Differential Expression and Sequence Conservation of theAnaplasma marginale msp2Gene Superfamily Outer Membrane Proteins

Abstract

Bacterial pathogens in the genera Anaplasma and Ehrlichia encode a protein superfamily, pfam01617, which includes the predominant outer membrane proteins (OMPs) of each species, major surface protein 2 (MSP2) and MSP3 of Anaplasma marginale and Anaplasma ovis, Anaplasma phagocytophilum MSP2 (p44), Ehrlichia chaffeensis p28-OMP, Ehrlichia canis p30, and Ehrlichia ruminantium MAP1, and has been shown to be involved in both antigenic variation within the mammalian host and differential expression between the mammalian and arthropod hosts. Recently, complete sequencing of the A. marginale genome has identified an expanded set of genes, designated omp1-14, encoding new members of this superfamily. Transcriptional analysis indicated that, with the exception of the three smallest open reading frames, omp2, omp3, and omp6, these superfamily genes are transcribed in A. marginale-infected erythrocytes, tick midgut and salivary glands, and the IDE8 tick cell line. OMPs 1, 4, 7 to 9, and 11 were confirmed to be expressed as proteins by A. marginale within infected erythrocytes, with expression being either markedly lower (OMPs 1, 4, and 7 to 9) or absent (OMP11) in infected tick cells, which reflected regulation at the transcript level. Although the pfam01617 superfamily includes the antigenically variable MSP2 and MSP3 surface proteins, analysis of the omp1-14 sequences throughout a cycle of acute and persistent infection in the mammalian host and tick transmission reveals a high degree of conservation, an observation supported by sequence comparisons between the St. Maries strain and Florida strain genomes.

Tick cell lines: tools for tick and tick-borne disease research

“…For example, levels of expression of the major surface proteins MSP1a and 1b in tick cells and bovine erythrocytes correlated with their roles as adhesins for the different host cells [44], and levels of expression of outer membrane proteins encoded by the msp2 gene superfamily differed markedly between tick and bovine cells [45]. In A. phagocytophilum, the immunodominant p44 antigen predominated in human cells but not in tick cells and might be involved in regulatory changes that mediate survival of the pathogen by immune modulation after tick transmission [46].…”

Analysis of membrane protein genes in a Brazilian isolate of Anaplasma marginale

“…These genes can be separate or grouped in structures similar to an operon . Within this group, OMP2, OMP3 and OMP6 are probably pseudogenes, as their transcripts have not been detected in erythrocyte stages of different A. marginale isolates (Noh et al 2006, Ramos et al 2007). …”

“…2). According to Noh et al (2006), this variation is probably associated with nucleotide substitutions in the central region of this gene, which maintain the reading frame but introduce variations in amino acids. The genes that encode OMPs 7-9 share large areas of identity at the 5' and 3' termini, where recombination can occur, while C and N terminal areas exhibit relative conservation.…”

In vitro cultivation of Anaplasma marginale and A. phagocytophilum in tick cell lines: a review

“…In addition, in vitro cultivation of A. marginale in tick cells has been used in comparative studies with infected bovine erythrocytes for differential bacterial gene transcriptional analyses and expression profile of outer membrane proteins to search for potential A. marginale vaccine candidates GARCIA-GARCIA et al, 2004;NOH et al, 2006), and in RNA interference approaches for functional studies to discover genes/proteins that are differentially expressed in tick cells in response to infection with A. marginale (DE LA FUENTE et al, 2007;KOCAN et al, 2009). These studies indicate that A. marginale affects the expression of tick genes important for tick survival and pathogen multiplication; thus, a molecular mechanism occurs by which tick cell gene expression mediates the development of the pathogen through ticks.…”