Biomedical subjects

M D Griswold

Publications and source records attributed to M D Griswold.

At least 73 records · Page 4Linked to original sources

PubMed1989

Cellular localization of fibronectin gene expression in the seminiferous tubule.

The cellular location of fibronectin expression within the seminiferous tubule was investigated in order to better understand testicular cell functions and cell-cell interactions. Peritubular cells were shown to actively synthesize and secrete fibronectin in culture by the detection of a radiolabeled 220 kDa secreted protein that is immunologically similar to fibronectin and by the quantitation of fibronectin in peritubular cell conditioned medium with a fibronectin enzyme-linked immunosorbent assay. Sertoli cells did not produce detectable levels of fibronectin when assayed by either of these procedures. A 6.5 kb fibronectin messenger RNA was detected in freshly isolated or cultured peritubular cells, but no fibronectin gene expression was detected in Sertoli cells or developing germinal cells. Combined results imply that the peritubular cells are the only apparent site of fibronectin expression within the seminiferous tubule. During the development of the testis the levels of fibronectin expression increased to a maximum at early puberty (15-day-old rats) and then slowly declined. The results demonstrate that fibronectin can be utilized as a unique functional and biochemical marker for peritubular cells when compared to other cell types in the seminiferous tubule. Production of fibronectin by peritubular cells provides an example of the ability of peritubular cells and Sertoli cells to cooperate in the production of individual components of the basement membrane of the seminiferous tubule. This cellular interaction is an example of a mesenchymal/stromal-epithelial interaction which is postulated to be important for the physiology of many tissues.

Animals↗

PubMed1989

Sulfated glycoprotein-1 (saposin precursor) in the reproductive tract of the male rat.

Sulfated glycoprotein-1 is one of the major protein secretion products of rat Sertoli cells in culture. This 70,000 Mr protein shares substantial sequence similarity with human prosaposin, the precursor of lysosomal saposins. Saposins are known to enhance the activity of lipid modifying enzymes presumably by solubilizing the lipids. We report here the immunolocalization of sulfated glycoprotein-1 in the cells and fluid of the male reproductive tract. The protein is present in secondary lysosomes of Sertoli cells and also in the luminal fluid of seminiferous tubules and epididymis. The highest concentrations of the protein are in seminiferous tubule fluid and rete testis fluid, while relatively low amounts are found in cauda epididymal fluid and serum. Sulfated glycoprotein-1 is believed to be involved in degradation of lipids in residual bodies and may also assist in modification of membrane lipids during sperm maturation.

Animals↗

PubMed1989

Function of vitamin A in normal and synchronized seminiferous tubules.

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.

Amino Acid Sequence↗

PubMed1989

Testosterone induction of cellular proteins in cultured Sertoli cells from hypophysectomized rats and rats of different ages.

Testosterone is essential for the maintenance of spermatogenesis, and the Sertoli cell is thought to be an important target cell for the hormone in the seminiferous tubule. The direct response of Sertoli cells to testosterone in cell culture was studied by two-dimensional gel electrophoresis of radiolabeled cellular proteins. Changes in testosterone responsiveness with age and hormonal condition were studied by culturing Sertoli cells from 20- and 40-day-old normal rats and 40-day-old rats that had been hypophysectomized at 20 days of age. Two abundant proteins, numbered 1604 and 1605 for reference purposes, were consistently increased in response to testosterone treatment in all three sets of cultured Sertoli cells. Two other proteins, 1602 and 1603, were decreased with testosterone in all three Sertoli cell cultures. Densitometric scanning of the gels revealed changes in several proteins of low abundance (i.e. proteins that represent less than 0.2% of the total incorporated radioactivity on the gel) in response to testosterone. The majority of the changes in response to testosterone were in these low abundance proteins. Protein profiles from testosterone-treated cell cultures as well as control (no hormone) Sertoli cell cultures differed among the three groups of cells. This indicates that differences in Sertoli cell function in vivo due to age and hormonal condition are reflected in culture by protein profiles.

Aging↗

PubMed1989

Specific mRNAs in Sertoli and germinal cells of testes from stage synchronized rats.

