Pathways in pluripotency and differentiation of embryonic cells

Abstract

Pluripotency - the potential to differentiate into derivatives of the three embryonic germ layers endoderm, ectoderm and mesoderm - is the main characteristic of embryonic stem (ES) cells. ES cells are derived from the inner cell mass (ICM) of a pre-implantation blastocyst and can self-renew indefinitely in culture. Because of their differentiation capabilities, ES cells can potentially be used in cell-based therapies in human medicine as well as for toxicology screening and drug testing. Moreover, ES cells can be used to study early differentiation events and developmental decisions. As the pig is an important large-animal model in biomedical research the first two studies presented in this thesis focused on the culture of pluripotent cells from pig blastocysts. As mentioned in the introduction, porcine stem cells can also be a potential source for in vitro meat, a possible alternative for conventional meat, produced from stem cells cultured and differentiated into muscle cells in vitro. Therefore, the subjects of the second part of this thesis address muscle development and differentiation. It took over 17 years to generate ES cell lines from human blastocysts since the derivation of the first mouse ES cell line in 1981. While early embryology of mice and rats is highly similar mouse ES cell culture conditions do not yield ES cells from rat, and germline competent rat ES cells were just recently derived using small molecule inhibitors. It is therefore perhaps not surprising that we were unable to generate true ES cell lines from the pig using conventional procedures. However, by examining the temporal and spatial expression pattern in porcine embryos of factors important in mouse pluripotency, and through exclusion of culture conditions, the results reported in this thesis will benefit future research into the generation of ES cell lines from the pig. Although porcine ICM cells differentiate in culture, these differentiated cells may still be used to provide progenitor cells. The results on the generation of neural progenitor cells from cultured porcine ICM cells can be of use when testing the safety of neural progenitor-transplantation in human medicine. Characterization of genes such as Cazip and investigating the functional role of proteins such as SARCOSIN, which are involved in muscle development and differentiation, is important for the development of therapeutics in muscle disease. Also for the production of in vitro meat, knowledge on muscle differentiation is essential. The generation of in vitro meat is not a new idea; in 1932 Winston Churchill argued that: ‘Fifty years hence we shall escape the absurdity of growing a whole chicken in order to eat the breast or wing by growing these parts separately under a suitable medium’ 49. Suffice to say that this claim was somewhat overconfident and more fundamental research is necessary to achieve the production of cultured meat.