Embryo Project Encyclopedia Articles

Implantation is a process in which a developing embryo, moving as a blastocyst through a uterus, makes contact with the uterine wall and remains attached to it until birth. The lining of the uterus (endometrium) prepares for the developing blastocyst to attach to it via many internal changes. Without these changes implantation will not occur, and the embryo sloughs off during menstruation. Such implantation is unique to mammals, but not all mammals exhibit it. Furthermore, of those mammals that exhibit implantation, the process differs in many respects between those mammals in which the females have estrous cycles, and those mammals in which the femals have menstrual cycles. Females in the different species of primates, including humans, have menstrual cycles, and thus similar processes of implantation.

Among other functions, the Notch signaling pathway forestalls the process of myogenesis in animals. The Notch signaling pathway is a pathway in animals by which two adjacent cells within an organism use a protein named Notch to mechanically interact with each other. Myogenesis is the formation of muscle that occurs throughout an animal's development, from embryo to the end of life. The cellular precursors of skeletal muscle originate in somites that form along the dorsal side of the organism. The Notch signaling pathway is active in multiple aspects of somitogenesis, and it continues to be a critical regulator during myogenesis. Throughout the life of an organism, Notch signaling prevents the differentiation of muscle progenitor cells into muscle cells. Such preventions help maintain populations of progenitor cells that can remain dormant until the growth or repair of muscle is necessary, at which point the Notch signal to the muscle progenitor cells is disrupted, and the muscle progenitor cells differentiate into muscle fibers and cells. Without Notch signaling, myogenesis proceeds prematurely and dissipates before mature muscle can form.

Among other functions, the Notch signaling pathway contributes to the development of somites in animals. It involves a cell signaling mechanism with a wide range of functions, including cellular differentiation, and the formation of the embryonic structures (embryogenesis). All multicellular animals use Notch signaling, which is involved in the development, maintenance, and regeneration of a range of tissues. The Notch signaling pathways spans two cells, and consists of receptor proteins, which cross one cell's membrane and interacts with proteins on adjacent cells, called ligands. The physical interaction of receptors and ligands directs the genetic response of the first cell to produce proteins that define the type of cell it will become. One of the earliest discovered roles of the Notch signaling pathway in vertebrates is in somite formation (somitogenesis). Somitogenesis is the formation of somites, which are sphere-like structures in early vertebrate embryos that are the first visible signs of segmentation. Somites then help to define many tissues and features of the adult animal's body. The Notch signaling pathway plays at least two distinct roles during somitogenesis: the first is maintenance of an oscillating protein gradient, called the segmental clock, and the second is establishing the polarity of somites. Mutations to genes in the Notch pathway can result in birth defects characterized by abnormal development of bones of the spine and ribs, like spondylocostal dysostosis. Additionally, dysfunction in the pathway linked to cancer progression, HIV-related complications, and Alzheimer´s disease, among other disorders.