Parte et al. Stem Cells Dev.
Very small embryonic like cells (VSEL) are a type of stem cell that appears to be found in bone marrow and other tissues of the body, presumably as a remnant of embryonic or embryonic-like cells left over from development. In a recent paper it was demonstrated that these cells may be found in the ovary surface epithelium in adult rabbit, sheep, monkey and menopausal human.
Indian scientists found two distinct populations of putative stem cells of variable size were detected in the ovary surface epithelium: one being smaller in size around the range of 1-3 micrometers and the other being of a size approximate to the surrounding erythrocytes.
The smaller cells resembled VSELs and were pluripotent in nature with nuclear Oct-4 and cell surface SSEA-4. The larger cells were 4-7micrometers and possessed cytoplasmic localization of Oct-4 and minimal expression of SSEA-4. The scientists believed that the larger cells were possibly the progenitor germ cells.
The VSEL cells were capable of spontaneously differentiating into oocyte-like structures, parthenote-like structures, embryoid body-like structures, cells with neuronal-like phenotype and embryonic stem (ES) cell-like colonies. They expressed Oct-4, Oct-4A, Nanog, Sox-2, TERT, and Stat-3 as detected by RT-PCR.
Germ cell markers like c-Kit, DAZL, GDF-9, VASA and ZP4 were immuno-localized in oocyte-like structures formed from the VSEL.
These studies are interesting because prior to this there were reports of bone marrow derived cells being implicated in production of oocytes. Specifically, Jonathan Tilley from Harvard reported that bone marrow transplantation can give rise to new oocytes that are donor derived http://www.ncbi.nlm.nih.gov/pubmed/17664466.
If these studies are reproducible it may be that adult stem cells could be useful in the treatment of infertility. Conversely it may be possible to repair oocytes of women who have undergone chemo/radiation therapy. Interestingly, Tilly’s group also published that ovarian tissue contains VSEL-like cells http://www.ncbi.nlm.nih.gov/pubmed/20188358