RT Journal Article SR Electronic T1 Otx2 Regulates Subtype Specification and Neurogenesis in the Midbrain JF The Journal of Neuroscience JO J. Neurosci. FD Society for Neuroscience SP 4856 OP 4867 DO 10.1523/JNEUROSCI.5158-04.2005 VO 25 IS 19 A1 Bertrand Vernay A1 Muriel Koch A1 Flora Vaccarino A1 James Briscoe A1 Antonio Simeone A1 Ryoichiro Kageyama A1 Siew-Lan Ang YR 2005 UL http://www.jneurosci.org/content/25/19/4856.abstract AB The transcription factor Otx2 is required to determine mesencephalic versus metencephalic (cerebellum/pons) territory during embryogenesis. This function of Otx2 primarily involves positioning and maintaining the mid-hindbrain organizer at the border between midbrain and anterior hindbrain. Otx2 expression is maintained long after this organizer is established. We therefore generated conditional mutants of Otx2 using the Cre/loxP system to study later roles during rostral brain development. For inactivation of Otx2 in neuronal progenitor cells, we crossed Otx2flox/flox animals with Nestin-Cre transgenic animals. In Nestin-Cre/+; Otx2flox/flox embryos, Otx2 activity was lost from the ventral midbrain starting at embryonic day 10.5 (E10.5). In these mutant embryos, the mid-hindbrain organizer was properly positioned at E12.5, although Otx2 is absent from the midbrain. Hence, the Nestin-Cre/+; Otx2flox/flox animals represent a novel mouse model for studying the role of Otx2 in the midbrain, independently of abnormal development of the mid-hindbrain organizer. Our data demonstrate that Otx2 controls the development of several neuronal populations in the midbrain by regulating progenitor identity and neurogenesis. Dorsal midbrain progenitors ectopically expressed Math1 and generate an ectopic cerebellar-like structure. Similarly, Nkx2.2 ectopic expression ventrally into tegmentum progenitors is responsible for the formation of serotonergic neurons and hypoplasia of the red nucleus in the midbrain. In addition, we discovered a novel role for Otx2 in regulating neurogenesis of dopaminergic neurons. Altogether, these results demonstrate that Otx2 is required from E10.5 onward to regulate neuronal subtype identity and neurogenesis in the midbrain.