EXPRESSION OF THE NEURAL CELL-ADHESION MOLECULE AND POLYSIALIC ACID DURING EARLY MOUSE EMBRYOGENESIS

The expression of the neural cell adhesion molecule (N-CAM) and alpha 2-8 linked polysialic acid (PSA), which is believed to be predominantl y expressed on N-CAM, was investigated during early embryonic developm ent of the mouse (embryonic days 7.5 to 10.0). By immunocytochemistry, in tissue sections, N-CAM and PSA were not detectable at embryonic da y 7.5 but were expressed in the prominent body regions such as somites , unsegmented mesoderm, developing heart, and neuroectoderm at embryon ic day 8.0 N-CAM and PSA immunoreactivities were always predominantly associated with the plasma membrane. No tissue could be detected which was positive for PSA but negative for N-CAM. In Western blot analysis of whole embryos, by contrast, only the lightly sialylated and PSA-ne gative 180 and 140 kD isoforms of N-CAM were present at embryonic day 8.0 and strong expression of PSA-bearing, heavily sialylated N-CAM was not detectable before embryonic day 10.0. In Western blot analysis of N-CAM immunoaffinity purified from whole embryos and digested with ne uraminidase as well as in Northern blot analysis, the 120 kD isoform o f N-CAM or its corresponding mRNA were not expressed in detectable amo unts during the time period investigated. (C) 1994 Wiley-Liss, Inc.