Neural tube patterning and subsequent neuronal cell type specification constitute keys events during neurogenesis. We investigate the role of Msx1 and Msx2 in these processes in the embryonic spinal cord. Using mouse strains constructed in the laboratory that express lacZ or Gfp reporters under the control of Msx1 or Msx2 regulatory sequences, respectively, we have analyzed the dynamic expression pattern of these two transcription factors during neurogenesis. Inactivation of both genes results in mispatterning of the dorsal aspect of the embryonic spinal cord and neuron specification defects. We are working towards the identification of Msx gene targets, to dissect the transcriptional network that leads from undifferentiated neural progenitors to mature neurons. This project should provide new insights into the mechanisms of neuronal cell specification in the mammalian central nervous system.