The zebrafish hlx-1 gene belongs to the H2.0 subfamily of homeobox gen
es and is closely related to the mouse Dbx gene with respect to both h
omeodomain homology (96.7 %) and neural expression during embryogenesi
s. Analysis of hlx-1 expression by in situ hybridization reveals sever
al particularly interesting features. In late gastrula embryos, hlx-1
transcripts are detected within a circular area in the region of the p
resumptive rostral brain. Subsequently, the expression domain becomes
restricted to the hypoblast and undergoes dynamic changes involving co
nversion into a longitudinal stripe which elongates and retracts follo
wing a temporal sequence. The site of transient hlx-1 expression along
the ventral midline of the rostral neurectoderm, which in part corres
ponds to the prechordal plate, suggests a role in the determination of
head mesoderm as well as in patterning of the rostral brain. As the m
idline stripe gradually disappears, the hlx-1 gene becomes regionally
expressed within the diencephalon and at a specific dorsoventral level
along the hindbrain and spinal cord. In the hindbrain, expression is
initiated in dorsoventrally restricted transversal stripes which corre
late with the segmental pattern of rhombomeres. The stripes fuse into
bilateral columns that are later converted to two series of paired tra
nsversal stripes at the rhombomere borders. This pattern is consistent
with the proposed subdivision of hindbrain segments into rhombomere c
enters separated by border regions.