Sertoli cell proteins in the human seminiferous tubule

Understanding the Underlying Molecular Mechanisms of Meiotic Arrest during In Vitro Spermatogenesis in Rat Prepubertal Testicular Tissue

In vitro spermatogenesis appears to be a promising approach to restore the fertility of childhood cancer survivors. The rat model has proven to be challenging, since germ cell maturation is arrested in organotypic cultures. Here, we report that, despite a meiotic entry, abnormal synaptonemal complexes were found in spermatocytes, and in vitro matured rat prepubertal testicular tissues displayed an immature phenotype. RNA-sequencing analyses highlighted up to 600 differentially expressed genes between in vitro and in vivo conditions, including genes involved in blood-testis barrier (BTB) formation and steroidogenesis. BTB integrity, the expression of two steroidogenic enzymes, and androgen receptors were indeed altered in vitro. Moreover, most of the top 10 predicted upstream regulators of deregulated genes were involved in inflammatory processes or immune cell recruitment. However, none of the three anti-inflammatory molecules tested in this study promoted meiotic progression. By analysing for the first time in vitro matured rat prepubertal testicular tissues at the molecular level, we uncovered the deregulation of several genes and revealed that defective BTB function, altered steroidogenic pathway, and probably inflammation, could be at the origin of meiotic arrest.

Immunohistochemical Localization of Insulin-Like Growth Factor-I Receptor (IGF-IR) in the Developing and Mature Rat Testes

It has been suggested that insulin-like growth factor-I (IGF-I) plays an important role in the regulation of spermatogenesis in the testes. Its signal is mediated predominantly by the IGF-I receptor (IGF-IR). Signalling through IGF-IR has been shown to have a potent survival function. IGF-IR, a transmembrane tyrosine kinase, is widely expressed across many cell types. In this study, we demonstrated the distribution of IGF-IR in testes of differently aged rats. Anti-IGF-IR is a rabbit polyclonal antibody raised against a peptide mapping at the carboxy terminus of the IGF-IR of human origin. Testicular specimens were fixed in Bouin's solution and embedded in paraffin. The paraffin-embedded sections were processed for standard immunohistochemistry by the labelled streptavidin-biotin technique. At postnatal day 19, IGF-IR immunoreactivity was seen moderately in spermatogonia, and slightly both in leptotene and zygotene primary spermatocytes. At postnatal day 35, immunoreactivity was seen slightly both in the pachytene primary spermatocytes and Leydig cells. Although there was intense immunoreactivity in the Leydig cells and in the elongated spermatids on days 50 and 70, the intensity of reaction was decreased in the elongated spermatids in the 10th month. Our results suggest that IGF-IR may play significant roles in testicular function and germ cell development.

Expression and localization of growth factors and their receptors in the mammalian testis. Part I: Fibroblast growth factors and insulin-like growth factors

It is now well established that normal development and function of testis are mediated by endocrine and paracrine pathways including hormones, growth factors and cytokines as well as by direct cell-to-cell contacts depending on tight, adhering and gap junctions. In the last two decades, several growth factors were identified in the testis of various mammalian species. Growth factors are shown to promote cell proliferation, regulate tissue differentiation, and modulate organogenesis. Interestingly, most of these peptides are expressed not only in the adult mammalian testis during spermatogenesis but also during testicular morphogenesis in prenatal and postnatal life. Our study was launched to provide an overview of the expression, localization, and putative physiological roles of growth factors and their receptors in the mammalian testis. The growth factors considered in this part of our review are fibroblast growth factors and insulin-like growth factors. These factors are found in testicular cells in prenatal, postnatal, and adult animals and are implicated in the regulation of important testicular activities including testicular cord morphogenesis, modulation of testicular hormone secretion and control of spermatogenesis.

