I know it seems like an absurd question to start with: can a foetus without egg and sperm even exist? As scientists show in a recently published article in the journal Cell 1, at least for mouse embryos in the lab, it is not only possible, it is a reality. These researchers used EPS, short for extended pluripotent stem cells, cells which can give rise to any tissue in the body and are derived from adult cells from say, the ear or the skin. Adult cells from the mouse ear were treated with a cocktail of transcription factors to reset them back to stem cells. Once as EPS, these cells grew and assembled into structures resembling those forming by embryos in a dish, at which stage they were transferred into a mouse womb. At this point, some of those implanted embryos started developing like any normal embryo would. Into a foetus.
However The process was not perfect. Not in every instance the implantation succeeded and the tissue organisation didn’t seem to be totally alright. Possibly this reassembled embryo lacks some factors only the egg carries or the exact mix of growth factors was suboptimal. Be it as it may, we are not yet able to produce a full term foetus without eggs of sperm. Not for mice, even less for humans. Not was it the objective of the team. The objective of the study was to try to understand the process of tissue sheet formation during embryonic development. How this process affects implantation and, in turn, pregnancy success. It is therefore a tool not an end. So, back to our first question: can we make a foetus without egg and sperm? And the final answer is no. We can only reproduce the initial stages of embryonic formation and implantation, but we cannot (yet) produce a viable healthy foetus. Interesting is, however, that it is possible to reprogram a single cell in a mouse ear to produce an initially viable embryo barely indistinguishable from a normal one. Isn’t science amazing?
Ronghui Li et al (2019) Generation of Blastocyst-like Structures from Mouse Embryonic and Adult Cell Cultures Cell doi: 10.1016/j.cell.2019.09.029↩