Function of Vitamin A in Normal and Synchronized Seminiferous Tubules^a

Abstract

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.

Retinoids and spermatogenesis: Lessons from mutant mice lacking the plasma retinol binding protein

“…A slow, chronic, desquamation of immature germ represents another early feature of VAD in the Rbp4-null mutant mice. Loss of germ cell through desquamation has also been described in vitamin A-deficient rats (Unni et al, 1983;Griswold et al, 1989) as well as in mice lacking RAR␣ (Lufkin et al, 1993). These data underline a critical role of RA signalling in maintaining the cohesiveness of the seminiferous epithelium, which may be achieved either by controlling the permeability of Sertoli cell tight junctions (Unni et al, 1983;Huang et al, 1988), or the expression of cell adhesion molecules holding together Sertoli and germ cells (reviewed in Mruk and Cheng, 2004).…”

Mammalian gonocyte and spermatogonia differentiation: recent advances and remaining challenges

“…Studies have demonstrated that in VAD adult mice, all differentiated germ cells are lost from the seminiferous tubules and the only cells remaining are undifferentiated type A spermatogonia and Sertoli cells (Mitranond et al 1979, Van Pelt & de Rooij 1990. However, once these rats are administered vitamin A, normal spermatogenesis can be rescued (Morales & Griswold 1987, Griswold et al 1989. At first, studies demonstrated that normal spermatogenesis could only resume if vitamin A (retinol) was given to the deficient mice and that the same results were not observed upon Gonocyte and spermatogonia differentiation R141 RA administration (Ahluwalia & Bieri 1971, Huang et al 1983.…”

Expression of retinoic acid receptor alpha in the germline is essential for proper cellular association and spermiogenesis during spermatogenesis

“…The abnormalities that occur at specific stages of spermatogenesis as a result of vitamin A deficiency (VAD) have been extensively studied, particularly in the rat de Rooij et al, 1994;Eskild and Hansson, 1994;Griswold et al, 1989). Although the morphological changes in spermatogenesis upon VAD have been well documented, the molecular mechanisms underlying these changes are still largely unknown and are likely to be complex.…”