Figure 4. ES Motor Neurons Acquire Defined Caudal Brachial Motor Pool Identities.

A) Molecularly defined LMC motor pools in caudal brachial spinal cord: Scip⁺ pool innervates flexor carpi ulnaris (FCU), Pea3⁺/Isl1⁺ pool innervates cutaneous maximus (CM), and Pea3⁺/Lhx1⁺ motor pool innervates latissimus dorsi (LD) muscles.

B) Scip and Pea3 expression in E13.5 mouse spinal cord.

C) A subset of FoxP1⁺ LMC neurons expresses Scip at caudal brachial E13.5 mouse spinal cord.

D) Cells in day 6 embryoid bodies express FoxP1, Scip, Pea3 and Hoxc8. A subset of FoxP1⁺ LMC neurons expresses Scip but not Pea3. Scip⁺ motor neurons co-express Hoxc8.

E) FoxP1⁺ ES motor neurons acquire Pea3 expression in response to GDNF treatment on day 5–6. Pea3⁺ motor neurons express Hoxc8.

F) Mutually exclusive expression of Pea3 and Scip in ES motor neurons. A majority of Pea3⁺ ES motor neurons express Isl1 but not Lhx1.

G) Quantification of Pea3 and Scip expressing FoxP1⁺ ES motor neurons in the presence and absence of GDNF. The fraction of Pea3⁺ but not Scip⁺ LMC neurons was increased upon GDNF treatment (p<0.001). Results from three independent experiments (mean ± SEM).

H) Quantification of Lhx1 and Isl1 expression in Pea3⁺ motor neurons. Significantly greater fraction of Pea3⁺ ES motor neurons expressed Isl1 compared to Lhx1 (p<0.001). Results from three independent experiments (mean ± SEM).