In a paper in the Sept 20, 2007, issue of Nature, researchers reported on a marker that can be used to isolate cells that, by using the right culturing conditions, can be coaxed into becoming multipotent stem cells.
"Using this new marker, we were able identify these cells in their native environment and isolate them with a high level of efficiency. We were also able to expand them over many months, and they remained multipotent," first author Marco Seandel told BioWorld Today. Seandel is a researcher at the Howard Hughes Medical Institute and researcher/medical oncology fellow at Memorial Sloan-Kettering Cancer Center in New York.
The precursors to the stem cells, which the researchers termed multipotent adult spermatogonial-derived stem cells, or MASCs, were isolated from the testicles.
A paper published in Nature last year also described culturing pluripotent stem cells from adult sperm precursors, but it is not clear whether the cells described in the new paper are the same cells as those described in last year's article.
The protein expression patterns of the two cell types appear to be different, and senior author Shahin Rafii, director of the Ansary Stem Cell Center for Regenerative Medicine at Weill Cornell Medical College and a Howard Hughes Medical Institute investigator, told BioWorld Today that the cells described in the current work "have the capacity not only to give rise to sperm, but also to convert into multipotent adult stem cells."
In the newly published work, Seandel, Rafii and their colleagues were able to derive several different tissue types from the MASCs, including cells from all three embryonic germ layers. When MASC cells were injected into mice, they were able to form functional blood vessels that integrated with the host's circulatory system.
Considering their multipotency, the cells are surprisingly different from embryonic stem cells in terms of their biochemistry. The cells "don't produce certain proteins that were previously thought to be critical for multipotency," Seandel said. "It looks like they may use a different machinery than embryonic stem cells" to achieve their regenerative potential.
For men, if the research pans out, it may make stem cells if not quite as cheap and plentiful as beer, then certainly more easily accessible than they are now.
Whether the same is true for women remains to be seen. Rafii said that ovaries may harbor a similar type of stem cell, but he cautioned that the area still is "very murky." Even if they do exist, and can be isolated, the differences between the male and female biological clock may come into play. While males stay fertile into advanced age, females, with a modicum of luck, do not tend to need the kinds of major medical procedures that stem cells could come in handy for until they are past childbearing age.
Then again, in the long run, the question of whether ovarian cells are as good as sperm cells for making adult stem cells may turn out be irrelevant altogether. For one thing, GPR125 may turn out to be a more general marker for stem cells within other organs.
The scientists have been studying its distribution in adult tissue, and while they did not want to discuss their results in detail before peer-reviewed publication, Seandel said that the marker is expressed on fewer than than 1 percent of adult cells and "could be very interesting in other tissue types."
Rafii pointed out that the marker itself has "tremendous commercial value." The function of GPR125 is unknown, but as far as its role as a marker goes, it also is irrelevant. "There are very few good surface markers" for stem cells, he said. "Now we have found a marker that is expressed on undifferentiated spermatogonial cells."
MASC cells also are likely to enable new types of experiments because of the sheer ease with which the cells can be expanded. Normally, Rafii said, "adult organs have a very limited number of stem cells, which are difficult to purify and differentiate in the lab into tissues for therapeutic use." In contrast, the MASC cells "can self-renew indefinitely and differentiate into grams and grams of tissue for organ regeneration."
The potential for organ regeneration, of course, is in the uncertain future. But a plentiful source of stem cells will allow the design and optimization of experiments today. "We might be able to come up with strategies to reprogram other cells," Seandel said. "This particular stem cell type is probably going to open up doors for others."