Project description:Epigenetic regulation of mutually exclusive transcription within the var gene family is important for infection and pathogenesis of the malaria parasite Plasmodium falciparum. var genes are kept transcriptionally silent via heterochromatic clusters located at the nuclear periphery; however, only a few proteins have been shown to play a direct role in var gene transcriptional regulation. Importantly, the chromatin components that contribute to var gene nuclear organization remain unknown. Here, we adapted a CRISPR-based immunoprecipitation-mass spectrometry approach for de novo identification of factors associated with specific transcriptional regulatory sequences of var genes. Tagged, catalytically inactive Cas9 (“dCas9”) was targeted to var gene promoters or introns, cross-linked, and immunoprecipitated with all DNA, proteins, and RNA associated with the targeted locus. Chromatin immunoprecipitation followed by sequencing demonstrated that genome-wide dCas9 binding was specific and robust. Proteomics analysis of dCas9-immunoprecipitates identified specific proteins for each target region, including known and novel factors such as DNA binding proteins, chromatin remodelers, and structural proteins. We also demonstrate the ability to immunoprecipitate RNA that is closely associated to the targeted locus. Our CRISPR/dCas9 study establishes a new tool for targeted purification of specific genomic loci and advances understanding of virulence gene regulation in the human malaria parasite.
Project description:Histone modifications represent one of the key factors contributing to proper genome regulation. One of the histone modifications involved in gene silencing is H3K9 methylation, which is found in the chromosomes across different eukaryotes and controlled by SU(VAR)3-9 and its orthologs. Although SU(VAR)3-9 was discovered over two decades ago, little is known about the details of its chromosomal distribution pattern. To fill in this gap, we used DamID-seq approach and obtained high-resolution genome-wide profiles for SU(VAR)3-9 in two somatic and two germline tissues of fruitfly.
Project description:The P. falciparum genome is equipped with several subtelomeric gene families that are implicated in parasite virulence and immune evasion. The members of these gene families are uniformly positioned within heterochromatic domains of the genome and are thus subject to variegated expression. The best-studied example is that of the var gene family encoding the major parasite virulence factor P. falciparum erythrocyte membrane protein 1 (PfEMP1). Transcriptional regulation of other subtelomeric gene families and their role in parasite biology is much less understood. Here, we investigated the mode of transcriptional control of var, rif, stevor, phist and pfmc-2tm families by comparative genome-wide transcriptional profiling of transgenic parasite lines. Our results establish a clear functional distinction between var and non-var transcriptional control mechanisms. Unlike var promoters, we find that promoters of non-var families are not silenced by default. Moreover, we show that mutually exclusive transcription is unique to the var gene family.