Age-Dependent Inhibition of Neural Crest Migration by the Notochord Correlates with Alterations in the S103L Chondroitin Sulfate Proteoglycan

Abstract

In avian embryos, the notochord inhibits neural crest migration, resulting in the absence of neural crest cells from the perinotochordal space. Here, we test whether temporal changes in the ability of the notochord to inhibit neural crest migration correlate with alterations in the S103L chondroitin sulfate proteoglycan (CSPG). Because CSPGs are abundant in the perinotochordal space and the inhibitory effects of the notochord are chondroitinase sensitive bothin vivoandin vitro,we examined the distribution and biochemical nature of a large CSPG whose core protein is recognized by the S103L antibody. The S103L CSPG is specific to the perinotochordal space during the course of neural crest migration and codistributes with the HNK-1 carbohydrate. Biochemical characterization reveals that the S103L CSPG bears the HNK-1 epitope and is the only HNK-1 immunoreactive proteoglycan present around the notochord at these stages. Following neural crest migration, the S103L CSPG staining is maintained in the perinotochordal region and also is expressed later in cartilage. In 4-day-old embryos, however, the S103L CSPG undergoes a reduction of HNK-1 immunoreactivity. To examine the temporal nature of the notochord's inhibitory ability, we assayed the effects on neural crest migration of grafting notochords from 2- to 5-day-old donor quail embryos into 2-day-old host chick embryos. Donor notochords from 2- to 3-day-old embryos inhibit neural crest cell migration, whereas the degree of inhibition is reduced or absent when notochords are derived from ≥4-day-old donors. This suggests that older notochords lose their inhibitory ability. Interestingly, preincubation of younger notochords with the HNK-1 antibody blocks the inhibitory effect, suggesting that glycosylation of the perinotochordal matrix may be important. The time when the notochord loses its inhibitory ability as assessed by ourin vivografting assay correlates with the biochemical and immunocytochemical changes in the notochordal S103L antigen. These data suggest that a species of S103L CSPG, which is expressed by the early notochord and bears the HNK-1 epitope, may be important for the inhibition of neural crest migration.