The Japanese researcher whose claim of a major breakthrough in stem cell research was discredited resigned after the government lab where she worked failed to replicate her results.

Haruko Obokata said in a statement Friday that she was leaving the Riken Center for Developmental Biology after the lab concluded the stem cells she said she had created probably never existed. The center said it had stopped trying to match Obokata's results.

"Now, I am just exhausted. For the results to end this way is just perplexing," she said.

Obokata initially was lauded for leading the research that raised hopes for a discovery of a simple way to grow replacement tissue. But questions about the validity of the research prompted Riken scientists, including Obokata, to retract two scientific papers.

The allegations of research misconduct prompted a shake-up at Riken.