|Budget Amount *help
¥1,200,000 (Direct Cost: ¥1,200,000)
Fiscal Year 2001: ¥1,200,000 (Direct Cost: ¥1,200,000)
Heterogeneous nuclear ribonucleoprotein (hnRNP) B0 is a testis-specific splicing isoform of hnRNP A2/B1 which is a kind of nuclear RNA binding proteins. The in vitro analysis demonstrated that B0 specifically binds to single-stranded telomere DNA and has a relation to the maintenance and function of telomere. For purpose of clarifying in vivo role of B0, we further studied about B0 using a developmental engineering.
1) The coding sequence of human hnRNP B0 was introduced in the pEF-BOS (translation elongation factor promoter) expression vector.
2) pEF-BOS-B0 construct was microinjected in fertilized eggs obtained from BDF1 mice and transgenic mice were generated as previously described. As the result, seven independent founder mice carrying B0 transgene (B0-TG mice) were obtained. Four stably expressed B0 transgene in whole body, and three of them showed decreased birthrate.
3) Systematical analysis of #257 founder which carrying a single copy of B0 revealed that the decreased birth rate
of B0-TG mice was not caused by the developmental anomalies but was caused by the poor fertility of male mice. In B0-homozygote male mice, which expressed increased level of B0 protein, the spermatogenesis stops in the stage of the haploidic round spermatid after the meiosis, and the round spermatids fall into apoptosis. It was clarified that the abnormality of molecular level is already seen at the Pachyten stage of the meiosis prophase in which the homologous recombination of the chromosome occur. However, the telomere length did not apparently change as it anticipates at the beginning, and change in the individual lifespan are not clear at present, either. There was no morphological change in the organs except for the testis.
In summary, it was clarified by the study using developmental engineering that B0 protein has in vivo role only in the testis and suppresses the maturation of spermatogenesis. At present, the further analysis of molecular level is advanced, including and it the telomere function in meiosis. The B0-Tg mice seem to give important information as a model animal of male infertility. Less