Pre-Implantation Human Embryo Development Quiz

Pre-Implantation Human Embryo Development: Key Stages and Processes

• Pre-implantation human embryo development refers to the process by which a fertilized egg develops into a blastocyst.
• Carnegie stages are a series of developmental stages used to describe the development of the human embryo from fertilization through to the end of the embryonic period.
• The first stage of pre-implantation human embryo development is syngamy, which occurs when a sperm cell fuses with an egg cell, resulting in the formation of a zygote.
• The early embryo is encapsulated within the zona pellucida (ZP), which is a protective glycoprotein layer that plays an essential role for embryo development up to the compaction stage by clustering the embryonic cells.
• Pronuclei (PN) are haploid nuclei around 30μm in diameter containing the genetic material from the sperm and the oocyte.
• The zygote then undergoes a series of mitotic cell divisions to form a multicellular embryo. Each division results in daughter cells called blastomeres.
• The first mitotic division, which occurs approximately 24h after fertilization, is controlled by the sperm-derived centrosome in humans.
• The second division of the human embryo occurs approximately 2 days after fertilization.
• By the third round of mitotic cell division, eight-cell stage, a major developmental transition occurs – the maternal to zygotic transition (MZT) and subsequent embryonic genome activation (EGA).
• Oocyte-specific genes are downregulated and the embryo genes are upregulated during MZT/EGA, enabling the embryo to take over transcription and translation of its own metabolic, cell cycle and apoptosis regulating proteins.
• The MZT/EGA occurs in waves (first at 2-cell stage followed by a second wave at 4-cell stage).
• Pre-implantation human embryo development is important for understanding early human development and for improving in vitro fertilization techniques.