Embryo Project Encyclopedia Articles

As mice embryos develop, they undergo a stage of development called gastrulation. The hallmark of vertebrate gastrulation is the reorganization of the inner cell mass (ICM) into the three germ layers: ectoderm, mesoderm, and endoderm. Mammalian embryogenesis occurs within organisms; therefore, gastrulation was originally described in species with easily observable embryos. For example, the African clawed frog (Xenopus laevis) is the most widely used organism to study gastrulation because the large embryos develop inside a translucent membrane. Domestic chicken (Gallus gallus) gastrulation was also an early model organism because researchers could open the egg during development to look inside. Despite the challenges associated with studying mammalian gastrulation, the common house mouse (Mus musculus) has helped to shed light on the unique adaptations associated with mammalian development, and on the subtle differences in structure that give rise to significant divergence in late embryogenesis.

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.