A Chinese hamster transcription start site atlas that enables targeted editing of CHO cells

Gene expression is a key determinant of phenotypes that made Chinese Hamster Ovary (CHO) cells, with their human-like glycosylation profile and high protein titers, one of the most widely used cells for the production of therapeutic proteins and biopharmaceuticals. Engineering CHO gene expression thus holds a key to improve drug quality and cost effective production. However, the success of engineering gene expression or ectopic activation of silent genes to optimize desired pathways requires accurate annotation of the underlying regulatory elements and the transcription start site (TSS). Unfortunately, to date, most TSSs of CHO-expressed genes and the ~50% of hamster genes that are silent in CHO were computationally predicted and are frequently inaccurate. To oust this hurdle, we report revised TSSs annotations for 15,308 Chinese Hamster genes and 4,145 non-coding RNAs based on experimental data from CHO K1 cells and 10 hamster tissues. In the example of the glycosyltransferase gene Mgat3, we further demonstrate how accurate annotations readily facilitate activating silent genes by CRISPRa. Together, we envision that our annotation and data from the Chinese Hamster will provide a rich resource for the CHO community, improve genome engineering efforts and additionally aid comparative and evolutionary studies. Overall design: Examination of transcription start sites in the Chinese Hamster in various tissues and cell-lines using csRNA-seq and 5'GRO-seq . Total-RNA and ATAC-seq and backgrounds sRNA and GRO-seq were additionally performed.