In all bilaterian animals, the mesoderm is one of the three primary germ layers in the very early embryo. The other two layers are the ectoderm (outside layer) and endoderm (inside layer), with the mesoderm as the middle layer between them.The mesoderm forms mesenchyme, mesothelium, non-epithelial blood cells and coelomocytes. Mesothelium lines coeloms. Mesoderm forms the muscles in a process known as myogenesis, septa (cross-wise partitions) and mesenteries (length-wise partitions); and forms part of the gonads (the rest being the gametes). Myogenesis is specifically a function of mesenchyme.
The mesoderm differentiates from the rest of the embryo through intercellular signaling, after which the mesoderm is polarized by an organizing center. The position of the organizing center is in turn determined by the regions in which beta-catenin is protected from degradation by GSK-3. Beta-catenin acts as a co-factor that alters the activity of the transcription factor tcf-3 from repressing to activating, which initiates the synthesis of gene products critical for mesoderm differentiation and gastrulation. Furthermore, mesoderm has the capability to induce the growth of other structures, such as the neural plate, the precursor to the nervous system.
Mesenchyme () is a type of connective tissue found mostly during embryonic development of bilateral animals (triploblasts). It is composed mainly of ground substance with few cells or fibers. It can also refer to a group of mucoproteins resembling mucus found, for example, in certain types of cysts. It is most easily found as a component of Wharton’s jelly.
The vitreous body of the eye is of a similar tissue.In invertebrate zoology, the term refers to free cells loosely arranged in a matrix.
One of the three organs of the adult, e.g. muscles, spine and circulatory system.
That part of the mesoderm of an embryo that develops into connective tissue, bone, cartilage, etc.