A treatment which used vitamin A depletion followed by vitamin A repletion was used to synchronize seminiferous tubules to a few related stages of the cycle of the seminiferous epithelium. The success of the synchronization procedure was dependent on the age and size of the rat at the initiation of the experiment (20 days of age and 35-40 g) and the extent to which the vitamin A deficiency had progressed. Administration of retinol was done when the only viable germinal cells in the testis were preleptotene spermatocytes and type A spermatogonia but if the deficiency was prolonged spermatogenesis did not recover. Once established synchrony appeared to be sustained at least through several consecutive cycles. A combination of molecular probes was used to determine if the synchronized testes displayed stage specific variations in Sertoli cell and germinal cell mRNA levels as has been reported for normal asynchronized rats. Sertoli cells in the synchronized testes were shown by quantitative in situ hybridization and by Northern blot analysis to have stage specific variations in the levels of mRNA for transferrin, sulfated glycoprotein-1, and sulfated glycoprotein-2. The mRNA levels in the different stages were qualitatively similar to those in equivalent stages previously reported for testes from asynchronous rats. The germinal cell content of the synchronized testes were examined with Northern blots probed with nick-translated protamine 1 and transition protein 1 cDNAs.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1988

Biosynthesis and molecular cloning of sulfated glycoprotein 1 secreted by rat Sertoli cells: sequence similarity with the 70-kilodalton precursor to sulfatide/GM1 activator.

Sulfated glycoprotein 1 (SGP-1) is one of the abundant proteins secreted by rat Sertoli cells. Pulse-chase labeling shows that SGP-1 is synthesized as a cotranslationally glycosylated 67-kilodalton (kDa) precursor which is posttranslationally modified to a 70-kDa form before secretion to the extracellular space. A plasmid cDNA library was constructed from immunopurified mRNA, and two overlapping clones coding for the entire protein coding sequence were isolated. The cDNAs represent 27 nucleotides of 5' noncoding sequence, 1554 nucleotides of coding sequence, and 594 nucleotides of 3' noncoding sequence. The derived SGP-1 sequence contains 554 amino acids and has a molecular weight of 61,123. Four potential N-glycosylation sites occur within the sequence. An internal region of SGP-1 shows 78% sequence identity with the 67 N-terminal amino acids described for human sulfatide/GM1 activator (SAP-1). Sequence comparisons suggest that SGP-1 is the precursor to sulfatide/GM1 activator; however, the secretion of the protein from Sertoli cells is distinct from the proteolytic processing and lysosomal compartmentalization which have been described for human fibroblasts. The presence of internal sequence similarity suggests that three additional binding sites may occur in SGP-1. Northern blots show similar levels of expression for the 2.6-kilobase SGP-1 mRNA in all tissues examined. The site of SGP-1 synthesis in testis was localized to Sertoli cells by immunofluorescence and in situ hybridization.

Amino Acid Sequence↗

PubMed1988

Suppression of lymphocyte proliferation by proteins secreted by cultured Sertoli cells.

Secreted proteins from cultured rat Sertoli cells were assessed for effects on phytolectin-stimulated rat splenic lymphocytes. Sertoli cell proteins (SCP) suppressed DNA, RNA and protein synthesis in stimulated rat splenic lymphocytes whether added at 0, 4, 24 and 48 h after culture initiation. SCP preparations were not toxic to cells. SCP suppressive activity was heat stable but was not associated with the carbohydrate component of SCP preparations. SCP also suppressed the proliferation of lymphoid and non-lymphoid cell lines from several different animal species but did not inhibit proliferation-independent lysis of YAC-1 target cells by rat natural killer cells. These results suggest that Sertoli cells synthesize inhibitory factors that might be secreted into seminal plasma. Furthermore, our results demonstrate that one mode of action of these factors is suppression of cell proliferation.

Animals↗

PubMed1988

Protein secretions of Sertoli cells.

