On January 18^th 2023, three pioneers in the field of Biomolecular Condensates shared their cutting-edge research and insights into condensate research, and discussed the future directions and perspectives of the field.

The event was the second online symposium of the 10-part series jointly organized by Science/AAAS and Westlake University, entitled “Biomolecular Condensates”, and was broadcast live to a global audience of over 11,000 viewers. The open nature of the symposium allowed for ideas to be openly discussed on a global platform, with participants from universities, hospitals, scientific research institutions and pharmaceutical companies submitting questions and sharing ideas on the research discussed.

Dr. Tony Hyman (Max Planck Institute), Dr. Amy Susanne Gladfelter (University of North Carolina at Chapel Hill), and Dr. Hong Zhang (Institute of Biophysics, Chinese Academy of Sciences) shared their latest insights into how liquid-liquid phase separation is regulated and functional in cells, with the symposium co-chaired by Dr. Peiguo Yang (Westlake University) and Dr. Stella Hurtley (Editor-in-Chief of Science/American Association for the Advancement of Science).

SPEAKERS

Dr. Tony Hyman, Max Planck Institute of Molecular Cell Biology and Genetics

Topic: “Liquid phase separation and organization of cytoplasm”

Dr. Amy Susanne Gladfelter, University of North Carolina at Chapel Hill

Topic: “Sequence-encoded environmental responses in condensates”

Dr. Hong Zhang, Institute of Biophysics, Chinese Academy of Sciences

Topic: “Calcium transients on the ER surface trigger liquid-liquid phase separation of the autophagosome-initiating FIP200 complex”

CO-CHAIRS

Dr. Yang Peiguo, Assistant Professor of the School of Life Sciences, Westlake University

Dr. Stella Hurtley, Editor-in-Chief of Science/American Association for the Advancement of Science

RESEARCH HIGHLIGHTS

Cellular compartmentalization is a key feature of both eukaryotic and prokaryotic cells. Lipid membrane-bound organelles comprise most of the well-studied organelles. More recently, membrane-less organelles, or biomolecular condensates, have emerged as another key organizing principle within cells. The study of biomolecular condensates and related phase separation processes have become a vibrant, multi-disciplinary research field. The first demonstrations of P granule as a liquid droplet a decade ago heralded the explosion of condensate research in both physiological processes and human disease-related processes.

Biomolecular condensate research has provided mechanistic explanations for basic biology and has potential implications in designing new therapeutics for human disease.

Dr. Tony Hyman, one of the leading pioneers in the field of liquid-liquid phase separation, opened proceedings with his research focusing on how the formation of liquid phases within a liquid cytoplasm impacts the formation of membrane-less compartments of macromolecules inside living cells.

In 2009, his team took P granules (P granules) in the germ cells of nematodes as the research object and discovered for the first time that this puncta structure that assembles rapidly during embryo division has typical liquid-like characteristics. This landmark discovery introduced the classic chemical physics concept of "phase transition" into cell biology and opened a new era of understanding cellular compartmentalization.

In this symposium, Dr. Hyman systematically introduced the typical characteristics of liquid-liquid phase separation from the most basic concept of thermodynamics and took the development of nematode embryos as an example to demonstrate how subtle temperature changes fine-tune the asymmetric distribution of P granules via phase separation.

To conclude, three important questions were raised by Dr. Hyman regarding the future development of the field:

（1）   Can the concepts of equilibrium physics be applied to non-equilibrium cells?

（2）   What is the biochemical basis for cells to govern the emergence of condensation?

（3）   How do cells properly and accurately limit the size of a condensing compartment?

Dr. Hyman, in closing, also emphasized the importance of quantitative research methods in understanding the characteristics of liquid-liquid phase separation. We highly recommend that any researcher currently in or looking to enter this field of research watch Dr. Hyman’s full report at: https://live.vhall.com/v3/lives/watch/340760384.

In the second report of the symposium, Dr. Amy Gladfelter discussed the role of RNA in the assembly of condensates. The material property of condensates could be divergent, some of which are highly dynamic liquid-like, whereas others could behave more like gels or solids with less fluidity. Dr. Gladfelter shared her point of view on how the material property could be encoded by RNA higher-order structures. By in silico-directed evolution, Dr. Gladfelter built up an RNA library containing various kinds of mutants that are derived from the wild-type CLN3 RNA from the fungal model organism Ashbya gossypii. The mutant RNAs harbor the same protein binding sites as the wild-type CLN3 and are identical in molecular weight and nucleotide compositions to the wild-type CLN3. The mutants exhibit different higher-order structures compared to the WT transcript.

