Xenbase Image ID: 153582

Figure 3. Relay of L/R Information from the Node to the LPM and Establishment of Side-Specific Gene Expression in the LPM In the chick, the Cerberus-related gene Car (indicated in red) is initially expressed bilaterally in the anterior region of the embryo, including the cells immediately adjacent to the node (A). At stage 5, Car begins to fade on the right and it is maintained in the left, concomitant with the appearance of lefty-1 expression (in green) in the left side of the node and midline, and of Nodal (in purple) in a left domain adjacent to lefty-1 (see detail in [A]). Left and right sides are as indicated in (A). By stage 7- (B), Car is completely absent from the right paraxial mesoderm, and in the left its expression coincides with the appearance of a second Nodal domain in the LPM; the medial domains of lefty-1 and Nodal also expand anteriorly at this stage as the node regresses. At stage 7 (C), BMPs (in light purple) are expressed bilaterally in the LPM, and the second domain of Nodal (in purple) consolidates in the cells that also express Car (in red). Nodal represses SnR (in orange) on the left side, so that Pitx2 (in light blue) can be expressed. The lower panel in (C) shows a scheme of the cascade of negative interactions that establishes side-specific gene expression in the LPM (see main text for details). Briefly, Car protein on the left side antagonizes the repression of Nodal transcription by BMPs. In turn, Nodal represses SnR, which is itself a repressor of Pitx2, so that SnR is expressed on the right and Pitx2 in the left LPM. The green arrow indicates positive autoregulation, since Nodal activates its own expression in the presence of EGF-CFC cofactors (see main text and Figure 4). The red asterisk indicates antagonism at the protein–protein level, to distinguish it from the rest of the interactions, which act at the transcriptional level. Some of the genes depicted are also expressed in structures other than the LPM, such as the somites, but this is not indicated for simplicity. Image published in: Capdevila J et al. (2000) Copyright © 2000. Image reproduced with permission of the Publisher, Elsevier B. V. Larger Image Printer Friendly View

Return to previous page