Stem cells and DNA methylation reprogramming in pigs
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] In mammals, the majority of cells in the body contain the same genome as other cells. The concept of nuclear totipotency has been well demonstrated by cloning animals generated by somatic cell nuclear transfer. Thus the fundamental difference between a stem cell and a differentiated cell is their distinct epigenetic identity. Upon fertilization, the paternal and maternal genomes undergo extensive epigenetic reprogramming to establish the totipotent state of a zygote. The pluripotent state is then restricted in the inner cell mass (ICM) of a blastocyst where embryonic stem cells are derived. Epigenetically, there is a wave of genome-wide DNA demethylation post fertilization and de novo methylation around implantation. The implanted epiblast further differentiates and generates various cells of the three germ layers (ectoderm, mesoderm and endoderm). Multipotent stem cells can be derived from embryonic and adult tissues, such as skin, bone marrow and nervous system. The hypothesis of the thesis was that the epigenetic modifications are dynamically associated with the developmental stages and determine the cell identity. In Chapter 3, we isolated and characterized the multipotency of porcine skin-derived progenitors (SKPs) and fetal brain-derived neural stem cells (NSCs). In Chapter 4, we found porcine SKPs could incorporate into the early embryos and contribute to various somatic tissues of the three germ layers in postnatal chimeras. However, this developmental potential was compromised when they differentiated into fibroblasts. In addition, NSCs failed to incorporate into the host embryos and contribute to chimeric piglets. The distinct developmental potential of SKPs, NSCs and fibroblasts is probably attributed to their different epigenetic states since they shared the same genome. In Chapter 5, we observed locus-specific dynamic DNA methylation reprogramming in early porcine embryos. The local DNA methylation reprogramming in early embryos is diverse and is probably associated with the multiple functions of DN
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