As was stated in the introduction, many of the functions of the Sertoli cells are apparently carried out by the protein secretions of these cells. The use of Sertoli cell cultures and appropriate biochemical and immunological techniques has allowed the characterization of some of these secretion products. It is likely that many of the functions of the Sertoli cells are necessary because of the presence of the blood-testis barrier. Many growth and nutritive factors which are necessary for cell viability are available to most cells via the serum. The germinal cells within the adluminal compartment do not have access to serum factors and one of the functions of the Sertoli cells is to synthesize serum-like components and secrete them into the adluminal compartment. The historical description of Sertoli cells as "nurse cells" thus appears to have been accurate. The nurse-cell function is most clearly demonstrated by the proposed mechanism by which germinal cells obtain ferric ions. The Sertoli cells have developed a system to move serum-derived iron through their own cytoplasm and to secrete it bound to newly synthesized testicular transferrin molecules which can deliver it to specific receptors on the germinal cell surface (Huggenvik et al., 1984). Functionally, all of the secreted proteins from Sertoli cells which have been characterized or proposed fall into one of five basic classes. First, Sertoli cells secrete a number of transport proteins including transferrin, ceruloplasmin, and ABP. The proposed function of these proteins is the transport of Fe3+, Cu2+, and androgens to the germinal cells or to the epididymis (ABP). Second, Sertoli cells synthesize and secrete a number of proteins which have a hormone-like or growth factor-like activity. AMH is a clear and well-documented example of this type of product while the evidence for inhibin, somatomedin C, EGF-like growth factor, and seminiferous growth factor will require further corroboration. Third, Sertoli cells secrete proteins which have enzymatic activities. Plasminogen activator is the best characterized example of this class of products and the alpha-lactalbumin-like activity is of potential interest. The fourth class of Sertoli cell secretion products includes those proteins which contribute to the basement membrane, namely, type IV collagen and laminin. Finally, there is a very important group of Sertoli cell secretion products for which there is, as yet, no evidence for a defined function. This group includes SGP-1 and SGP-2 which are the major sertoli cell products in rats and which have been well-characterized biochemically.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1988

Transferrin and sulfated glycoprotein-2 messenger ribonucleic acid levels in the testis and isolated Sertoli cells of hypophysectomized rats.

Both FSH and testosterone act on Sertoli cells in the testis. It is possible that the action of these hormones on Sertoli cells results in an increased capacity for the cells to carry out their prescribed functions, among which are the synthesis and secretion of specific glycoproteins. Changes in the testicular levels of two specific mRNAs in hypophysectomized hormone-treated rats were determined by solution hybridization to cRNA probes. The mRNAs coding for transferrin and sulfated glycoprotein-2 (SGP-2), both of which are secretion products of Sertoli cells, decreased dramatically in the testis of hypophysectomized rats that were maintained for 20 days untreated with hormones. If hypophysectomy was done to rats at 20 days of age, daily injections for a subsequent 20 days with FSH or FSH in combination with testosterone partially maintained both transferrin and SGP-2 mRNA levels. Testosterone alone was ineffective in 20-day-old rats. In contrast, if hypophysectomy was performed on 40-day-old rats, daily injections of testosterone alone or in combination with FSH were most effective in maintaining higher levels of the specific mRNAs. When the Sertoli cells from rats hypophysectomized at 20 days of age were placed in cell culture, FSH again was most effective in the stimulation of transferrin mRNA above control levels. However, when the Sertoli cells from the rats hypophysectomized at 40 days of age were placed in culture, FSH was slightly stimulatory, but testosterone had no effect on the transferrin mRNA levels. Neither FSH nor testosterone affected the levels of SGP-2 mRNA in the cultured cells regardless of the age of the animal at the time of hypophysectomy. Additional in vivo studies were done in which the rats were hypophysectomized at 20 days of age, allowed to regress for 17 days, and then injected daily with hormones for 3 days. The levels of transferrin and SGP-2 mRNA in this experiment were stimulated by FSH alone or by a combination of FSH and testosterone to an extent similar to that in the cultured cells. These studies showed that FSH is most important in the younger rats and testosterone is most important in the older rats in the maintenance of specific mRNA levels. In addition, the level of stimulation observed with either hormone is different depending on whether the hormone is given in culture or in vivo.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1988

Molecular biology of the Sertoli cell.

