Sharing = Caring? – Asymmetric RNA Segregation depends on the replicative age of cells
When a cell divides, the correct distribution of cellular content, such as RNAs, to daughter cells is essential. By tagging RNAs with the new diSpinach aptamer in combination with a self-made microfluidics device, researchers at the Institute of Functional Epigenetics (IFE) at Helmholtz Munich followed RNAs over multiple cellular divisions in order to study the dynamics of RNA inheritance at the single-cell level.
During each round of cell division, many cellular components have to be duplicated and accurately distributed among the mother and the daughter cell so that both contain all the components required for cell viability and fitness. However, in some cases, the distribution of the components is not equal. This asymmetric segregation is essential for cell viability, adaptation to changing environments, evolutionary fitness, as well as for the development of multicellular organisms.
In budding yeast, for example, damaged material is asymmetrically distributed and accumulates in the mother cells to support rejuvenation of their daughter cells. In mammals, a dysregulation of asymmetric inheritance could trigger cancer development. While in the last decades a lot was learned about replicative aging, there are only a few studies that address how replicative age affects asymmetric RNA inheritance.
A novel technique to study asymmetric inheritance in single cells
To this end, the research team around Igor Kukhtevich, a Postdoc at the IFE and the first author of the study, developed an approach to study the asymmetric distribution of RNAs in single cells by live-cell microscopy. “We tagged the RNA by introducing the new ‘light-up’ diSpinach RNA aptamer into the corresponding gene. This RNA aptamer binds different fluorophores that can be easily added to the culturing media and allows for visualization of the RNA under the microscope”, explained I. Kukhtevich. The researchers combined their tagging approach with a self-made microfluidic device that enables parallel long-term imaging of cells over multiple rounds of cell division. “Our novel approach can not only be used for quantifying RNA and protein levels over time but also allowed us to track the RNA transport from mother to daughter cells”, Igor added.
Loss of asymmetric RNA inheritance is linked to the replicative age of mother cells
Interestingly, the researchers found that during cell division, more of specific RNAs is segregated into daughters than retained in mother cells. “Our next step was to identify how this asymmetric distribution of RNA is established. After manipulating the RNA transport machinery, we could observe that the RNA signal in the daughter cell is lower than before.”, said Robert Schneider, Director of the IFE and corresponding author. “This means that the asymmetric segregation of RNA during cell division is an active process.” The group of researchers investigated next whether the RNA distribution during replicative aging – and indeed, this is what they observe. Older mothers share less RNA with their daughters than younger ones.
Altogether, the results show for the first time how RNA is actively inherited over multiple generations and that the replicative age of cells plays an important role in the process. “This study is just a start. With our approach, we now can uncover the molecular principles of RNA transport and inheritance”, concluded R. Schneider. “Moreover, it can be used to address key questions about phenotypic heterogeneity, as observed in cancer cells, for example.”