Segmental Variation in a Duplicated msp2 Pseudogene Generates Anaplasma marginale Antigenic Variants

Abstract

Anaplasma marginale is a prototypical highly antigenically variant bacterial pathogen dependent on the sequential generation of major surface protein 2 (Msp2) outer membrane variants to establish persistent infection. Msp2 is encoded by a single expression site, and diversity is achieved by gene conversion of chromosomally encoded msp2 pseudogenes. Analysis of the full complement of msp2 pseudogenes in the St. Maries strain revealed identical sequences in different loci. The Florida strain shared the same locus structure, but in the loci where the St. Maries strain had two identical pseudogenes, the Florida strain had one whose sequence was identical to the St. Maries sequences, while the sequence of the second pseudogene differed. Consequently, we hypothesized that the msp2 pseudogene repertoire arose via gene duplication, allowing structural variation to occur in one copy but the utility of the other to be retained. Using comparative genomics, we first established that duplication of msp2 pseudogenes is common among A. marginale strains: all seven examined strains had at least one duplicate pair in which either the genes in the pair were maintained as identical copies or the genes contained segmental changes. We then demonstrated that a minimal segmental change in a duplicated pseudogene locus is sufficient for immune escape from the broad antibody response generated in a natural host, as is a completely divergent pseudogene sequence in an otherwise conserved locus. The results support a model in which a locus first duplicates, resulting in a second identical copy, and then progressively incorporates changes to generate an msp2 repertoire capable of generating sufficient antigenic variants to escape immunity and establish persistent infection.

Overexpressed pseudogenes, DUXAP8 and DUXAP9, promote growth of renal cell carcinoma and serve as unfavorable prognostic biomarkers

“…Pseudogenes, genomic DNA sequences similar to normal genes, are regarded as defunct relatives of functional genes [5, 6]. Pseudogenes are generally divided into two main types: processed (or retrotransposed) pseudogene and non-processed (or duplicated) pseudogenes [7–9]. After the first discovery of pseudogene structure in 5S DNA of Xenopus laevis by C. Jacq et al in 1977 [10], increasing studies have demonstrated that dysregulation of pseudogenes plays key roles in development of human disorders and these deregulated pseudogenes may act as promising therapeutic targets for diseases [11, 12].…”

Omp2b Porin Alteration in the Course of Evolution of Brucella spp.

“…For example, in Anaplasma marginale the major surface protein Msp2 is encoded by a single expression site, and diversity is achieved by gene conversion of chromosomally encoded msp2 pseudogenes (Graça et al, 2015). A model was proposed where msp2, through gene conversion, progressively incorporates changes to produce an msp2 repertoire capable of generating sufficient antigenic variants to escape immunity and establish persistent infection (Graça et al, 2019). We may see a similar situation from the present omp2 study, with the progressive changes of the Omp2b porin cited above, altering the porin both functionally and antigenically.…”

Refinement of an established large-animal model to understand the tick-pathogen-host interface

“…Passive transfer from either infected or immunized animals does not confer protection to naïve animals (137). The A. marginale Msp2 and Msp3 will create variants of themselves through nonreciprocal homologous recombination, theoretically allowing for immune evasion (138,139). When an antibody response is generated to Msp2 and Msp3, the variants are cleared, and then a subsequent generation of new variants appears to which the antibodies do not respond, as if in a complex game of cat and mouse (140).…”

“…Msp2 is flanked by conserved C and N terminal regions with a hypervariable region (HVR) in the middle (141). The variation encoded in the msp2 locus comes from partial or whole hypervariable regions from msp2 pseudogenes that are recombined into the HVR of the msp2 operon, creating a new variant (139). The number of pseudogenes varies per strain, but there are multiple pseudogenes allowing for many different variants to be produced.…”

“…The number of pseudogenes varies per strain, but there are multiple pseudogenes allowing for many different variants to be produced. It has been reported that this variation leads to loss of protective antibody responses (139).…”