Xenbase Image ID: 137032

Fig. 1. A comparison of the axolotl and Xenopus mesendoderm GRNs. (a) The axolotl mesendoderm GRN and (b) the simplified Xenopus mesendoderm GRN. Arrow and bar heads represent, respectively, activation and repression. The ‘A’ indicates that an input is, in Boolean terms, an ‘AND’ gate. The ‘S’ indicates a synergy between the two transcription factors, i.e. β-catenin activates Nodal1 and this activation is enhanced by Nodal autoregulation. Otherwise, multiple inputs consisting of only one type (repression or activation) correspond to an ‘OR’ gate. When both types are present, the repression and activation inputs are treated as two ‘OR’ gates coupled by an ‘AND’ gate. Red lines show interactions which are the same in both networks and blue lines show those which differ. In (b) solid lines indicate experimentally verified links and dashed lines indicate links which are inferred from the Xenopus mesendoderm network, and which need to be verified experimentally. (c) Table summarising the main differences between the axolotl and Xenopus mesendoderm GRNs. Row 1: At least 6 Nodal genes are found in Xenopus, compared with 2 Nodal genes in axolotl. Row 2: There are seven Mix genes in Xenopus and one Mix gene in axolotl. Row 3: VegT acts to activate expression of Nodal, Mix and Brachyury in Xenopus, but in axolotl VegT does not activate these genes. Row 4: Siamois is a gene found in Xenopus but not axolotl. Row 5: In Xenopus, β-catenin acts in two different ways on Nodal: β-catenin enhances Nodal autoregulation of Xnr1 and Xnr2, and the expression of Xnr5 and Xnr6 is activated by β-catenin in the presence of VegT. In axolotl, Nodal1 can be activated by β-catenin alone and we also assume that it can enhance Nodal autoregulation. Row 6: Mix and Brachyury mutually repress each other in Xenopus, but, in axolotl, Mix is required for the expression of Brachyury. (For interpretation of the references to colour in this figure caption, the reader is referred to the web version of this paper.) Image published in: Brown LE et al. (2014) © 2014 The Authors. This image is reproduced with permission of the journal and the copyright holder. This is an open-access article distributed under the terms of the Creative Commons Attribution license Larger Image Printer Friendly View

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