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Escherichia coli K-12 and K-12 hybrid strains constructed to express a polysialic acid capsule, the Kl antigen, were able to efficiently use sialic acid as a sole carbon source. This ability was dependent on induction of at least two activities: a sialic acid-specific transport activity, and an aldolase activity specific for cleaving sialic acids. Induction over basal levels required sialic acid as the apparent inducer, and induction of both activities was repressed by glucose. Induction also required the intracellular accumulation of sialic acid, which could be either added exogenously to the medium or accumulated intraceliularly through biosynthesis. Exogenous sialic acid appeared to be transported by an active mechanism that did not involve covalent modification of the sugar. Mutations affecting either the transport or degradation of sialic acid prevented its use as a carbon source and have been designated nanT and nanA, respectively. These mutations were located by transduction near min 69 on theE. coli K-12 genetic map, between argG and glnF. In addition to being unable to use sialic acid as a carbon source, aldolase-negative mutants were growth-inhibited by this sugar. Therefore, the intracellularly accumulated sialic acid was toxic in aldolase-deficient E. coli strains. The dual role of aldolase in dissimilating and detoxifying sialic acids is consistent with the apparent multiple controls on expression of this enzyme.

A phage endoneuraminidase that specifically cleaves alpha-2, 8-1inked polysialic acid has been found to be a useful probe for examining the biological role of this sugar moiety on the neural cell adhesion molecule (NCAM). The enzyme caused a 3.3-fold increase in the rate of NCAM-dependent aggregation of membrane vesicles from chicken embryonic brain, without the nonspecific effects previously encountered with the use of exoneuraminidases. The enhancement of aggregation was closely correlated with removal of sialic acid as assessed by electrophoretic mobility. Extension of this analysis to cultures of spinal ganglia indicated that removal of sialic acid by the endoneuraminidase results in an increase in the thickness of neurite bundles. This enhancement of fasciculation was reversed by addition of anti-NCAM Fab, suggesting that the enzyme treatment was not toxic and did not produce nonspecific effects on adhesion. Injection of the enzyme into the eyes of 3.5-d chicken embryos consistently produced a striking array of abnormalities in those parts of the neural retina that contained the highest concentrations of NCAM at the time of injection. These perturbations included a dramatic thickening of the neural epithelium in the posterior eye, a failure of cells in this region to elongate radially, formation of an ectopic optic fiber layer, and an incomplete association of the presumptive pigmented epithelium with the neural retina. These results provide the first direct evidence that the polysialic acid on NCAM has a regulatory effect on adhesion between living cells, and that the amount of this carbohydrate is critical for the normal morphogenesis of nerve tissue.The neural cell adhesion molecule (NCAM) t is a cell-surface glycoprotein that serves as a ligand in the formation of cellcell bonds (see references 9, 26, and 27 for review). The binding appears to involve the direct interaction between NCAMs on each cell, and therefore represents an example of homophilic adhesion (31). NCAM is expressed on a variety of cell types in the vertebrate embryo, including primitive neuroepithelia (36), neurons (29, 32), glial cells (14, 23), and muscle cells (15). Adhesion of neurons to muscle, glia, and other neurons has been found to be mediated at least in part by NCAM, and appears to be an essential event in the formation of nerve-muscle contacts that lead to synapses ~ Abbreviations used in this paper: endo-N, the soluble endoneuraminidase from K1F bacteriophage; NCAM, neural cell adhesion molecule.(30), guidance of axon growth cones along marginal pathways of the central nervous system (36), and the formation of neurite fascicles (29). In addition, antibodies to NCAM have been shown to alter the histogenesis of the retina in vitro (3).The complex glycan chains associated with NCAM have a very unusual structure including one or more relatively long unbranched homopolymers of alpha-2, 8-1inked sialic acid residues (6,7,12,43). Removal of the sialic acid by commercial exoneuraminidases results in an increase in the app...

Three prokaryotic-derived probes to identify and study the temporal expression of oligo-or poly(sialic acid) also recognized rat brain membranes, further substantiating the presence of poly(sialic acid) in rat brain. This conclusion was confirmed by using a mutant of E. coli K1 that was defective in the synthesis of poly(sialic acid) and could only transfer sialic acid to exogenous acceptors of oligo-or poly(sialic acid). Sialyl polymer synthesis was restored in the mutant when brain membranes were added as exogenous acceptor.Sialic acid occurs primarily as the terminal, nonreducing sugar on N-asparaginyl-linked glycoproteins often attached to galactosyl residues of bi-, tri-, or tetraantennary sugar chains. Rarely, however, sialic acid exists internally to form polysialosyl chains of various lengths. A well-characterized poly(sialic acid) is a capsular polysaccharide, the K1 anti-

Lactoferrin (Lf) is a sialic acid (Sia)-rich, iron-binding milk glycoprotein that has multifunctional health benefits. Its potential role in neurodevelopment and cognition remains unknown. To test the hypothesis that Lf may function to improve neurodevelopment and cognition, the diet of postnatal piglets was supplemented with Lf from days 3 to 38. Expression levels of selected genes and their cognate protein profiles were quantitatively determined. The importance of our new findings is that Lf (1) upregulated several canonical signaling pathways associated with neurodevelopment and cognition; (2) influenced ~10 genes involved in the brain-derived neurotrophin factor (BDNF) signaling pathway in the hippocampus and upregulated the expression of polysialic acid, a marker of neuroplasticity, cell migration and differentiation of progenitor cells, and the growth and targeting of axons; (3) upregulated transcriptional and translational levels of BDNF and increased phosphorylation of the cyclic adenosine monophosphate (cAMP) response element-binding protein, CREB, a downstream target of the BDNF signaling pathway, and a protein of crucial importance in neurodevelopment and cognition; and (4) enhanced the cognitive function and learning of piglets when tested in an eight-arm radial maze. The finding that Lf can improve neural development and cognition in postnatal piglets has not been previously described.Electronic supplementary materialThe online version of this article (doi:10.1007/s12035-014-8856-9) contains supplementary material, which is available to authorized users.