Geyer Brian C, Fletcher Samuel P, Griffin Tagan A, Lopker Michael J, Soreq Hermona, Mor Tsafrir S
The School of Life Sciences and Biodesign Institute, Arizona State University, Tempe, AZ 85287-4501, USA.
BMC Biotechnol. 2007 May 30;7:27. doi: 10.1186/1472-6750-7-27.
Codon usage differences are known to regulate the levels of gene expression in a species-specific manner, with the primary factors often cited to be mRNA processing and accumulation. We have challenged this conclusion by expressing the human acetylcholinesterase coding sequence in transgenic plants in its native GC-rich sequence and compared to a matched sequence with (dicotyledonous) plant-optimized codon usage and a lower GC content.
We demonstrate a 5 to 10 fold increase in accumulation levels of the "synaptic" splice variant of human acetylcholinesterase in Nicotiana benthamiana plants expressing the optimized gene as compared to the native human sequence. Both transient expression assays and stable transformants demonstrated conspicuously increased accumulation levels. Importantly, we find that the increase is not a result of increased levels of acetylcholinesterase mRNA, but rather its facilitated translation, possibly due to the reduced energy required to unfold the sequence-optimized mRNA.
Our findings demonstrate that codon usage differences may regulate gene expression at different levels and anticipate translational control of acetylcholinesterase gene expression in its native mammalian host as well.
已知密码子使用差异以物种特异性方式调节基因表达水平，常被提及的主要因素是mRNA加工和积累。我们通过在转基因植物中以其富含GC的天然序列表达人乙酰胆碱酯酶编码序列，并与具有（双子叶）植物优化密码子使用和较低GC含量的匹配序列进行比较，对这一结论提出了质疑。
我们证明，与天然人类序列相比，在表达优化基因的本氏烟草植物中，人乙酰胆碱酯酶“突触”剪接变体的积累水平增加了5至10倍。瞬时表达分析和稳定转化体均显示积累水平显著增加。重要的是，我们发现这种增加不是乙酰胆碱酯酶mRNA水平升高的结果，而是其翻译的促进，这可能是由于展开序列优化的mRNA所需能量减少所致。
我们的研究结果表明，密码子使用差异可能在不同水平上调节基因表达，并预计在其天然哺乳动物宿主中也存在乙酰胆碱酯酶基因表达的翻译控制。
