The function of FSTL3 (follistatin like 3, ENSG00000070404) is as follows. Isoform 1 or the secreted form is a binding and antagonizing protein for members of the TGF-beta family, such as activin, BMP2 and MSTN. Inhibits activin A-, activin B-, BMP2- and MSDT-induced cellular signaling; more effective on activin A than on activin B. Involved in bone formation; inhibits osteoclast differentiation. Involved in hematopoiesis; involved in differentiation of hemopoietic progenitor cells, increases hematopoietic cell adhesion to fibronectin and seems to contribute to the adhesion of hematopoietic precursor cells to the bone marrow stroma. Isoform 2 or the nuclear form is probably involved in transcriptional regulation via interaction with MLLT10. {ECO:0000269|PubMed:11948405, ECO:0000269|PubMed:15451575, ECO:0000269|PubMed:15574124, ECO:0000269|PubMed:16336961, ECO:0000269|PubMed:17868029, ECO:0000269|PubMed:17878677}.