HUMAN STX POLYSIALYLTRANSFERASE FORMS THE EMBRYONIC FORM OF THE NEURAL CELL-ADHESION MOLECULE - TISSUE-SPECIFIC EXPRESSION, NEURITE OUTGROWTH, AND CHROMOSOMAL LOCALIZATION IN COMPARISON WITH ANOTHER POLYSIALYLTRANSFERASE, PST

PST and STX are polysialyltransferases that form polysialic acid in th e neural cell adhesion molecule (NCAM), although it is not known why t hese two polysialyltransferases exist, In the present study, we have f irst isolated cDNA encoding human STX, which includes 5'-untranslated sequence, Northern blot analysis, using this cDNA and PST cDNA previou sly isolated by us, demonstrated that PST and STX are expressed in dif ferent fetal and adult tissues. STX is primarily expressed in embryoni c tissues, but only modestly in adult heart, brain, and thymus, PST, o n the other hand, is continuously expressed in adult heart, brain, thy mus, spleen, small and large intestines, and peripheral blood leukocyt es, In various parts of adult brain, the relative amount of PST and ST X appears to be substantially different depending on the regions, The analysis by in situ hybridization of mouse adult brain, however, sugge sts that polysialic acid in the hippocampal formation is synthesized b y both STX and PST, HeLa cells doubly transfected with the isolated ST X cDNA and N-CAM cDNA supported neurite outgrowth much better than HeL a cells expressing N-CAM alone, However, polysialic acid synthesized b y PST appears to be a better substratum than that synthesized by STX. Moreover, the genes for PST and STX were found to reside at chromosome 5, band p21 and chromosome 15, band q26, respectively, These results, taken together, strongly suggest that PST and STX are expressed disti nctly in tissue-specific and cell-specific manners and that they appar ently have distinct roles in development and organogenesis.