Follistatin (FST) is a glycosylated single-chain protein that is expressed in a wide variety of tissues.1 Activin stimulates pituitary FSH secretion whereas Inhibin and Follistatin are inhibitory.2 Follistatin has been shown to be a potent activin-binding protein which acts by neutralizing the actions of the Activins.3 The activin-follistatin binding complex is generally considered to be composed of one activin and two follistatin molecules, and the affinity of binding between follistatin and activin is similar to that of activin for its receptor. Several isoforms of follistatin of molecular weight 31 – 39 kDa have been identified. Molecular analysis of the isoforms indicate that follistatin is encoded by a single gene and that the variety of isoforms arise from alternative splicing, glycosylation and proteolytic cleavage. Alternative splicing occurs at the 3’-terminal of the gene resulting in a precursor form of 317 and 344 amino acids4, and then following subsequent cleavage of the 29 amino acid signal peptide, generates 2 mature follistatin isoforms of 288 and 315 amino acids (namely Follistatin-288 and Follistatin-315).
The ratio of Follistatin isoforms present in different tissues and bodily fluids varies, as does their relative binding affinities. Follistatin-288 is the predominant form present in human follicular fluid; whereas the main form in serum is Follistatin-315.5 Follistatin-288 has a greater capacity to bind and neutralize activin and is approximately 10-fold more potent than Follistatin-315 in suppressing FSH secretion from rat pituitary cells in vitro. In addition, Follistatin-288 also binds with much greater affinity to heparin sulfate proteoglycans located on the cell surface and extracellular matrix, indicating that the Follistatin-288 isoform is primarily a membrane-bound form of Follistatin, whereas Follistatin-315 is a circulating form.

References:
1. Lin SY et al. Reproduction. 126(2):133-148, 2003.
2. Robertson DM et al. Biochem Biophys Res Commun. 126(1):220-226, 1985.
3. Nakamura T et al. Science. 247(4944):836-838, 1990.
4. Shimasaki S et al. Biochem Biophys Res Commun. 152(2):717-723, 1988.
5. Schneyer AL et al. Endocrinology. 137(1):240-247, 1996.
6. HHS Publication, 5th ed., 2007. Biosafety in Microbiological and Biomedical Laboratories. Available http://www.cdc.gov/biosafety/publications/bmbl5/BMBL5
7. DHHS (NIOSH) Publication No. 78–127, August 1976. Current Intelligence Bulletin 13 – Explosive Azide Hazard. Available http:// www.cdc.gov/niosh.

Follistatin ELISA AL-117
 

Kalra B, Patel A, Kommareddy V, Ganapathy K, Mistry S, Budhavarapu V, Savjani G, Pasternack A, Ritvos O, Hyvonen M, Kumar A. Development of Novel Specific ELISAs for all Inhibins, Activins and their Binding Proteins FST and FSTL3. Poster presented at 98th Annual Endocrine Society Meeting; 2016 Apr 1-3; Boston, MA.

All Products Cited Activin A ELISA AL-110; Inhibin A ELISA AL-123; Inhibin B ELISA AL-107; Activin B ELISA AL-150; Activin AB ELISA AL-153, Follistatin ELISA AL-117, Follistatin Like 3 ELISA AL-152

Kristensen SG. Altered Levels of TGF-Beta Superfamily Growth Factors in Small Antral Follicle Fluids from Polycystic Ovaries. Poster session presented at the International Congress of Endocrinology, 2018 Dec 1-4, Cape Town South Africa. (597).

All Products Cited: GDF-9 ELISA AL-176; AMH ELISA AL-105; Activin A ELISA AL-110; Activin B ELISA AL-150; Activin AB ELISA Al-153; Follistatin ELISA AL-117

Kristensen SG, Kumar A, Kalra B, Pors SE, Bøtkjær JA, Mamsen LS, Colmorn LB, Fedder J, Ernst E, Owens LA, Hardy K, Franks S, Andersen CY. Quantitative Differences in TGF-β Family Members Measured in Small Antral Follicle Fluids From Women With or Without PCO. J Clin Endocrinol Metab. 2019 Dec 1;104(12):6371-6384. doi: 10.1210/jc.2019-01094. PMID: 31287539.

