Novel insights into the glia limitans of the olfactory nervous system

Olfactory ensheathing cells (OECs) are often described as being present in both the peripheral and the central nervous systems (PNS and CNS). Furthermore, the olfactory nervous system glia limitans (the glial layer defining the PNS-CNS border) is considered unique as it consists of intermingling OECs and astrocytes. In contrast, the glia limitans of the rest of the nervous system consists solely of astrocytes which create a distinct barrier to Schwann cells (peripheral glia). The ability of OECs to interact with astrocytes is one reason why OECs are believed to be superior to Schwann cells for transplantation therapies to treat CNS injuries. We have used transgenic reporter mice in which glial cells express DsRed fluorescent protein to study the cellular constituents of the glia limitans. We found that the glia limitans layer of the olfactory nervous system is morphologically similar to elsewhere in the nervous system, with a similar low degree of intermingling between peripheral glia and astrocytes. We found that the astrocytic layer of the olfactory bulb is a distinct barrier to bacterial infection, suggesting that this layer constitutes the PNS-CNS immunological barrier. We also found that OECs interact with astrocytes in a similar fashion as Schwann cells in vitro. When cultured in three dimensions, however, there were subtle differences between OECs and Schwann cells in their interactions with astrocytes. We therefore suggest that glial fibrillary acidic protein-reactive astrocyte layer of the olfactory bulb constitutes the glia limitans of the olfactory nervous system and that OECs are primarily "PNS glia."

Burkholderia pseudomallei sequencing identifies genomic clades with distinct recombination, accessory, and epigenetic profiles

Burkholderia pseudomallei (Bp) is the causative agent of the infectious disease melioidosis. To investigate population diversity, recombination, and horizontal gene transfer in closely related Bp isolates, we performed whole-genome sequencing (WGS) on 106 clinical, animal, and environmental strains from a restricted Asian locale. Whole-genome phylogenies resolved multiple genomic clades of Bp, largely congruent with multilocus sequence typing (MLST). We discovered widespread recombination in the Bp core genome, involving hundreds of regions associated with multiple haplotypes. Highly recombinant regions exhibited functional enrichments that may contribute to virulence. We observed clade-specific patterns of recombination and accessory gene exchange, and provide evidence that this is likely due to ongoing recombination between clade members. Reciprocally, interclade exchanges were rarely observed, suggesting mechanisms restricting gene flow between clades. Interrogation of accessory elements revealed that each clade harbored a distinct complement of restriction-modification (RM) systems, predicted to cause clade-specific patterns of DNA methylation. Using methylome sequencing, we confirmed that representative strains from separate clades indeed exhibit distinct methylation profiles. Finally, using an E. coli system, we demonstrate that Bp RM systems can inhibit uptake of non-self DNA. Our data suggest that RM systems borne on mobile elements, besides preventing foreign DNA invasion, may also contribute to limiting exchanges of genetic material between individuals of the same species. Genomic clades may thus represent functional units of genetic isolation in Bp, modulating intraspecies genetic diversity.

Phagocytosis of bacteria by olfactory ensheathing cells and Schwann cells

Opportunistic bacterial infections of the nasal cavity could potentially lead to infection of the brain if the olfactory or trigeminal nerves are colonised. The olfactory nerve may be a more susceptible route because primary olfactory neurons are in direct contact with the external environment. Peripheral glia are known to be able to phagocytose some species of bacteria and may therefore provide a defence mechanism against bacterial infection. As the nasal cavity is frequently exposed to bacterial infections, we hypothesised that the olfactory and trigeminal nerves within the nasal cavity could be subjected to bacterial colonisation and that the olfactory ensheathing cells and Schwann cells may be involved in responding to the bacterial invasion. We have examined the ability of mouse OECs and Schwann cells from the trigeminal nerve and dorsal root ganglia to phagocytose Escherichia coli and Burkholderia thailandensis in vitro. We found that all three sources of glia were equally able to phagocytose E. coli with 75-85% of glia having phagocytosed bacteria within 24h. We also show that human OECs phagocytosed E. coli. In contrast, the mouse OECs and Schwann cells had little capacity to phagocytose B. thailandensis. Thus subtypes of peripheral glia have similar capacities for phagocytosis of bacteria but show selective capacity for the two different species of bacteria that were examined. These results have implications for the understanding of the mechanisms of bacterial infections as well as for the use of glia for neural repair therapies.

Guinea pig serum L-asparaginase: purification, and immunological relationship to liver L-asparaginase and serum L-asparaginases in other mammals

L-asparaginase, an enzyme used in the treatment of acute lymphocytic leukemia, is found in the serum of only a few mammalian groups, including the guinea pig and its close relatives in the superfamily Cavioidea. This report describes the purification and characterization of L-asparaginase from guinea pig serum. Antiserum against the purified enzyme cross-reacted with sera from other Cavioidean species but not with mouse serum. Relatively weak cross-reaction with unpurified L-asparaginase in guinea pig liver indicates a significant degree of evolutionary divergence.

Transcriptional co-activation at the ansB promoters: involvement of the activating regions of CRP and FNR when bound in tandem

Previous work with semi-synthetic promoters containing a single CRP binding site centred at 41.5 bp from the transcription start site has demonstrated enhanced transcription (synergism) when a second binding site, for CRP or FNR, is placed upstream at around -91 bp. The ansB promoter in Escherichia coli is co-activated in a co-dependent manner by one dimer each of CRP and FNR protein whose binding sites are at around -91 and -41 bp, respectively, from the transcription start site. Similarly, the homologous ansB promoter in Salmonella is co-activated by two dimers of CRP which function synergistically. The binding sites at the E. coli promoter have been changed by mutation to provide a number of active promoter derivatives carrying other combinations of FNR and CRP binding sites. The co-dependent versus synergistic interaction of these activators and their requirement for known activating regions have been examined. The results demonstrate that FNR can co-activate when located upstream at around -91 bp in combination with either FNR or CRP downstream. When FNR occupies the downstream site the promoter is co-dependent on an upstream activator, but not when CRP occupies this site. Activating region 1 in CRP (defined by substitutions at residue H159) and its putative equivalent in FNR (defined by substitutions at S73) are mainly required in the upstream activator; the putative equivalent in FNR of activating region 3 of CRP (defined by substitutions at G85 and K52, respectively) is mainly required in the dimer which binds downstream. Activating region 1 of FNR is required only in the downstream subunit of the upstream activator in a promoter which is co-dependent on two FNR dimers. These data suggest that both bound upstream and downstream activators interact with RNA polymerase to promote transcription, and that co-dependence is determined by the nature of the activator plus the promoter context.