Cloning and expression of an alpha-2,8-polysialyltransferase (STX) from Xenopus laevis

Polysialic acid (polySia) is a carbohydrate structure found on neural celladhesion molecules (N-CAM). Two polysialyltransferases (polySiaTs) thatcatalyze synthesis of polySia have been described, and designatedPST-1/PST/ST8SiaIV and STX/ST8SiaII. We cloned a polySiaT (xSTX) from anonmammalian vertebrate, Xenopus laevis . xSTX had 80% amino acidsimilarity to the rat STX. This clone induced polySia expression whentransfected into polySia-negative COS-1 cells. Northern blot analysis ofwhole embryos at different stages of development revealed that xSTX mRNAwas most abundantly expressed in premetamorphic stages. The relative levelof xSTX and N-CAM mRNAs was also examined and found to change in parallelto the extent of polysialylation on N-CAM. In adult tissues, the expressionof xSTX mRNA was restricted to brain, eye and heart, which also expressedpolySia. These results suggest that xSTX is the major enzyme responsiblefor the synthesis of polysialylated N-CAM in embryos at certain stages ofdevelopment and also in adult tissues.