RNA delivery goes live 

During the first days after fertilisation, long before cells become a heart, a brain or a placenta, molecular instructions are already being delivered to precise locations inside the early cells. The instructions are carried by RNA, and where they end up determines what each cell becomes. 

ARMI researchers Associate Professor Jenny Zenker and Dr Hongbin Jin have developed a method to watch that process as it happens, in living mouse embryos, at the molecular level. 

Their work, published this month in Methods in Molecular Biology  (Springer Nature), as a chapter titled ‘Imaging spatiotemporal RNA and protein dynamics in mouse embryos’, describes a technique that allows simultaneous real-time imaging of both RNA and protein within a single living cell. Associate Professor Zenker and Dr Jin detail how fluorescently tagged molecules can be tracked as they move through the embryo, revealing not just where RNA ends up, but how it gets there.  

They demonstrate their method on a gene called Cdx2, which plays a critical role in specifying which cells will form the placenta but not the embryo during early mouse development. Using the technique, Dr Jin and Associate Professor Zenker visualise Cdx2 RNA transcripts as they are transported along microtubule filaments – the internal scaffolding of the cell – to their target location. The imaging captures that transport in second-by-second detail. 

Associate Professor Zenker said the technique allows them to visualise targeted RNA delivery events inside cells in unprecedented detail. It can be applied to any RNA transcript and any protein of interest. 

“This technique shows that RNA molecules are actively guided to specific sites within the cell,” she said. “The precision of that guidance has direct consequences for how the embryo develops. Being able to watch it in real time, in a living mammalian embryo, gives us a level of insight that simply was not possible before.” 

The technique builds on the PP7 stem loop system, an established molecular tool used to tag and track RNA across a range of animal models. Dr Jin and Associate Professor Zenker have adapted and refined it specifically for use in preimplantation mouse embryos, optimising microinjection protocols, microscope settings and imaging parameters to keep embryos viable throughout the imaging process. The result is a reproducible, step-by-step method that other laboratories can apply to study RNA dynamics in their own research contexts. This is important because knowing RNA exists in a cell is not enough, knowing where in the cell the RNA is located influences the cell’s fate. 

The newly published book chapter sits within a broader program of research in the Zenker Group focused on how RNA positioning and translation shapes cell fate in the early embryo. This work will contribute to the early detection of developmental issues and, in the future, improve the efficiency of stem cell-derived regenerative therapies. 

A 2023 study published in Nature Communications established that apicobasal RNA asymmetries – differences in RNA distribution between the top and bottom of a cell – regulate which cells become the embryo and which become the supporting tissues surrounding it. 

This work was supported by NHMRC Ideas Grant APP2002507, NHMRC Investigator Grant APP2009409, and the Sylvia and Charles Viertel Senior Medical Fellowship.