Interfering polysialyltransferase ST8SiaII/STX mRNA inhibits neurite growth during early hippocampal development

Polysialic acid (PSA) attached to NCAM is involved in cell–cell interactions participating in structural and functional plasticity of neuronal circuits. Two polysialyltransferases, ST8SiaII/STX and ST8SiaIV/PST, polysialylate NCAM. We previously suggested that ST8SiaII/STX is the key enzyme for polysialylation in hippocampus. Here, polysialyltransferase mRNA interference experiments showed that, knock down of ST8SiaIV/PST transcripts did not affect PSA expression, but PSA was almost absent from neuronal surfaces when ST8SiaII/STX mRNA was interfered. Non-polysialylated neurons bore a similar number of neurites per cell than polysialylated neurons. However, non-polysialylated processes were shorter and a lower density of synaptophysin clusters accompanied this reduced neuritic growth. Therefore, ST8SiaII/STX expression is essential to allow a correct neuritic development at initial stages of hippocampus ontogeny.