Pax3 and Pax7 are expressed in commissural neurons and restrict ventral neuronal identity in the spinal cord.

Pax3 and Pax7 are transcription factors sharing high sequence identity and overlapping patterns of expression in particular in the dorsal spinal cord. Analysis of Pax3 and Pax7 double mutant mice demonstrates that both genes share redundant functions to restrict ventral neuronal identity in the spinal cord. In their absence, the En1 expression domain is expanded dorsally but that of Evx1 is not affected. In addition, Pax3 and Pax7 are expressed in commissural neurons and double mutant embryos exhibit highly reduced ventral commissure. Our findings reveal two distinct regulatory pathways for spinal cord neurogenesis, only one of which is dependent on Pax3/7 and 6.