Motor Neuron Pools.
FGF signals diffuse rostrally and induce the expression of specific Hox genes in the lateral motor column (LMC) located at the brachial level of the spinal cord. The resulting FGF gradient divides the brachial spinal cord into the rostral (R) Hox5-positive and the caudal (C) Hoxc8-positive segments. This division consequently generates different signaling cascades at each end, that lead to different combinations of Hox gene expression profiles. These molecularly defined combinations induce differentiation of specific LMC motor pools that innervate different muscles in the periphery.
Abbreviations: FGF, Fibroblast Growth Factor; L, lateral; M, median; Sca, Scapulohumeralis Posterior Muscle; ALD, Anterior Latissimus Dorsi Muscle; Pec, Pectoralis Muscle;FCU, Flexor Carpi Ulnaris Muscle; LMC, Lateral motor column; R, Rostral; C, Caudal.