From blastocyst to egg cylinder: analysis of peri-implantation embryogenesis

• Applicant: Dr. Ivan Bedzhov
• Subject Area: Developmental Biology
• Term: from 2015 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 278835329

Four and a half days after fertilization the mouse embryo comes for the first time in direct contact with the maternal environment and initiates implantation. In turn, the maternal tissues proliferate and engulf the embryo making it relatively inaccessible for direct observations and experimental manipulations. Thus, the peri- implantation embryogenesis is largely unexplored and probably the most enigmatic period of mouse development. Just within 24 hours the implanting blastocyst dramatically changes its shape transforming into an elongated egg cylinder. At that time the pluripotent epiblast undergoes global reorganization from a simple ball of cells into a cup- shaped polarized epithelium surrounding a central proamniotic cavity. The emergence of this new organization of the embryonic lineage provides a platform for establishment of the germ layers building the embryo proper. Apoptosis was originally considered as the driving force for reshaping the epiblast during the peri-implantation stages. Contrary to this view we found a previously unknown, apoptosis- independent morphogenic event that reorganizes the epiblast into radially polarized rosette-like structure, serving as a foundation for proper establishment of the egg cylinder. Taking advantage of novel methods for embryo and embryonic stem-cell cultures we will dissect the processes of epiblast polarization and lumenogenesis on cellular and molecular levels. To elucidate the developmental regulation of epiblast morphogenesis we will investigate signalling circuits involved in pluripotent state transitions in relation to acquisition of epithelial polarity.

• DFG Programme: Independent Junior Research Groups