Figure 3.

A–C, A spindle-derived GDNF-independent signal is required for γ-MN development. Wnt7a^ON putative γ-MNs are localized within the motor neuron nucleus of P0 (A), P4 (B), and P15 (C) control mice. D–F, Wnt7a labeling is eliminated in P0 (D), P4 (E), and P15 (F) Pva::Cre; Isl2::DTA mutant mice. G–I, Wnt7a^ON γ-MNs are localized within the ventral spinal cord of P0 (G) and P5 (H) Egr3^−/− mice, but are lost at P15 (I). J–J″, In control mice, NeuN^OFF/ChAT^ON γ-MNs (arrows in J″) intermingle with NeuN^ON/ChAT^ON α-MNs at P4. K–K″, NeuN^OFF/ChAT^ON γ-MNs are absent in P4 Pva::Cre; Isl2::DTA mice. L–L″, In P0 wild type mice, Wnt7a^ON putative γ-MNs (arrow) are localized within the Cm motor pool, identified by coexpression of Islet1 and Pea3. Scale bar: A–L″, 100 μm.