Sertoli Cells Produce Vitamin-Binding Proteins

PETER M. Fetterolf; MICHAEL K. Skinner

doi:10.1111/j.1749-6632.1987.tb25078.x

The seminiferous tubule in the rat testis is composed primarily of three cell types, Sertoli cells, peritubular myoid cells, and germinal cells in various stages of development. Tight junctions near the basal surfaces of adjacent Sertoli cells contribute to a blood-testis barrier, which creates a unique microenvironment within the tubule. The barrier effectively blocks passage of small and large molecules from plasma into the seminiferous tubule compartment formed by Sertoli cells.' Consequently, plasma constituents required for most stages of germinal cell development apparently must first pass through Sertoli cells. One approach to understanding the role of Sertoli cells in the maintenance and control of spermato-genesis is to determine the function of proteins secreted by the cell and then to monitor or to manipulate their function under various conditions. For example, Sertoli cells produce testicular transferrid and testicular ceruloplasmin,3 which specifically bind components (iron and copper, respectively) that are believed essential for germinal cell development. Vitamins are required for proper metabolic function and consequently germi-nal cell development. Vitamin deficiencies can have dramatic effects on the morphology of the seminiferous tubule and a negative effect on spermat~genesis.~ Vitamins that reach the inside of cells from plasma are quickly bound to proteins. Free vitamins would therefore be unlikely to exist in high concentrations in Sertoli cell cytosol and could not readily diffuse through the plasma membrane to developing germ cells. Further, the blood-testis barrier probably prevents diffusion of vitamins directly from the bloodstream to developing germinal cells. A logical, testable, hypothesis is that Sertoli cells synthesize and secrete proteins that bind and transport vitamins to germinal cells. Preliminary results are reported that suggest that Sertoli cells in serum-free primary monoculture secrete a substance that binds riboflavin with a high affinity. Twenty-day-old rats were killed by cervical dislocation, the testes were removed , and Sertoli cells were ~ r e p a r e d .

Sertoli Cells Produce Vitamin-Binding Proteins

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