First person – Ramesh Rijal Free

Ramesh Rijal

How would you explain the main findings of your paper in lay terms?

Some animals use seasonal cues to anticipate starvation during winter and store food as body fat for hibernation. A similar process occurs in the unicellular eukaryote Dictyostelium discoideum, which uses a secreted signal to monitor the local cell density, and when there is a high density of cells that will soon outgrow the local food supply, the cells stop dividing but continue to grow (accumulating mass and protein). We found that Dictyostelium cells accumulate extracellular polyphosphate at high cell densities, and the extracellular polyphosphate inhibits cell division and causes cells to retain ingested nutrients by preventing the digestion and excretion of the ingested food. This might allow cells to accumulate large amounts of nutrients in anticipation of starvation.

Were there any specific challenges associated with this project? If so, how did you overcome them?

In many instances, I took images of live cells. Dictyostelium cells are very sensitive to light, so long laser exposure can cause damage to the cells. It was challenging to optimize the correct microscopic parameters to perform the fluorescence recovery after photobleaching (FRAP) experiment that allowed us to analyze cell membrane fluidity. Another challenge was the COVID-19 pandemic. As a young family with a toddler, we constantly worried about contracting COVID-19, and we had to adjust our professional and personal schedules to be as safe as possible. However, we were happy to accomplish our work using effective communication and adjusted schedules.

When doing the research, did you have a particular result or ‘eureka’ moment that has stuck with you?

Our lab has previously shown that Dictyostelium cells accumulate extracellular polyphosphate, and the concentration of polyphosphate reaches a maximum (∼705 µg/ml) when cell density reaches ∼20×10⁶ cells/ml. The corresponding high concentration of polyphosphate inhibits the proliferation of Dictyostelium cells and causes an increase in cell mass. We have elucidated a mechanism by which Dictyostelium cells in a nutrient-limited environment sense cell density and store nutrients in anticipation of starvation. It was exciting to determine that polyphosphate causes an increase in cell mass by inhibiting exocytosis to retain the ingested food. Another exciting moment came when I found that polyphosphate reduces cell membrane fluidity, a physical property of the membrane that is critical for efficient membrane recycling and exocytosis. Importantly, polyphosphate is found in all kingdoms of life, and in independent research I have found that bacterial polyphosphate exerts similar effects on human immune cells, such as macrophages, to promote survival of bacteria and cause infection. It is rewarding to find that studying the fundamental mechanism of cell density sensing in simple eukaryotic model systems, such as Dictyostelium, can help us understand the complex mechanisms bacterial pathogens utilize to survive in humans.

Why did you choose Journal of Cell Science for your paper?

As a cell biologist, I always aim to have my papers published in journals that accept research papers with exciting and novel findings. Journal of Cell Science is at the forefront of publishing impactful works on a wide range of topics in cell biology.

Have you had any significant mentors who have helped you beyond supervision in the lab? How was their guidance special?

I want to say thank you to my postdoctoral supervisor, Dr Richard Gomer, who encouraged me to pursue my hypotheses. Richard taught me that one key characteristic needed to become an independent investigator is to be able to think differently to others. I want to acknowledge my postdoctoral mentors, Dr Gyanu Lamichhane from Johns Hopkins University School of Medicine and Drs Bruce Riley and Joseph A. Sorg from the Department of Biology at Texas A&M University, for providing guidance, motivation and support for many years. Without my supervisor and mentors, I would not be the independent researcher I am today.

What motivated you to pursue a career in science, and what have been the most interesting moments on the path that led you to where you are now?

I already had a love for science when I was a schoolkid. During school, my aim was to become a mathematician or physicist, because I was always intrigued by equations and mathematical formulas, and I was very good at solving mathematical problems. However, after high school, I met with the late Dr Vishwanath Prasad Agrawal, my undergraduate supervisor. Dr Agrawal instilled in me the enthusiasm to understand biochemical pathways in living organisms. I want to say thank you to Dr Agrawal; because of his mentoring, I completed my bachelor's degree in Biochemistry and received a meritorious achievement award from the Prime Minister of Nepal. Without Dr Agrawal, I would not be working in this field today.

Who are your role models in science? Why?

I am always fascinated by how things work in nature. People who make exciting discoveries in science are true role models for me. I am always inspired by their passion for understanding the fundamental relationships between living and non-living things.

What's next for you?

I am applying for assistant professor positions in the USA. My research focuses on polyphosphate biology at the host–microbe interface. Polyphosphate is critical to eukaryotic as well as bacterial cell physiology, but the molecular mechanisms of its involvement in host–pathogen interactions have not been systematically investigated. I want to gain new insights into how bacteria use polyphosphate to manipulate macrophages, which is expected to significantly impact our understanding of the fundamental mechanisms of bacterial pathogenesis.

Tell us something interesting about yourself that wouldn't be on your CV

I love to cook. In my opinion, cooking and wet lab experiments are very similar. Both need good preparation, focus and proper execution. I also enjoy traveling, hiking, and off-roading with my family.