EFFECT OF IN OVO RETINOIC ACID EXPOSURE ON FOREBRAIN NEURAL CREST - IN-VITRO ANALYSIS REVEALS UP-REGULATION OF N-CAM AND LOSS OF MESENCHYMAL PHENOTYPE

In a prior study of in ovo exogenous retinoic acid (RA) exposure, we o bserved a prolonged expression of cell surface N-CAM in cranial neural crest (NC) cells exhibiting migratory failure. In the present studies , we employed an experimental strategy in which embryos were first exp osed to exogenous RA in ovo and incubated for 45-60 hr; this was follo wed by extirpation and in vitro culturing of these same RA-exposed cra nial neural tubes. NC cell outgrowth from the explant was assayed, as was the immunohistochemical localization of HNK-1 and N-CAM antigens. In RA-exposed explants, the size of the NC cell. outgrowths were compa rable to controls. However, almost all NC cells lost their mesenchymal phenotype and were arranged in an ''epithelioid'' pattern of tightly packed polygonal cells that expressed N-CAM at adjacent cell boundarie s. By contrast, control NC cells were flattened and multipolar in shap e and expressed HNK-1, rarely co-expressing N-CAM, These observations indicate that RA modulates NC cell N-CAM expression and microanatomica l phenotype, a finding consistent with prior in ovo studies of RA-expo sure. Several possible explanations are considered. (C) 1994 Wiley-Lis s, Inc.