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Legro R, Dodson W, Estes S, Kunselman A, Coutifaris C, Dokras A. Effect of Weight Loss and Hormonal Suppression Alone and in Combination on Bioactive Gut and Ovarian Peptide Hormones in Women with Polycystic Ovary Syndrome Journal of the Endocrine Society, Volume 3, Issue Supplement_1, April-May 2019, MON-233, https://doi.org/10.1210/js.2019-MON-233

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Naseem H, Dreixler J, Mueller A, Tung A, Dhir R, Chibber R, Fazal A, Granger JP, Bakrania BA, deMartelly V, Rana S, Shahul S. Antepartum Aspirin Administration Reduces Activin A and Cardiac Global Longitudinal Strain in Preeclamptic Women. J Am Heart Assoc. 2020 Jun 16;9(12):e015997. doi: 10.1161/JAHA.119.015997. Epub 2020 Jun 4. PMID: 32495688; PMCID: PMC7429043.

All Products Cited: Activin A ELISA AL-110; Follistatin ELISA AL-117, Follistatin-Like 3 ELISA AL-152
 

Paajanen J, Ilonen I, Lauri H, Järvinen T, Sutinen E, Ollila H, Rouvinen E, Lemström K, Räsänen J, Ritvos O, Koli K, Myllärniemi M. Elevated Circulating Activin A Levels in Patients With Malignant Pleural Mesothelioma Are Related to Cancer Cachexia and Reduced Response to Platinum-based Chemotherapy Clin Lung Cancer. 2019 Oct 25. pii: S1525-7304(19)30287-6. doi: 10.1016/j.cllc.2019.10.013. [Epub ahead of print]

All Products Cited: Activin A ELISA AL-110; Activin B ELISA AL-150; Follistatin ELISA AL-117; Follistatin Like 3 ELISA AL-152
 

Panagiotou G, Ghaly W, Upadhyay J, Pazaitou-Panayiotou K, Mantzoros CS. Serum Follistatin Is Increased in Thyroid Cancer and Is Associated With Adverse Tumor Characteristics in Humans. J Clin Endocrinol Metab. 2021 Apr 23;106(5):e2137-e2150. doi: 10.1210/clinem/dgab041. PMID: 33493282

All Products Cited: Follistatin ELISA AL-117; Follistatin Like 3 ELISA AL-152; Activin A ELISA AL-110; Activin B ELISA AL-150; Stanniocalcin 2 ELISA AL-143; Free IGF-I ELISA AL-122
 

Panagiotou G, Papakonstantinou E, Vagionas A, Polyzos SA, Mantzoros CS. Serum Levels of Activins, Follistatins, and Growth Factors in Neoplasms of the Breast: A Case-Control Study. J Clin Endocrinol Metab. 2019 Feb 1;104(2):349-358. doi: 10.1210/jc.2018-01581. PubMed PMID: 30388235.

All Products Cited: Activin A ELISA AL-110; Activin B ELISA AL-150; Follistatin ELISA AL-117; Follistatin Like 3 ELISA AL-152; IGF-I ELISA AL-121; Total IGFBP-4 ELISA AL-126; Intact IGFBP-4 ELISA AL-128

Perakakis N, Mougios V, Fatouros I, Siopi A, Draganidis D, Peradze N, Ghaly W, Mantzoros CS. Physiology of Activins/Follistatins: Associations With Metabolic and Anthropometric Variables and Response to Exercise. J Clin Endocrinol Metab. 2018 Oct 1;103(10):3890-3899. doi: 10.1210/jc.2018-01056. PubMed PMID: 30085147; PubMed Central PMCID: PMC6179167.

All Products Cited: Activin A ELISA AL-110; Activin B ELISA AL-150; Follistatin ELISA AL-117; Follistatin-like 3 ELISA AL-152

Shah A, Dodson WC, Kris-Etherton PM, Kunselman AR, Stetter CM, Gnatuk CL, Estes SJ, Allison KC, Sarwer DB, Sluss PM, Coutifaris C, Dokras A, Legro RS. Effects of Oral Contraception and Lifestyle Modification on Incretins and TGF-ß Superfamily Hormones in PCOS. J Clin Endocrinol Metab. 2021 Jan 1;106(1):108-119. doi: 10.1210/clinem/dgaa682. PMID: 32968804; PMCID: PMC7765645

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All Products Cited: Activin A ELISA AL-110; Activin B ELISA AL-150; Follistatin ELISA AL-117
 

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