Biogenesis of Mammalian miRNA - MicroRNAs as Tools in Biopharmaceutical Production - page 15

Chapter 2
Biogenesis of Mammalian miRNA

Stephen L. Clarke, McKale R. Davis and Ramanjulu Sunkar

Abstract MicroRNA (miRNA) are small noncoding molecules approximately 22
nucleotides in length that mediate translational repression of target messenger RNA
(mRNA) transcripts. miRNA play important roles in cellular differentiation and
proliferation, regulation of cellular metabolism, and are associated with en-
hanced tumorigenesis observed with many cancers. These small RNA molecules
function by binding with imperfect complementarity to sequences located in
the 3 untranslated region (UTR) of target mRNA. MiRNA are expressed from
both intergenic or intronic regions of the genome in an RNA polymerase II-
dependent manner and their expression is subject to both feed-forward and negative
feedback regulatory loops. Nascent transcripts known as primary miRNA (pri-
mRNA) undergo nuclear processing to generate

∼

60-80 nt precursor miRNA
(pre-miRNA) containing imperfect stem-loop structures. Pre-miRNA are sub-
sequently exported out of the nucleus whereupon they are further processed
by the RNase III enzyme Dicer resulting in the formation of a 20-24 nt

miRNA duplex. Thermodynamic stability of each strand determines which strand
of the miRNA duplex will be retained within the RNA-induced silencing complex
(RISC) to function as the mature miRNA. This mature miRNA then guides the RISC
to sequences within the 3 UTR of target mRNAs to repress protein translation. Due
to the roles that miRNA have in regulating cellular proliferation and metabolism,
they could potentially interfere with recombinant protein expression in cell-based
systems.

∼

Keywords MicroRNA · Biogenesis · Transcription · Translational repression

S. L. Clarke ( ) M. R. Davis

Department of Nutritional Sciences, Oklahoma State University, Stillwater, OK, USA
e-mail: [e-mail]
M. R. Davis
e-mail: [e-mail]
R. Sunkar
Department of Biochemistry & Molecular Biology, Oklahoma State University,
Stillwater, OK, USA
e-mail: [e-mail]

·