Interestingly, the condensates formed by these RNAs and Whi3 RNA binding protein exhibit differences in size and morphology. Meanwhile, the higher-order structure of RNA strongly affects the partition coefficient of protein and RNA composition in the condensate. In addition, Dr. Gladfelter discovered that Whi3 condensates induced by more structured RNA exhibit slower fusion behavior via optical tweezer, indicating altered condensate material properties. More interestingly, higher-order structure numbers of CLN3 RNA are significantly different in fungi isolated from different climate conditions. For example, strains isolated from Wisconsin contain more structured CLN3; in contrast, CLN3 is less structured in fungi isolated from Florida, with a hotter climate. This suggests that the material property of Whi3-CLN3 condensate could be important in fungi adaptation to different environmental temperatures.

The final speaker, Dr. Hong Zhang from the Institute of Biophysics, Chinese Academy of Sciences, introduced their most recent progress in regulating autophagy by liquid-liquid phase separation. The onset of autophagosome is initiated by forming an isolation membrane (IM), which occurs at the endoplasmic reticulum. At the molecular level, the FIP200 complex forms condensate to initiate autophagy at the endoplasmic reticulum, but what signal triggers FIP200 condensation at the endoplasmic reticulum is elusive. Dr. Zhang's group discovered that treatment of the fast Ca²⁺ chelator BAPTA-AM blocks the formation of starvation-induced FIP200 puncta. However, the slow Ca²⁺ chelator EGTA-AM fails to inhibit this process, suggesting that FIP200 puncta formation is dependent on local and transient Ca²⁺ signal. Additionally, autophagy initiation is attenuated when the ER-specific Ca²⁺ channel of IP3R2/3 is knocked down. To further measure Ca²⁺ concentration on ER, Dr. Zhang's group designed a fusion reporter of Ca²⁺ transients which consists of the transmembrane domain of ER-resident CYB5 and the fast Ca²⁺ probe of GCaMP6f (GCaMP6f-CYB5). With this reporter, they confirmed that BAPTA-AM indeed blocks the Ca²⁺ oscillations on the outer surface of ER under starvation or Torin treatment. They further demonstrated that the knockout of the ER transmembrane protein EI24 causes persistent Ca²⁺ oscillations, which induces the accumulation of small-sized unclosed autophagic structures. To further confirm that ER Ca²⁺ transients could directly induce FIP200 puncta, they used RCI treatment or knocked down IP3R2/3 in EI24 KO cells to reduce Ca²⁺ oscillations on the ER surface. They found that FIP200 puncta formation is indeed suppressed. The discovery fills the gap in understanding the critical trigger signal of autophagy initiation and provides an important basis for further studying the molecular mechanism of autophagy.

Upon conclusion of the three in-depth reports, an open discussion session was held whereby the speakers and co-chairs put forward many insights into the current and future directions of the field.

To view the full playback and open discussion of ‘Biomolecular Condensates’ jointly organized by Science/AAAS and Westlake University, please visit: https://live.vhall.com/v3/lives/watch/340760384

We would like to wholeheartedly thank Dr. Tony Hyman, Dr. Amy Gladfelter, Dr. Hong Zhang, Dr. Peiguo Yang, and Dr. Stella Hurtley for actively participating and joining us for the second symposium in the 10-part series and openly sharing their insights and discoveries to a global audience.

Stay tuned for part 4 in the symposium series “Dynamic Molecular Systems” coming up on March 30, 2023 (20:00 - 22:00pm ET) / March 31, 2023 (08:00 – 10:00am UTC+8). We look forward to you registering for the event and joining us in the livestream.

Science/AAAS and Westlake University Symposium Series

Part 1 | Gene Editing | https://live.vhall.com/v3/lives/watch/925591016

Part 2 | Biomolecular Condensates | https://live.vhall.com/v3/lives/watch/340760384

Part 3 | Protein Engineering | https://live.vhall.com/v3/lives/watch/537973129

Part 4 | Dynamic Molecular Systems | Time/Date: 8-10 pm, March 30, 2023 (ET) / 8-10 am, March 31, 2023 (UTC+8)