LHX3 and amyotrophic lateral sclerosis: Sixth, we observed that LHX3 expression, a marker of MNs innervating epaxial muscles, was negative in MNs (Fig. 2l), while FOXP1 expression, a marker of MNs innervating limb muscles (LMC), was detected in all control and ALS MNs (Fig. 2m; Supplementary Fig. 6g).