otp1 functions and CA neuron differentiation. Anterior is left and dorsal is up (except for B, dorsal view) in all panels. Eyes have been removed. A, B, anti-TH antibody labels the PT diencephalic CA neurons at 38 hpf . Co-labelling with otp1 is evident in a fraction of TH-positive neuroblasts in the PT (arrowhead). C, D, motionless (mot) embryos display a severe reduction of cell numbers across all DA populations of the zebrafish brainstem, including the diencephalic ones (34 hpf) . Herein, absence of mot functions drastically inhibits the differentiation of otp1 positive cells, more in the PT (arrowhead) then in the PO (arrow). E, F, microinjection of otp1 morpholino oligonucleotide lowers the number of TH-labelled DA neuroblasts in the PT (arrowhead) of 48 hpf embryos that were labelled with neurogenin1 (ngn1), a marker of specific neuronal populations in the forebrain. cf, cephalic flexure; e, eye; ep, epiphysis; h, hypothalamus; mb, midbrain; ot, optic tectum; p, pallium; th, thalamus.