Role of the transcriptional coactivator CBP/p300 in linking basic helix-loop-helix and CREB responses for follicle-stimulating hormone-mediated activation of the transferrin promoter in Sertoli cells

Sertoli cells are the epithelial cells responsible for the onset of pubertal development and the maintenance of spermatogenesis in the adult. Transferrin is one of the major secretory products expressed by differentiated Sertoli cells. Investigation of the transcriptional control of transferrin gene expression provides insight regarding the regulation of Sertoli cell differentiation. The optimal activation of the mouse transferrin promoter (mTf) by FSH requires the synergistic actions of the cAMP response element-binding protein (CREB) binding to the cAMP response element-like proximal region II (PRII) and the basic helix-loop-helix (bHLH) binding to the E-box. Proximal region II alone is sufficient for cAMP-mediated activation. The proximity of the PRII and E-box (220 base pairs apart) suggests the possibility of interaction between CREB and bHLH proteins. Such an interaction can be mediated by transcriptional integrators such as CREB-binding protein (CBP) and/or p300 and may stabilize the binding of trans-acting factors to their respective cis-elements. Such an interaction may also provide a mechanism for cell-specific promoter activation. The hypothesis tested in this study was that CBP/p300 is required for the synergistic activation of the transferrin promoter involving PRII and E-box through the formation of a ternary complex. In the Sertoli cells, both CBP and p300 proteins are expressed. The effect of CBP/p300 on transferrin promoter activation and, hence, Sertoli cell function was studied by using antisense oligonucleotides (AS-oligo). In the presence of CBP/p300 AS-oligo, activity of the FSH-induced mTf-chloramphenicol acetyl transferase (CAT) was significantly lower as compared to the respective controls. Interestingly, AS-oligo had no effect on cAMP-induced activation of the transferrin promoter reporter construct (mTf-CAT). Mutations in the E-box (EB*) significantly reduced the FSH response. The presence of AS-oligo had no further effect on the FSH-mediated activation of the EB*-mTf-CAT construct but reduced cAMP-mediated activation. Mutations in the CRE-like PRII (PRII*) also significantly reduced the FSH response. Activation of the PRII*-mTf-CAT in response to cAMP was completely abolished. The presence of AS-oligo had no further effect on the FSH- or cAMP-mediated activation of the PRII*-mTf-CAT construct. In Sertoli cells, CBP/p300 was coimmunoprecipitated with CREB and the bHLH protein E47. These observations suggest that CBP/p300 appears to be involved in regulating FSH-mediated activation of the transferrin promoter by linking bHLH and CREB activities.

Physiopathology of spermatogenic arrest

OBJECTIVE

To review the world literature on the etiology, physiopathology, and treatment of spermatogenesis arrest.

STUDY SELECTION

All the pertinent literature on spermatogenic arrest has been selected. Most studies related to this topic have been identified through Medline and through published literature.

PATIENTS

Spermatogenic arrest has been diagnosed by testicular biopsy in men of reproductive age who had either severe oligospermia (partial arrest) or azoospermia (complete arrest), normal testicular volume, and depending on the etiology normal, high, or low levels of gonadotropins.

INTERVENTIONS

The effects of heat, radiotherapy, and chemotherapy have been reported. Depending on the etiology of spermatogenic arrest, different hormonal treatments have been tested.

MAIN OUTCOME MEASURE

Level of interruption of germ cell differentiation in testicular biopsy have been determined. Improvement of the sperm count or appearance of mature sperm after an hormonal treatment have been observed.

RESULTS

Spermatogenic arrest can occur at spermatogonial level in case of gonadotropin insufficiency or after germ cell damage due to chemotherapy or radiotherapy. The arrest is most frequently observed at primary spermatocyte level. Reversible arrest at that level can be due to heat, infections, hormonal and nutritional factors. Irreversible arrest at primary spermatocyte or spermatid level have a genetic origin due to chromosomes anomalies either in somatic cells or in germ cells.

CONCLUSIONS

Spermatogenic arrest is usually due to genetic factors resulting in irreversible azoospermia. However some cases may be consecutive to hormonal, thermic, or toxic factors and may be reversible either spontaneously or after a specific treatment.

Anatomy of the insulin-like growth factor system in the human testis

OBJECTIVE

To study the cellular patterns of gene expression for insulin-like growth factors I and II (IGF-I and IGF-II), their receptors and specific high-affinity binding proteins (IGFBPs) in the human testis.

DESIGN

In situ hybridization histochemistry was used to localize messenger ribonucleic acids (mRNAs) for IGF-I and IGF-II, the IGF-I and IGF-II receptors and IGFBP-1 to 6 in fresh-frozen testis sections from healthy young men who died of trauma.

