March 2 (UPI) -- There's no such thing as an egg stem cell, according to new research released Monday by scientists at the Karolinska Institute in Sweden.
Researchers collected and analyzed more than 24,000 cells from the ovarian cortex of 21 patients. The team also analyzed thousands of cells from the ovarian medulla.
The existence of the so-called egg stem cell is a hotly debated topic, but the latest analysis -- published in the journal Nature Communications -- turned up no evidence of such a cell type.
"The question is controversial since some research has reported that such cells do exist, while other studies indicate the opposite," study co-author Fredrik Lanner, researcher in obstetrics and gynecology at the institute, said in a news release.
The existence of an egg stem cell is important to the development of treatments for involuntary childlessness. Stem cells are cells capable of differentiating into other types of cells and have been used to develop a variety of health treatments.
"Involuntary childlessness and female fertility are huge fields of research," said co-author Pauliina Damdimopoulou, researcher in obstetrics and gynecology at Karolinska. "This has been a controversial issue involving the testing of experimental fertility treatments."
The new analysis revealed several common ovarian cells, including ocytes, granulosa cells, immune cells, endothelial cells, perivascular cells and stromal cells, but no egg stem cells.
The study's finding match the results of several animal studies that failed to turn up evidence of an egg stem cell. Scientists hope their efforts will provide an improved understanding of the cell map of the human ovary.
"The lack of knowledge about what a normal ovary looks like has held back developments," Damdimopoulou said. "This study now lays the ground on which to produce new methods that focus on the egg cells that already exist in the ovary. This could involve letting egg cells mature in test tubes or perhaps developing artificial ovaries in a lab."