Dr. Marcella O’Reilly

Postdoctoral Fellow at Columbia University

What achievement are you most proud of to date?

Definitely achieving my PhD and being able to publish my work. As an undergraduate, I really wasn’t sure if I was cut out for a PhD but I genuinely loved my PhD journey. I absolutely had bad days and doubted myself but in the end, it paid off because it allowed me to work as a postdoc at Columbia University with leaders in my field.

Growing up on a dairy farm in Ireland, concepts like the genetics of pedigree cow breeding and the protein content of milk formed a routine, though initially not well-understood, aspect of Dr. Marcella O’Reilly’s childhood. When she was 4 or 5 years old, her parents introduced her to a cartoon called “Once Upon a Time…Life” where anthropomorphic cells went about their daily lives, each fulfilling its own role to keep the body functioning. The cells of the circulatory system in particular caught her fancy; She enjoyed watching the red blood cells carry oxygen throughout the body, and the white blood cells as they chased and caught pathogens. Marcella credits the latter especially for igniting her fascination for health and immunity.

At school, this interest only continued. “I felt as though my mind absorbed biology quicker than other subjects,” Marcella remembers. “I remember thinking at age 16 that I would love to have a career in research, particularly in the area of human health.” After high school, she enrolled at University College Dublin, where she pursued a degree in Pharmacology (or the study of drugs actions in the body). During this time, she had an opportunity to spend a summer in Dr. Breandán Kennedy’s lab, where she got to experience research first-hand by studying the process of eye development in zebrafish. During her time in Dr. Kennedy’s lab, he taught her important foundational skills in scientific writing, as well as many basic research skills. By the end of her undergraduate program, Marcella felt that although she enjoyed working at the bench, she “really didn’t understand what a PhD encompassed and was scared at the thought of starting something [she] knew little about.” However, still taken by the workings of the immune system and hoping to gain more lab experience, Marcella started looking for other research opportunities. Her former mentor, Dr. Kennedy, coached her during this process, and with his help, she was able to secure a position as a research assistant for Dr. Fiona McGillicuddy, who at the time was starting up her own lab at UCD to study the link between diet, obesity, and high-density lipoprotein (HDL) cholesterol function in mice and humans. There, she dove headfirst into the world of obesity-induced inflammation and its effect on metabolism. Under the guidance of Dr. McGillicuddy, she was able to further hone her critical thinking, project planning, and manuscript writing skills; all important skills for research. With Dr. McGuillicuddy’s guidance and encouragement, Marcella decided to pursue her PhD in the same lab, where, under the co-mentorship of Dr. McGillicuddy and Dr. Helen Roche, she studied how dietary fats drive changes in cholesterol metabolism.

“Had you told me at the start of my PhD that this is where I would be now, I never would have believed you. I’m surrounded by some of the best scientists in my field and I get to work with and learn from them.”

After graduating with a PhD, Marcella joined Dr. Muredach Reilly’s lab as a postdoctoral fellow at Columbia University, where she has been since 2019. “Moving to New York and surviving was no mean feat,” she laughs. “Had you told me at the start of my PhD that this is where I would be now, I never would have believed you. I’m surrounded by some of the best scientists in my field and I get to work with and learn from them.” Her current work revolves around the behavior of adipocyte cells, which store the body’s excessive nutrients as fat, during obesity and inflammation. “The human body has all these mechanisms in place to maintain homeostasis (balance),” Marcella explains. Many diseases and conditions can be explained as a loss of homeostasis, and obesity is no different. To better understand how adipocyte cells behave differently in obesity, Marcella is studying a number of novel genes that were found to be differentially expressed in the adipocyte cells of obese compared to lean individuals. Interestingly, because these genes do not code for protein material, their functions remain a mystery. Marcella hopes that her work can help scientists better understand the imbalance of nutrients and hormones during obesity and diabetes so that therapies can be designed to improve human health.

Marcella credits each of her mentors with shaping her into who she is now. From her undergraduate mentor, Dr. Kennedy, who first introduced her to the world of research, to her PhD mentors Dr. McGillicuddy and Dr. Helen Roche, who played an important part in building up the skills she needed to continue on in her field. Most importantly, she reflects “Fiona encouraged me to pursue a PhD and without that I probably would not be where I am today.” She describes Dr. Reilly, her current mentor, as someone who “will always keep you looking forward and encourage you to develop fresh ideas”. “It’s important to have mentors who care about your future,” she concludes. “I have been very lucky to have found some amazing mentors… each one wanted to see me [become] successful and helped me in [every] way to move forward to the next step in my career.” 

I have been very lucky to have found some amazing mentors… each one wanted to see me [become] successful and helped me in [every] way to move forward to the next step in my career.” 


by Lucie Zhu

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