The apportionment of zygotic totipotency: Origins, mechanisms and consequences for natural and assisted reproduction in the mouse model

• Applicants: Privatdozent Dr. Michele Boiani; Professor Dr. Georg Fuellen; Professor Dr. Wojciech Makalowski, Ph.D.
• Subject Area: Reproductive Medicine, Urology
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 450038723

In mammals, the two blastomeres resulting from the 1st zygotic division are deemed equally totipotent, able to form two monozygotic twins. However, the first cleavage plane differs among embryos, distributing the constituents of the ooplasm differently among the two blastomeres, questioning equal potentiality. We propose that intracytoplasmic sperm injection –widely used in assisted reproduction– helps to investigate potentiality in a controlled manner, by imposing the site of oocyte fertilization and thus cleavage orientation. Motivated by Xenopus and sea urchin data, we hypothesize that the mouse blastomeres are most similar to each other when the 1st cleavage plane runs along the animal-vegetal axis, yet they are most different from each other when it runs perpendicular. The transcriptomes of blastomeres will be combined with those of our recent meta-analysis of conventional 2-cell embryos, where transcription patterns of, e.g., Tead1 and Cops3 do correlate with blastomere similarity as per our hypothesis. Additional gene(s) X may be revealed in the present study. To reach beyond correlation and establish causality, we deplete gene products directly at the protein level in oocytes prior to fertilization. We assess developmental consequences and subject Tead1-, Cops3- and gene X-depleted embryos to proteomics to confirm the specificity of the protein depletion. During the course of the project we shall answer two questions: 1) if and how the orientation of the 1st cleavage plane introduces functional variation among the blastomeres; and 2) if and how maternal protein deposits in mammalian oocytes are decisive for potentiality and development.

• DFG Programme: Research Grants