Differential distribution of V1 interneuron subdivisions along the rostrocaudal axis of the spinal cord.

<p>(A–A″) Immunofluorescence labeling on transverse section at brachial levels of embryonic spinal cord at e12.5 shows that V1 interneurons are subdivided into 3 large subsets (arrows) containing Foxp2 (cyan). Foxp4 is detected in a portion of these Foxp2⁺ V1 neurons (white). (B–B″) At thoracic levels, Foxd3⁺ V1 neurons form 2 groups (arrows) that contain Foxp2 (in green/cyan) and Foxp4 (in red/white). (C–C″) At lumbar levels, V1 interneurons distribute among 3 groups (arrows) and the ratio between Foxp2⁺ neurons and Foxp4⁺/Foxd3⁺ cells decreased compared to brachial or thoracic levels. (D–D″) At brachial levels, Nurr1 is detected in subsets (arrowheads) within 2 large V1 groups containing Foxp2 (yellow). (E–E″) At thoracic levels, Nurr1⁺ subsets (white) are intermingled with Foxp2⁺ group (cyan and green) close to the central canal and/or (in/with Foxp2⁺ group close) to motor neurons as indicated by arrowheads. (F–F″) At lumbar levels, Nurr1⁺ subsets are included in 2 groups of V1 that contain Foxp2 (yellow) indicated by arrowheads or Foxd3 and Foxp2 (white). (G–G″) At brachial levels, Arx is present in a few number of Foxd3⁺ V1 neurons (magenta) as indicated by arrowhead. (H–I″) By contrast, at thoracic and lumbar levels, Arx is observed in subsets of Foxd3⁺ (magenta) and of Foxd3⁺/Nurr1⁺ (white) V1 neurons (arrowheads). (J–J″) At brachial levels, Pax2 expression defines subsets in Foxd3⁺ (magenta) and in Foxp2⁺/Foxd3⁺ (white) V1 interneurons (arrowheads). (K–K″) At thoracic levels, Pax2 is distributed in Foxd3⁺ (magenta), Foxd3⁺/Foxp2⁺ (white) and Foxp2⁺ subsets (yellow) as indicated by arrowheads. (L–L″) At lumbar levels, Pax2⁺ subsets (yellow or white) are located within V1 containing Foxp2 located medially or close to motor neurons (arrowheads). (M–M″) At brachial levels, BhlhB5 is detected in subsets of Foxd3⁺ V1 neurons (cyan) located close to the central canal or to motor neurons. Prdm8 is present in small subsets of V1 neurons located close to V1 progenitor domain or more ventrally, close to motor neurons. A small subset of V1 that co-express BhlhB5 and Prdm8 (white) is observed in the vicinity of the motor neurons (arrowheads). (N–N″) At thoracic levels, the amount of V1 neurons that contain BhlhB5 (cyan), or BhlhB5 and Prdm8 (white) indicated by arrowheads, is increased while a few number of Prdm8⁺ V1 cells is detected. (O–O″) At lumbar levels, the amount of cells corresponding to Prdm8⁺ (magenta) or BhlhB5⁺ V1 neurons (cyan) decreases while BhlhB5⁺/Prdm8⁺ co-expressing V1 (white) indicated by arrowheads, increase compared to the thoracic region. (P–P″) At brachial levels, Pou4F1 is present in a few Foxp2⁺ V1 neurons (cyan) indicated by arrowheads. Renshaw cells (red) are distributed in 3 groups (arrows) with very few containing Foxp2 (yellow) indicated by arrowhead. (Q–Q″) At thoracic levels, the amount of Renshaw cells (red) decreases (arrow) while Foxp2⁺ V1 expressing Pou4F1 (cyan) slightly increases (arrowheads). (R–R″) At lumbar levels, similar to thoracic levels, the amount of Renshaw cells (red) decreases (arrow) but Pou4F1⁺ subset (cyan) is detected dorsally, close to motor neurons (arrowheads). Scale bar = 100 µm.