Author

Jon Moulton
http://www.gene-tools.com     Email

Published on SDB CoRe: Jan 31 2012

Tools & Techniques: Molecular Techniques
Organism: Zebrafish, Xenopus, Chick, Mouse, Axolotl, Human, Medaka, Lamprey
Stage of Development: Embryo

Object Description

The figure shows the chemical structure of a short section of a Morpholino-RNA heteroduplex.  Hydrogen bonding between bases are shown as dashed lines.  Typically Morpholinos are synthesized as 25-mers, so the continuing backbones of Morpholino and RNA are also represented as dashed lines. 

Introduction to Morpholinos

Morpholino oligonucleotides are synthetic molecules used to knock down gene expression, either by blocking translation or modifying splicing.  Morpholinos consist of DNA bases on an uncharged backbone that may be complementary to a sequence in RNA.  When the Morpholino encounters that RNA, the Morpholino binds to the complementary sequence and can get in the way of many processes that would otherwise occur at that RNA sequence.  They can also inhibit microRNA activity.

Morpholinos are typically about 25 bases long and about 8200 Da mass.  The backbone of a Morpholino oligo has a morpholine ring instead of a sugar and a dimethylamino phosphorodiamidate instead of an anionic phosphodiester; the phosphorodiamidate has no charge.  With no charge on its backbone, Morpholinos do not bind strongly to proteins that bind nucleic acids.  Therefore they are not degraded by nucleases, do not trigger innate immunity through Toll-like receptors, and do not activate catalytic nucleic acid degrading systems like RNase-H or RISC.

Morpholinos do not readily cross most cell membranes, so they must be put into the nuclear/cytosol compartment of cells using a delivery technique.  For embryos of many creatures, the oligos can be microinjected into the early zygote.  Electroporation may be used to make cultured cells permeable and is also used in embryos.  Delivery reagents like Endo-Porter can be used with cultures and sometimes with organ explants.  Vivo-Morpholino are Morpholino oligos with delivery moieties covalently attached and can deliver the oligos into most cells from the bloodstream of adult animals.

References

Summerton, J., Weller, D. Morpholino Antisense Oligomers: Design, Preparation and Properties. Antisense & Nucleic Acid Drug Development, 1997, 7:187-195.

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