Morpholino

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Not to be confused with morpholine.

Segment of a Morpholino-RNA heteroduplex, 8-mer shown

A Morpholino, also known as a Morpholino oligomer and as a phosphorodiamidate Morpholino oligomer (PMO), is a type of oligomer molecule (colloquially, an oligo) used in molecular biology to modify gene expression. Its molecular structure has DNA bases attached to a backbone of methylenemorpholine rings linked through phosphorodiamidate groups. Morpholinos block access of other molecules to small (~25 base) specific sequences of the base-pairing surfaces of ribonucleic acid (RNA). Morpholinos are used as research tools for reverse genetics by knocking down gene function.
This article discusses only the Morpholino antisense oligomers, which are nucleic acid analogs. The word "Morpholino" can occur in other chemical names, referring to chemicals containing a six-membered morpholine ring. To help avoid confusion with other morpholine-containing molecules, when describing oligos "Morpholino" is often capitalized as a trade name, but this usage is not consistent across scientific literature.
Gene knockdown is achieved by preventing cells from making a targeted protein.^[1] Knocking down gene expression is a method for learning about the function of a particular protein; in a similar manner, causing a specific exon to be spliced out of a protein can help to determine the function of the protein moiety encoded by that exon or can sometimes knock down the protein activity altogether. These molecules have been applied to studies in several model organisms, including mice, zebrafish, frogs and sea urchins.^[2] Morpholinos can also modify the splicing of pre-mRNA.^[3]
Morpholinos are in development as pharmaceutical therapeutics targeted against pathogenic organisms such as bacteria^[4] or viruses^[5] and genetic diseases.^[6] The Morpholino drug eteplirsen from Sarepta Therapeutics received accelerated approval from the US Food and Drug Administration for treatment of some mutations causing Duchenne muscular dystrophy.^[7]