The "nurse cell" concept developed as a result of the morphological relationships between germ cells and Sertoli cells, and because of the junctional barrier defined by Sertoli cells which allowed the creation of a compartment in which the constituents could be regulated by Sertoli cells. The molecular approach to studies of the role of Sertoli cells in spermatogenesis has already led to a better understanding of the "nurse cell" concept. Molecular studies on the function of Sertoli cells have for the most part been dependent on the Sertoli cell culture techniques which were first published in 1975 (Dorrington and Fritz 1972; Steinberger et al. 1975a; Welsh and Wiebe 1975). As a result of this technical innovation Sertoli cells which remained responsive to hormones and which continued to carry on secretory activities could be obtained relatively free of other cell types. In the spent medium from cultured Sertoli cells specific secretion products could be detected such as ABP, transferrin, and SGP-2; components with inhibin-like activity; and metabolic products such as lactate. Thus, for the first time some molecular correlates to the "nurse cell" role of Sertoli cells have been described. In addition to the close morphological relationships between germ cells and Sertoli cells it has now been demonstrated that protein products of the Sertoli cells directly interact with germ cells. The Sertoli cell-mediated iron transport to germ cells via transferrin is the clearest demonstration of this interaction. Both SGP-1 and SGP-2 interact with spermatozoa and can be found tightly associated with the plasma membrane of these cells. As more of the secretion products of Sertoli cells are characterized the important role of these cells in spermatogenesis and spermiogenesis will be underscored. The identification and characterization of the Sertoli cell secretion products is important information to obtain, but an understanding of the function of these products also requires temporal knowledge about their synthesis. The interdependence of the morphological observations of the testis and the new technology of molecular biology is most clearly illustrated by the studies involving quantitative in situ hybridization. This technique has been utilized to quantify the amount of transferrin and SGP-2 mRNA present in Sertoli cells associated with different stages of the cycle of the seminiferous epithelium and to establish positively the Sertoli cell location of a specific mRNA (Morales et al. 1987). The technique is potentially applicable to any Sertoli cell specific protein product for which a cDNA probe becomes available.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1987

Uptake and metabolism of retinol in cultured Sertoli cells: evidence for a kinetic model.

When cultured Sertoli cells derived from 20-day-old weanling rats were supplied [3H]retinol bound to serum retinol binding protein-transthyretin complex, [3H]retinol was rapidly incorporated and [3H]retinyl esters were synthesized. Within 28 h after administration, 83% of the labeled retinoids were accounted for as retinyl esters (64% as retinyl palmitate). Sertoli cells derived from vitamin A deficient rats and supplied [3H]retinol in culture under identical conditions likewise incorporated [3H]retinol and synthesized retinyl esters. In contrast to normal Sertoli cells, vitamin A deficient Sertoli cells eventually metabolized virtually all of the cellular [3H]retinol to retinyl esters. The primary metabolic fate of retinol administered to Sertoli cell cultures was the synthesis of retinyl esters under all conditions tested. However, administration of [3H]retinol bound to serum retinol binding protein gave metabolic profiles having a higher proportion of retinyl esters and lower proportions of unresolved polar material than administration of [3H]retinol alone. The kinetics of retinol uptake and intracellular retinyl ester synthesis in cultured Sertoli cells was complex. An initial, rapid phase of [3H]retinol incorporation lasting 30 min was followed by a slower rate of incorporation and a concomitant decrease in the intracellular concentration of [3H]retinol. During the time course the specific activity of [3H]retinyl palmitate eventually exceeded that of intracellular [3H]retinol. These observations suggest that two intracellular pools of retinol may exist in Sertoli cells.

Animals↗

PubMed1987

Biosynthesis and molecular cloning of sulfated glycoprotein 2 secreted by rat Sertoli cells.

Sulfated glycoprotein 2 (SGP-2) is the major protein secreted by rat Sertoli cells. Pulse-chase labeling shows that SGP-2 is synthesized as a cotranslationally glycosylated 64-kDa precursor that is modified to a negatively charged 73-kDa form before intracellular cleavage to the mature 47- and 34-kDa subunits. A plasmid cDNA library was constructed from immunopurified mRNA, and a recombinant clone containing the entire protein coding sequence of SGP-2 was isolated. The 1857-nucleotide cDNA consists of a 297-nucleotide 5' noncoding segment, a 1341-nucleotide coding segment, and a 219-nucleotide 3' noncoding sequence. The 5' noncoding region contains five ATG codons followed by four short open reading frames. The derived SGP-2 sequence has a molecular weight of 51,379 and contains six potential N-glycosylation sites. Proteolytic processing sites for the preproprotein were determined by amino-terminal sequencing of the isolated SGP-2 subunits. Northern blots show a wide tissue distribution for the 2.0-kb SGP-2 message, and computer sequence analysis indicates a significant relationship between SGP-2 and human apolipoprotein A-I.

