Transforming growth factor-β (TGF-β)  is a multifunctional peptide
that controls proliferation, differentiation and other functions in many cell
types. TGF-β-1 is a peptide of 112 amino acid residues derived by
proteolytic cleavage from the C-terminal of a precursor protein. A number of
proteins are known to be related to TGF-β-1 [1,2,3]. They are listed below.
Two other forms of TGF-β have been found, they are known as TGF-β-2
Mullerian inhibitory substance (MIS), produced by the testis, which is
responsible for the regression of the Mullerian ducts in the male embryo.
Inhibins, which inhibit the secretion of follitropin by the pituitary
gland, and activins which have the reverse action. Inhibins are heterodimer
of an α chain and a β-A or a β-B chain; activins are either
homodimers of β-A chains or heterodimers of a β-A and a β-B chain.
All three chains are related to TGF-β.
Bone morphogenetic proteins  BMP-2, BMP-3 (osteogenin), BMP-3B (GDF-10),
BMP-4 (BMP-2B), BMP-5, BMP-6 (VGR-1), BMP-7 (OP-1) and BMP-8 (OP-2) which
induce cartilage and bone formation and which are probably involved in the
control of the production of skeletal structures during development.
Embryonic growth factor GDF-1, which may mediate cell differentiation
events during embryonic development.
Growth/development factor GDF-5 , a protein whose gene, when mutated in
mice, is the cause of brachypodism, a defects which alters the length and
numbers of bones in the limbs.
Growth/development factor GDF-3, GDF-6, GDF-7, GDF-8 (myostatin) and GDF-9.
Mouse protein nodal, which seems essential for mesoderm formation.
Chicken dorsalin-1 (dsl-1) which may regulate cell differentiation within
the neural tube.
Xenopus vegetal hemisphere protein Vg1, which seems to induce the overlying
animal pole cells to form mesodermal tissue.
Drosophila decapentaplegic protein (DPP-C), which participates in the
establishment of dorsal-ventral specification.
Drosophila protein screw (scw) which also participates in the establishment
of dorsal-ventral specification.
Drosophila protein 60A.
Caenorhabditis elegans larval development regulatory growth factor daf-7.
Mammalian glial cell line-derived neurotrophic factor (GDNF), a distantly
related member of this family which acts as neurotrophic factor for
dopaminergic neurons of the substantia nigra.
Proteins from the TGF-β family are only active as homo- or heterodimer;
the two chains being linked by a single disulfide bond. From X-ray studies of
TGF-β-2 , it is known that all the other cysteines are involved in
intrachain disulfide bonds. As shown in the following schematic
representation, there are four disulfide bonds in the TGF-βs and in inhibin
β chains, while the other members of this family lack the first bond.
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