that in the absence of Arkadia, SnoN associates with crucial Nodal/Smad2/3 target genes, preventing their activation.…”

The zinc-finger protein CNBP is required for forebrain formation in the mouse

“…Other genes, such as Lim1, Otx2,Nodal,Smad2,Foxh1,Arkadia,Hex,Oto,Dkk1,Hesx1, Nog and Chrd, are also essential for murine head development (Episkopou et al, 2001;Hoodless et al, 2001;Shawlot et al, 1999;Yamamoto et al, 2001). However, the brain defects are considerably different among these mutants.…”

“…Similarly, gene knockout techniques have proved to be powerful tools for identifying the molecular regulation of many developmental processes. For example, genes such as Lim1 (Lhx1 -Mouse Genome Informatics) (Shawlot and Behringer, 1995), Otx2 (Matsuo et al, 1995;Acampora et al, 1995), Smad2 (Waldrip et al, 1998;Nomura and Li, 1998), Nodal , Foxh1 (Hoodless et al, 2001;Yamamoto et al, 2001), Arkadia (Episkopou et al, 2001), Hex (Martinez Barbera et al, 2000), Oto (Zoltewicz et al, 1999), Hesx1 (Dattani et al, 1998) and Dkk1 (Mukhopadhyay et al, 2001;Shawlot et al, 1999;Yamamoto et al, 2001) have been demonstrated to be essential for normal head development by targeted gene disruption in mice. However, studies using such knockout techniques are limited to known genes.…”