For species that rely on sexual reproduction, including mice and men, offspring can only happen if sperm from the male fertilize eggs from the female. Even artificial fertilization techniques depend on donors for both of these cells. However, a new study shows that mouse pluripotent stem cells can differentiate into functional sperm. These sperm were successfully used to produce healthy, fertile offspring and provide the most comprehensive model yet for generating male germ cells in a test tube.
Pluripotent stem cells have allowed scientists to study how each and every cell in the body is formed. Brain cells, heart cells, and livers cells are just some examples of the cell types made from these stem cells and now being used in patients as experimental cell therapies. However, some cell types remain difficult to make from pluripotent stem cells, particularly sperm cells.
Among all cell types, germ cells are unique for many reasons. First, unlike all other cells, which carry 46 chromosomes, germs cells only have 23 chromosomes, with the egg having all its chromosomes from the mother, and sperm having all its chromosomes from the father.
Furthermore, they are the only cells that parents actually pass to their offspring, which makes them, according to ASHBi Director Mitinori Saitou, one of the authors of the study, «the driving force that sustains and evolves a species.»
Although more research is needed, scientists have made significant strides in producing sperm cells from pluripotent stem cells, at least for mouse. The process is generally broken into three stages that mimic natural development. First, the stem cells are differentiated into primordial germ cells, then into spermatogonia stem cells, which is when the male sex is determined, and finally sperm.
Spermatogonia stem cells are what allow the male to produce sperm for a lifetime, but this second stage has proven to be the most difficult to recreate in the laboratory.
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Materials provided by Kyoto University. Note: Content may be edited for style and length.