Figure 3: Foxp1 misexpression induces LMC motor pool markers.

(a) Analysis of cervical LMC motor pools in E12.5 Foxp1^+/+, Foxp1^−/− and Hb9::Foxp1; Foxp1^−/− embryos. All LMC motor pools were lost in Foxp1^−/− embryos. The Pou3f1⁺ MNs in Foxp1^−/− embryos represent the expanded HMC MN population (identified by their medial position). Insets depict Islet1 co-staining of the same section. The Etv4 motor pool was restored in Hb9::Foxp1; Foxp1^−/− embryos (white arrows), with some Foxp1⁺/Etv4⁺ MNs located more dorsally (arrowhead). The Nkx6.1 and Pou3f1 motor pools were not restored in Hb9::Foxp1; Foxp1^−/− embryos, although a small number of Foxp1⁺/Pou3f1⁺ MNs were identified (yellow arrows). Scale bar, 50 μm. (b) Control Hb9::GFP ESC-derived MNs did not express any LMC motor pool markers. Hb9::Foxp1 ESC-derived MNs expressed Etv4 and Pou3f1 at high levels, but did not express Nkx6.1. Boxed regions are depicted as single-colour images below each image. Scale bars, 50 μm. (c) Quantification of motor pool markers in ESC-derived MNs (mean±s.e.m.; n=2 independent experiments, 938 Hb9::GFP MNs and 723 Hb9::Foxp1 MNs total; Student’s t-test). Etv4: **P=0.009. Pou3f1: **P=0.008. (d) Foxp1 misexpression did not alter the percentage of Pou3f1⁺/Foxp1⁻ ESC-derived HMC-like MNs (mean±s.e.m.; n=3 independent experiments, 390 Hb9::GFP MNs and 255 Hb9::Foxp1 MNs total).