Fogarty Lab - Our Research

Background: Early Development of the Embryo

A human being is made up of billions upon billions of cells with highly specialised functions. But we all began as a single cell with the potential to become anything. This cell is known as the zygote, and it occurs in the stage immediately after the sperm fertilizes the egg. The zygote is a totipotent stem cell – the only of its kind- which means it has the potential to become all cells of the growing embryo and all of the extra-embryonic structures which are the structures that support the embryo during pregnancy.

Over the following days the zygote will divide into more and more cells until there are around 100 cells by day 5 or 6 of development. These cells are arranged into in a fluid filled ball called the blastocyst with a small mass of cells inside. The cells that make up the outer layer of the blastocyst are trophectoderm cells. 90% of all cells in the blastocyst are trophectoderm cells. These are also a type of stem cell, with the ability to renew themselves and specialise into different trophoblast cells that make the placenta.

The steps of early embryonic development from the zygote to blastocyst. (Source: inviTRA)

The placenta is a temporary organ that is attached to the growing fetus via the umbilical cord. A complex network of blood vessels in the placenta provides the fetus with oxygen and nutrients whilst taking away waste. It also acts as a barrier between mother and fetus, preventing some harmful substances from reaching the fetus, and makes hormones important for development. Given its many vital roles, if the placenta does not develop or function correctly, it can lead to conditions such as:

• Preeclampsia (caused by the placenta not invading deep enough, resulting in the placenta not receiving enough blood)
• Infertility
• Miscarriage

Some of the complex functions of the placenta in human development. (Source: Zero To Finals YouTube Channel)

Understanding how the placenta grows may help us understand and treat these disorders but how can we do this? The early stages of pregnancy are not well understood due to ethical and practical challenges. In the UK, regulated research on human embryos is permitted. The embryos used in this research are donated by patients who have undergone fertility treatment and have embryos that are no longer needed for their family-building needs. There have been amazing advances in recent years which allow us to study early embryonic development and trophoblast cells in a culture dish. In the Fogarty lab we use trophoblast stem cells isolated from the blastocyst stage of the embryo. We can grow these cells in culture and direct them to become other cell types or trophoblast organoids.

Organoids are miniature versions of organs or tissues with some of the same structure and function. Trophoblast organoids mimic many of the properties of early pregnancy and placenta development. Some of the things we study using this system are gene expression and signalling pathways.

Gene expression: Most cells in the body contain all of your DNA, but it is the genes that are turned “on” or expressed that will be made into protein and give your cells their special characteristics.

Genes in DNA that are expressed become RNA which become proteins. (Source: National Cancer Institute)

Signalling pathways: A series of interactions passing between proteins in a cell, starting at a receptor on the cells surface, which usually leads to a change in cell function, such as promoting the survival of a cell or the generation of energy. Signalling pathways often end in changing gene expression.

Our Research

Our research aims to identify and study signalling pathways that are essential in development of the placenta. One pathway we are particularly interested in is the WNT signalling pathway which plays roles many roles in development such as cell specialisation, cell renewal and cell migration. We believe that it controls the change of the trophectoderm into the trophoblast.

The WNT signalling pathway is incredibly complicated! (Source: CUSABIO)

One of the ways we are studying this is by preventing the normal activity of the WNT signalling pathway with chemicals called small molecule inhibitors which we add to liquid the cells reside in. We also achieve this by genetically altering the cells so they produce a protein known to interfere with the pathway. With the pathway disrupted, we can study the cells and see how this affects their development from trophectoderm to trophoblast.

We will examine this using advanced imaging techniques. Cells with active WNT signalling will be labelled with a fluorescent marker which we can then follow with time-lapse imaging of live cells. This will allow us to see how many cells have active signalling, where they are in the embryo/structure, and if there are changes in these parameters as development continues.

These studies will begin in trophoblast cell lines and organoids and before moving onto human embryos. If we can understand how the process of placenta development works in healthy embryos and pregnancy, we can begin to understand what defects may occur in the complications of pregnancy.