Vassella E, Acosta-Serrano A, Studer E, Lee S H, Englund P T, Roditi I
Institut für Zellbiologie, Universität Bern, CH-3012 Bern, Switzerland.
J Mol Biol. 2001 Sep 28;312(4):597-607. doi: 10.1006/jmbi.2001.5004.
Transmission of Trypanosoma brucei by the tsetse fly entails several rounds of differentiation as the parasite migrates through the digestive tract to the salivary glands of its vector. Differentiation of the bloodstream to the procyclic form in the fly midgut is accompanied by the synthesis of a new coat consisting of EP and GPEET procyclins. There are three closely related EP isoforms, two of which (EP1 and EP3) contain N-glycans. To identify the individual EP isoforms that are expressed early during synchronous differentiation in vitro, we exploited the selective extraction of GPI-anchored proteins and mass spectrometry. Unexpectedly, we found that GPEET and all isoforms of EP were coexpressed for a few hours at the onset of differentiation. At this time, the majority of EP1 and EP3 molecules were already glycosylated. Within 24 hours, GPEET became the major surface component, to be replaced in turn by glycosylated forms of EP, principally EP1, at a later phase of development. Transient transfection experiments using reporter genes revealed that each procyclin 3' untranslated region contributes to differential expression as the procyclic form develops. We postulate that programmed expression of other procyclin species will accompany further rounds of differentiation, enabling the parasite to progress through the fly.
布氏锥虫通过采采蝇传播需要经历几轮分化，因为寄生虫在其媒介的消化道中迁移至唾液腺。寄生虫在蝇类中肠内从血流形式分化为前循环形式的过程中，会合成一种由EP和GPEET前循环蛋白组成的新被膜。有三种密切相关的EP亚型，其中两种（EP1和EP3）含有N -聚糖。为了鉴定在体外同步分化早期表达的单个EP亚型，我们利用了糖基磷脂酰肌醇（GPI）锚定蛋白的选择性提取和质谱分析技术。出乎意料的是，我们发现GPEET和所有EP亚型在分化开始时共同表达了几个小时。此时，大多数EP1和EP3分子已经糖基化。在24小时内，GPEET成为主要的表面成分，在发育后期又依次被糖基化形式的EP（主要是EP1）所取代。使用报告基因的瞬时转染实验表明，随着前循环形式的发育，每个前循环蛋白3'非翻译区都有助于差异表达。我们推测，随着进一步的分化轮次，其他前循环蛋白种类的程序性表达将会出现，使寄生虫能够在蝇体内继续发育。
