Signalling molecules

Inducing signalling molecules are substances that act on a group of responding target cells and are released from a signalling center. This group includes growth factors, cytokines and hormones. They consist of glycoproteins, polypeptides and peptides.

TGF-β Superfamily
The family of transforming growth factors β (TGF-β) was discovered in virus-transformed cells. TGF-β inhibit cell division and stimulate the secretion of extracellular matrix components. TGF-β is involved in the specification of body axes, the formation of mesoderm, cartilage and bone.

FGF Superfamily
The family of fibroblast growth factors (FGF) includes more than 10 members important for both embryonic and postnatal periods of life. A group of factors was discovered in 1974. The factors work in close association with the extracellular matrix and their function requires binding to heparan sulfate. It transmits a signal via the MAP-kinase pathway, stimulates the growth of limbs, contributes to the regionalisation of the brain and to the specification of the dorsoventral arrangement.

Hedgehog Family
This group got its name from fruit fly larvae with a recessive allele of the hh (spiny belly) gene. A special member of the family is the Sonic Hedgehog gene, which is responsible for the dorsoventral arrangement of the neural tube and the anteroposterior arrangement of the limbs. The Indian Hedgehog gene is important in skeletal development.

Wnt Family
Wnt is a water-insoluble single-chain polypeptide. Its signalling pathway contains two sites of repression. Wnt has an important function in kidney development and myotome formation.

Delta-Notch System
The components of the system are the ligand' (Delta) and the receptor' (Notch). Both are built into the cell membrane and their interaction is possible only in close cell contact. The Delta-Notch system is important for neurogenesis and somitogenesis.

Other factors
Other inducing factors include:
 * LIF family - maintains mouse germ cell pluripotency and induces human kidney development,
 * Insulin family - growth regulation,
 * Neurotrophic factors (NTFs) - necessary for the survival of neurons.

Related articles

 * Growth factors
 * Cytokines
 * Signal transmission in cells