Figure 6. Conservation of V1 clade organization and transcriptional diversity between frog and mouse.

A. Mouse V1 clades are conserved in the frog. Antibodies against FoxP2, Pou6f2, MafA, and Sp8 transcription factors (green) label subsets of En1+ V1 interneurons (red) in lumbar spinal cord of NF54–55 tadpoles. Shown is a ventral hemi-section of spinal cord with the central canal and outer edge indicated (dotted line).

B. Spatial distribution plots of V1^FoxP2, V1^Sp8, V1^Pou6f2, and V1^MafA at the lumbar level in NF54–55 tadpole (left) and P0 mouse (right). Frog and mouse V1 clades have similar settling positions. Frog spinal cords were resized to mouse-like proportions (see STAR Methods). Plotted are interneurons from at least 20 lumbar spinal cord hemi-sections from at least 2 animals.

C. Frog V1 clades are mutually exclusive in their expression. The bar plot shows the percentage of V1s expressing a singular or combination of clade markers, FoxP2, Sp8, Pou6f2 and MafA. Shown is mean ± SEM, n = 2–4 animals

D. V1 molecular subsets are present in similar proportions in the frog and mouse. Upper bar plot shows the percentages of V1s expressing a given transcription factor in lumbar NF54–55 tadpole (black) and P0 mouse (gray) spinal cords determined by IHC. Lower bar plot shows the fold change in percentage of V1 subsets between the frog and mouse; no change larger than 2-fold observed. Shown is mean ± SEM (2TF: n = 2–6 animals; 3TF: n = 2 animals).

E. V1 interneurons marked by two and three transcription factors reveal species-enriched subsets. Shown is fold enrichment of V1^2TF and V1^3TF interneurons with > 2-fold enrichment in NF54–55 frog (black) or P0 mouse (gray) spinal cord.

F-I. Mouse thoracic-enriched populations of V1 are present and enriched at the thoracic levels in frog. V1^Nr4a2+Otp, V1^Sp8+Otp, V1^Nr4a2+FoxP2, V1^MafB+FoxP2 populations are present in the frog (gray) thoracic spinal cord (left) and significantly enriched compared to the lumbar level (right). The same rosto-caudal enrichment was reported in the mouse (black). Shown is mean ± SEM for n = 2–6 animals with significant differences (p < 0.05) plotted.