CONICET | Buscador de Institutos y Recursos Humanos

The free-living ciliate Tetrahymena thermophila is a unicellularmodel organism in which landmark biological processeshave been discovered, such as the first description oftelomerase activity and the molecular structure of telomeres,the mechanism of self-splicing RNA and ribozymes,the function of histone acetylation in transcription regulationand a number of pioneer experiments on theinterference (RNAi) mechanism for programmed genomerearrangements, among others.In contrast to most eukaryotic cells that require sterolsin their membranes, Tetrahymena spp. satisfies its vegetativegrowth synthesizing tetrahymanol (a surrogate sterolsimilar to the hopanoids found in bacteria). Nevertheless,if a sterol is present, the biosynthesis of tetrahymanol isimmediately repressed and the sterol is incorporated intothe membrane through an unknown pathway. Tetrahymenaspp. has potential biotechnology applications in biocatalysisconverting cholesterol to pro-vitamin D3 for the use inthe foodstuff and synthesis industry7,8. In this regard, thestudy of cholesterol uptake could contribute to optimizingthe biotransformation process as well as to understand pathwaysof sterol endocytosis which fulfill important functionsin higher eukaryotes and share similarity with this unicellularorganism.To date, at least four distinct pathways of endocyticuptake have been identified: endocytosis of small vesiclesfrom parasomal sacs, uptake of larger vesicles at the base ofthe oral apparatus (phagosomes), endocytosis coupled withthe exocytosis of dense-core secretory vesicles (membraneturnover) and endocytic membrane recovery upon phagosomefusion, at a cortical site (cytoproct)3.We performed an assay to identify the endocytic pathwayinvolved in cholesterol uptake.