The acquisition of motoneuron subtype identity and motor circuit formation.
Experiments in chick embryos using classical transplantation techniques introduced by Viktor Hamburger are reviewed; these demonstrated that chick-limb innervating motoneurons become specified by extrinsic signals prior to axon outgrowth and that they selectively grow to appropriate muscles by actively responding to guidance cues within the limb. More recent experiments reveal that fast/slow and flexor/extensor subclasses of motoneurons are distinct by E4-5 and that they exhibit patterned spontaneous activity while still growing to their targets. These observations are then related to the combinatorial code of LIM transcription factor expression, which has been hypothesized to specify motoneuron subtypes.
Landmesser
L T
LT
Department of Neurosciences, Case Western Reserve University, School of Medicine, 10900 Euclid Ave, Cleveland, OH 44106-4975, USA. ltl@po.cwru.edu
D000818:Animals; D001369:Axons / Q000502:physiology; D019070:Cell Lineage; D002642:Chick Embryo; D005121:Extremities / Q000196:embryology / Q000294:innervation* / Q000637:transplantation; D018507:Gene Expression Regulation, Developmental; D005865:Gestational Age; D018398:Homeodomain Proteins / Q000502:physiology; D051379:Mice; D009024:Morphogenesis; D009046:Motor Neurons / Q000145:classification / Q000166:cytology*; D018656:Muscle Fibers, Fast-Twitch / Q000166:cytology; D018657:Muscle Fibers, Slow-Twitch / Q000166:cytology; D013045:Species Specificity; D014157:Transcription Factors / Q000502:physiology; D014183:Transplantation, Heterologous
D018398:Homeodomain Proteins; D014157:Transcription Factors