Abstract
BackgroundCodon 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.ResultsWe 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.ConclusionOur 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.
Highlights
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
BMC Biotechnology 2007, 7:27 http://www.biomedcentral.com/1472-6750/7/27 while the available genome-scale analyses done for several plant species demonstrate that codon bias in plants is adaptive [11,12], heterologous gene expression studies in plants led to a tentative conclusion that translation efficiency of the foreign genes is often considered secondary to mRNA processing and stability as a determinant for expressivity [13]
The rare codons present in human AChE-S (hACHE-S) were changed in the synthetic plant-expression optimized ACHE gene to more frequently used alternatives so that the codon adaptiveness index (CAI, for definition see the Methods section) would match that of the most abundant nuclearencoded plant protein – the small subunit of ribulose bisphosphate carboxylase (RuBisCO, Fig. 2 and Table 1)
Summary
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. The enzyme is known for its role in the termination of synaptic transmission by hydrolyzing acetylcholine, but during the past decade evidence has been gathered indicating its critical role in various processes such as development, stress responses, innate immunity, and bioscavenging [14] This complex array of functions is enabled through the complex molecular biology of the ACHE gene: the intricate control of its transcription, alternative splicing and translation and the intricate post-translational events governing its function such as subcellular targeting, glycosylation, proteolytic processing, membrane anchoring and proteinprotein interactions [14]. Non-cholinergic functions of AChE are underscored by identification of AChE-like activity and genes potentially encoding the enzyme in several plant species [21,22,23]
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