An Alba-domain protein required for proteome remodelling during trypanosome differentiation and host transition

Abstract

The transition between hosts is a challenge for digenetic parasites as it is unpredictable. For Trypanosoma brucei subspecies, which are disseminated by tsetse flies, adaptation to the new host requires differentiation of stumpy forms picked up from mammals to procyclic forms in the fly midgut. Here we show that the Alba-domain protein Alba3 is not essential for mammalian slender forms, nor is it required for differentiation of slender to stumpy forms in culture or in mice. It is crucial, however, for the development of T. brucei procyclic forms during the host transition. While steady state levels of mRNAs in differentiating cells are barely affected by the loss of Alba3, there are major repercussions for the proteome. Mechanistically, Alba3 aids differentiation by rapidly releasing stumpy forms from translational repression and stimulating polysome formation. In its absence, parasites fail to remodel their proteome appropriately, lack components of the mitochondrial respiratory chain and show reduced infection of tsetse. Interestingly, Alba3 and the closely related Alba4 are functionally redundant in slender forms, but Alba4 cannot compensate for the lack of Alba3 during differentiation from the stumpy to the procyclic form. We postulate that Alba-domain proteins play similar roles in regulating translation in other protozoan parasites, in particular during life-cycle and host transitions.

Differentiation granules, a dynamic regulator of T. brucei development

“… Proximal proteomes of Alba 3 and 4 were analysed in a WT ( A ) or of Alba 4 in a TbDYRK-/- cell background ( B ). Proteins previously identified as part of stress granules are in Orange 16 , potential interactors with Alba 3 with # (procyclic) and * (stumpy) 38 , known and suspected components of the quorum-sensing pathway in Purple 27 , 29 , 66 – 70 . When available, common names are indicated in the figure for readability.…”

Chemical inhibition of bromodomain proteins in insect stage African trypanosomes perturbs silencing of the Variant Surface Glycoprotein repertoire and results in widespread changes in the transcriptome

“…Given the observation that large numbers of genes show similar expression patterns, we favor a model wherein I-BET151 treatment influences the expression of one or a few RNA binding proteins that themselves regulate large numbers of genes through interaction with their 3' UTRs 66,67 . RNA binding proteins have been shown to be critical for postranscriptional regulation in trypanosomes (reviewed in 68 ) and have also been implicated in differentiation processes in both bloodstream [69][70][71][72] and insect stage forms [73][74][75][76] . Indeed we find that 8 of the 11 RBPs reported by Vigneron to be differentially expressed during insect stage development were differentially expressed in our dataset, including RBP10 (Tb927.8.2780), which is upregulated 2 fold after I-BET151 treatment and also upregulated at early metacyclic stages 31 .…”

Chemical Inhibition of Bromodomain Proteins in Insect-Stage African Trypanosomes Perturbs Silencing of the Variant Surface Glycoprotein Repertoire and Results in Widespread Changes in the Transcriptome

“…Given the observation that large numbers of genes show similar expression patterns, we favor a model wherein I-BET151 treatment influences the expression of one or a few RNA-binding proteins that themselves regulate large numbers of genes through interaction with their 3′ untranslated regions (UTRs) ( 66 , 67 ). RNA-binding proteins have been shown to be critical for postranscriptional regulation in trypanosomes (reviewed in reference 68 ) and have also been implicated in differentiation processes in both bloodstream ( 69 – 72 ) and insect-stage ( 73 – 76 ) forms. Indeed, we find that 8 of the 11 RBPs reported by Vigneron et al to be differentially expressed during insect stage development were differentially expressed in our data set, including RBP10 (Tb927.8.2780), which is upregulated 2-fold after I-BET151 treatment and also upregulated at early metacyclic stages ( 31 ).…”