An Anomalous Type IV Secretion System in Rickettsia Is Evolutionarily Conserved

Bacterial type IV secretion systems (T4SSs) comprise a diverse transporter family functioning in conjugation, competence, and effector molecule (DNA and/or protein) translocation. Thirteen genome sequences from Rickettsia, obligate intracellular symbionts/pathogens of a wide range of eukaryotes, have revealed a reduced T4SS relative to the Agrobacterium tumefaciens archetype (vir). However, the Rickettsia T4SS has not been functionally characterized for its role in symbiosis/virulence, and none of its substrates are known.Superimposition of T4SS structural/functional information over previously identified Rickettsia components implicate a functional Rickettsia T4SS. virB4, virB8 and virB9 are duplicated, yet only one copy of each has the conserved features of similar genes in other T4SSs. An extraordinarily duplicated VirB6 gene encodes five hydrophobic proteins conserved only in a short region known to be involved in DNA transfer in A. tumefaciens. virB1, virB2 and virB7 are newly identified, revealing a Rickettsia T4SS lacking only virB5 relative to the vir archetype. Phylogeny estimation suggests vertical inheritance of all components, despite gene rearrangements into an archipelago of five islets. Similarities of Rickettsia VirB7/VirB9 to ComB7/ComB9 proteins of epsilon-proteobacteria, as well as phylogenetic affinities to the Legionella lvh T4SS, imply the Rickettsiales ancestor acquired a vir-like locus from distantly related bacteria, perhaps while residing in a protozoan host. Modern modifications of these systems likely reflect diversification with various eukaryotic host cells.We present the rvh (Rickettsiales vir homolog) T4SS, an evolutionary conserved transporter with an unknown role in rickettsial biology. This work lays the foundation for future laboratory characterization of this system, and also identifies the Legionella lvh T4SS as a suitable genetic model

Glutamatergic Gene Expression Is Specifically Reduced in Thalamocortical Projecting Relay Neurons in Schizophrenia

BACKGROUND: Impairment of glutamate neurons which relay sensory and cognitive information from the medial dorsal thalamus to the dorsolateral prefrontal cortex and other cortical regions may contribute to the pathophysiology of schizophrenia. In this study we have assessed the cell-specific expression of glutamatergic transcripts in the medial dorsal thalamus. METHODS AND MATERIALS: We used laser-capture microdissection to harvest two populations of medial dorsal thalamic cells, one enriched with glutamatergic relay neurons, and the other with GABAergic neurons and astroglia, from postmortem brains of subjects with schizophrenia (n=14) and a comparison group (n=20). Quantitative polymerase chain reaction (QPCR) of extracted RNA was used to assay gene expression in different cell populations. RESULTS: The transcripts encoding the ionotropic glutamate receptor subunits NR2D, GluR3, GluR6, GluR7, and the intracellular proteins GRIP1 and SynGAP1 were significantly decreased in relay neurons but not in the mixed glial and interneuron population in schizophrenia. DISCUSSION: Our data suggest that reduced ionotropic glutamatergic expression occurs selectively in neurons giving rise to the cortical projections of the medial dorsal thalamus in schizophrenia, rather than in thalamic cells which function locally. Our findings indicate that glutamatergic innervation is dysfunctional in the circuitry between the medial dorsal thalamus and cortex