Title

The relative levels of translin-associated factor X (TRAX) and testis brain RNA-binding protein determine their nucleocytoplasmic distribution in male germ cells.

Document Type

Article

Publication Date

2004

Keywords

Biological-Transport-Active, COS-Cells, Carrier-Proteins, Cell-Nucleus, Cytoplasm, DNA-Primers, DNA-Binding-Proteins, Female, Immunohistochemistry, In-Vitro, Male, Mice, Mice-Knockout, Models-Biological, Nuclear-Proteins, Plasmids, Pregnancy, Recombinant-Proteins, Spermatocytes, Spermatozoa, Subcellular-Fractions, SUPPORT-U-S-GOVT-P-H-S, Transfection

JAX Source

J Biol Chem 2004 Jul; 279(30):31514-23.

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.