Columbia’s broad biology program and rotations allowed Carla to explore jumping into a new field while maintaining a safety net of familiarity.
PhD candidate Carla Hoge’s career plans evolved to include discoveries in vertebrate recombination.
Growing up, Carla Hoge wanted to be a veterinarian. But after taking evolution classes as an undergraduate—one of which included a trip to the Galápagos Islands—Hoge decided to go all-in on genomics.
Today, Hoge is a PhD candidate in Dr. Molly Przeworski’s lab in the Columbia University Department of Biological Sciences, where she studies meiotic recombination localization in vertebrates. She’s benefited from mentorship throughout her time at Columbia and has enjoyed paying that forward as a teaching assistant and mentor.
Hoge grew up in suburban Pittsburgh and attended the University of Pennsylvania with the goal of applying to MD/PhD programs in veterinary science. “I was really interested in animals,” she recalls. “Every chance that I got to interact with animals, that was my ideal.”
As an undergrad, Hoge conducted research on stem cell biology and its connection to colon cancer. She took her first evolution class junior year as a degree requirement for her dual BA/MS biochemistry program—and she was hooked. She took four more classes senior year and even visited the Galápagos, which played a central role in the development of Charles Darwin’s theory, for a class on the history of evolution. “That trip was life-changing,” she recalls. While there, she participated in a community science project working with local high school students to study how human activity impacts sea lions.
Realizing that a veterinary program wouldn’t afford her the opportunity to conduct evolution research, Hoge changed tacks and applied to PhD programs in biology instead.
"I've had really wonderful experiences mentoring and teaching. That has given me a very clear idea of what I would like to do with my life.”
An interview with Przeworski, who would one day become her adviser, convinced Hoge that Columbia was the place for her. Also, Columbia’s biology program is broad and allows students to rotate in various labs before committing to one—both boons to Hoge, who was going to be jumping fields. The program “included research that was more similar to what I had done for my master’s, and that gave me a little bit of security,” she says. If she realized evolution wasn’t for her, she could fall back on biochemistry research.
Hoge has stuck with evolution. In the Przeworski lab, she studies a rapidly-evolving protein called PRDM9. The protein is considered essential for reproduction in some mammals—mice that lose PRDM9 are sterile—but it has been lost many times throughout evolution. “My goal was to show that this protein does the same thing in nonmammalian vertebrates as it does in mammals,” Hoge explains. Many species have multiple copies of the gene that codes from PRDM9; her team picked corn snakes as their model organism because corn snakes have only one complete copy of the gene.
“My entire rotation, I could not make heads or tails of what was going on in this species,” Hoge recalls. “I definitely thought it was my fault because I was learning to code, and I had never done computational research before.” Hoge persevered with the project after officially joining the Przeworski lab her second year. “It took a couple years before we were really convinced by what we were seeing,” she says.
Many mammals rely on the PRDM9 protein for meiotic recombination, an essential part of reproduction wherein chromosomes pair up and trade DNA. But what Hoge found is that, unlike mammals, corn snakes also use promoter-like features for meiotic recombination. (Promoters are short pieces of DNA that indicate where replication should begin.) The latter mechanism was previously considered a back-up for animals that lack PRDM9. “Corn snakes use both of these two different mechanisms that were thought to be mutually exclusive,” Hoge explains. “We just stumbled upon this by accident because we picked this species that it turns out does this really cool thing.”
Hoge’s experience with corn snakes has piqued her interest in conducting research using nonmodel systems—in other words, branching outside of traditional options such as mice and fruit flies. In addition to her work with corn snakes, she’s also looked at bleaching tolerance in coral samples collected across the Great Barrier Reef.
“There are so many challenges with working with nonmodel systems, to be clear,” she says. Keeping the animals alive in the lab is one. “But when you can make it happen, there’s just so much cool biology to be learned.”
These days, Hoge doesn’t work directly with animals. “I have extracted some DNA and RNA from corn snake samples in my time, but I have not yet held a live corn snake—not as a part of lab, anyway,” she says. “99% of my time is spent studying DNA sequences on a computer.”
Outside of the lab, Hoge enjoys spending time with friends. She hosts board game nights, carrying on a Wednesday night tradition started by her Columbia cohort. And she enjoys rock climbing. Rock climbing routes present a solvable problem, she explains, as opposed to the problems scientists grapple with, which often lack clear solutions.
Hoge credits her adviser with much of her success in the program. She was a third-year PhD student when the COVID-19 pandemic hit, and Przeworski “just stepped up” when Hoge was struggling with her mental health, she says. “I've been very blessed and grateful to receive some really great mentorship from her.”
Hoge will defend her thesis in December. She is seeking a position that puts equal emphasis on research and teaching in an institution that supports its instructors. “I care a lot about teaching,” she explains. “I want the people around me to care a lot about teaching as well.”
Hoge says her time working with younger students at Columbia has helped to crystallize her next steps. “I've had really wonderful experiences mentoring and teaching,” she says. “That has given me a very clear idea of what I would like to do with my life.”