One of the most intriguing questions in biology is how a single cell (zygote) has the potential to give rise to all cell types of an organism, known as totipotency. Afterwards this potential is progressively lost along cleavage divisions to allow cell specification and differentiation. Upon fertilization a single cell embryo is generated, and it has the potential to activate a series of coordinated events that lead to the achievement of the totipotent state. These events encompass an extensive epigenetic reprogramming of the parental genomes, 3D chromatin organization reorganization and zygotic genome activation (ZGA). The overall purpose of this project is to deepen our understanding of the mechanisms underlying the oocyte-to-zygote transition (OZT) in mammals. The understanding of ZGA is very promising, not only from the intellectual point of view in the developmental biology field, but also these factors will be useful for cell reprogramming in regenerative medicine to generate the first totipotent cell lines.
The first aim of the project is to address whether and how epigenetic reprogramming modulates 3D chromatin structure in zygotes. Shortly after fertilization, both parental genomes undergo genome wide demethylation. Paternal DNA becomes largely demethylated. Though, changes in maternal genome are less evident. This DNA demethylation can proceed passively by dilution through replication, or actively, mediated by several mechanisms including catalysis by the methylcytosine dioxygenase Tet3. Given the asymmetry between the parental genomes, both in terms of epigenetic landscape and the chromatin compartmentalization, it would be interesting to determine how epigenetic changes in the paternal pronuclei lead to a reorganization of the chromatin. More specifically, the aim of this project is one the one hand, to assess how DNA methylation modulates compartmentalization on paternal and maternal genome; and in the other hand, determine the effect of histone methylation on chromatin compartmentalization, due to the asymmetry between the maternal/paternal genome in the histone marks. The preliminary results using a Tet3 conditional knock-out model, point to weaker compartmentalization in the zygotic genome, suggesting a role of Tet3 in chromatin organization. Whether if this change is due to the DNA demethylation activity of Tet3 is yet to be determined.
The main aim of the second part of the project is to identify a candidate regulator of the zygotic genome activation. A key question is which proteins are essential for activation of embryonic transcription during ZGA. It is conceivable that these regulators are maternally inherited from the oocyte. Based on a previous screen of potential regulators of ZGA carried out in the laboratory, one promising candidate factor was chosen to study in detail. It will be analyzed if the candidate is essential for embryonic development and its involvement in the regulation of ZGA. The knock down of the candidate show a reduction in the major ZGA transcripts, suggesting an implication of this candidate in the regulation of ZGA in mammals.
Unfortunately, this project has to be terminated prematurely after these 5 months, as the hosting research group has moved its location from IMBA to Max Planck Institute of Biochemistry (MPIB), Germany. The proposal was submitted in the Society and Enterprise panel, as IMBA is a non-academic institution. However, the MPIB has an academic status, which makes it impossible the transfer of the fellowship. Because of that, no further conclusions have been obtained in this short period of the project.
