What is the difference between FS-344 and FS-315?

FS-344 and FS-315 are two protein isoforms produced by alternative splicing of the FST gene. FS-315 contains a C-terminal acidic tail that electrostatically masks a heparin-binding surface in the N-terminal domain, biasing the protein toward systemic circulation. FS-344 lacks the acidic tail, exposes the heparin-binding surface, and binds cell-surface heparan-sulfate proteoglycans with high affinity. Functionally, FS-344 localizes more strongly to tissue surfaces and extracellular matrix and acts in an autocrine/paracrine mode, while FS-315 circulates and acts more systemically. Both isoforms bind activin A and myostatin with similar high affinity.

Does follistatin only bind myostatin?

No. Follistatin binds activin A with very high (picomolar) affinity, myostatin (GDF-8) with low-nanomolar affinity, and additional TGF-β-superfamily ligands including GDF-11 and various BMPs with varying affinities. The activin-binding activity was the basis for its original isolation and characterization in the 1980s; the myostatin-binding activity was recognized later, after myostatin was identified in 1997. Follistatin is therefore best described as a multi-ligand TGF-β-superfamily antagonist rather than a myostatin-specific antagonist.

How does follistatin neutralize its ligand?

Crystallographic studies show that two follistatin monomers wrap around one activin or myostatin dimer in a configuration that nearly completely encircles the ligand, physically occluding both the type-I and type-II receptor-binding surfaces. The bound complex is then trafficked to lysosomes for degradation. The mechanism is therefore both steric blockade and active ligand removal, distinguishing follistatin from simple competitive antagonists.

Is follistatin a hormone?

Follistatin is not a hormone in the classical sense. It does not bind a dedicated receptor or generate its own signaling output. It is a high-affinity ligand-trap that sequesters and removes activin, myostatin, and related TGF-β-family ligands, thereby derepressing the pathways those ligands normally suppress. Its biological effects are indirect — they reflect the consequences of activin/myostatin pathway inhibition rather than direct receptor agonism.

Why is FS-344 studied in muscle research?

FS-344 neutralizes myostatin, the principal endogenous negative regulator of skeletal-muscle mass identified by Se-Jin Lee's laboratory in 1997. In transgenic-overexpression and gene-therapy animal-model studies, follistatin produces marked skeletal-muscle hypertrophy reminiscent of the myostatin-null phenotype. The tissue-bound HSPG-binding character of FS-344 makes it particularly useful in tissue-localized research models. The activin-neutralizing activity contributes additionally, as activin A also reinforces catabolic signaling in muscle.

What is the relationship between follistatin and FSH?

Follistatin was originally isolated from porcine ovarian follicular fluid in 1987 as a factor that suppressed FSH release from cultured anterior-pituitary cells. The mechanism is indirect: follistatin binds and neutralizes activin A, which is the direct stimulator of FSH transcription and secretion in pituitary gonadotropes. By sequestering activin A, follistatin reduces FSH output. This was the founding observation in the follistatin literature and remains a foundational topic in reproductive-endocrinology research.

Has follistatin been approved as a therapy?

No follistatin-based therapy has been approved by major Western regulatory agencies as of this writing. Exploratory clinical-research programs have investigated follistatin gene therapy in sporadic inclusion body myositis and Becker muscular dystrophy, and other activin/myostatin pathway antagonists (such as bimagrumab and various anti-myostatin antibodies) have been investigated in muscle-wasting and metabolic indications. None has produced an approved therapy. Follistatin is studied as a research tool, not as a medicine.

Is FS-344 stable in solution?

Recombinant FS-344 is supplied lyophilized and is generally stable at -20 °C or below for extended periods in the dry state. Once reconstituted in sterile buffer, FS-344 should be stored at 4 °C for short-term use and aliquoted and frozen at -20 °C or -80 °C for longer-term storage. Repeated freeze-thaw cycles should be avoided. Activity is verified by activin-neutralization reporter assays.

How is recombinant follistatin produced?

Research-grade recombinant follistatin (FS-344 or FS-315) is typically produced in mammalian expression systems — HEK293 or CHO cells — to ensure proper disulfide-bond formation, glycosylation, and folding required for activin/myostatin binding. Bacterial expression systems do not produce correctly folded glycosylated follistatin. The recombinant protein is purified by chromatography and supplied lyophilized for laboratory reconstitution.

What is the difference between follistatin and decoy ActRIIB?

Follistatin binds the activin/myostatin ligands themselves. Decoy ActRIIB-Fc is an engineered soluble form of the type-II activin receptor extracellular domain that also binds these ligands. The two approaches converge mechanistically — both sequester the ligand — but differ in selectivity profile and pharmacokinetics. Decoy receptors typically bind a somewhat different ligand set with different affinities and have a longer circulating half-life. Comparing the two in research models helps separate ligand-specific from receptor-specific effects.

Does follistatin affect GDF-11?

Yes. GDF-11 is a TGF-β-superfamily ligand closely related to myostatin (about 90% sequence identity in the mature domain), and follistatin binds GDF-11 with affinity comparable to myostatin. This cross-reactivity matters in interpreting research-model studies, because GDF-11 has distinct biological roles in development and tissue homeostasis that may contribute to the phenotype of follistatin treatment alongside the muscle-targeted myostatin neutralization.

Is FS-344 a small molecule?

No. FS-344 is a 344-amino-acid disulfide-cross-linked glycoprotein. It is a full-size protein reagent, not a small molecule. Reconstitution, handling, and assay use require techniques appropriate to recombinant proteins, including avoidance of foaming, attention to buffer composition, and protection against repeated freeze-thaw and prolonged room-temperature storage.

Follistatin-344 1mg – Research Grade Myostatin Pathway Peptide lyophilized vial with bacteriostatic water for research

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Follistatin-344 1mg – Research Grade Myostatin Pathway Peptide

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Follistatin-344 is one of the most discussed peptides in muscle biology and myostatin pathway research. It is studied extensively for its role in regulating members of the transforming growth factor-beta (TGF-β) family, with a focus on muscle development, recovery pathways, cellular growth signaling, and tissue adaptation mechanisms. Dr. Jay's Follistatin-344 1mg is manufactured to strict quality standards and intended exclusively for laboratory research and educational purposes.

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