PSA-NCAM

Poly-Sialated Neural Cell Adhesion Molecule (PSA-NCAM) is present on the cell surface of developing granule neurons of the adult brain. It permits cells or axons to interact with their neighbours, thereby allowing them to respond to guidance or targeting cues, which are essential for the development and function of the nervous system (Cremer et al. 2000).

NCAM is a member of the immunoglobulin (Ig) superfamily that mediates cell-to-cell interactions or cell-to-extracellular adhesion and recognition functions (Walsh and Doherty, 1997). Moreover, NCAM is highly poly-sialated during late embryonic and early postnatal stages (Muhlenhoff et al., 1998).

The poly-sialic acid (PSA) portion of NCAM is known to be essential in several developmental events, including cell migration (Hu et al., 1996), axon growth (Doherty et al., 1990), nerve branching (Landmesser et al., 1990; Daston et al., 1996), pathfinding (Tang et al., 1992), and synaptic arrangement (Seki and Rutishauser, 1998).

Although, in the adult brain, PSA expression disappears from most of brain regions, persistent PSA expression is found in several restricted regions, including the olfactory bulb and hippocampus (Seki and Arai, 1993). In the adult hippocampus, PSA-NCAM has been reported to contribute to several phenomena in relation to hippocampal plasticity, such as the induction of long-term potentiation and long-term depression (LTD) (Becker et al., 1996), learning behavior (Becker et al., 1996; Murphy et al., 1996), and axonal regeneration and sprouting after injury (Aubert et al., 1998).

PSA-NCAM is expressed in developing granule cells in the DG and their axonal projections, the mossy fibres. Each granule cell grows a single axon, which forms synapses with the proximal dendrites of the CA3 pyramidal cells of the hippocampus (Cremer et al. 2000). Because PSA-NCAM is involved in axonal guidance and development of neurons, it can be used to identify young, immature neurons, similar to CRMP-4.