Molecular Mechanism of Somite Development

From third week of gestation, notochord and the neural folds begin to gather at the center of the embryo to form the paraxial mesoderm. Paraxial mesoderm separates into blocks of cells called somitomers at the lateral sides of the neural tube of the head region. At the beginning of the third week somitomeres take ring shapes and form blocks of somites from occipital region to caudal region. Although somites are transient structures, they are extremely important in organizing the segmental pattern of vertebrate embryos. Somites give rise to the cells that form the vertebrae and ribs, the dermis of the dorsal skin, the skeletal muscles of the back, and the skeletal muscles of the body wall and limbs. Somitogenesis are formed by a genetic mechanism that is regulated by cyclical expression of genes in the Notch, Wnt and fibroblast growth factor signaling pathways. The prevailing model of the mechanism governing somitogenesis is the clock and wave front . Somitogenesis has components of periodicity, separation, epithelialization and axial specification. According to this model, the clock causes cells to undergo repeated oscillations, with a particular phase of each oscillation defining the competency of cells in the presomitic mesoderm to form a somite. Any disruption in this mechanism can be cause of severe segmentation defects of the vertebrae and congenital anomalies. In this review, we discuss the molecular mechanisms underlying the somitogenesis which is an important part of morphogenesis. [Archives Medical Review Journal 2013; 22(3.000): 362-376]