IMMUNOLOCALIZATION OF RETINOL-BINDING PROTEIN AND PROFILES OF ITS MESSENGER-RNA AS RELATED TO TESTICULAR DEVELOPMENT IN THE BEEF BULL

A study was conducted to identify the cell types that express retinol- binding protein (REP) in the bovine testis and to compare relative ste ady-state levels of REP mRNA expression at different times of testicul ar development. At the ages of 10 (n = 3), 20 (it = 8), and 34 (ii = 7 ) wk, Angus bulls were bled three times at 1.5-hr intervals, then surg ically castrated. Blood samples were analyzed fur follicle-stimulating hormone (FSH), luteinizing hormone (LH), and testosterone (T), by rad ioimmunoassay and the degree of seminiferous tubule development was ev aluated histologically in sections of fixed tissue samples stained wit h hematoxylin and eosin. Immunolocalization of REP was based on the bi otin-strepavidin-horseradish peroxidase method. Testis weight and conc entrations of LH and T increased with age (P < 0.05), but those of FSH did not change (P > 0.05) between 10 and 34 wk. Seminiferous tubules at 10 wk contained immature Sertoli cells and gonocytes whereas, at 20 wk, spermatogonia and few spermatocytes were detected. At 34 wk, Sert oli cells appeared differentiated and spermatids were observed. REP wa s immunolocalized in Sertoli, Leydig, and peritubular cells at the age s of 10, 20, and 34 wk. Furthermore, no differences in staining betwee n Sertoli cells from tubules with or without germ cells were detected. Northern hybridization of testicular RNA with an REP cDNA probe revea led the presence of a 1.4-Kb mRNA, which was similar to previous REP t ranscripts found in other bovine tissues. Quantitative slot blot analy sis revealed that steady-state REP mRNA levels were 50% higher at 10 w k (P < 0.05) than at 20 and 34 wk of age. (C) Elsevier Science Inc. 19 98.