Amino Acid Sequence↗

PubMed1987

Stage-dependent levels of specific mRNA transcripts in Sertoli cells.

Localization and stage-dependent levels of transferrin and sulfated glycoprotein-2 (SGP-2) mRNAs were examined in rat testes by in situ and soluble hybridization of mRNA with a single-stranded RNA probe prepared with the SP65 vector. Biotinylated RNA probes were identified in testicular tissue by using a biotinylated glucose oxidase-avidin system followed by a treatment with an appropriate electron carrier and a tetrazolium salt. This procedure demonstrated that the anatomical site of transferrin and SGP-2 gene expression was the Sertoli cells. Tritium-labeled RNA probes were visualized by radioautography. Negative and positive controls as well as in situ hybridization in Sertoli and myoid cells in culture indicated again that the cytoplasm of Sertoli cells was the anatomical site of transferrin and SGP-2 expression. Quantitative radioautography revealed cyclic variations in the level of both transferrin and SGP-2 mRNAs. The level of transferrin mRNA was relatively high from Stage I to Stage VIII. At Stage IX, the level decreased acutely and remained low in Stage X. The level of transcripts increased dramatically at Stage XIII, remaining high until Stage XIV. In the case of SGP-2 mRNAs, levels of transcripts were similar in most stages except at Stages VII and VIII, where higher levels were observed. These data were substantiated by similar results obtained by solution hybridization of both recombinant cRNAs with mRNAs from selected seminiferous tubules staged by transillumination. Thus, our results demonstrated a stage-specific regulation of transferrin and SGP-2 mRNA levels in Sertoli cells.

Animals↗

PubMed1987

Transport of iron and transferrin synthesis by the seminiferous epithelium of the rat in vivo.

The transport of radioactive iron across the seminiferous tubules was analyzed in vivo by light-microscope quantitative radioautography. At 5 min after a single intratesticular injection of 55Fe-transferrin, a strong labeling of the basal aspect of the seminiferous epithelium was observed. Between 30 min and 2 h, the labeling on the basal aspect of the seminiferous epithelium decreased. This decrease was accompanied by a substantial increase of the radioautographic reaction over the cellular elements in the adluminal compartment. These results were consistent with the demonstration of 59Fe associated with meiotic spermatocytes and differentiating spermatids isolated by velocity sedimentation from testes injected with 59Fe-transferrin. Furthermore, after a single intratesticular injection of 59Fe-labeled human transferrin, radiolabeled rat transferrin was immunoprecipitated from homogenates of isolated tubules with a specific antibody and appeared as a single radioactive band on fluorographs of urea/polyacrylamide gels. Similarly, 59Fe-labeled rat transferrin but not 125I-transferrin was immunoprecipitated from rete testis fluids of testes infused with either 59Fe- or 125I-labeled human transferrin. Finally, the synthesis of testicular transferrin in vivo was demonstrated in fluorographs of immunoprecipitated transferrin after an intratesticular injection of 35S-methionine in rats whose livers were excluded from the general circulation by ligation of both the hepatic artery and the portal vein. Thus, our results demonstrated a unidirectional system of iron transport from the basal compartment of the seminiferous epithelium to the germ cells in the adluminal compartment involving two distinct transferrins, i.e., a serum transferrin and a testicular transferrin synthesized by the seminiferous epithelium.

Animals↗

PubMed1987

Transferrin messenger ribonucleic acid: molecular cloning and hormonal regulation in rat Sertoli cells.

