title: The relative levels of translin-associated factor X (TRAX) and testis brain RNA-binding protein determine their nucleocytoplasmic distribution in male germ cells.
abstract: Testis brain RNA-binding protein (TB-RBP), the mouse orthologue of human translin, is an RNA and single-stranded DNA-binding protein abundant in testis and brain. Translin-associated factor X (TRAX) was identified as a protein that interacts with TB-RBP and is dependent upon TB-RBP for stabilization. Using immunohistochemistry to investigate the subcellular locations of TB-RBP and TRAX during spermatogenesis, both proteins localize in nuclei in meiotic pachytene spermatocytes and in the cytoplasm of subsequent meiotic and post-meiotic cells. An identical subcellular distribution is seen in female germ cells. Western blot analysis of germ cell protein extracts reveals an increased ratio of TRAX to TB-RBP in meiotic pachytene spermatocytes compared with the post-meiotic round and elongated spermatids. Using COS-1 cells and mouse embryonic fibroblasts derived from TB-RBP null mice as model systems to examine the shuttling of TB-RBP and TRAX, we demonstrate that TRAX contains a functional nuclear localization signal and TB-RBP contains a functional nuclear export signal. Coexpression of both proteins in COS-1 cells and TB-RBP-deficient mouse embryonic fibroblasts reveals that the ratio of TRAX to TB-RBP determines their subcellular locations, i.e. increased TRAX to TB-RBP ratios lead to nuclear localizations, whereas TRAX remains in the cytoplasm when TB-RBP levels are elevated. These subcellular distributions require interaction between TB-RBP and TRAX. We propose that the subcellular locations of TB-RBP and TRAX in male germ cells are modulated by the relative ratios of TRAX and TB-RBP.
authors.affiliation: Center for Research on Reproduction and Women's Health, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA.
authors.forename: Yoon Shin
authors.initials: YS
authors.lastname: Cho
authors.forename: Vargheese M
authors.initials: VM
authors.lastname: Chennathukuzhi
authors.forename: Mary Ann
authors.initials: MA
authors.lastname: Handel
authors.forename: John
authors.initials: J
authors.lastname: Eppig
authors.forename: Norman B
authors.initials: NB
authors.lastname: Hecht
mesh_terms: D000818:Animals; D001483:Base Sequence; D001693:Biological Transport, Active; D019556:COS Cells; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D017931:DNA Primers / Q000235:genetics; D004268:DNA-Binding Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D005260:Female; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D008954:Models, Biological; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D010957:Plasmids / Q000235:genetics; D011247:Pregnancy; D016601:RNA-Binding Proteins; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D013090:Spermatocytes / Q000378:metabolism; D013094:Spermatozoa / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism; D014162:Transfection
chemical_list: D002352:Carrier Proteins; D017931:DNA Primers; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D016601:RNA-Binding Proteins; D011994:Recombinant Proteins; C498303:Tsn protein, mouse; C498306:Tsnax protein, mouse