PROJECT SUMMARY Nuclear export is an essential process for cellular viability, and nuclear export factor (NXF) proteins are considered to be critical for transporting RNA from the nucleus to be translated. NXF1 is the primary exporter of RNAs in eukaryotes and is essential for cellular viability. Gene duplicates of NXF1 have independently arisen across eukaryotes, and in Drosophila have evolved new functions distinct from NXF1. In mammals, there are three additional NXF gene duplicates, all are X-linked and considered paralogs of the ancestral NXF1. While NXF1 function has been well-characterized in somatic cells of mice, far less is known about the three NXF gene duplicates. Two of the three X-linked NXF duplicates in mouse (NXF2 and NXF7) are primarily expressed in the testis but have not been studied to the extent of the somatic NXF1. NXF2 is expressed predominantly in testicular germ cells, with loss of mouse Nxf2 resulting in subfertility or infertility depending on the genetic background. The molecular mechanism leading to the fertility defects in mice lacking Nxf2 remain unclear. I am well-positioned to discover the molecular mechanism of this infertility phenotype because I have already generated and backcrossed independent mouse lines of Nxf2Δ/Y and NXF2FLAG/Y mice for >5 generations. I hypothesize mouse Nxf2 evolved testicular germ cell-specific cytoplasmic functions to transport RNAs between the nuclear pore and the intercellular bridges connecting germ cells. This hypothesis is supported by my discoveries that NXF2 localizes almost exclusively to the cytoplasm and interacts with proteins known to associate with cytoplasmic portion of the nuclear pore and intercellular bridges. I will continue to use the mouse models I have generated to test my hypothesis through molecular, biochemical, and sequencing techniques. I expect to uncover the mechanism by which mouse Nxf2 is necessary for testicular germ cell development and to further our understanding of nuclear export, testicular germ cells, fertility, and RNA biology.