Human embryonic stem cells (hESCs) are obtained from a small group of cells found very early in the development of the embryo. Cells taken from one embryo can be made to multiply in the laboratory to create a ‘cell line’, like the cell line we used in our project, which was derived from an embryo in 1998. hESCs can be used in research to improve our understanding of how the egg can develop into a complex organism. Moreover, in the laboratory hESCs can be differentiated to specialized cells like heart or nerve cells, which can then be studied to understand more about how and why diseases develop. These specialised cells can also be used to study how cells react to new drugs and if these new drugs can be used to treat a specific disease. This is of great importance, as it allows studying cells that are not easily obtained from patients, such as brain cells.
More than a decade ago, there was a major breakthrough in stem cell research - researchers discovered that it is possible to “reprogram” specialised adult cells into cells that behave like ESCs. These cells were termed induced pluripotent stem cells (iPSCs). Human induced pluripotent stem cells (hiPSCs) share common features with hESCs, such as being pluripotent. hiPSCs can be easily obtained by reprogramming, for example, skin cells. The technology is quite new and researchers do not yet know precisely how the process of reprogramming works. Although pluripotent stem cells (PSCs, which include both hESCs and hiPSCs) may become great tools, some concerns have been raised over their safety.
All cells are produced from other cells by the process of cell division. Cell division occurs when one cell divides to produce two new cells (daughter cells). The new cells produced by cell division are genetically identical to the parent cell because they each receive a copy of all the chromosomes it has in its nucleus. PSCs, however, seem to be prone to errors in passing the correct number of chromosomes to daughter cells. Therefore, it is important to understand the molecular mechanisms that ensure that each daughter cell receives the correct number of chromosomes needed to function normally. Although these mechanisms have been extensively studied in differentiated cells, nearly nothing is known in pluripotent cells.
All chromosomes in a cell have a specialised region - termed the centromere – that is essential for the correct segregation of chromosomes to the daughter cells. The centromere is defined by the presence of CENP-A, a chromatin-bound histone protein, and it is the region of the chromosome where the kinetochore can assemble. The kinetochore is a multi-protein complex that serves as the site of attachment for microtubules, which pull sister chromatids apart during cell division, ensuring each daughter cell has the same number of chromosomes. If the centromere is somehow defective, cells can no longer pass the correct number of chromosomes to their daughter cells.
This project aimed to determine centromere assembly, maintenance and kinetochore function in PSCs, to understand if the genome-wide remodelling of chromatin during reprogramming affects centromere assembly and function and to modify centromere composition to understand if it is possible to obtain safer and more stable iPSCs.
