Byers Jennifer, Eichinger Daniel
Department of Medical Parasitology, New York University School of Medicine, New York, NY 10010, USA.
Exp Parasitol. 2005 Jul;110(3):203-6. doi: 10.1016/j.exppara.2005.02.019. Epub 2005 Apr 1.
The DNA content of Entamoeba parasites appears to be regulated by an unusual mechanism. This conclusion, however, was based on experiments that examined parasites grown in media that did not contain short chain fatty acids (SCFAs) normally found in the colonic lumen. Since one of these SCFAs, butyrate, is known to affect DNA replication in eukaryotic cells, we examined the effect of SCFAs on Entamoeba trophozoite DNA content. Similar to reports from others, we found that Entamoeba invadens trophozoite cultures grown in conventional medium (TYI-S-33) contained cells with 2N, 4N, 8N, and 16N amounts of DNA. In contrast, cultures grown in TYI medium containing colonic SCFAs added in place of glucose contained a minor population with 2N, a major population with 4N, and very few cells with higher amounts of DNA. SCFAs also prevented the normal increase in the number of nuclei per cell in trophozoites that were induced to encyst. These results suggest that E. invadens trophozoite stage parasites growing in the intestine in the presence of high amounts of SCFAs have a ploidy range restricted to 2N/4N. Axenic growth of trophozoites in the absence of SCFAs, however, appears to allow trophozoites to increase the amount of DNA per cell, which they must do during the normal encystment process.
溶组织内阿米巴寄生虫的DNA含量似乎受一种不同寻常的机制调控。然而，这一结论是基于在不含通常存在于结肠腔中的短链脂肪酸（SCFAs）的培养基中培养寄生虫的实验得出的。由于这些SCFAs之一丁酸已知会影响真核细胞中的DNA复制，我们研究了SCFAs对溶组织内阿米巴滋养体DNA含量的影响。与其他研究报告相似，我们发现，在传统培养基（TYI-S-33）中培养的侵袭内阿米巴滋养体培养物中含有DNA含量为2N、4N、8N和16N的细胞。相比之下，在添加结肠SCFAs以替代葡萄糖的TYI培养基中培养的培养物中，少数细胞的DNA含量为2N，多数细胞的DNA含量为4N，DNA含量更高的细胞极少。SCFAs还阻止了诱导形成包囊的滋养体中每个细胞的细胞核数量正常增加。这些结果表明，在存在大量SCFAs的情况下在肠道中生长 的侵袭内阿米巴滋养体阶段寄生虫的倍性范围限制在2N/4N。然而，在没有SCFAs的情况下滋养体的纯培养生长似乎允许滋养体增加每个细胞的DNA量，这是它们在正常包囊形成过程中必须做的。
