Follistatin 288 is a secreted glycoprotein that was first identified as a follicle-stimulating hormone inhibiting substance in ovarian follicular fluid . Human follistatin 288 cDNA encodes a 317 amino acid (aa) protein with a 29 aa signal sequence, and a 288 aa mature region. Follistatin shows the highest affinity for activins due to its extended configuration. Genetic deletion of follistatin in mice, or expression of only the Follistatin form, is perinatally lethal due to defects of lung, skin and musculoskeletal system. Follistatins also regulate hematopoietic stem cell adhesion to fibronectin via FS2.