First person – Matthew Zdradzinski

Matthew Zdradzinski

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

Cdc42 is a protein that is known to play critical roles in neuron growth. The gene encoding Cdc42 produces two distinct versions of the Cdc42 protein through RNA splicing. The two Cdc42 RNAs localize to different parts of the neuron. We found that this differential RNA localization is driven by RNA segments called untranslated regions, which are not used to encode the protein. This means that the two versions of Cdc42 RNA are translated into proteins in different regions of the neuron and they distinctly drive growth of those regions, which is important for both neuron development and the neuron's response to injury. Taken together, our findings uncover new functions for protein isoforms driven by their RNA templates being sent to different parts of the neuron.

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

When we were looking for ways to isolate the effects of the different Cdc42 isoforms, we designed siRNAs to separately target each isoform. Target sequences were quite restricted as the two mRNAs only differ by their 3′ exons. We were only able to specifically knock down the palmitoyl-Cdc42, but not the prenyl-Cdc42 isoform. To overcome this, we depleted neurons of both Cdc42 isoforms by targeting shared sequences and combined this with rescue plasmids encoding isoform-specific siRNA-resistant Cdc42s. This ended up being a blessing in disguise because it allowed us to not only study the role of each isoform but also to dissect effects of mRNA localization. Through these rescue experiments, we were able to manipulate the 3′ UTRs and the modification site of the proteins. Running into that wall ended up opening new doors and ideas for this project, so that we could link effects of RNA localization to subsequent post-translational modifications of the encoded proteins.

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

Much of our initial manuscript submission was limited to sensory neurons that only extend axonal processes and not dendrites. After hearing back from reviewers, we realized that we should go back and determine whether prenyl-Cdc42-encoding and palmitoyl-Cdc42-encoding mRNAs have differential functions in axons versus dendrites. Based on previous work, we had presumed prenyl-Cdc42 only has axonal functions and palmitoyl-Cdc42 only has dendritic functions. However, we had seen that prenyl-Cdc42-encoding mRNA localizes to both axons and dendrites. When we did this and repeated our rescue experiments in primary cortical neurons we found that prenyl-Cdc42 drives axon extension and palmitoyl-Cdc42 drives dendrite extension. However, unexpectedly, we found that prenyl-Cdc42 increases dendritic branching. Seeing this effect was incredibly exciting. These two isoforms, whose protein products only differ by 10 amino acids at the C-terminus, are affecting two separate aspects of dendritic growth. We now have a completely new direction to take our research, all thanks to a suggestion we got from reviewers.

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

Journal of Cell Science has been a staple in the field of cellular biology since its inception. While the experiments included in our manuscript focus on neuronal biology and specifically subcellular localization, the effects of subcellularly localized protein synthesis and the post-translational modifications that we found likely extend to all polarized cell types. Thus, we felt that publishing in JCS would bring this mechanism to the attention of the broader field of cell biology. I appreciate the ‘author-centric’ attitude of JCS showcased in this ‘First Person’ series.

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

A previous post-doc from our lab, Amar Kar, spent tireless hours mentoring me both in and out of the lab. In the lab, he was my main source of information and guidance, while outside of the lab, he was a close confidant and integral member of my support system. Coming into graduate school, I lacked any wet lab experience, which made me feel I was a step behind from the start. Amar really took the time not only to teach me technical skills in the lab but also help me better understand my strengths as a scientist. He helped me focus, think and examine my current ability, the path toward improvement and my future goals. Not only that, but I am sure he was tired of hearing me vent my frustrations, yet never made me feel like I couldn't come to him when I needed it. I owe a lot of my success and progress to him for all the time he put into helping me become a better scientist.

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?

During my undergraduate education I took a class called ‘Behavioral Neurobiology’. The course was taught by my academic advisor Dr. Aaron Cecala, who was really the only neuroscience staff member at my small school. The premise of the course was to read anywhere from five to ten research articles about a specific topic each week, and have our class discuss the topic along with the techniques used and even criticisms we had about the experiments. This was the first time I was asked to think deeply about real current scientific discoveries, and I absolutely loved it. Thinking and discussing not only the findings but the approach to answering these questions drove me to join Dr. Cecala's lab as an undergraduate researcher. If I had never taken that class or joined his lab, I don't think I would have pursued science.

Who are your role models in science? Why?

It may be a bit cliché, but I look up to the example my PhD mentor Dr. Jeffery Twiss sets for the lab. He works tirelessly, which is both inspiring and frustrating. Inspiring because I hope to one day be an accomplished PI in the same vein. Frustrating because I can't complain about working too much when he is so often the first person in the lab and the last person to leave.

What's next for you?

I am currently in the fourth year of my PhD and, after this publication, I am planning to get back to work in the lab. Leaving this school and lab still feels so far away but, after I graduate, I plan to get a post-doctoral position in neurobiology. I have enjoyed working on mRNA localization and axonal regeneration, but I am open to moving into other aspects of neuroscience. When I first thought of going to graduate school, I was fascinated by Alzheimer's disease and amyotrophic lateral sclerosis, so a return to a disease model of neuroscience could happen in my future. For now, I am focused on finishing my PhD and hopefully producing more data towards publications.

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

After I left undergraduate school, I made a decision to take time away from academia and travel the world. I may have taken a bit more time than I anticipated, almost 3 years, but in hindsight, I wouldn't trade that time for anything. In those 3 years I backpacked my way across the world. From Europe to Asia to South America, I spent months at a time exploring new places, meeting new people and experiencing cultures I would have never seen without my time away. I think my favorite memory of that time was when I was able to convince my friend to travel all the way to the Philippines with me. We had a mutual friend who grew up there and offered to let us stay with his family. The people there were some of the kindest I have ever encountered, and the culture is something I could have never imagined back home in Pennsylvania. While science is my passion, I found a love for the world in the time I took off.