Cell biology graduate student Sang-Ohk Shim GRD ’10, a Ph.D. candidate from South Korea, died Sunday in an apparent suicide, Graduate School Dean Jon Butler said in an e-mail to the Graduate School community Sunday evening.

Shim had been receiving psychiatric treatment for depression, but her death still came as a shock, friends said. She had told friends she had nearly finished her thesis, a research project on the role of a particular molecule in brain cell development and recovery, and she expected to receive her degree in September. She had gone out to dinner with other students and researchers in her Medical School neurobiology lab on Friday night, then spent much of Saturday working in the lab. On Sunday afternoon, she was pronounced dead at Yale-New Haven Hospital.

“She was very bright, a great scientist, wonderful to work with in the lab,” said Stephen Strittmatter, a neurology professor at the School of Medicine whose research group Shim joined about five years ago. “It’s a real shame what happened — a loss to the world, and to us, and to Yale, and to her family, and anyone you can think of.”

Shim came to Yale six years ago from the University of California, Berkeley, where she had worked as a research associate. Before that, she had earned bachelor’s and master’s degrees at Seoul National University in South Korea, according to her LinkedIn profile.

After earning her Ph.D., Strittmatter said, Shim planned to stay in New Haven as a postdoctoral research fellow or take a corporate job as a biomedical researcher. She also considered studying scientific intellectual property, he said. Wherever her career took her, she hoped to live in New England, where she loved to hike, friends said.

In the lab, she stood out for her work ethic, for the sharpness of her insights — and for her ability to make the lab a welcoming, warm environment, coworkers said.

“She was really a shining light in the lab, a joy to work around and be with,” said Erik Gunther, a research associate in Strittmatter’s lab. “And she was hella smart.”

Talkative and full of stories, it was Shim who encouraged the others in her lab to get together for drinks, meals and weekend parties, said William Cafferty, a research associate who shared a desk with Shim.

She was always ready to throw dinner parties with exquisitely cooked Korean food, sample New Haven’s newest restaurant or organize a hiking daytrip, Cafferty added. With friends from the lab, she would frequently hike on weekends in Macedonia Brook State Park and other parts of New England.

Her friends knew Shim suffered from depression, Gunther said.

“But you wouldn’t know it, talking to her,” he said. “She was really upbeat.”

Shim spent a year as the vice president of the Yale Biotechnology & Pharmaceutical Society, where she organized educational events down to the last detail, fellow member Yong Pan GRD ’11 said.

“It was always the small things I appreciated in her,” Pan said. “There are lots of other people who plan things but are really reluctant to commit themselves to actions, but she was the opposite of that — she always volunteered herself and made sure the details things were right.”

As Strittmatter’s research group, Shim’s friends in the Korean community and other members of the YBPS tried to cope with the news Monday, Shim’s mother and sister flew to New Haven from South Korea, where all her relatives live. There may be a memorial service, Butler said in his e-mail, though friends said they would wait for Shim’s family before planning anything. Butler also encouraged members of the Yale community to speak to counselors at Yale Mental Health and Counseling or at the Yale Chaplain’s Office.

Shim was last in the lab Saturday, when she spent the evening working alongside Cafferty, her deskmate. Learning of her death the very next day came as a shock, Cafferty said.

“She was all about everyone else,” he said by phone from the lab. “When she was around, she was always up and effervescent, so maybe when she was down, we just didn’t see her.”

He added: “Right now I’m sort of a bit foggy. I’m sort of staring at her empty desk right now.”