Regulatory gene expression patterns reveal transverse and longitudinal subdivisions of the embryonic zebrafish forebrain

To shed light on the organization of the rostral embryonic brain of a lower vertebrate, we have directly compared the expression patterns of dlx, fgf, hh, hlx, otx, pas, POU, winged helix and wnt gene family members in the fore- and midbrain of the zebrafish. We show that the analyzed genes are expressed in distinct transverse and longitudinal domains and share expression boundaries at stereotypic positions within thr fore- and midbrain. Some of these shared expression boundaries coincide with morphological landmarks like the pathways of primary axon tracts. We identified a series of right transverse diencephalic domains suggestive of neuromeric subdivisions within the rostral brain. in addition, we identified four molecularly distinct longitudinal subdivisions and provide evidence for a strong bending of the longitudinal rostral brain axis at the cephalic flexure. our data suggest a strong conservation of early forebrain organization between lower and higher vertebrates. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.