MSTN (myostatin; HGNC:4223, NCBI Gene ID 2660) is a human locus mapped to chromosome band 2q32.2 that encodes latent pro-myostatin dimer cleaved by BMP1/tolloid to mature C-terminal Myostatin / GDF8 dimer (109 aa per monomer). MSTN acts in ACVR2B/ACVR2A-ALK4/5-SMAD2/3-SMAD4 negative regulation of skeletal muscle mass, together with FST (Follistatin Endogenous Myostatin Antagonist Gene), ACVR2B (Activin Receptor Type-2B Gene), and ACVR2A (Activin Receptor Type-2A Gene). Encodes myostatin (GDF-8), the autocrine/paracrine TGF-beta family chalone that restricts skeletal muscle fiber hypertrophy and hyperplasia.
Approved Symbol
MSTN
Chromosomal Locus
2q32.2
Encoded Product
Latent pro-myostatin dimer cleaved by BMP1/tolloid to mature C-terminal Myostatin / GDF8 dimer (109 aa per monomer)
Primary Pathway
ACVR2B/ACVR2A-ALK4/5-SMAD2/3-SMAD4 negative regulation of skeletal muscle mass
Clinical / Therapeutic Role
Loss-of-function mutations cause extreme hypermuscularity; target of apitegromab, taldefgrobep & bimagrumab in SMA, sarcopenia & GLP-1 lean-mass preservation
Gene Structure & Expression
Genomic Organization & Cytogenetic Locus: 3-exon gene on chromosome 2q32.2 encoding a 375-amino-acid preproprotein that homodimerizes via a C-terminal cystine knot and is cleaved twice: first by furin to separate the N-terminal inhibitory propeptide from the 109-residue mature C-terminal dimer (forming a circulating latent complex), and locally in muscle by BMP1/tolloid metalloproteinases to release active myostatin.
Cellular & Tissue Expression Profile: Expressed almost exclusively in developing somitic myotomes and adult skeletal muscle fibers (particularly fast-twitch glycolytic type II fibers), with minimal expression in adipose tissue and myocardium.
Molecular Function & Pathways
Biochemical & Physiological Mechanism: Active C-terminal myostatin homodimers bind cell-surface Activin Receptor Type-2B (ACVR2B) and Type-2A (ACVR2A), recruiting type I serine/threonine kinase receptors ALK4 (ACVR1B) or ALK5 (TGFBR1) to phosphorylate SMAD2 and SMAD3, which complex with SMAD4 to repress the myogenic regulatory factors MYOD1, MYOG, and MYF5 while inhibiting AKT1-mTORC1 protein synthesis and inducing FOXO1/3 atrogenes (atrogin-1/FBXO32 and MuRF1/TRIM63).
Clinical & Therapeutic Significance
Human Genetic Variants & Disease Phenotypes: Identified in mice by Alexandra McPherron and Se-Jin Lee in 1997 as GDF-8; natural loss-of-function mutations in MSTN cause the classic "double-muscling" phenotype in Belgian Blue and Piedmontese cattle, whippet dogs, and humans (where a homozygous splice-site mutation c.373+5G>A was found in a child with gross muscle hypertrophy).
Therapeutic & Clinical Pharmacology: Major biopharmaceutical target for reversing muscle atrophy in spinal muscular atrophy (SMA), Duchenne muscular dystrophy, sarcopenia, cancer cachexia, and for preserving lean muscle mass during GLP-1 receptor agonist weight loss via latent-myostatin antibodies (apitegromab), myostatin-binding fusion proteins (taldefgrobep alfa), follistatin (FST) AAV gene therapy, and anti-ACVR2A/2B antibodies (bimagrumab).