'The question is controversial since some research has reported that such cells do exist, while other studies indicate the opposite,' says study co-author Dr Fredrik Lanner, researcher in obstetrics and gynaecology at the Karolinska Institutet, Sweden.
Although it was generally accepted that the ovary ceases to function when a woman enters menopause, there remained the theory that adult ovaries contained stem cells capable of differentiating into eggs. If correct, the existence of these egg stem cell would have been fundamental to helping women who are infertile.
In order to finally ascertain whether egg stem cell existed or not the Karolinska research team analysed thousands of cells collected from the ovarian cortex and medulla. This enabled them to build a complete cell map of the human ovary.
They found various common cell types, including oocytes, granulosa cells, immune cells, endothelial cells, perivascular cells and stromal cells, but they did not find any stem cells. This, therefore, has shown that egg stem cells do not exist and reinforced the idea of a limited ovarian reserve.
The study's co-author Dr Pauliina Damdimopoulou, a researcher in obstetrics and gynaecology at the Karolinska Institutet, Sweden hopes the new comprehensive ovary map will lead to improved methods of treating female infertility.
'The lack of knowledge about what a normal ovary looks like has held back developments,' Dr Damdimopoulou says. '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.'