Alternate expression of the HNK-1 epitope in rhombomeres of the chick embryo.

Rhombomeres are regarded as the manifestation of innate segmentation within the vertebrate CNS. To investigate developmental changes occurring in the CNS and PNS, a series of chick embryos were immunostained with several monoclonal antibodies. The HNK-1-immunoreactivity (IR) appeared in rhombomeres (r) 3 and r5 around stage 15, when r2 and r4 were not stained. This alternate pattern is similar to the Krox-20 gene expression in the mouse embryo. At levels of r2 and r4, HNK-1+ neural crest cell masses were attached to the CNS forming cranial sensory ganglia. In these rhombomeres, an accumulation of neuroepithelial cells near the cranial nerve root and early development of neuroblasts in the basal plate were observed. The above observations seem to suggest that the alternate HNK-1-IR in rhombomeres might be related to the expression of cell adhesion molecules, and therefore also to the adhesion of the cranial ganglion precursors to the CNS, which takes place every other rhombomere in the preotic region. Thus, the alternate pattern of the HNK-1-IR seems to be related to the morphogenesis of preotic branchial nerves.