Intracellular life of protozoan Toxoplasma gondii:Parasitophorous vacuole establishment and survival strategies

Toxoplasma gondii is a protozoan of worldwide distribution and the agent of toxoplasmosis.It is estimated that 30%–50%of the world population could be infected with this parasite.Although the infection in immunocompetent individuals is mostly asymptomatic,the disease in immunosuppressed and pregnant is a risk condition.As a member of the phylum Apicomplexa,T.gondii has an obligatory intracellular lifestyle;therefore,invading a host cell and establishing it inside a parasitophorous vacuole(PV)are mandatories for the survival of this parasite.The construction of a perfect intracellular niche for T.gondii requires the secretion of an arsenal of proteins from unique secretory organelles.These proteins will remodel the vacuolar environment and the host cell organization and functions,allowing the parasite to access essential nutrients and stay“invisible”inside a host cell.In the present review,we will discuss the main steps involved in the PV formation and its differentiation to tissue cyst,focusing mainly on the strategies employed in the acquisition of nutrients and proteins involved in host cell modification.

甜菊愈伤组织细胞中的液泡膜内突和液泡内囊泡

对生长在分化培养基上的甜菊（Steviarebaudiana）愈伤组织分生区细胞的液泡膜内突和液泡内囊泡，进行了超微结构和酸性磷酸酶（AcPase）细胞化学研究。在不同液泡化时期的细胞中，都存在不同大小和形态的液泡膜内突，它们有的缺乏明显的内含物；有的含有许多小泡或复杂膜系；有的含有一个较大的具许多小泡或复杂膜系的膜束缚囊泡。在液泡内还存在一些游离的液泡内囊泡，它们通常具两层紧贴的界膜或为多层同心膜，推测它们来自液泡膜内突。AcPase定位结果显示，液泡膜及其内突通常缺乏酶活性，而液泡内囊泡却具酶活性，提示液泡内囊泡在功能上与溶酶体类似。