描述：
Activins, members of the TGFβ superfamily, are disulfide linked dimeric proteins that
were originally purified from gonadal fluids as proteins that stimulated pituitary
follicle stimulating hormone (FSH) release. Activin proteins have since been shown
to have a wide range of biological activities including: mesoderm induction, neural
cell differentiation, bone remodeling, hematopoiesis and roles in reproductive physiology.
Activins are produced as precursor proteins with an aminoterminal
propeptide that is cleaved to release the carboxyterminal bioactive ligands.
Activins are homodimers or heterodimers of the various β subunit isoforms. Five β
subunits (mammalian βA, βB, βC, βE and Xenopus βD) have been cloned. The nomenclature reflects the subunit composition of the proteins:
Activin A (βA βA), ActivinB (βBβB), and Activin AB (βA βB).
Activin A, Activin B, and Activin AB are present in gonadal tissues and are biologically
active proteins. However, little is known about the contribution of the other β subunits to
Activin formation and function since knockouts of βC and βE in mice do not exhibit a phenotype.
At the amino acid sequence level, the mature human βA subunit is 100% identical to mouse βA,
while the mature human and mouse βB subunits share 98% identity.
The mature βA and βB subunits share less than 80% amino acid identity.
Mice with targeted mutations of βA, βB, or both genes do not show mesodermal defects,
indicating Activin is not involved in mesoderm formation in mammals as it is in Xenopus.
Also, the double homozygous mutants have the whole spectrum of defects
associated with either mutation alone, suggesting that Activin βA and βB
do not compensate for one another, nor do they have overlapping functions.
Similar to other TGFβ family members, Activins exert their biological activities
through binding to the heterodimeric complex composed of two membrane spanning
serinethreonine kinases designated type I and type II. Activin binds directly to ACT RII,
the complex then associates with ACT RI and initiates signaling through the SMADs.
原厂资料：
Activins, members of the TGFβ superfamily, are disulfide linked dimeric proteins that
were originally purified from gonadal fluids as proteins that stimulated pituitary
follicle stimulating hormone (FSH) release. Activin proteins have since been shown
to have a wide range of biological activities including: mesoderm induction, neural
cell differentiation, bone remodeling, hematopoiesis and roles in reproductive physiology.
Activins are produced as precursor proteins with an aminoterminal
propeptide that is cleaved to release the carboxyterminal bioactive ligands.
Activins are homodimers or heterodimers of the various β subunit isoforms. Five β
subunits (mammalian βA, βB, βC, βE and Xenopus βD) have been cloned. The nomenclature reflects the subunit composition of the proteins:
Activin A (βA βA), ActivinB (βBβB), and Activin AB (βA βB).
Activin A, Activin B, and Activin AB are present in gonadal tissues and are biologically
active proteins. However, little is known about the contribution of the other β subunits to
Activin formation and function since knockouts of βC and βE in mice do not exhibit a phenotype.
At the amino acid sequence level, the mature human βA subunit is 100% identical to mouse βA,
while the mature human and mouse βB subunits share 98% identity.
The mature βA and βB subunits share less than 80% amino acid identity.
Mice with targeted mutations of βA, βB, or both genes do not show mesodermal defects,
indicating Activin is not involved in mesoderm formation in mammals as it is in Xenopus.
Also, the double homozygous mutants have the whole spectrum of defects
associated with either mutation alone, suggesting that Activin βA and βB
do not compensate for one another, nor do they have overlapping functions.
Similar to other TGFβ family members, Activins exert their biological activities
through binding to the heterodimeric complex composed of two membrane spanning
serinethreonine kinases designated type I and type II. Activin binds directly to ACT RII,
the complex then associates with ACT RI and initiates signaling through the SMADs.
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