Oral Presentation ESA-SRB-APEG-NZSE 2022

Spatial real-time RNA asymmetries differentiate translation capacity of inner and outer cells in the preimplantation mouse embryo (#220)

Azelle Hawdon 1 , Niall D Geoghegan 2 , Anja Elsenhans 3 , Charles Ferguson 4 , Robert G Parton 4 5 , Jennifer Zenker 1
  1. Australian Regenerative Medicine Institute, Monash University, Melbourne, Victoria, Australia
  2. Walter and Eliza Hall Institute of Medical Research, Department of Medical Biology, University of Melbourne, Melbourne, Victoria, Australia
  3. Department of Biology, University of Duisburg-Essen, Germany
  4. Institute for Molecular Biosciences and Centre for Microscopy and Microanalysis, University of Queensland, Brisbane, Queensland, Australia
  5. Centre for Microscopy and Microanalysis, University of Queensland, Brisbane, Queensland, Australia

RNA localisation has indispensable roles for establishing asymmetries and coordinating cell fate decisions during early embryogenesis across many non-mammalian species1-4. To direct the spatiotemporal distribution of RNA within the cells of an embryo5, the microtubule-cytoskeleton provides highly sophisticated trafficking pathways6-7. Yet, it remains unknown whether subcellular heterogeneities exist during mammalian preimplantation development and how they contribute to cell fate.

Here, using advanced live imaging we visualise global RNA transcripts at high spatiotemporal resolution from fertilisation to the blastocyst stage in the living preimplantation mouse embryo. For the first time, we discover apicobasal RNA asymmetries specific to outer cells of the 16-cell stage embryo, which coincides with cell fate decisions and the emergence of the pluripotent inner cell mass. Highly clustered RNAs accumulated proximal to the basal membrane, while more dispersed RNA foci were identified apically as the embryo reaches the late 16-cell stage. The targeted distribution of membrane-less RNA molecules is facilitated by the microtubule-cytoskeleton, associated with lysosomes which serve as RNA transport vehicles. Furthermore, real-time tracking of RNA revealed distinct RNA subpopulations located in apical and basal regions of outer 16-cell stage blastomeres. Apically located RNA foci were more dynamic and accompanied an enrichment of translation components. Intriguingly, our discoveries of spatiotemporal RNA heterogeneities determining differential translation capacity are unevenly inherited by outer and inner daughter cells during subsequent cell divisions.

Here we provide novel insights into a subcellular mechanism driving asymmetric RNA localisation and compartmentalised translational regulation in outer cells of the 16-cell stage embryo, which may contribute to cell fate decisions during mammalian embryogenesis by serving as a fine-tuned mechanism for the control of gene expression. We envision that deciphering the spatiotemporal processes underpinning early embryogenesis may facilitate the development of techniques to target subcellular structures with precision for applications in regenerative and assisted reproductive medicine.

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