Wnt3 and Wnt3a mark the MDO and the dorsal thalamus. Analysis of expression dynamics of indicated marker genes at 15 and 28 hpf. At 15 hpf, wnt3 and wnt3a are expressed in the MDO primordium (MDO-p) and maintained in the organizer at 28 hpf. Cross section analysis of the left hemisphere reveals that wnt3a expression is adjacent to shh expression at the ventricular zone of the organizer (D), whereas wnt3 expression co-localizes with shh expression at 28 hpf (F). In the diencephalon, expression of wnt3a is located between the lhx5 expression domain (G, H) and the irx1b expression domain (K, L). Consistently, wnt3a is co-expressed with otx2 (I, J) suggesting that wnt3a marks the MD organizer territory at 15 hpf and 28 hpf. MDO, PTh, prethalamus, Th, thalamus, *-p, *-primordium.