Figure 2.

AS Kir4.1 Is Required for Maintenance of FαMN Size

(A) Left: breeding scheme. AS-Kir4.1cKO and cre-negative control animals were bred with ChAT-GFP mice for MN visualization. Right: total FαMN (ChAT⁺/MMP-9⁺/NeuN⁺), SαMN (ChAT⁺/MMP-9⁻/NeuN⁺), and γMN (ChAT⁺/MMP-9⁻/NeuN⁻) numbers are equivalent in AS-Kir4.1cKO and cre-negative control mice at the indicated ages (n = 3 mice/group, mean ± SEM, lumbar spinal cord, Welch’s t test).

(B, D, and F) Representative images of lumbar MNs at P14 (B), P30 (D), and 6 months (F). Arrowheads denote example FαMNs (scale bar, 50 μm).

(C, E, and G) Quantification of MN size at P14 (C), P30 (E), and 6 months (G) (n = 3 mice/group, >100 MN counts/animal, boxplot, Mann-Whitney test).

(H) Schematic of retrograde labeling of MN pools using intramuscular injection of fluorescent cholera toxin subunit B (CTSB) in the tibialis anterior (TA) muscle.

(I) Representative images of retrograde-labeled ventral horn MNs in AS-Kir4.1cKO and cre-negative control mice. Arrowheads denote example putative FαMNs (scale bar, 50 μm).

(J) Quantification of ChAT-GFP⁺CTSB⁺ MN soma area from (G) (n = 3 mice/group, >50 MN counts/animal, boxplot, Mann-Whitney test). ^∗p < 0.05, ^∗∗∗p < 0.001. Edges of boxplots denote interquartile range (25^th–75^th percentile) with whiskers denoting 1.5 times the interquartile range and black line denoting the median value.