Molecular regulation of the macroschizont to merozoite differentiation in Theileria annulata

Q Science (General);QH301 Biology;QH426 Genetics

Pieszko, Marta ; Shiels, Brian

University:University of Glasgow

Department:Institute of Biodiversity Animal Health and Comparative Medicine

关键词: Theileria, differentiation, ApiAP2, Apicomplexa, regulators, gametocytogenesis, transcription factors, DNA motifs, merozoite, molecular regulation;   

Others  :  http://theses.gla.ac.uk/6079/1/2015pieszkophd.pdf.pdf

来源: University of Glasgow

【 摘 要 】

Theileria annulata is an intracellular, tick-transmitted apicomplexan parasite, which causes tropical theileriosis in cattle. It undergoes a complex life cycle with several distinct stages occurring within the bovine host and tick vector. ApiAP2 proteins are key candidate transcription factors for regulation of stage specific gene expression across apicomplexans. They are differentially expressedin specific developmental stages and certain ApiAP2s bind specifically to unique DNA sequence motifs. Identification of stage-specific expression of putative transcriptional regulators, the motifs they bind to and potential target genes provided the rationale for this study to understand the molecular mechanisms that control stage differentiation to the merozoite in T. annulata. The results demonstrated that T. annulata ApiAP2s show marked differences in expression levels during the parasite life cycle. ApiAP2 target DNA motifs orthologous to those in Plasmodium and Cryptosporidium were also discovered in Theileria intergenic regions, indicating that the genes downstream are potential targets of Theileria ApiAP2s. These motifs were also found in upstream regions of up-regulated TaApiAP2 genes, suggesting possible auto-regulation and aninteraction network of ApiAP2 transcription factors. Importantly ApiAP2 fusion proteins up-regulated during differentiation to the merozoite stage bound to their predicted specific DNA motifs validating that ApiAP2 DNA-binding domain structure is conserved across Apicomplexa genera. Evidence was also produced that AP2 proteins play important roles in steps that commit a cell to differentiate: TA13515D is the orthologue of the AP2G factor in Plasmodium that is a major regulator of gametocytogenesis: TA16485 may be involved in down-regulation of genes during merogony and expression of TA11145 at a higher level in a cell line competent for merogony relative to a line severelly attenuated indicated involvement in regulation of this differentiation step. Discovery of multiple nuclear factors binding to a 2x(A)CACAC(A) motif implicated in autoregulation of TA11145, together with phylogenetic evidence for a clade of related domains that bind this motif suggest that multiplecompeting ApiAP2s may operate to regulate stochastic commitment to merozoiteproduction. Based on this data an updated stage differentiation model has been generated, with up regulation of the TA11145 gene a key event. A C-box motif association with genes implicated in establishment of the transformed host cell (TashAT, SVSP) suggests it could be important for deregulation of this event as the parasite undergoes stage differentiation. In contrast the inverse G-box was found associated with genes up-regulated from merozoite to piroplasm. EMSA analysis of parasite nuclear extract with a G/Cbox motif probe showed that the motif is an active binding site for a stage regulated nuclear factor. Specific binding of candidate TA12015 protein to theG/C-box motif was unable to be confirmed. Taken together, these results provided evidence that ApiAP2 proteins areregulators of stage-specific gene expression in T.annulata. They also provide insight into probable ApiAP2 interaction networks and support the postulation of a differentiation mechanism conserved across the Apicomplexa. Finally, the data suggests that this mechanism is stochastic and is likely to occur via a positive feedback loop generating a threshold that commits the cell to differentiate to the next stage of the life cycle.