CSTF2T, also known as tauCSTF-64, is a paralog of CstF-64, a component of the cleavage stimulation factor (CstF) that processes 3’-end formation and polyadenylation of mRNAs. The human CSTF2T/TauCSTF64 gene is located at 10q22-23, a site associated with neurological problems and male infertility. CSTF2T is expressed in all tissues and throughout meiosis in male germ cells. CstF-64 is also expressed ubiquitously; however because it is located on the X chromosome, its expression is temporarily silenced in germ cells by meiotic sex chromosome inactivation. During this inactivation, it is hypothesized that CSTF2T/TauCSTF64 can compensate for the loss of CstfF-64 expression. Recently, targeted disruption of CSTF2T/TauCSTF64 in mice has been shown to cause aberrant spermatogenesis and infertility providing more evidence for its importance in spermatogenesis.