Transcriptional codes and the control of neuronal identity.
The topographic assembly of neural circuits is dependent upon the generation of specific neuronal subtypes, each subtype displaying unique properties that direct the formation of selective connections with appropriate target cells. Studies of motor neuron development in the spinal cord have begun to elucidate the molecular mechanisms involved in controlling motor projections. In this review, we first describe the actions of transcription factors within motor neuron progenitors, which initiate a cascade of transcriptional interactions that lead to motor neuron specification. We next highlight the contribution of the LIM homeodomain (LIM-HD) transcription factors in establishing motor neuron subtype identity. Importantly, it has recently been shown that the combinatorial expression of LIM-HD transcription factors, the LIM code, confers motor neuron subtypes with the ability to select specific axon pathways to reach their distinct muscle targets. Finally, the downstream targets of the LIM code are discussed, especially in the context of subtype-specific motor axon pathfinding.
Shirasaki
Ryuichi
R
Gene Expression Laboratory, The Salk Institute for Biological Studies, La Jolla, California 92037, USA. shirasaki@salk.edu
Pfaff
Samuel L
SL
D000818:Animals; D002454:Cell Differentiation / Q000502:physiology; D004525:Efferent Pathways / Q000166:cytology / Q000196:embryology* / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental / Q000502:physiology; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D009046:Motor Neurons / Q000166:cytology* / Q000378:metabolism; D018482:Muscle, Skeletal / Q000196:embryology / Q000294:innervation* / Q000378:metabolism; D013116:Spinal Cord / Q000166:cytology / Q000196:embryology* / Q000378:metabolism; D013234:Stem Cells / Q000166:cytology* / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
D018398:Homeodomain Proteins; D014157:Transcription Factors