A gene expression comparison of Trypanosoma brucei and Trypanosoma congolense in the bloodstream of the mammalian host reveals species-specific adaptations to density-dependent development

Abstract

In the bloodstream of mammalian hosts Trypanosoma brucei undergoes well-characterised density-dependent growth control and developmental adaptation for transmission. This involves the differentiation from proliferative, morphologically ‘slender’ forms to quiescent ‘stumpy’ forms that preferentially infect the tsetse fly vector. Another important livestock trypanosome, Trypanosoma congolense, also undergoes density-dependent cell-cycle arrest although this is not linked to obvious morphological transformation. Here we have compared the gene expression profile of T. brucei and T. congolense during the ascending phase of the parasitaemia and at peak parasitaemia in mice, analysing species and developmental differences between proliferating and cell-cycle arrested forms. Despite underlying conservation of their quorum sensing signalling pathway, each species exhibits distinct profiles of gene regulation when analysed by orthogroup and cell surface phylome profiling. This analysis of peak parasitaemia T. congolense provides the first molecular signatures of potential developmental competence, assisting life cycle developmental studies in these important livestock parasites. Furthermore, comparison with T. brucei identifies candidate molecules from each species that may be important for their survival in the mammalian host, transmission or distinct tropism in the tsetse vector.

The zinc finger proteins ZC3H20 and ZC3H21 stabilise mRNAs encoding membrane proteins and mitochondrial proteins in insect‐form Trypanosoma brucei

“…It is also possible is that some of the plasma membrane proteins that are regulated by ZC3H20 are needed for procyclic form differentiation. Several of them are already increased in stumpy forms at both RNA (Silvester et al, ) and protein (Dejung et al, ) levels, including trans‐sialidases, amastin‐like protein, flabarin and PSSA‐2 (Supplementary Table , sheet 1). One mRNA that was mildly decreased, relative to wild type, after 24‐hr cis ‐aconitate treatment of cells lacking ZC3H20 encoded PIP39, a protein phosphatase.…”

“…One mRNA that was mildly decreased, relative to wild type, after 24‐hr cis ‐aconitate treatment of cells lacking ZC3H20 encoded PIP39, a protein phosphatase. PIP39 protein is undetectable in bloodstream forms but appears in stumpy forms, along with a roughly twofold increase in PIP39 mRNA (Silvester et al, ). PIP39 depletion delays differentiation to the procyclic form (Szoor, Ruberto, Burchmore, & Matthews, ).…”

“…For example, the mRNA encoding the protein kinase NRKA (Tb927.4.5390) is bound by both RBP10 (Mugo & Clayton, ) and ZC3H20, but the mRNA level was unaffected by ZC3H20 RNAi. NRKA is increased in stumpy forms (Silvester et al, ) and its depletion inhibited differentiation of stumpy to procyclic forms (Alsford, Glover, & Horn, ; Domingo‐Sananes et al, ). The NRKA mRNA is by no means the only one that appears to be subject to dual regulation by RBP10 and ZC3H20.…”

“…Binding of RBP10 to its target mRNAs, probably via the sequence UA(U) 6 in 3′‐UTRs, targets the mRNAs for translational repression and destruction (Mugo & Clayton, ). Levels of RBP10 protein and mRNA decline in stumpy forms (Dejung et al, ; Silvester, Ivens, & Matthews, ) and when bloodstream forms are incubated at maximal density in vitro (Mugo & Clayton, ). In procyclic forms, RBP10 is undetectable and its target mRNAs are generally abundant and well translated.…”

Infections With Extracellular Trypanosomes Require Control by Efficient Innate Immune Mechanisms and Can Result in the Destruction of the Mammalian Humoral Immune System

“…Candidate genes were subsequently validated, confirming their role in density sensing in vivo, leading to the identification of the putative RNA-binding protein RBP7 as a key component in both quorum sensing and cell-cycle arrest (44,45). Interestingly, the quorum sensing observed in T. brucei is also observed in T. congolense although in the latter, density-dependent cell-cycle arrest does not result in actual stumpy form formation and does not follow exactly the same gene regulation profile (46). It does however prepare the parasite for transmission to its definite insect host.…”