Sertoli Cells Produce Vitamin-Binding Proteins

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

Purification of a paracrine factor, P-Mod-S, produced by testicular peritubular cells that modulates Sertoli cell function

A testicular paracrine factor, P-Mod-S, was purified from conditioned medium obtained from serum-free cultures of peritubular cells. Stimulation of testicular transferrin production by cultured Sertoli cells was utilized as a bio-assay for P-Mod-S. A bioactive protein with an apparent molecular weight of 50,000 under physiological conditions was isolated by high pressure size exclusion chromatography. P-Mod-S was found to have an affinity for heparin and bound to a heparin affinity column. Two forms of P-Mod-S were purified with reverse-phase chromatography. The less hydrophobic form was referred to as P-Mod-S (A) and is a 56,000 molecular weight protein. The more hydrophobic form was referred to as P-Mod-S (B) and is a 59,000 molecular weight protein. Purification of P-Mod-S (A) and P-Mod-S (B) from peritubular cell-radiolabeled secreted proteins revealed that both proteins contain radioactivity. This result demonstrates active synthesis and secretion of P-Mod-S by peritubular cells. Although the amino acid composition of the two proteins indicates distinct differences in the content of several amino acids, the relationship of P-Mod-S (A) and P-Mod-S (B) is unknown at present. A greater than 1000-fold increase in the specific activity of P-Mod-S was achieved with the purification procedure utilized. P-Mod-S can account for essentially all the bioactivity present in crude peritubular cell-secreted protein preparations. The effects of the two forms of P-Mod-S on both transferrin and androgen-binding protein production by Sertoli cells was examined. Purified forms of P-Mod-S were found to have a greater effect on Sertoli cell function than any individual regulatory agent previously known to influence the cell, including follicle-stimulating hormone. The significance of peritubular cell-Sertoli cell interactions mediated via P-Mod-S to spermatogenesis and testicular function is discussed, as well as insight provided into general mesenchymal-epithelial cell interactions

Pennsylvania Community College Students Interested in Earning Baccalaureate Degrees: A Qualitative Analysis of Their Decision-Making Experiences

This qualitative narrative research study explores the reasons that undergraduate transfer students make college and career planning decisions. The insights of community college students who expressed interest in completing a bachelor’s degree but did not enroll at a university were compared with the perspectives of university students enrolled in a bachelor’s degree program who had successfully transferred from a community college. The student input was analyzed to determine if there were differences in their decision-making experiences. Sixteen undergraduate students enrolled at higher education institutions in Pennsylvania responded to open-ended questions related to choosing a college and degree major, navigating the transfer admissions process, and participating in extracurricular activities. The participants provided viewpoints for ways in which they engaged with academic advising and transfer student support services and the influences that motivated their decisions. The qualitative data analysis resulted in nine emergent themes related to community college transfer student decision-making. The study concludes with a discussion and recommendations for further investigation. Understanding the student decision-making experiences of community college transfer students provides fellow-students, parents, education leaders, and policymakers with insights to support student success

Effects of Investigator Activity on Ring-Billed Gull Behavior and Reproductive Performance

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