Figure 5. Temporal pattern of V1 clades emergence during the Xenopus swim-to-walk transition.

A. At escape swimming stages, NF35–38, V1s show little diversity. The Pou6f2, FoxP2, and Sp8 clades are absent, and around 50–60% of V1s are marked by MafA and MafB.

B. At free-swimming stages, NF44–47, V1s start to diversify. The Pou6f2 and FoxP2 clades emerge.

C. During metamorphosis, with limb emergence, the Sp8 clade emerges and V1s acquire the four clade organization observed in the mouse.

D. Percentage of V1 interneurons expressing a single clade marker (FoxP2, Pou6f2, Sp8, MafA) in axial (NF35–38), thoracic (NF44–47 and NF54–55) or lumbar spinal cord (NF54) (mean ± SEM, n = 4–10 animals).

E. The sequence of V1 clade emergence. MafA present in escape swimming. MafA, Pou6f2, FoxP2 present in free-swimming. All four clades present at limb-circuit stages.

F. Entropy analysis of “diversity” index based on transcription factor expression shows a significant increase in overall transcriptional diversity between NF35 and NF45, and a peak of diversity reached at NF54–55. The diversity at the peak matches that of the neonate mouse. Tadpole drawings adapted from Xenopus illustrations © Natalya Zahn (2022).¹¹⁷