Biology subjects

Lapsley, C.

Publications and source records attributed to Lapsley, C..

3 recordsLinked to original sources

bioRxiv2018

The ATR kinase of Trypanosoma brucei links DNA damage signalling and monoallelic control of surface antigen gene expression during antigenic variation

To evade mammalian immunity, Trypanosoma brucei switches the variant surface glycoprotein (VSG) expressed on its surface. Key to this reaction are controls exerted to ensure only one of many subtelomeric multigene VSG expression sites are transcribed at a time. DNA repair activities have to date been implicated only in catalysis of VSG switching by recombination, not transcriptional control. However, how VSG switching is signalled to guide the appropriate reaction, or to integrate switching into parasite growth, is unknown. Here we show that loss of ATR, a DNA damage signalling protein kinase, is lethal and causes increased nuclear genome lesions. ATR depletion also causes expression of mixed VSGs on the cell surface, increased transcription of genes from silent expression sites, and altered localisation of RNA Polymerase I and VEX1, factors involved in VSG transcription. The work therefore reveals that VSG expression control is mediated by a nuclear DNA damage signalling factor.

molecular biology↗

bioRxiv2018

RibonucleaseH1-targeted R-loops in surface antigen gene expression sites can direct trypanosome immune evasion

Switching of the Variant Surface Glycoprotein (VSG) in Trypanosoma brucei provides a crucial host immune evasion strategy that is catalysed both by transcription and recombination reactions, each operating within specialised telomeric VSG expression sites (ES). VSG switching is likely triggered by events focused on the single actively transcribed ES, from a repertoire of around 15, but the nature of such events is unclear. Here we show that RNA-DNA hybrids, called R-loops, form preferentially within sequences termed the 70 bp repeats in the actively transcribed ES, but spread throughout the active and inactive ES in the absence of RNase H1, which degrades R-loops. Loss of RNase H1 also leads to increased levels of VSG coat switching and replication-associated genome damage, some of which accumulates within the active ES. This work indicates VSG ES architecture elicits R-loop formation, and that these RNA-DNA hybrids connect T. brucei immune evasion by transcription and recombination.\n\nAuthor summaryAll pathogens must survive eradication by the host immune response in order to continue infections and be passed on to a new host. Changes in the proteins expressed on the surface of the pathogen, or on the surface of the cells the pathogen infects, is a widely used strategy to escape immune elimination. Understanding how this survival strategy, termed antigenic variation, operates in any pathogen is critical, both to understand interaction between the pathogen and host and disease progression. A key event in antigenic variation is the initiation of the change in expression of the surface protein gene, though how this occurs has been detailed in very few pathogens. Here we examine how changes in expression of the surface coat of the African trypanosome, which causes sleeping sickness disease, are initiated. We reveal that specialised nucleic acid structures, termed R-loops, form around the expressed trypanosome surface protein gene and increase in abundance after mutation of an enzyme that removes them, leading to increased changes in the surface coat in trypanosome cells that are dividing. We therefore shed light on the earliest acting events in trypanosome antigenic variation.

microbiology↗

bioRxiv2018

Genome-wide mapping reveals conserved and diverged R-loop activities in the unusual genetic landscape of the African trypanosome genome

R-loops are stable RNA-DNA hybrids that have been implicated in transcription initiation and termination, as well as in telomere homeostasis, chromatin formation, and genome replication and instability. RNA Polymerase (Pol) II transcription in the protozoan parasite Trypanosoma brucei is highly unusual: virtually all genes are co-transcribed from multigene transcription units, with mRNAs generated by linked trans-splicing and polyadenylation, and transcription initiation sites display no conserved promoter motifs. Here, we describe the genome-wide distribution of R-loops in wild type mammal-infective T. brucei and in mutants lacking RNase H1, revealing both conserved and diverged functions. Conserved localisation was found at centromeres, rRNA genes and retrotransposon-associated genes. RNA Pol II transcription initiation sites also displayed R-loops, suggesting a broadly conserved role despite the lack of promoter conservation or transcription initiation regulation. However, the most abundant sites of R-loop enrichment were within the intergenic regions of the multigene transcription units, where the hybrids coincide with sites of polyadenylation and nucleosome-depletion. Thus, instead of functioning in transcription termination, most T. brucei R-loops act in a novel role, promoting RNA Pol II movement or mRNA processing. Finally, we show there is little evidence for correlation between R-loop localisation and mapped sites of DNA replication initiation.

genomics↗