Abstract
The larval stage of Echinococcus granulosus sensu lato, resulting in cystic echinococcosis, a parasitic zoonosis, causes huge economic losses to the livestock industry and poses a threat to public health. Inhibitor of apoptosis proteins (IAPs) is a class of endogenous anti-apoptotic family, which plays a significant functional role in the regulation of organism’s development. Herein, to explore potential functions of IAPs in E. granulosus, two members of IAPs from E. granulosus (Eg-IAP and Eg-BIRP) were cloned, expressed, and molecularly characterized. Eg-IAP and Eg-BIRP encoded putative 331 and 168 residue proteins, respectively. Bioinformatic analysis showed that both proteins contained a type II BIR domain-the essential functional domain of IAPs. Fluorescence immunohistochemistry revealed that both proteins were ubiquitously localized in all life-cycle stages of E. granulosus. Our fluorescent quantitative PCR (RT-qPCR) results revealed relatively higher transcription levels of two Eg-IAPs in protoscoleces (PSCs) compared to the 18-day strobilated worms. We further used different concentrations of LCL161, a Smac-mimetic pan-IAPs inhibitor, to induce the apoptosis in PSCs in vitro, and revealed that the survival rate of PSCs and transcription levels of both genes were negatively correlated with the concentration of LCL161. While the results of light microscopy, transmission electron microscopy (TEM), and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay also showed a higher apoptotic rate in PSCs with the increasing concentrations of LCL161. Taken together, our findings provide the reasonable evidence that both Eg-IAP and Eg-BIRP have potential implication in critical anti-apoptotic roles during the development of E. granulosus.
Highlights
The larval stage of Echinococcus granulosus (E. granulosus) sensu lato is the causative agent of cystic echinococcosis (CE), a parasitic zoonosis with worldwide distribution (Othieno et al, 2018; Pan et al, 2018)
We evaluated the localization of Eg-Inhibitor of apoptosis proteins (IAPs) and Eg-BIRP at different stages of E. granulosus life cycle and estimated the relative transcription levels of two Eg-IAPs genes between PSCs and 18-day strobilated worms stages
Sequencing analysis showed that full-length Eg-IAP cDNA sequence comprised a 997 bp gene encoding 331 amino acids with a predicted molecular weight of 35.3 kDa
Summary
The larval stage of Echinococcus granulosus (E. granulosus) sensu lato is the causative agent of cystic echinococcosis (CE), a parasitic zoonosis with worldwide distribution (Othieno et al, 2018; Pan et al, 2018). Adult worms of E. granulosus, developing from protoscoleces (PSCs), reside in the small intestines of definitive hosts and release eggs containing oncospheres into the external environment through feces of definitive hosts. These oncospheres migrate to the liver and lungs of intermediate hosts and develop as larvae-hydatid cysts (Yin et al, 2018). The transmission cycle of E. granulosus would progress if definitive hosts ingest the fertile cysts, on which PSCs are found both joined to the germinal layer and free in the hydatid fluid filling the cyst cavity (Paredes et al, 2010; Wang et al, 2018)
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