The Occurrence of Malignancy in Trypanosoma brucei brucei by Rapid Passage in Mice

Abstract

Pleomorphic Trypanosoma brucei are best known for their tightly controlled cell growth and developmental program, which ensures their transmissibility and host fitness between the mammalian host and insect vector. However, after long-term adaptation in the laboratory or by natural evolution, monomorphic parasites can be derived. The origin of these monomorphic forms is currently unclear. Here, we produced a series of monomorphic trypanosome stocks by artificially syringe-passage in mice, creating snapshots of the transition from pleomorphism to monomorphism. We then compared these artificial monomorphic trypanosomes, alongside several naturally monomorphic T. evansi and T. equiperdum strains, with the pleomorphic T. brucei. In addition to failing to generate stumpy forms in animal bloodstream, we found that monomorphic trypanosomes from laboratory and nature exhibited distinct differentiation patterns, which are reflected by their distinct differentiation potential and transcriptional changes. Lab-adapted monomorphic trypanosomes could still be induced to differentiate, and showed only minor transcriptional differences to that of the pleomorphic slender forms but some accumulated differences were observed as the passages progress. All naturally monomorphic strains completely fail to differentiate, corresponding to their impaired differentiation regulation. We propose that the natural phenomenon of trypanosomal monomorphism is actually a malignant manifestation of protozoal cells. From a disease epidemiological and evolutionary perspective, our results provide evidence for a new way of thinking about the origin of these naturally monomorphic strains, the malignant evolution of trypanosomes may raise some concerns. Additionally, these monomorphic trypanosomes may reflect the quantitative and qualitative changes in the malignant evolution of T. brucei, suggesting that single-celled protozoa may also provide the most primitive model of cellular malignancy, which could be a primitive and inherent biological phenomenon of eukaryotic organisms from protozoans to mammals.

Mechanisms of life cycle simplification in African trypanosomes

“…To explore the initiation of this phenotypic change, we performed laboratory selection to generate monomorphism de novo. In five independently selected clonal lineages this generated consistent changes in the transcriptome, with key posttranscriptional regulators showing altered expression, including two with established roles in life cycle progression (RBP10, ZCH20); previous selections for monomorphism have also identified changes in posttranscriptional regulators 42,43 .…”

PAG3 promotes the differentiation of bloodstream forms in Trypanosoma brucei and reveals the evolutionary relationship among the Trypanozoon trypanosomes

“…For example, it has been demonstrated that several trypanosomal proteins such as RBP7, YAK or MEKK1, TbGPR89 and others are involved in the stumpy induction factor signaling pathway and cell differentiation in T. brucei (McDonald et al, 2018;Silvester et al, 2018;Rojas et al, 2019). Furthermore, a recent study which generated monomorphic T. brucei, from a pleomorphic strain, confirmed that changes in the transcriptome of nuclear genes were associated with this transformation (Cai et al, 2022). Unlike kinetoplast DNA, which is required for the development and adaption in the insect, nuclear genes seem to perform a more important function in the differentiation between the mammalian bloodstream stages.…”

“…Several cell surface proteins have also been proved to be responsible for the transduction of stumpy induction factor (SIF) signaling within cells (Mony and Matthews, 2015;McDonald et al, 2018;Rojas et al, 2019). Interestingly, defects in quorum sensing pathways have recently been reported in T. evansi and T. equiperdum but also in artificially selected monomorphic lines of T. brucei (Cai et al, 2022). These parasites are normally almost indistinguishable from each other, using a wide range of molecular markers (Gibson et al, 1980;Lun et al, 1992a;Lun et al, 1992b;Lai et al, 2008;Verney et al, 2020), which makes it all the more interesting that these differences map onto the quorum sensing pathways.…”