In this thesis, Chapter 1 presents the state of the literature on early development in humans and mice. Chapter 2 describes the development of gonadal and extragonadal PGCs in humans. Chapter 3... Show moreIn this thesis, Chapter 1 presents the state of the literature on early development in humans and mice. Chapter 2 describes the development of gonadal and extragonadal PGCs in humans. Chapter 3 investigates the status of XCI in human pre-implantation embryos. One X chromosome is indicated to be inactive in E4-E6 cells and E7 trophectoderm cells, whereas it becomes reactivated in E7 epiblast and primitive endoderm cells. Chapter 4 describes the entering of EVTs in maternal circulation (via decidual veins and lymphatic vessels) starts since W5.5, much earlier than previously accepted W8 (via decidual spiral arteries). Chapter 5 studies the spatial imprinting pattern of IGF2/H19 in human first-trimester placental villi. A normal imprinting pattern of IGF2/H19 is revealed in multi-site villi collections as in the embryo. Chapter 6 explores different consequences of Turner syndrome in mouse placenta. The significantly larger area of glycogen cells in XpO placental outer zone and the significantly higher expression of Ldha in XpO labyrinth zone suggest a more severe placental phenotype in E18.5 XpO placentas than in XmO placentas. Finally, Chapter 7 provides general discussion about the findings and discusses the future perspectives on assisted reproduction and new treatment for infertility, pregnancy complications. Show less