Morpholinos knockdown miRNA in Xenopus embryos - New paper (Aug/29/2007 )
Martello G, Zacchigna L, Inui M, Montagner M, Adorno M, Mamidi A, Morsut L, Soligo S, Tran U, Dupont S, Cordenonsi M, Wessely O & Piccolo S. MicroRNA control of Nodal signalling. Nature Advance Online Publication, August 2007. doi:10.1038/nature06100
Morpholinos blocking miRNA have been shown to be effective in Xenopus laevis. Acvr2a (activin receptor IIA) is a receptor for Nodal which has a target site in its 3'-UTR that can interact with the seed sequence of xla-miR-15 and xla-mir-16. A mixture of four Morpholinos targeting xla-miR-15 and xla-mir-16 caused Spemann's organizer to increase in size, expected from an increased response to Nodal. 35 nanograms of each Morpholino was mixed into the bolus, which was radially injected into the 4-cell stage embryo. This effect was reversed by coinjection of Cerebrus short (CerS) mRNA, which encodes a Nodal antagonist. Embryos in which Acvr2a was overexpressed by injection of an Acvr2a coding sequence with a modified 3'-UTR lacking targets for xla-miR-15 and xla-mir-16 appeared similar to the embryos which had been treated with Morpholinos targeting xla-miR-15 and xla-mir-16, including increased areas displaying Chd and Pintallavis mRNA (Organizer markers) after in situ hybridizations.
congratilation jon ! very smart work
I can't claim the work, Fred -- but I did design the Morpholino oligos for that project. This is the earliest developmental stage that I have heard of involving an miRNA regulatory circuit, and it is a tasty one: beta-catenin repressing miR-15/16 expression and miR15/16 repressing Acvr2a expression.
Hmmm, can I say "repressing the expression of an miRNA"? Expression usually refers to a protein, but in this case the functional product is a ribonucleic acid. Must I say "represses the activity of miR15/16"? That sounds like a physiological-level interaction. Perhaps "represses the transcription of miR15/16" would be best.
Just when we thought molecular biology was entirely solved (ouch! I bit my tongue while it was in my cheek!) along comes miRNA to make everything still more interesting.