Imaging ONEWORLD - 'Organization of translating secretome mRNAs on endoplasmic reticulum.' - Heejun Choi

Scientific Organisers: Stefanie Reichelt, Alex Sossick, Nick Barry, Alessandro Esposito and Kirti Prakash

The meeting will begin at 1pm BST.

As part of the 'Imaging ONEWORLD' series, the focus of these lectures is on microscopy and image analysis methods and how to apply these to your research. Almost all aspects of imaging such as sample preparation, labelling strategies, experimental workflows, ‘how-to’ image and analyse, as well as facilitating collaborations and inspiring new scientific ideas will be covered. Speakers will be available for questions and answers. The organisers, CRUK CI core facility staff, Gurdon Institute, MRC-LMB, MRC Cancer Unit and NPL will be able to continue the discussion and provide advice on your imaging projects.


  • Heejun Choi

    Howard Hughes Medical Institute

    Heejun Choi received B.S. in Chemistry and Biological Science from Virginia Tech before pursuing his doctoral work at the UW-Madison under the supervision of Dr. James C. Weisshaar.  He used single-particle tracking and single-cell time-lapse fluorescence microscopy to study how antimicrobial peptides CM15 and LL-37 kill Gram-negative bacterium Escherichia Coli through inducing reactive oxygen species (ROS) and freezes the chromosome and RNA Polymerase motion. Under the supervision of Dr. Jennifer Lippicontt-Schwartz, his current work focuses on understanding how the translation of secretome mRNAs is organized on the endoplasmic reticulum in human cells through monitoring single mRNAs and ribosomes.  

Speaker's Abstract

The endoplasmic reticulum (ER) has a complex morphology comprised of stacked sheets, tubules, and three-way junctions, which together function as a platform for protein synthesis of membrane and secretory proteins. Specific ER subdomains are thought to be spatially organized to enable protein synthesis activity, but precisely where these domains are localized is unclear, especially relative to the plethora of organelle interactions taking place on the ER. Here, we use single-molecule tracking of ribosomes and mRNA in combination with simultaneous imaging of ER to assess the sites of membrane protein synthesis on the ER. We found that ribosomes were widely distributed throughout different ER morphologies, but the synthesis of membrane proteins (including Type I, II, and multi-spanning) and an ER luminal protein (Calreticulin) occurred primarily at three-way junctions. Lunapark played a key role in stabilizing transmembrane protein mRNA at three-way junctions. We additionally found that translating mRNAs coding for transmembrane proteins are in the vicinity of lysosomes and translate through a cap-independent but the eIF2a-dependent mechanism. These results support the idea that discrete ER subdomains co-exist with lysosomes to support specific types of protein synthesis activities, with ER-lysosome interactions playing an important role in the translation of secretome mRNAs.