The Activin type I receptors transduce signals for a variety of members of the Transforming growth factor beta superfamily of ligands. This family of cytokines and hormones include activin, Anti-müllerian hormone

Anti-müllerian hormone

Anti-Müllerian hormone also known as AMH is a protein that, in humans, is encoded by the AMH gene. It inhibits the development of the Müllerian ducts in the male embryo. It has also been called Müllerian inhibiting factor , Müllerian-inhibiting hormone , and Müllerian-inhibiting substance...

 (AMH), bone morphogenetic proteins (BMPs), and Nodal. They are involved in a host of physiological processes including, growth

Cell growth

The term cell growth is used in the contexts of cell development and cell division . When used in the context of cell division, it refers to growth of cell populations, where one cell grows and divides to produce two "daughter cells"...

, cell differentiation, homeostasis

Homeostasis

Homeostasis is the property of a system that regulates its internal environment and tends to maintain a stable, constant condition of properties like temperature or pH...

, osteogenesis, apoptosis

Apoptosis

Apoptosis is the process of programmed cell death that may occur in multicellular organisms. Biochemical events lead to characteristic cell changes and death. These changes include blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, and chromosomal DNA fragmentation...

 and many other functions. There are three type I Activin receptors: ACVR1

ACVR1

Activin A receptor, type I also known as ALK-2 is a protein which in humans is encoded by the ACVR1 gene.- Function :...

, ACVR1B

ACVR1B

Activin receptor type-1B is a protein that in humans is encoded by the ACVR1B gene.ACVR1B or ALK-4 acts as a transducer of activin or activin like ligands signals. Activin binds to either ACVR2A or ACVR2B and then forms a complex with ACVR1B. These go on to recruit the R-SMADs SMAD2 or SMAD3...

, and ACVR1C

ACVR1C

The activin A receptor also known as ACVR1C or ALK-7 is a protein that in humans is encoded by the ACVR1C gene. ACVR1C is a type I receptor for the TGFB family of signaling molecules...

. Each bind to a specific type II receptor-ligand complex.

Despite the large amount of processes that these ligands regulate, they all operate through essentially the same pathway

TGF beta signaling pathway

The Transforming growth factor beta signaling pathway is involved in many cellular processes in both the adult organism and the developing embryo including cell growth, cell differentiation, apoptosis, cellular homeostasis and other cellular functions. In spite of the wide range of cellular...

: A ligand binds to a Type two receptor, which recruits and trans-phosphorylate a type I receptor. The type I receptor recruits a receptor regulated SMAD (R-SMAD) which it phosphorylates. The RSMAD then translocates to the nucleus where it functions as a transcription factor

Transcription factor

In molecular biology and genetics, a transcription factor is a protein that binds to specific DNA sequences, thereby controlling the flow of genetic information from DNA to mRNA...

.