Homeodomain transcription factors in the development of subsets of hindbrain reticulospinal neurons.

Hindbrain reticulospinal neurons are involved in complex neural functions that are mediated by spinal elements, including posture control and modulation of respiration and cardiovascular function. Recent descriptive studies with chick, mouse, and rat embryos have provided anatomical insight into the development of the different reticulospinal nuclei and the establishment of their axonal projection pathways into the spinal cord. In this study, we have addressed the molecular control of this process. Retrograde labeling of reticulospinal neurons in chick and mouse embryos combined with immunostaining for the homeodomain factors Lhx1/Lhx5, Lhx3/Lhx4, and Chx10 have defined transcriptional codes that label subsets of neurons with different axon projection patterns. Gain of function and loss of function experiments using in ovo electroporation implicate these transcription factors in the determination of reticulospinal neuron identity. Furthermore, our studies reveal novel gene interactions between the transcription factors analyzed that may determine the final patterns of reticulospinal axon projection.