Department of Biology, Northeastern University, Boston, MA 02115, USA.
Sunderland Pharmacy School, University of Sunderland, Sunderland SR1 3SD, UK.
Microbiology (Reading). 2014 Feb;160(Pt 2):330-339. doi: 10.1099/mic.0.072405-0. Epub 2013 Dec 4.
Giardia trophozoites differentiate into infectious cysts (encystment) in response to physiological stimuli; encystment is crucial for Giardia's transmission, survival and pathogenesis. In vitro, Giardia encysts when bile sequesters lipids necessary for this lipid auxotroph, and in vivo they encyst to infect new hosts. In this study, we investigated, for the first time, commitment to encystment in Giardia using both molecular and cellular techniques. We show that after 3-6 h in inducing conditions, encysting trophozoites continue to encyst regardless of whether the inducing stimulus remains. We propose that a trophozoite's inability to revert to a growing or dividing trophozoite represents a commitment to encystment. The onset of commitment correlated with the appearance of encystment specific vesicles (ESVs) and encystment specific protein synthesis. These observations suggest the involvement of regulatory pathways with the ability to 'remember' a transient signal long after its removal; a property that enables encysting trophozoites to complete the encystment process should the unfavourable triggering condition(s) change. The ability to form cysts in response to transient signals or, as we have highlighted in this paper, the ability of a small percentage of the population to form cysts without an inducer is vital for the maintenance of infection within populations.
贾第虫滋养体在生理刺激下分化为感染性囊（囊形成）；囊形成对于贾第虫的传播、生存和发病机制至关重要。在体外，当胆汁隔离这种脂类营养缺陷型所需的脂质时，贾第虫会形成囊；在体内，它们形成囊以感染新宿主。在这项研究中，我们首次使用分子和细胞技术研究了贾第虫的囊形成过程。我们发现，在诱导条件下 3-6 小时后，即使诱导刺激仍然存在，正在囊形成的滋养体仍会继续形成囊。我们提出，滋养体无法恢复为生长或分裂的滋养体，这代表了对囊形成的承诺。承诺的开始与囊形成特异性囊泡（ESV）和囊形成特异性蛋白质合成的出现相关。这些观察结果表明，调节途径具有“记住”短暂信号的能力，即使在去除信号后很长时间，这种能力使正在囊形成的滋养体能够在不利的触发条件改变时完成囊形成过程。对短暂信号形成囊的能力，或者正如我们在本文中强调的，一小部分群体在没有诱导剂的情况下形成囊的能力，对于在群体内维持感染至关重要。
