Human Embryo Development

"We have revealed the patterns of gene expression in the developing embryo just after it implants in the womb, which reflect the multiple conversations going on between different cell types as the embryo develops through these early stages. We were looking for the genetic conversations that will allow the head to start developing in the embryo and found that these were initiated by cells in the hypoblast, which would not normally contribute to building the body itself. They send the message to the adjoining embryo cells, which respond by saying 'OK, now we'll set ourselves aside to develop into the head end.'"

"Our goal has always been to enable insight to very early human embryo development in a dish to understand how our lives start. By combining our new technology of culturing human embryos with advanced sequencing methods, we have delved deeper into the key changes that take place at this incredible stage of human development when the embryo becomes remodeled to undertake its critical decisions at a time when so many pregnancies fail."

Magdalena Zernicka-Goetz, currently Caltech Bren Professor of Biology and Biological Engineering  

Four-week fetus   MedicineNet

Abstract:  A single cell characterisation of human embryogenesis identifies pluripotency transitions and putative anterior hypoblast centre: Lead author, Matteo Mole, University of Cambridge

Following implantation, the human embryo undergoes major morphogenetic transformations that establish the future body plan. While the molecular events underpinning this process are established in mice, they remain unknown in humans. Here we characterise key events of human embryo morphogenesis, in the period between implantation and gastrulation, using single-cell analyses and functional studies. First, the embryonic epiblast cells transition through different pluripotent states and act as a source of FGF signals that ensure proliferation of both embryonic and extra-embryonic tissues. In a subset of embryos, we identify a group of asymmetrically positioned extra-embryonic hypoblast cells expressing inhibitors of BMP, NODAL and WNT signalling pathways. We suggest that this group of cells can act as the anterior signalling centre to pattern the epiblast. These results provide insights into pluripotency state transitions, the role of FGF signalling and the specification of anterior-posterior axis during human embryo development."

Nature Communications

The first days' evolution of the human embryo has been mapped for the first time by scientists working out of Cambridge University in tandem with the Wellcome Sanger Institute. The team set their focus on the molecular linking between the hypoblast and the embryo, finding chemicals forwarded to the embryo from the hypoblast activate and inactivate various genes. Prior to this occurrence, the embryo has the potential to become any body cell, from a bone cell to a neuron. The scope is narrowed by the hypoblast intervention creating the "head" and the "tail". 

 

In essence, the earliest stage of the embryo before the vital 'communication' from the hypoblast turns it from a generalist toward a critically specific purpose in establishing the order and formation of the organism, whether human or animal. The discovery by these scientists might have application in the future in fully understanding and in the end, preventing, early miscarriages. 

 

Through the study of embryos in their first two weeks of existence -- the focus on how they transform from a clump of nondescript cells into an organized mass -- Cambridge University researchers found the answers they sought. The transformation speaks to the crucial step forward in instructing cells to produce a developing baby. The blueprint is there for the cells to follow, but should the function fail to develop as needed, the result is a failed pregnancy.

 

11 Weeks   whattoexpect.com

The insight gained by the researchers into the incubation period of nine months has been a hitherto elusive goal. While great strides have been realized, some of the intricacies of developmental details remained to be discovered. The formation of the "head-to-tail" axis, occurring at the end of the first week of the embryo's existence was one such mystery awaiting revelation. The axis is an invisible line running from top to bottom of an animal, forming the basis of the gastrointestinal tract, determining later growth and organization of the body's organs.

Once a fertilized egg latches to the womb wall, after a week it receives a chemical signal emanating from a different group of cells identified as a hypoblast. Signals from the hypoblast bring forward a cascade of genetic modifications within the embryo, instructing specific cells to begin the process of specializing. Embryos may be used in laboratory research until up to 14 days post-fertilization, when at this point ethics deem they must be destroyed.

39 Weeks   BabyCenter UK