Vitamin A-Induced Suppression/Enhancement of Protein Glycosylation and Neurulation

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Abstract
Glycoconjugates play major roles in many cellular functions, e.g. cell migration and cell-to-cell adherence, which are involved in neurulation. The maternal administration of vitamin A on gestation day 8.5 and 9.0 resulted in a high percentage of primary and secondary neurulation defects in gestation day 12 mouse embryos. The neuroepithelium of normal and abnormal embryos was analyzed by one- and two-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis and one-dimensional Western blots using concanavalin A (Con A) and peroxidase-conjugated wheat germ agglutinin (WGA) lectins. In vitamin A abnormal embryos, WGA binding was decreased to glycoproteins with apparent molecular weights of 15,000 and 30,000 daltons on Western blots, whereas in vitamin A normal embryos, WGA binding was increased to these glycoproteins on Western blots. Computer-aided fluorescence microscopy using fluorescein isothiocyanate (FITC)-conjugated lectins on 1-µm araldite plastic sections indicated a decrease in FITC-WGA binding to the free surface of nonneurulated neuroepithelium. These results suggest: (1) vitamin A administration may have induced a suppression of WGA-binding carbohydrate residues on 15,000- and 30,000-dalton glycoproteins in abnormal embryos, and (2) modification in the type, amount, and distribution of glycoconjugates may provide a basis for the cellular mechanisms of abnormal development of the neural tube.