Berna Sozen’s career has been defined by one question: How does a single fertilized egg become a human being?

Sozen first saw early human embryos when she participated in an IVF clinic internship in Turkey, and the mystery of their formation captured her attention. 

“I was struck by how much was happening in that tiny sphere of cells,” she says. “I knew I had to understand what was guiding that transformation.”

The First Few Weeks

As a developmental biologist at Yale School of Medicine, Sozen investigates the initial weeks following egg fertilization, or the period when embryonic stem cells decide what they will become and coordinate to build the body’s foundation. 

Her work covers many disciplines but seeks to answer fundamental inquiries like: How do cells know where to go, and what signals guide their choices? Why do some pregnancies thrive when others do not?

Sozen’s path to Yale was shaped by her circumstances. Growing up in Turkey in a family where no one held a college degree, she faced both financial constraints and systemic barriers to higher education. In resource-limited environments, fellowships are rare, and each application is high-stakes. 

“I wish more people understood how much scientific potential exists in places where opportunity is scarce,” she says. “I learned that if you get a chance at something, you must hold on to it like a diamond and never take it for granted.”

Stem Cell Discoveries

During her graduate work between Akdeniz University and the University of Cambridge, Sozen helped pioneer a breakthrough: Her research contributed to early work demonstrating that stem cells can self-organize to model early embryogenesis, or the development of an embryo, in a dish. This insight, developed alongside parallel advances from several groups worldwide, helped turn what began as a conceptual possibility into stem cell–based embryology, a now-thriving field providing unprecedented access to observe how embryos construct themselves.

Sozen’s team at Yale has expanded this research further, developing three-dimensional embryo models that capture the two-to-three-week window when the body plan forms, which was a previously unknown period of human development. But her most significant insight may be reframing how scientists understand the growth “decisions” themselves. The key lies in metabolic processes.

“By integrating metabolism to protein and genome regulation, we bring a systems-level perspective to morphogenesis, or the process by which an organism starts to take form,” she explains. “This reframes metabolism not as a passive background process but as an active spatial regulator of cell fate.”

This perspective connects maternal health and nutrition to developmental outcomes. Sozen’s work reveals how cells in different parts of the embryo interpret these signals distinctly to build diverse tissues. 

“These nutritional cues act as hidden signals that can influence how an embryo starts and whether it thrives,” she says.

The implications reach beyond basic science into regenerative medicine, where guiding cells into specific states is essential. Better understanding how metabolism directs cell fate decisions could inform treatments for infertility and miscarriage, as well as a variety of other developmental disorders.

Adversity and Opportunity

Sozen’s immigrant experience, she says, has been both a challenge and a strength. Following science across continents meant navigating unfamiliar systems while building a career, though those same struggles helped her become more resilient and strategic. 

 “At times, this made my path more difficult, requiring me to work harder to be understood, recognized, and taken seriously,” Sozen says. “I learned to quickly identify high-impact opportunities, communicate across cultures, and persist through uncertainty. In many ways, my immigrant journey has strengthened my curiosity, sharpened my focus, and taught me to value collaboration and diverse perspectives.”

Those viewpoints inform her lab culture. She strives to create an environment where people are seen, supported, and encouraged to take risks. “Access makes a real difference, and we all have a role in making it more equitable.”