Scientists are bringing us closer to the day where same-sex couples can finally have genetically mutual offspring…A child whose DNA is derived from both same-sex parents.
This could be made possible through a process known as in vitro gametogenesis (in vitro meaning outside of a live context and gametogenesis referring to the process of gamete formation such as a sperm or egg).
Although scientists have been able to transform, in mice, both embryonic and induced pluripotent stem cells (PSCs) into primordial germ cells (PGCs), which can give rise to fully mature and viable gametes and viable offspring (1), this feat has largely remained elusive in the context of humans. Fortunately, current work being done within the field is getting us much closer to that point!
Some might ask, “Well why not just replace DNA from a different cell in the body into an already established germ cell?” One of the major challenges that have been faced up until now have included getting the DNA into an appropriate state for functioning as a germ cell.
To more simply understand this problem, we must first understand that DNA is a lot more complicated than just an arrangement of nucleotides within a double-helical chemical structure. DNA can also be chemically modified with different “epigenetic marks” such as methylations in different patterns throughout the entire genome. Furthermore these methylations have a language of their own and can promote a number of different processes depending on where in the DNA they occur and what other factors are called nearby that can alter how those marks get interpreted within the cellular context. And to makes things even more complex, there are other epigenetic factors that are spatiotemporally organized along the entire genome with its own language to be interpreted. These epigenetic factors are important when it comes to specifying a particular fate of a cell. This is a process commonly called cellular differentiation and is important for distinguishing a kidney cell from a brain cell and so on. For DNA to confer the functionality of a sperm or an egg cell, they need to first adopt a specific epigenetic state that allows for the DNA to express a particular set of genes that are critical to the function of the mature gamete. This has been a central aim for current scientists.
A recent study has broken through a major barrier of transforming an induced human pluripotent stem cell (hiPSC) into a primordial germ cell-like cell (hPGCLC) (2). Although it is not yet capable of transforming from this state into a viable mature gamete, these new findings are taking us a huge step forward towards this end goal.
in vitro gametogenesis has huge implications for couples, both homosexual and heterosexual, that struggle with fertility. Gametogenesis in males versus females are quite different and getting a mature female gamete from a male differentiated cell may potentially present with its own set of challenges.
To stay current with some of the trends and new findings within this field, check out some of the key terms posted below and do a literature search on pubmed.gov.
in vitro gametogenesis, human primordial germ cell like cell, hPGCLC.
Hikabe, O., Hamazaki, N., Nagamatsu, G., Obata, Y., Hirao, Y., Hamada, N., Shimamoto, S., Imamura, T., Nakashima, K., Saitou, M., et al. (2016). Reconstitution in vitro of the entire cycle of the mouse female germ line. Nature 539, 299-303.
Yamashiro, C., Sasaki, K., Yabuta, Y., Kojima, Y., Nakamura, T., Okamoto, I., Yokobayashi, S., Murase, Y., Ishikura, Y., Shirane, K., et al. (2018). Generation of human oogonia from induced pluripotent stem cells in vitro. Science.