The Yale Cell Biology Department is excited to welcome Dr. Jonathon Ditlev as an upcoming seminar speaker on February 10th. Dr. Ditlev is a professor in the University of Toronto Department of Biochemistry and a Scientist in the Molecular Medicine Program at the SickKids Research Institute. His research focuses on understanding how biological phase separation regulates signal transduction in neuronal and immune cells, using a combination of biophysical analysis, biochemical reconstitution, and cell biology. In this interview, Dr. Ditlev shares the scientific questions currently driving his lab, what inspired his path into research, his interests outside of science, and his vision for the future of his lab.
What are the most exciting projects ongoing in your lab right now, and what are the big questions you’re aiming to answer?
There are a number of projects that I am very excited about, and I’ll try to keep their descriptions below brief! Our lab generally focuses on membrane-associated condensate biology, including the interplay of protein and lipid phase separation in controlling cellular functions. This enables us to investigate diverse biological systems using the lens of phase separation.
Two projects in the lab are aimed at understanding how phase separation of shank family proteins within postsynaptic densities in dendritic spines control actin polymerization and local RNA translation, two process that are essential for maintaining communication between neurons in the brain. We’ve discovered that missense mutations within a long intrinsically disordered region of shank2 and shank3 cause physical changes to their associated condensates and promote aberrant function. Perhaps most exciting is that unique missense mutations induce similar molecular phenotypes, indicating that there are common disease mechanisms across mutations.
Another project centers on our recent discovery that Cystic Fibrosis Transmembrane Conductance Regulator (CFTR), the chloride ion channel mutated in Cystic Fibrosis, undergoes lipid- and protein-coupled phase separation on membranes. We are now investigating how phase separation of CFTR is linked to its ion channel function and whether correcting aberrant phase separation induced by any of the 2000+ unique mutations linked with Cystic Fibrosis can rescue channel function with and without existing therapies.
In a study related by general principles of membrane-associated phase separation, we want to know why successful T cell signaling events require coupled lipid and protein phase separation. With the Levental Lab (University of Virginia) we found that the signaling protein LAT more readily undergoes phase separation when localized to cholesterol-rich lipid rafts. In Jurkat T cells, signaling only occurs when LAT is localized to lipid rafts by an unknown mechanism that we are actively investigating.
The final project that I am extremely excited about is in collaboration with the McGlade Lab at SickKids. We study the protein Numb and want to understand how its four expressed splice variants tune membrane-associated cellular processes. Our current data suggest that each isoform uniquely contributes to the formation and behavior of Numb-containing condensates, which we hypothesize will tune their function.
I am incredibly enthusiastic that we will gain better insight into the how general principles of phase separation regulate diverse membrane-associated cellular functions from these studies.
What originally inspired you to pursue a career in science? Were there other career paths you considered along the way?
For as long as I can remember, I have been interested in science, particularly biology. In elementary school, I used to watch NOVA on Sunday nights on PBS and always enjoyed participating in science fairs during middle school. In high school, my favorite classes were Biology, Chemistry, and Physics. When I enrolled in undergrad, I knew I wanted to pursue a career related to biology, but I was split between practicing medicine and research. I found that I greatly enjoyed my lab courses because of the thrill of potential discovery, even though all the labs were carefully constructed to guarantee positive results. During my junior year, I accepted a student research position in a lab where I was given two independent research projects. In one project, we studied how exposure to retinoic acid, which is a common preservative in eye drops, affected androgen receptor expression that is linked with a reduction in tear production in mouse lacrimal glands. In the other project, we investigated the potential for using bovine eyes instead of rabbit eyes for testing the toxicology of chemicals and products. Importantly, both projects required that me, my lab mates, and our professor work through emerging problems and develop solutions that enabled us to make new discoveries. This journey into bona fide research solidified my love of basic science and jumpstarted my scientific career.
What are your interests or hobbies outside of science?
Outside the lab, I love to cook. My wife and I have four children. Because we had children at a young age during my training, we didn’t have a lot of money to invest in other more expensive hobbies. Instead, we cooked because everyone needs to eat! I enjoy trying new recipes, cooking big family meals (like Thanksgiving dinner), and grilling everything from beef and fish to vegetables and dessert. I’ve recently picked up smoking meats using a standard Weber charcoal grill and would like to eventually invest in an indirect smoker (This probably shows a bit of the Texan in me). My enjoyment of cooking is directly related to my enjoyment of science and working in the lab. There is something incredibly satisfying about following a recipe and working to produce good food, much like the satisfaction gained from following a protocol to produce good, high-quality data.
Where do you see your laboratory in the next decade?
My long-range vision for the lab is directly linked to our recent discoveries where we have taken a bottom-up approach to understand fundamental mechanisms that control biomolecular condensate formation and function. These methods are extremely powerful. However, they are also limited. For example, the postsynaptic density is composed of at least 1000 different proteins at any given time. It gets even more complex when we consider communication between neurons in the human brain. In the human brain there are trillions of individual excitatory connections, each of which is regulated by a postsynaptic density. A back of the envelop calculation estimates that there are more than 14 trillion unique combinations of postsynaptic density proteins. This means that in the brain, very few postsynaptic densities are identical, unlike in reconstitution experiments where only a few proteins drive the formation of condensates (or model postsynaptic densities) that each behave more or less the same in any given experimental condition. Therefore, I foresee us combining our ever increasingly complex bottom-up biochemical and biophysical approaches with top-down cellular work to investigate and reveal how the collective behavior of proteins within the postsynaptic density regulates its function to promote communication between neurons. Through this lens, we will continue to investigate mechanisms of neurological disorders to generate therapeutics that correct aberrant phase behavior of postsynaptic densities composed of proteins with disease-linked mutations. Over the next ten years, I expect that we will use combined bottom-up / top-down approaches to understand biological function that emerges from our exciting projects described above.