REGIONAL DIFFERENCES BETWEEN VARIOUS AXIAL SEGMENTS OF THE AVIAN NEURAL CREST REGARDING THE FORMATION OF ENTERIC GANGLIA

The vagal neural crest adjacent to somites 1-7 gives rise to the enter ic ganglia along the entire digestive tract. It is generally assumed t hat formation of enteric ganglia in preumbilical gut is independent of the axial segment from which the neural crest originates. In postumbi lical gut, however, there is evidence that the axial segment of origin of the neural crest might be relevant to neural differentiation. In t his part of the gut, we previously identified a subpopulation of HNK-1 -immunoreactive cells within the enteric mesenchyme. This immunoreacti vity disappeared upon formation of the enteric nervous system. We stud ied the interaction between various axial segments of quail neural cre st and the microenvironment in aneural chicken hindgut using chorioall antoic membrane cocultures. We found that neural crest cells from vari ous axial segments could migrate into the gut and home to the correct sites. However, whereas vagal neural crest cells differentiated into e nteric neurons, neural crest cells from truncal segments mainly differ entiated into melanocytes. The HNK-1-immunoreactivity within the enter ic mesenchyme only disappeared when neural crest cell colonization was followed by differentiation into enteric neurons and subsequent forma tion of enteric ganglia. To determine whether differentiation of neura l crest cells in chorioallantoic membrane cocultures was influenced by the prolonged presence of the neural tube and notochord, we developed a new coculture system, using neural crest cells cultured in vitro. W e found that the differentiation of vagal and trunk neural crest cells within the enteric mesenchyme was not influenced by the prolonged pre sence of the neural tube and notochord after 24 h, suggesting that the re are intrinsic differences between these neural crest cell populatio ns. Upon prolonged in vitro culturing, the properties of vagal neural crest cells changed, and concomitantly, they lost the ability to diffe rentiate into enteric neurons and instead differentiated into melanocy tes. We conclude that the disappearance of the HNK-1-immunoreactivity within the enteric mesenchyme is correlated with formation of enteric ganglia. In our experimental system, cells from the vagal neural crest are more capable of neural differentiation in the hindgut than cells from other axial levels of the neural crest.