Vitamin A is clearly an important factor in spermatogenesis. Some of the new data on metabolism of retinoids in the testis has contributed to our understanding of the mechanism(s) involved in the action of vitamin A. It is probable that the requirement of the testis of vitamin A deficient rats for retinol but not retinoic acid involves access of the retinoids to various testicular compartments. Retinol may be required by germinal cells because of a requirement for esterification in order to be successfully transported by the Sertoli cells. Existing evidence suggests that both the Sertoli cells and the germinal cells have specific requirements for retinoids. In the vitamin A deficient rat there appears to be a developmental block at preleptotene spermatocyte and type Al spermatogonia stages. This block is removed by retinol and germinal cell development reinitiates in a synchronous manner. The synchronous testis model offers a number of advantages for the study of molecular events associated with the cycle of the seminiferous epithelium and the development of germinal cells as well as for investigations into the mechanism of action of the retinoids.

Retinoic acid receptor α (RARA), a retinoic acid-dependent transcription factor, is expressed in both somatic and germ cells of the testis. Rara-null male mice with global Rara mutations displayed severely degenerated testis and infertility phenotypes. To elucidate the specific responsibility of germ cell RARA in spermatogenesis, Rara was deleted in germ cells, generating germ cell-specific Rara conditional knockout (cKO) mice. These Rara cKO animals exhibited phenotypes of quantitatively reduced epididymal sperm counts and disorganized germ cell layers in the seminiferous tubules, which worsened with aging. Abnormal tubules lacked lumen, contained vacuoles, and showed massive germ cell sloughing, all characteristics similar to those observed in Rara-null tubules. Spermatocyte chromosomal spreads revealed a novel role for germ cell RARA in modulating the integrity of synaptonemal complexes and meiotic progression. Furthermore, the initiation of spermatogenesis from spermatogonial stem cells was decreased in Rara cKO testes following busulfan treatment, supporting a role of germ cell RARA in spermatogonial proliferation. Collectively, the evidence in this study indicates that RARA produced in male germ cells has a broad spectrum of functions throughout spermatogenesis, which includes the maintenance of seminiferous epithelium organization, the integrity of the meiotic genome, and spermatogonial proliferation and differentiation. The results further suggest that germ cell RARA has dual functions: intrinsically in germ cells, balancing proliferation and differentiation of spermatogonia, and controlling genome integrity during meiosis; and extrinsically in the crosstalks with Sertoli cells, controlling the cell junctional physiology for coordinating proper spatial and temporal development of germ cells during spermatogenesis.

: A wiper is a safety device removing rain and debris from windshield and ensuring visibility of drivers. If contact pressure distribution between rubber of the blade and the windshield is unbalanced, unwanted noise, vibration, and abrasion of the blade can occur and sometimes fatal accidents could occur. To improve the safety of the wiper, there have been many researches on the contact pressure analysis of the wiper, but the analysis results were not converged or require much computational time due to material nonlinearity of the rubber and contact conditions between the blade rubber and the windshield. In this research, a simple model with 1D beam and 2D shell elements was used for the contact pressure analysis instead of the 3D blade model. The simplified model saved computational time of the analysis and resolved convergence problems. The accuracy of the analysis results was verified by comparing them with experimental results for different rail spring curvatures. P: push force to press the frame, N θ : angle between the glass and the frame, rad H : height of the frame, mm L1, L2 : left-sided and right-sided length of the frame from a loading point P, mm

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