Topology of otp1 transcripts in forebrain compartments. Anterior is top in A, B and D dorsal views, otherwise left and lateral view panels. Eyes have been removed in C. A (12 hpf), B (24 hpf), early otp1 expression foci (blue) occur at the anteromedial edge of pax2.1 (red) pattern in the optic stalks, as shown by double WISH. C, D, Co-labelling with anti-acetylated α-tubulin antibody (brown) and otp1 riboprobe (blue) demonstrates that the anterior otp1 cell cluster is delimited by the supraoptic tracts and those of the anterior and posterior commissures (36 hpf). E, F, mbl embryos are not altered in the dorsal extension of the PO otp1 cluster, if compared with control embryos (19 hpf). cf, cephalic flexure; d, diencephalon; h, hypothalamus; l, lens; mb, midbrain; op, optic primordia; or, optic recess; os, optic stalks; r, retina; rh, rostral hypothalamus; sot, supraoptic tract; t, telencephalon; tac, tract of the anterior commissure; tpoc, tract of the postoptic commissure; vt, ventral thalamus.