title: Deciphering the principles that govern mutually exclusive expression of Plasmodium falciparum clag3 genes.
abstract: The product of the Plasmodium falciparum genes clag3.1 and clag3.2 plays a fundamental role in malaria parasite biology by determining solute transport into infected erythrocytes. Expression of the two clag3 genes is mutually exclusive, such that a single parasite expresses only one of the two genes at a time. Here we investigated the properties and mechanisms of clag3 mutual exclusion using transgenic parasite lines with extra copies of clag3 promoters located either in stable episomes or integrated in the parasite genome. We found that the additional clag3 promoters in these transgenic lines are silenced by default, but under strong selective pressure parasites with more than one clag3 promoter simultaneously active are observed, demonstrating that clag3 mutual exclusion is strongly favored but it is not strict. We show that silencing of clag3 genes is associated with the repressive histone mark H3K9me3 even in parasites with unusual clag3 expression patterns, and we provide direct evidence for heterochromatin spreading in P. falciparum. We also found that expression of a neighbor ncRNA correlates with clag3.1 expression. Altogether, our results reveal a scenario where fitness costs and non-deterministic molecular processes that favor mutual exclusion shape the expression patterns of this important gene family.
authors.affiliation: ISGlobal, Barcelona Ctr. Int. Health Res. (CRESIB), Hospital Clínic-Universitat de Barcelona, 08036 Barcelona, Catalonia, Spain Institute for Research in Biomedicine (IRB), 08028 Barcelona, Catalonia, Spain.
authors.forename: Núria
authors.initials: N
authors.lastname: Rovira-Graells
authors.affiliation: Institute for Research in Biomedicine (IRB), 08028 Barcelona, Catalonia, Spain.
authors.forename: Valerie M
authors.initials: VM
authors.lastname: Crowley
authors.affiliation: ISGlobal, Barcelona Ctr. Int. Health Res. (CRESIB), Hospital Clínic-Universitat de Barcelona, 08036 Barcelona, Catalonia, Spain.
authors.forename: Cristina
authors.initials: C
authors.lastname: Bancells
authors.affiliation: ISGlobal, Barcelona Ctr. Int. Health Res. (CRESIB), Hospital Clínic-Universitat de Barcelona, 08036 Barcelona, Catalonia, Spain.
authors.forename: Sofía
authors.initials: S
authors.lastname: Mira-Martínez
authors.affiliation: Institute for Research in Biomedicine (IRB), 08028 Barcelona, Catalonia, Spain Catalan Institution for Research and Advanced Studies (ICREA), 08010 Barcelona, Catalonia, Spain.
authors.forename: Lluís
authors.initials: L
authors.lastname: Ribas de Pouplana
authors.affiliation: ISGlobal, Barcelona Ctr. Int. Health Res. (CRESIB), Hospital Clínic-Universitat de Barcelona, 08036 Barcelona, Catalonia, Spain Institute for Research in Biomedicine (IRB), 08028 Barcelona, Catalonia, Spain Catalan Institution for Research and Advanced Studies (ICREA), 08010 Barcelona, Catalonia, Spain alfred.cortes@cresib.cat.
authors.forename: Alfred
authors.identifier: http://orcid.org/0000-0003-0730-6582
authors.initials: A
authors.lastname: Cortés
mesh_terms: D005786:Gene Expression Regulation; D020868:Gene Silencing; D017125:Genes, Protozoan; D017930:Genes, Reporter; D006570:Heterochromatin / Q000378:metabolism; D006657:Histones / Q000378:metabolism; D005810:Multigene Family; D010957:Plasmids; D010963:Plasmodium falciparum / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic; D022661:RNA, Untranslated / Q000378:metabolism; D015533:Transcriptional Activation
chemical_list: D006570:Heterochromatin; D006657:Histones; D022661:RNA, Untranslated