WNT EXPRESSION PATTERNS IN CHICK-EMBRYO NERVOUS-SYSTEM

Several lines of evidence suggest that Wnt genes play a critical role in regulating development of the vertebrate embryo. To address the rol e that this family may play in the development of the chicken central nervous system (CNS), we have used a PCR based strategy to clone parti al sequences for Wnt genes. At least six different Wnt genes are expre ssed in the developing CNS of the chick embryo. The domains of express ion overlap either partially or completely, and are expressed in spati al domains that prefigure morphological subunits of the embryonic neur al tube. Wnt-1 and Wnt-4 are first expressed in the open neural plate in the region of the presumptive mesencephalon. Wnt-3a expression is f irst observed in the rhombencephalic regions of the open neural plate. After neural tube closure, when the embryonic subdivisions of the neu ral tube became apparent, Wnt-1, Wnt-3a and Wnt-4 are all broadly expr essed in partially overlapping domains in the mesencephalon and caudal diencephalon, as well as in the rhombencephalon and spinal cord. The mesencephalic expression patterns are subsequently modified such that Wnt-1 and Wnt-4 are expressed in a characteristic ring just rostral to the isthmus, at the mesencephalic/metencephalic junction; and Wnt-1 a nd Wnt-3a expression become restricted to the dorsal midline. Wnt-1, W nt-3a, Wnt-4, Wnt-5a and Wnt-8b are expressed in one or two caudal sub divisions of the developing diencephalon, the synencephalon and poster ior parencephalon, but do not extend ventral to the zona limitans inte rparencephalica. In contrast, Wnt-7b is expressed in the anterior pare ncephalon. Both Wnt-7b and Wnt-8b are expressed in telencephalic porti ons of the secondary prosencephalon. The timing and spatial distributi on of Wnt-gene expression in the chick embryo further support the gene ral hypothesis that Wnt genes play key roles in patterning the develop ing vertebrate nervous system.