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Endogenous protein phosphorylation was investigated in cultured rat Sertoli cells after treatment with folliclestimulating hormone (FSH) 3',, N-morpholinepropanesulfonic acid (Mops), EGTA, ATP, and cAMP were from Sigma.

Ca2+-dependent protein phosphorylation and the role of calmodulin in this process was investigated in subcellular fractions of primary cultures of rat Sertoli cells. Significant Ca2+/calmodulin-dependent protein phosphorylation in Sertoli cells was restricted to the cytosol fraction. The calmodulin dependence of these effects was confirmed by using the calmodulin inhibitor trifluoperazine. Purification of Calmodulin. Calmodulin was either obtained from Calbiochem (bovine brain) or purified from bovine brain or rat testis using filtration on Sepharose 4B and affinity chromatography on a W-7 affinity column (22). Calmodulin activity was determined by using the assay for calmodulin-sensitive phosphodiesterase. The purity ofthe preparations was analyzed by NaDodSO4/polyacrylamide gel electrophoresis.Purification and Assay of Phosphodiesterase. The procedure for the partial purification of calmodulin-sensitive phosphodiesterase from bovine brain was essentially that described by Cheung and Lin (23). Phosphodiesterase activity was assayed by the method of Thompson and Appleman (24).Preparation ofCell Fractions. Primary cultures ofrat Sertoli cells were prepared from testes of 20-to 22-day-old rats as described (25). Cells growing in culture flasks were collected in cold 50 mM Pipes, pH 7.0/10 mM MgCl2/50 mM NaCl with and without 0.1 mM phenylmethylsulfonyl fluoride and dispersed by sonication (2.5-3.5 W) for 15 sec. After centrifugation at 27,000 X g for 10 min, portions ofthe supernatant were used to assay for endogenous protein phosphorylation. When subcellular fractions were required, the cells were collected in 50 mM Pipes, pH 7.0/50 mM NaCl and then homogenized in a glass Dounce homogenizer (small clearance pestle). After homogenization, MgCl2 was added to a final concentration of 10 mM. Subcellular fractions (100,000 X g cytosol and particulate fractions) were prepared from homogenates as described by Li and Hsie (26). The crude nuclear fraction obtained after Triton extraction (26) was further purified by centrifugation through sucrose as described by Prashad et al (27). Nuclei were rinsed and resuspended in homogenization buffer prior to assay. Purity ofthe subcellular fractions was monitored by assaying for lactate dehydrogenase activity (28) and 5'-nucleotidase activity (29) in different fractions. Contamination of particulate and nuclear fractions with soluble proteins was <5% (n = 5). Contamination of the soluble fraction with particulate protein was <5% (n = 3) and of the nuclear fractions with particulate protein was <10% (n = 3).In Vitro Phosphorylation. Reaction mixtures (150 ,ul) 760The publication costs ofthis article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U. S. C. §1734 solely to indicate this fact.

We extracted intermediate filament proteins (IFP) that were insoluble in in detergent from cultured rat Sertoli and peritubular cells after labeling with [35S] methionine and resolved them by two-dimensional polyacrylamide gel electrophoresis, autoradiography and Western blotting. We found that vimentin was the predominant IFP in both Sertoli and peritubular cells. However, while two isoelectric variants of vimentin were observed in Sertoli cells, only one was detected in peritubular cells. In addition, vimentin in Sertoli cells generated a large number of breakdown products, many differing in molecular weight and isoelectric point when compared to peritubular cells. These findings suggested that a Ca2+-activated protease, usually found in cells containing vimentin, was capable of generating proteolytic fragment patterns that were specific to cell type. Monoclonal antibodies were generated against IFP extracted from cultured Sertoli cells and their reactivity monitored by indirect immunofluorescence using Sertoli cells, peritubular cells and intact testis. One monoclonal antibody, designated IFP-SC, was an immunoglobulin (IgM) that produced a vimentin-like immunofluorescent pattern in cultured Sertoli cells. This pattern consisted of an extensive filamentous network that extended throughout the cell and surrounded the nucleus. In cultured peritubular cells, IFP-SC generated a diffuse, nonfilamentous immunoreactivity. IFP-SC reacted with components of seminiferous tubules and displayed immunoreactivity associated with Sertoli cells but not with elements of the seminiferous peritubular cell wall. Because immunofluorescent patterns were distinctly specific to cell type in cultured cells and in the intact tissue, monoclonal antibody IFP-SC is useful for the quantitative evaluation of cell cross-contamination of Sertoli and peritubular cells and, therefore, allows a precise characterization of functional events specific to cell type and monitoring of the differentiation state of cells with time in culture.