RESULTS

Insulin-like growth factor I mRNA was not detected. Insulin-like growth factors II mRNA was abundant in testicular blood vessels and peritubular connective tissue. Both IGF-I and IGF-II receptor mRNAs were most abundant in the germinal epithelium. Insulin-like growth factor binding protein 1 mRNA was not detected. Binding protein-2 mRNA was expressed in both Leydig and Sertoli cells. Binding protein-3 mRNA was detected only in the endothelium of testicular blood vessels. Binding protein-4 mRNA was also localized in endothelium but, in addition, was present in Leydig cells and interstitial connective tissue. Binding protein-5 mRNA was abundant in connective tissue and was detected at low levels in Leydig cells. Binding protein-6 mRNA was present in some of the peritubular cells and in some cells of the interstitial compartment.

CONCLUSION

Our results suggest that IGFs may play significant roles in testicular function and germ cell development.

Growth factors and testicular development

During the last 5 years significant advances have been achieved in defining the endocrine, paracrine and cellular interactions required for normal testicular development. Numerous paracrine factors are likely to regulate spermatogenesis throughout the cycle of the seminiferous epithelium. These factors create the local hormonal milieu required for germ cell proliferation, meiosis and differentiation. The studies of the c-kit oncogene and the stem cell growth factor in the migration and survival of the primordial germ cells to the genital ridge during development have defined at least 1 important role of growth factors in spermatogenesis. 72, 142-146, 148, 149, 154, 159 It is likely that in the next 5 years the role of many of these other paracrine factors in the regulation of testicular development will be determined.

Sertoli-germ cells interactions in the human testis

In previous histoimmunochemical studies we reported that transferrin (TF) and insulin-like growth factor I (IGF-I) are present in the cytoplasm of the Sertoli cells of the adult human testis. Receptors for TF were found mainly in adluminal germ cells and type I receptors for IGF-I both in Sertoli and germ cells. Using electron microscopy, evidence of transfer of both TF and IGF-I from the Sertoli to the germ cells through a receptor-mediated endocytosis mechanism was also found. In this paper we report the results of the histoimmunochemical localization of alpha inhibin in the human fetal, prepubertal and adult testis. In 8- to 14-week-old fetal testes a positive immunostaining was found mainly in the interstitial cells, whereas no staining was found in the germ cords. In the prepubertal testis the immunostaining was present in the Sertoli cells but not in the interstitial cells. In the adult human testis the immunostaining was present not only in the Sertoli cells but also in the spermatocytes and in several Leydig cells. Using electron microscopy and immunogold labeling the presence of alpha inhibin immunoreactivity was found in the rough endoplasmic reticulum and in the Golgi cisternae of both Sertoli and Leydig cells. Moreover we found evidence of transfer of alpha inhibin from the Sertoli to the germ cells through receptor-mediated endocytosis.

Immunolocalization of inhibin alpha-subunit in the human testis. A light- and electron-microscopy study

The localization of inhibin alpha-subunit in the human testis was studied at the light- and electron-microscope level with immunostaining techniques. Antibodies against specific fragments of porcine and human inhibin alpha-subunits were utilized. At light microscopy, inhibin alpha-subunit immunoreactivity was detected in Sertoli cells, spermatocytes and in some Leydig cells. At electron microscopy, gold labeling was found in the cisternae of the Golgi apparatus and in the endoplasmic reticulum of Sertoli and Leydig cells. Gold labeling for inhibin was also found in coated vesicles in the cytoplasm of Sertoli cells as well as in coated pits and coated vesicles in the cytoplasm of some spermatocytes. The results of the present study suggest that, in the human testis, inhibin is produced by Sertoli and Leydig cells and is taken up by spermatocytes, on which it might act in a paracrine manner.

Albumin localization in the testis of adult golden hamsters by use of immunohistochemistry

There is an increasing interest in different biochemical roles of albumin (Alb) in respect to testicular function. For this reason, Alb was localized by the peroxidase-antiperoxidase technique in the testis of adult golden hamsters. A strong Alb immunoreactivity occurred in the interstitial space and on the surface of Leydig cells. A few Sertoli cells showed a strong Alb response under the appearance of so-called leakages traversing Sertoli-Sertoli cell junctions. Spermatogonia reacted strongly, while spermatids and sperms showed rather a mild, or moderate response. Spermatocytes remained unstained. When similar maturation stages of seminiferous tubules were compared, the number of reacting cells varied strikingly. Our results support the assumption that Alb or a protein with an Alb-like immunoreactivity exerts diverse functions of the testis.