Impact of the Polysialyltransferases ST8SiaII and ST8SiaIV on Polysialic Acid Synthesis during Postnatal Mouse Brain Development

Abstract

Polysialic acid (polySia), a post-translational modification of the neural cell adhesion molecule (NCAM), is the key regulator of NCAM-mediated functions and crucial for normal brain development, postnatal growth, and survival. Two polysialyltransferases, ST8SiaII and ST8SiaIV, mediate polySia biosynthesis. To dissect the impact of each enzyme during postnatal brain development, we monitored the developmental changes in NCAM polysialylation in wild-type, ST8SiaII-, and ST8SiaIV-deficient mice using whole brain lysates obtained at 10 time points from postnatal days 1 to 21 and from adult mice. In wildtype and ST8SiaIV-null brain, polySia biosynthesis kept pace with the rapid increase in brain weight until day 9, and nearly all NCAM was polysialylated. Thereafter, polySia dropped by ϳ70% within 1 week, accompanied by the first occurrence of polySia-free NCAM-140 and NCAM-180. In ST8SiaII-null brain, polySia declined immediately after birth, leading to 60% less polySia at day 9 combined with the untimely appearance of polySia-free NCAM. Polysialyltransferase deficiency did not alter NCAM expression level or isoform pattern. In all three genotypes, NCAM-140 and NCAM-180 were expressed at constant levels from days 1 to 21 and provided the major polySia acceptors. By contrast, NCAM-120 first appeared at day 5, followed by a strong up-regulation inverse to the decrease in polySia. Together, we provide a comprehensive quantitative analysis of the developmental changes in polySia level, NCAM polysialylation status, and polysialyltransferase transcript levels and show that the predominant role of ST8SiaII during postnatal brain development is restricted to the first 15 days. Polysialic acid (polySia)2 is a unique post-translational modification primarily of the neural cell adhesion molecule NCAM (1-3). Composed of ␣2,8-linked N-acetylneuraminic acid, polySia forms a large negatively charged and highly hydrated glycan structure that can extend beyond the protein core. Attachment of polySia to NCAM doubles the hydrodynamic radius of the extracellular part of NCAM, thereby increasing the intermembrane space and disrupting the adhesive properties of NCAM and other cell adhesion molecules (4 -6). Removal of polySia by treatment with endoneuraminidase, a bacteriophage-derived enzyme that specifically cleaves polySia (7), demonstrated intervention of polySia in dynamic cellular processes as different as migration of neuronal precursor cells, axonal outgrowth, synaptogenesis, physiological and morphological synaptic plasticity, and control of circadian rhythm (8 -15). Although polySia levels are high during embryonic development, expression in the adult is restricted to brain regions of persistent neural plasticity such as the subventricular zone, the rostral migratory stream toward the olfactory bulb, the hippocampus, and the hypothalamo-neurohypophyseal system (16 -18).The outstanding role of polySia in controlling NCAM interactions became apparent by the lethal phenotype of mice lacking polySia while retaining normal NCAM expr...

Polysialylation of the Synaptic Cell Adhesion Molecule 1 (SynCAM 1) Depends Exclusively on the Polysialyltransferase ST8SiaII in Vivo

“…During postnatal brain development, prominent signals for polySia-SynCAM 1 were observed between P1 and P11, whereas polysialylation of SynCAM 1 was drastically down-regulated thereafter, resulting in a sharp drop between P11 and P15. This time course followed the previously described down-regulation of ST8SiaII transcript level, which dropped by 95% during postnatal brain development, with the strongest reduction between P5 and P11 (27).…”

“…At this stage, NCAM is completely polysialylated (27), whereas only a small subfraction of SynCAM 1 is modified by polySia (13). This raises the question whether polysialylation of SynCAM 1 is restricted to particular iso-and/or glycoforms in vivo.…”

Regulation of Glycan Structures in Murine Embryonic Stem Cells

“…Cell surface "stage-specific carbohydrate antigens" have historically been used as markers during embryogenesis (14,(83)(84)(85)(86)(87)(88)(89)(90), where they correlate with cellular interactions during developmental transitions in pre-and postimplantation embryos (8,75,91,92). Glycans also influence numerous cellular functions, such as modulating cell signals and regulating the balance between cell adhesion versus migration during embryogenesis (8,93,94). Cell movements during gastrulation are influenced by cell surface glycan structures, including glycoproteins (2,3,7,8), proteoglycans (95)(96)(97), and glycolipids (98,99).…”

Differential effects of Pax3 on expression of polysialyltransferases STX and PST in TGF-β-treated normal murine mammary gland cells

“…STX is the major polysialyltransferase during embryogenesis, and plays dominated role in PSA synthesis in cancer cells, 28 whereas PST is mainly expressed in mouse or human adult brain. 36,37 In our current study, mRNA level of STX was obviously higher than that of PST in NMuMG cells undergoing TGF-b-induced EMT, as a result of Pax3 upregulation.…”