What is segmentation clock?

The vertebrate segmentation clock is a molecular oscillator that regulates the periodicity of somite formation. Recent publications report the first identification of a molecular mechanism involved in the regulation of the pace of this oscillator.

What is a somite?

Somites are blocks of mesoderm that are located on either side of the neural tube in the developing vertebrate embryo. The first pair of somites forms in the anterior part of the trunk, adjacent to the notochord; the remainder then follow, budding off the mesoderm sequentially, from head to tail.

What does the clock and wavefront model propose?

Clock and Wavefront model The model postulates the existence of a longitudinal positional information gradient down the AP axis of vertebrate embryos, which interacts with a smooth cellular oscillator (the clock), to set the time in each cell at which it will undergo a catastrophe.

What is the determination Front set by?

The determination front is manifest by the expression of a bHLH gene called Mesp2 (thylacine) in the anterior three somitomeres, marking future somite boundaries (Oginuma et al., 2008). Genes downstream of FGF were activated with a distinct expression profile during somite segmentation.

How does Somitogenesis work?

Somitogenesis is the process by which somites form. Somites are bilaterally paired blocks of paraxial mesoderm that form along the anterior-posterior axis of the developing embryo in segmented animals. In vertebrates, somites give rise to skeletal muscle, cartilage, tendons, endothelium, and dermis.

What is somite segmentation?

The somites are formed by segmentation from the anterior end of the presomitic mesoderm (PSM), which is unsegmented and posterior to the most recently formed somite. Each somite is subdivided into anterior (rostral) and posterior (caudal) compartments that differ in their properties and gene expression.

What part is somite?

In vertebrates, somites subdivide into the sclerotomes, myotomes, syndetomes and dermatomes that give rise to the vertebrae of the vertebral column, rib cage and part of the occipital bone; skeletal muscle, cartilage, tendons, and skin (of the back). The word somite is sometimes also used in place of the word metamere.

How does somite segmentation occur?

Somite formation in the vertebrate embryo is a classic paradigm of segmentation (Fig. 1A-C). A: A typical chick embryo reveals the somite (s) pattern in pairs along the vertebrate axis and neural tube (nt) with the unsegmented presomitic mesoderm (PSM) in the posterior direction.

What induces somite formation?

Somite formation can be induced by Noggin-secreting cells. As cells within the paraxial mesoderm begin to come together, they are termed somitomeres, indicating a lack of complete separation between segments. The outer cells undergo a mesenchymal–epithelial transition to form an epithelium around each somite.

What is the clock and wave mechanism of somitogenesis?

Somitogenesis can be described by the “clock and wave” mechanism, in which the oscillating signal (clock) is provided by cascading genetic networks while a gradient of fibroblast growth factor (FGF) provides the somite boundaries (wave).

How are somites involved in the development of the body?

Distinct regions of each somite become specific tissue and cell types as the body matures. Somitogenesis can be described by the “clock and wave” mechanism, in which the oscillating signal (clock) is provided by cascading genetic networks while a gradient of fibroblast growth factor (FGF) provides the somite boundaries (wave).

What happens to the segmentation clock in chick?

When the notochord is ablated during somitogenesis in the chick embryo, the proper number of somites forms, but the segmentation clock is delayed for the posterior two thirds of the somites. The anterior somites are not affected.

Is the segmentation clock model evolutionarily conserved?

Generally speaking, however, the segmentation clock model is highly evolutionarily conserved. Intrinsic expression of “clock genes” must oscillate with a periodicity equal to the time necessary for one somite to form, for example 30 minutes in zebrafish, 90 minutes in chicks, and 100 minutes in snakes.