The CHO miRNA Transcriptome - MicroRNAs as Tools in Biopharmaceutical Production - page 52

Fig. 4.1 miRNA expression in the context of biopharmaceutical production. Small non-coding
RNAs referred to as microRNA (miRNAs) are transcribed from intergenic loci (1) or processed from
intronic sequences of coding genes (not shown). After transcription of primary miRNA transcripts
(pri-miRs, 2) from miRNA genes in an RNA Polymerase II (RNAPII) dependent manner, pri-miRs
are processed into a ∼ 70 base long precursor miRNA (pre-miR, 3) that becomes exported into
the cytoplasm via Exportin 5 (4). In the cytoplasm the pre-miR gets incorporated into a protein
complex consisting of RNaseIII enzyme Dicer, the RNA binding protein TRBP as well as members
of the AGO protein family (5). Cleavage of the miRNA loop ( dicing ) results in the formation of
the RNA-induced silencing complex (RISC) with the mature 22 base-long miRNA in its core (6).
Depending on partially complementary sequence matches between a miRNA and its mRNA targets,
the RISC is directed to an mRNA molecule—most frequently its 3 untranslated regions (UTR)—
resulting in either post-transcriptional repression or degradation (6). By these means, miRNAs
become important regulatory molecules amidst many important cellular pathways (7), which in the
context of biopharmaceutical production suggest an application of miRNAs as targets for cell line
engineering and as biomarkers in cell line development and bioprocess development

miRNAs are related to specific phenotypes. This will further enable the development
of miRNA-based tools both for better prediction and control of CHO cell behavior
under bioprocessing relevant conditions.

4.2 MicroRNAs in the Context of Biopharmaceutical

Production: EngimiRs and Biomarkers

Two future applications of miRNAs in the context of biopharmaceutical production
are currently envisioned as most promising by the research community (Fig. 4.1 ):
first, the use of miRNAs as targets for cell engineering approaches (engimiRs)