Surupa Chakraborty, Amity University Kolkata
The Latin phrase “omne vivum ex ovo” attributed to William Harvey and summarized as ‘all living things come from eggs’ highlight the central importance of the mammalian egg. Reconstitution of oogenesis in a culture system serves as a useful technique to generate eggs from pluripotent stem cells which can be used to carry out the integrated sequence of oogenesis in mammals.
Scientists have recently identified a set of transcription factors that promote the transformation of pluripotent mice stem cells into immature egg cells called oocytes. Each of the factors NOBOX, FIGLA, TBPL2, SOHLH1, STAT3, DYNLL1, SUB1, and LHX8 were essential to trigger oocyte growth from primordial to the primary follicle. The immature egg-like cells, generated in the process, were not viable for reproduction as they did not undergo further meiosis to form daughter cells. However, in an additional set of experiments, when the researchers introduced wild type mouse sperms into the culture, the oocytes were competent for fertilization and underwent subsequent cleavage until they hit the 8-cell stage of embryonic development.
They monitored the global changes in gene expression profiles and functional screening in in-vitro mouse oocytes derived from primordial, primary, secondary and small and large antral follicles. They also identified the molecular and biological processes that triggered the meiotic and developmental transitions. This technology provides an alternative source of ooplasm which will help researchers to further explore the vast possibilities in the fields of reproductive biology and medicine.
Further knowledge of the gene regulatory network that controls the oocyte growth will help us in understanding the molecular basis of development of a high-quality mammalian egg. Nobuhiko Hamazaki of Kyushu University, a co-author of this study believes that this research can aid in the cloning of endangered mammalian species because of the vast number of oocytes produced by this novel technique. They believe that these enucleated transcription-factor-induced-stem cells derived oocytes are devoid of any abnormalities and can even help women with fertility issues and mitochondrial diseases to have healthy children.
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Source: Reconstitution of the oocyte transcriptional network with transcription factors. Nobuhiko Hamazaki 1, Hirohisa Kyogoku 2, Hiromitsu Araki 3, Fumihito Miura 3, Chisako Horikawa 4, Norio Hamada 4 5, So Shimamoto 4, Orie Hikabe 4, Kinichi Nakashima 4, Tomoya S Kitajima 2, Takashi Ito 3, Harry G Leitch 6 7, Katsuhiko Hayashi 8, (2020), Nature, doi: http://10.1038/s41586-020-3027-9
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