Transferrin-specific cDNA clones were isolated from a rat liver cDNA library prepared from transferrin-enriched mRNA. Hybrid selection and sequence analysis confirmed that the selected clone contained the carboxy-terminal coding region of the transferrin mRNA. Northern blot analysis was used to demonstrate the presence of transferrin mRNA in liver and Sertoli cells. Transferrin mRNA levels were measured in total RNA isolated from cultured rat Sertoli cells after treatment with FSH, insulin, retinol, and testosterone. The results showed a 2- to 4-fold increase in the level of transferrin mRNA, which peaked on the fourth day of culture after initiation of treatment, with FSH, insulin, retinol, and testosterone. This induction is gene specific, since no change in the mRNA levels for either the catalytic or regulatory subunits of cAMP-dependent protein kinase was observed. The effects of hormones, vitamin A (retinol), and Bu2 cAMP on transferrin mRNA and transferrin secretion (measured by RIA) in cultured Sertoli cells were compared. In general, a direct relationship between the amount of transferrin mRNA present in the cells and the amount of transferrin secreted into the culture medium was observed. These results demonstrate the important role that vitamin A, testosterone, and peptide hormones play in modulating transferrin gene expression in Sertoli cells.

Animals↗

PubMed1987

Retinol-induced stage synchronization in seminiferous tubules of the rat.

Vitamin A deficiency (VAD) in rats causes a progressive germ cell depletion and cessation of spermatogenesis resulting in seminiferous tubules which contain only Sertoli cells, spermatogonia and a small number of preleptotene spermatocytes. Spermatogenesis can be rapidly restored by the administration of retinol. Our preliminary studies suggested a partial stage synchronization of many seminiferous tubules in VAD male rats subsequently treated with retinol. To confirm this observation and to achieve a better synchronization, VAD rats received 2 SC injections of retinol suspended in sesame oil followed by daily oral administrations of 0.5 mg of retinol. In all rats an almost perfect synchronous stage development of seminiferous tubules evolved in a predictable manner and was maintained through 2 spermiations.

Animals↗

PubMed1986

Purification and characterization of a sulfated glycoprotein secreted by Sertoli cells.

Sulfated glycoprotein 2 (SGP-2), the major secretion product of Sertoli cells, was purified from cell culture medium by reverse-phase high-performance liquid chromatography. The native protein consists of disulfide-linked monomers of 41,000 and 29,000 daltons which have a strong tendency to associate into multimers. The purified SGP-2 was subjected to amino acid analysis and contained high levels of Asx (11.1%), Glx (15.1%), and leucine (11.5%). The oligosaccharides on the purified SGP-2 were analyzed to determine the monosaccharide compositions and the molecular weights of the intact carbohydrate moieties. SGP-2 was shown to be 23.7% carbohydrate and consisted of 1% fucose, 3.5% mannose, 4.1% galactose, 7.1% N-acetylglucosamine, and 8.0% N-acetylneuraminic acid. No N-acetylgalactosamine was detected. When the SGP-2 was digested with proteases, the intact oligosaccharides were chromatographed over a Bio-Gel P-6 column and found to elute in a single symmetrical peak of approximately 3,300 g/mol. On the basis of these results, the oligosaccharides on SGP-2 were proposed to consist of triantennary chains similar to those found on fetuin. When the 35SO4(2-)-labeled SGP-2 was digested with Pronase, the free amino acids could be separated by chromatography from the oligosaccharide. The 35SO4(2-) was shown to be associated with the oligosaccharide portion of SGP-2.

Amino Acids↗

PubMed1986

The use of specific cDNA probes to assay Sertoli cell functions.

The use of cDNA probes to measure the functional state of Sertoli cells in culture or in vivo offers a number of advantages, including sensitivity and cellular specificity. Experiments done with cultured Sertoli cells suggest that the transferrin mRNA levels are regulated by FSH, insulin, vitamin A, and testosterone. Questions relating to the specificity of the action of the hormones and vitamin A on the transferrin mRNA or on other mRNA will require the use of additional hybridization probes. It is clear that most agents which stimulate spermatogenesis also stimulate transferrin mRNA accumulation in cultured Sertoli cells. Testosterone, however, has only a small stimulatory effect on the cultured Sertoli cells. In the in vivo measurements we have completed thus far, the level of transferrin mRNA in the testis seems to correlate well with the spermatogenic condition of the testis. In immature rats, hypophysectomized rats, and vitamin A deficient rats, spermatogenesis is abbreviated and the levels of transferrin mRNA in the Sertoli cells are correspondingly low. If this correlation holds up under additional scrutiny, assays of the transferrin mRNA levels may be effective screens for the toxic or stimulatory activities of a variety of pharmaceuticals which could affect spermatogenesis.

Animals↗