THE RNA-BINDING AND DNA-BINDING PROTEIN TB-RBP IS SPATIALLY AND DEVELOPMENTALLY-REGULATED DURING SPERMATOGENESIS

Testis brain RNA-binding protein (TB-RBP) suppresses translation in vi tro and attaches mRNAs to microtubules by binding to conserved element s in the 3' untranslated regions (UTRs) of specific testis and brain m RNAs. Purification of TB-RBP from testicular and brain cytoplasmic ext racts has revealed that mouse TB-RBP is 99% identical to the human pro tein translin, a recombination ''hot spot'' binding protein associated with chromosomal translocations. Using a cDNA encoding TB-RBP, the ge ne copy number and the developmental expression of TB-RBP have been an alyzed by Southern blotting, Northern blotting, and in situ hybridizat ion. in the mouse, TB-RBP is encoded by a single copy gene. In mouse t estes, three TB-RBP mRNAs of about 1.2, 1.7, and 3.0 kb are developmen tally regulated with high levels of expression in meiotic and postmeio tic germ cells. A fourth TB-RBP transcript of about 3.2 kb is seen in the brain. In situ hybridization confirms high revels of testicular TB -RBP mRNAs in meiotic and postmeiotic cells, with the highest levels o f TB-RBP mRNAs in pachytene spermatocytes and round spermatids of the mouse and in round spermatids of the rat. RNase H digestion assays rev eal that the three TB-RBP mRNAs of mouse testes result from processing differences in their 3' untranslated regions. These data demonstrate that multiple TB-RBP mRNAs are primarily expressed in meiotic and post meiotic germ cells in the mammalian testis, and although the specific RNA-binding ability of TB-RBP appears limited to brain and testis, TB- RBP mRNAs are widely expressed. (C) 1998 Wiley-Liss, Inc.