FSTL3(Follistatin-Like 3) also known as FLRG or FOLLISTATIN-RELATED GENE, is a member of the follistatin-module protein family, which is composed of extracellular matrix-associated glycoproteins though to act in a paracrine manner to bind morphogens or growth/differentiation factors and regulate their activity during development. The FSTL3 gene extends over 7 kbp and contains 5 exons. By Southern blot analysis of somatic cell hybrids and FISH, Hayette et al.(1998) localized the FSTL3 gene to chromosome 19p13. Using recombinant mouse Fstl3, Tsuchida et al.(2000) found that Fstl3bound both activin and BMP2 and had a higher affinity for activin. Overexpression of Fstl3 inhibited BMP2-induced cell signaling in a reporter assay. In addition to the translocation in a case of B-cell chronic lymphocytic leukemia from which FSTL3 was isolated, Hayette et al.(1998) also observed rearrangement of the FSTL3 gene in a case of B-cell non-Hodgkin lymphoma and in a case of B-cell mantle zone lymphoma, suggesting that FSTL3 may be involved in the leukemogenesis process.