The Vibrio cholerae var regulon encodes a metallo-ß-lactamase and an antibiotic efflux pump, which are regulated by VarR, a LysR-type transcription factor.

The genome sequence of V. cholerae O1 Biovar Eltor strain N16961 has revealed a putative antibiotic resistance (var) regulon that is predicted to encode a transcriptional activator (VarR), which is divergently transcribed relative to the putative resistance genes for both a metallo-ß-lactamase (VarG) and an antibiotic efflux-pump (VarABCDEF). We sought to test whether these genes could confer antibiotic resistance and are organised as a regulon under the control of VarR. VarG was overexpressed and purified and shown to have ß-lactamase activity against penicillins, cephalosporins and carbapenems, having the highest activity against meropenem. The expression of VarABCDEF in the Escherichia coli (ΔacrAB) strain KAM3 conferred resistance to a range of drugs, but most significant resistance was to the macrolide spiramycin. A gel-shift analysis was used to determine if VarR bound to the promoter regions of the resistance genes. Consistent with the regulation of these resistance genes, VarR binds to three distinct intergenic regions, varRG, varGA and varBC located upstream and adjacent to varG, varA and varC, respectively. VarR can act as a repressor at the varRG promoter region; whilst this repression was relieved upon addition of ß-lactams, these did not dissociate the VarR/varRG-DNA complex, indicating that the de-repression of varR by ß-lactams is indirect. Considering that the genomic arrangement of VarR-VarG is strikingly similar to that of AmpR-AmpC system, it is possible that V. cholerae has evolved a system for resistance to the newer ß-lactams that would prove more beneficial to the bacterium in light of current selective pressures.

The leucine-rich repeats of LINGO-1 are not required for self-interaction or interaction with the amyloid precursor protein.

LINGO-1 (leucine rich repeat and Ig domain containing Nogo receptor interacting protein-1) is a central nervous system transmembrane protein which simultaneously interacts with the Nogo-66 receptor and p75(NTR) or TROY on neurons to form a receptor complex responsible for myelin-mediated neurite outgrowth inhibition. On oligodendroglial cells, LINGO-1 interacts with p75(NTR) to constitutively inhibit multiple aspects of oligodendrocyte differentiation. Recently, LINGO-1 was identified as an in vivo interacting partner of the amyloid precursor protein (APP) and, correspondingly, cellular LINGO-1 expression was found to augment the release of the Abeta peptide, the potential causative agent of Alzheimer's disease. In addition, the recombinant LINGO-1 ectodomain has been shown to self-interact in solution and after crystallisation. Here, we have used deletional mutagenesis to identify the regions on LINGO-1 that are involved in homo- and heterotypic interactions. We have found that the N-terminal region containing the leucine-rich repeats along with the transmembrane and cytoplasmic domains of LINGO-1 are not required for self-interaction or interaction with APP.

LINGO-1-mediated inhibition of oligodendrocyte differentiation does not require the leucine-rich repeats and is reversed by p75(NTR) antagonists.

LINGO-1 is a potent negative regulator of oligodendrocyte differentiation and hence may play a pivotal restrictive role during remyelination in demyelinating diseases such as multiple sclerosis. However, little is known as to which stages of oligodendrocyte differentiation are inhibited by LINGO-1, which domains of the protein are involved and whether accessory proteins are required. Here, we show that LINGO-1 expression in the human oligodendroglial cell line MO3.13 inhibited process extension and this was reversed by an anti-LINGO-1 antibody or the antagonist LINGO-1-Fc. LINGO-1 expression was also found to inhibit myelin basic protein transcription in the rat oligodendroglial cell line CG4. Both of these inhibitory actions of LINGO-1 were abrogated by deletion of the entire ectodomain or cytoplasmic domains but, surprisingly, were unaffected by deletion of the leucine-rich repeats (LRRs). As in neurons, LINGO-1 physically associated with endogenous p75(NTR) in MO3.13 cells and, correspondingly, its inhibition of process extension was reversed by antagonists of p75(NTR). Thus, LINGO-1 inhibits multiple aspects of oligodendrocyte differentiation independently of the LRRs via a process that requires p75(NTR) signalling.