Wntexpression patterns in chick embryo nervous system

Several lines of evidence suggest that Wntgenes play a critical role in regulating development of the vertebrate embryo. To address the role that this family may play in the development of the chicken central nervous system (CNS), we have used a PCR based strategy to clone partial sequences for Wntgenes. At least six different Wntgenes are expressed in the developing CNS of the chick embryo. The domains of expression overlap either partially or completely, and are expressed in spatial domains that prefigure morphological subunits of the embryonic neural tube. Wnt-1and Wnt-4are first expressed in the open neural plate in the region of the presumptive mesencephalon. Wnt-3aexpression is first observed in the rhombencephalic regions of the open neural plate. After neural tube closure, when the embryonic subdivisions of the neural tube became apparent, Wnt-1, Wnt-3aand Wnt-4are all broadly expressed 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-1and Wnt-4are expressed in a characteristic ring just rostral to the isthmus, at the mesencephalic/metencephalic junction; and Wnt-1and Wnt-3aexpression become restricted to the dorsal midline. Wnt-1, Wnt-3a, Wnt-4, Wnt-5aand Wnt-8bare expressed in one or two caudal subdivisions of the developing diencephalon, the synencephalon and posterior parencephalon, but do not extend ventral to the zona limitans interparencephalica. In contrast, Wnt-7bis expressed in the anterior parencephalon. Both Wnt-7band Wnt-8bare expressed in telencephalic portions of the secondary prosencephalon. The timing and spatial distribution of Wnt-gene expression in the chick embryo further support the general hypothesis that Wntgenes play key roles in patterning the developing vertebrate nervous system.