Functions and clinical significance of cold shock proteins in the testis

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Spermatogenesis is a complex process ; a diploid spermatogonium undergoes mitosis and develops into primary spermatocytes. As a result of two meiotic divisions and spermiogenesis, spermatozoa are produced. These processes are controlled by the germ cell - Sertoli cell interactions, and the tightly regulated expression of many genes. In addition to these, spermatogenesis has a unique feature. Unless the testis temperature is maintained to be lower than the body cavity temperature, germ cells will die. To elucidate the molecular mechanisms of spermatogenesis, we tried to isolate genes the expression of which are induced by the testis temperature (32 degree C) and analyze their involvement in male spermatogenesis. The major findings are as follows ; 1) We cloned the mouse cDNA of the cold shock protein, rbm3, and showed that it is expressed in the Sertoli cells of the testis and that its expression is decreased in the cryptorchid testis. 2) By using the yeast hybrid screening method, we tried to identify the RNAs that interact with the cold shock protein Cirp, but no success. 3) We determined the cold shock response element in the DNA sequence of the mouse cirp gene. By using yeast 1-hybrid screening method, we are isolating the protein that binds to this element. 4) Homozygous mutant mice that are deficient in cirp gene were produced. At present no abnormality in phenotypes is apparent. 5) We found that cirp is consticutively expressed the rat neuronal cells and that the expression decreases after transient forebrain ischemia or exposure to H2O2.6) Three proteins that interact with Cirp were isolated by the yeast 2-hybrid screening method. 7) We identified several genes whose expressions are increased in cultured cells by the cold stress.