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Figure 2 | EvoDevo

Figure 2

From: The Nodal signaling pathway controls left-right asymmetric development in amphioxus

Figure 2

Left-right asymmetric expression of developmental regulatory genes during amphioxus embryogenesis. All images are of B. floridae, taken from the dorsal view. ‘L’ marks the left side, ‘R’ marks the right side, and the asterisk (*) marks the anterior. Double arrowheads indicate stronger expression patterns, and single arrowheads indicate relatively weaker expression patterns. White arrowheads indicate the midline. Scale bar, 100 μm. (A-F) At the onset of neurulation (stage N0), Nodal and Gdf1/3 are expressed symmetrically on both the left and the right sides of the embryo. Lefty is expressed on the left side, while Cerberus is expressed on the right side; these are the first signs of asymmetrical gene regulation. Pitx is expressed on the left side of a fraction of embryos, suggesting that Pitx is just starting to be transcribed. (G-K) At the early neurula stage (N1), Nodal becomes expressed preferentially on the left side, while Gdf1/3, Lefty, and Pitx are expressed exclusively on the left side. Additionally, Lefty is also expressed at the midline. Cerberus transcripts are found on the right side and also at the midline. (L-P) At the mid-neurula stage (N2), Nodal, Gdf1/3, Lefty, and Pitx are expressed exclusively on the left side while Cerberus is expressed at the midline. (Q-S) At the late neurula stage (N3), some organ-specific genes already display asymmetric expression. Expression of FoxE4, Nkx2.1, and Hand is biased towards the right side.

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