Development of the mesencephalic trigeminal nucleus requires a paired homeodomain transcription factor, Drg11.

The mesencephalic trigeminal nucleus (Me5) innervates muscle spindles and is responsible for receiving and transmitting proprioception from the oro-facial region. Molecular mechanisms underlying the development of the Me5 are poorly understood. Evidence is provided here that transcription factor Drg11 is required for Me5 development. Drg11 was expressed in the Me5 cells of the embryonic and early postnatal mouse brains, and the Me5 cells were absent in Drg11-/- mice at birth. The absence of the Me5 cells in Drg11-/- mice appeared to be caused by increased cell death in the Me5 during embryonic development. In postnatal Drg11-/- mice, Me5 cell innervation of masseter muscle spindles was undetectable, while robust trigeminal motoneuron innervation of masseter muscle fibers was detected. The postnatal body weight of Drg11-/- mice was notably less than that of wild-type mice, and this might result, in part, from disruption of the oro-facial proprioceptive afferent pathway. Taken together, our results demonstrate an essential role for Drg11 in the development of the Me5.