Fig. 6. Comparison of regulatory gene expression in the lamprey brain. Whole-mount in situ hybridization in stage 26 lamprey embryos. (A) Expression of LjPax6. An arrow indicates the dorsal hindbrain that does not express this gene. (B) Expression pattern of LjDlx1/6. Transcripts are detected in the telencephalon (TE), thalamus (TH), upper lip (UL), lower lip (LL) and velum (VE). (C) Expression of LjTTF1 in the hypothalamus (HPT) and endostyle (ES). (D) LjPax2/5/8. Transcripts are found at the mid-hindbrain boundary (MHB), velar epithelium and endostyle. (E) LjOtxA is expressed in the MHB, the midbrain (MB), the diencephalon (DI), the olfactory placode (OP) and the pharyngeal ectoderm (PE). (F) Immunohistochemical staining of nerve tracts. The habenular commissure (hc), medial longitudinal fascicle (mlf), posterior commissure (pc), posterior optic tract (pot), supraoptic tract (sot) and ventral longitudinal fascicle (vlf) are stained. Abbreviations: ch, optic chiasm; DI, diencephalon; EP, epiphysis; ES, endostyle; FMB, fore-midbrain boundary; hc, habenular commissure; HPT, hypothalamus; ISN, interstitial nucleus; LL, lower lip; MB, midbrain; mlf, medial longitudinal fascicle; MHB, mid-hindbrain boundary; NT, notochord; OE, oral ectoderm; OP, olfactory placode; OPT, optic stalk; pc, posterior commissure; pot, posterior optic tract; PP1 & PP2, pharyngeal pouches; sa, intraencephalic sulcus; sot, supraoptic tract; TE, telencephalon; UL, upper lip; vlf, ventral longitudinal fascicle.