Expression of a human cDNA in moss results in spliced mRNAs and fragmentary protein isoforms

Abstract

Production of biopharmaceuticals relies on the expression of mammalian cDNAs in host organisms. Here we show that the expression of a human cDNA in the moss Physcomitrella patens generates the expected full-length and four additional transcripts due to unexpected splicing. This mRNA splicing results in non-functional protein isoforms, cellular misallocation of the proteins and low product yields. We integrated these results together with the results of our analysis of all 32,926 protein-encoding P. patens genes and their 87,533 annotated transcripts in a web application, physCO, for automatized codon-optimization. A thus optimized cDNA results in about eleven times more protein, which correctly localizes to the ER. An analysis of codon preferences of different production hosts suggests that similar effects also occur in non-plant hosts. We anticipate that the use of our methodology will prevent so far undetected mRNA heterosplicing resulting in maximized functional protein amounts for basic biology and biotechnology.