Immunohistochemical localization of gamma-enolase in early human embryos

gamma-Enolase has been believed to be distributed only in the neurons and it was frequently labelled as neuron-specific enolase. However, recent precise studies have suggested a wider distribution of the protein. It can also be found in neuroendocrine cells, some mesodermal tissues, and some malignant tumors originating from tissues without the antigen in a normal condition. In early rat embryos, before the formation of neural tissues, a sensitive immunoassay system revealed a substantial amount of gamma-enolase, though it is not yet clear where the antigen is located. In the present study, tissue distribution of gamma-enolase in early human embryos was studied using an immunohistochemical method and it was suggested that the protein is present not only in neural tissue primordium but also in most tissues in the youngest embryo of 6.3 mm crown-rump length. Many of the immunoreactive non-neural tissues, however, lost immunoreactivity with the advancement of the embryonic stage while neural tissues became more intensely stained. In the embryo of 24 mm length, the staining pattern was almost the same as that of reported adult men. In embryonic tissues such as notochord and mesonephros, which disappear in the due course of growth, the antigen was also found. These findings will suggest that the antigen is rather common in undifferentiated tissues but then localizes in neural elements with advancing age. Our findings may be useful in explaining why early rat embryos, before the formation of neural tissues, showed a considerable amount of gamma-enolase and why many undifferentiated tumors, originating from tissues which did not have the antigen in normal condition, revealed the antigen.