Multiple cadherin superfamily members with unique expression profiles are produced in rat testis

Classical cadherins in the testis: how are they regulated?

Cadherins (CDH) are crucial intercellular adhesion molecules, contributing to morphogenesis and creating tissue barriers by regulating cells' movement, clustering and differentiation. In the testis, classical cadherins such as CDH1, CDH2 and CDH3 are critical to gonadogenesis by promoting the migration and the subsequent clustering of primordial germ cells with somatic cells. While CDH2 is present in both Sertoli and germ cells in rodents, CDH1 is primarily detected in undifferentiated spermatogonia. As for CDH3, its expression is mainly found in germ and pre-Sertoli cells in developing gonads until the establishment of the blood-testis barrier (BTB). This barrier is made of Sertoli cells forming intercellular junctional complexes. The restructuring of the BTB allows the movement of early spermatocytes toward the apical compartment as they differentiate during a process called spermatogenesis. CDH2 is among many junctional proteins participating in this process and is regulated by several pathways. While cytokines promote the disassembly of the BTB by enhancing junctional protein endocytosis for degradation, testosterone facilitates the assembly of the BTB by increasing the recycling of endocytosed junctional proteins. Mitogen-activated protein kinases (MAPKs) are also mediators of the BTB kinetics in many chemically induced damages in the testis. In addition to regulating Sertoli cell functions, follicle stimulating hormone can also regulate the expression of CDH2. In this review, we discuss the current knowledge on regulatory mechanisms of cadherin localisation and expression in the testis.

The transcription factors Junb and Fosl2 cooperate to regulate Cdh3 expression in 15P-1 Sertoli cells

In Sertoli cells of the testis, cadherins (Cdh) are important cell-to-cell interaction proteins and contribute to the formation of the blood-testis barrier being essential for germ cells' protection. P-cadherin or Cdh3 is only expressed in Sertoli cells from embryonic to prepubertal development. Interestingly, the expression profile of Cdh3 correlates with that of activating protein-1 (AP-1) transcription factors during Sertoli cells development. To assess their potential implications in the regulation of Cdh3, different AP-1 transcription factors were overexpressed in 15P-1 Sertoli cells. We found that the overexpressions of Junb and Fosl2 activated Cdh3 promoter. ChIP-qPCR assay and luciferase reporter assay with 5' promoter deletions and site-directed mutagenesis confirmed the recruitment of Junb and Fosl2 to an AP-1 regulatory element at -47 bp in the proximal region of Cdh3 promoter in 15P-1 cells. These findings were further supported by histone modification markers and chromatin accessibility surrounding Cdh3 promoter in mouse testis. Moreover, the knockdowns of Junb and/or Fosl2 by siRNA decreased Cdh3 protein levels. Taken together, these data suggest that in 15P-1 Sertoli cells, the AP-1 family members Junb and Fosl2 are responsible for the regulation of Cdh3 expression, which requires the recruitment of both factors to the proximal region of the Cdh3 promoter.

The Central Role of Cadherins in Gonad Development, Reproduction, and Fertility

Cadherins are a group of membrane proteins responsible for cell adhesion. They are crucial for cell sorting and recognition during the morphogenesis, but they also play many other roles such as assuring tissue integrity and resistance to stretching, mechanotransduction, cell signaling, regulation of cell proliferation, apoptosis, survival, carcinogenesis, etc. Within the cadherin superfamily, E- and N-cadherin have been especially well studied. They are involved in many aspects of sexual development and reproduction, such as germline development and gametogenesis, gonad development and functioning, and fertilization. E-cadherin is expressed in the primordial germ cells (PGCs) and also participates in PGC migration to the developing gonads where they become enclosed by the N-cadherin-expressing somatic cells. The differential expression of cadherins is also responsible for the establishment of the testis or ovary structure. In the adult testes, N-cadherin is responsible for the integrity of the seminiferous epithelium, regulation of sperm production, and the establishment of the blood-testis barrier. Sex hormones regulate the expression and turnover of N-cadherin influencing the course of spermatogenesis. In the adult ovaries, E- and N-cadherin assure the integrity of ovarian follicles and the formation of corpora lutea. Cadherins are expressed in the mature gametes and facilitate the capacitation of sperm in the female reproductive tract and gamete contact during fertilization. The germ cells and accompanying somatic cells express a series of different cadherins; however, their role in gonads and reproduction is still unknown. In this review, we show what is known and unknown about the role of cadherins in the germline and gonad development, and we suggest topics for future research.

Effect of the combined administration of vitamin-E and 5-aminosalicylic acid on acrylamide-induced testicular toxicity

OBJECTIVES

This study aimed to evaluate the comparative protective antioxidant effect of 5-aminosalicylic acid (5-ASA) and vitamin-E against acrylamide (ACR)-induced testicular toxicity in rats.

METHODS

This study was performed at King Fahad Medical Research Centre, Jeddah, KSA. A total of 49 adult Wistar rats (250 ± 20 gm) that were 60 days old were divided into seven groups (control, ACR alone, ACR + 5-ASA, ACR + Vitamin-E, ACR + 5-ASA + Vitamin-E, Vitamin-E alone, 5-ASA alone). Acrylamide [45 mg/kg (bw)/day] and vitamin-E [200 mg/kg (bw)/day] were gavaged orally, and 5-ASA [25 mg/kg (bw)/day] were injected intra-peritoneally for five consecutive days after one day of observation. Rats were sacrificed by cervical dislocation. Histopathology of the testis, enzyme linked immunosorbent assay (ELISA) of testosterone, the lactate dehydrogenase (LDH) assay and a caudal sperm count were performed.

RESULTS

Rats treated with ACR showed signs of aggression and rough coats, with reduced food and water intake. ACR treated rats showed histopathological changes in the form of a sloughed seminiferous epithelium in the tubular lumen with no multinucleated giant cells. Shrinkage of seminiferous tubules with widening of the interstitial space was also observed with atrophy and the shedding of normal mucosa. Our results indicated that maximum protection was conveyed by the combined antioxidant effect of vitamin-E and 5-ASA on testicular histopathology.

CONCLUSION

We conclude that acrylamide-induced degeneration of seminiferous tubules can be partially reversed by the administration of 5-ASA and vitamin-E and suggests restricting exposure to ACR.

Understanding cadherin EGF LAG seven-pass G-type receptors

The cadherin epidermal growth factor (EGF) laminin G (LAG) seven-pass G-type receptors (CELSRs) are a special subgroup of adhesion G protein-coupled receptors, which are pivotal regulators of many biologic processes such as neuronal/endocrine cell differentiation, vessel valve formation, and the control of planar cell polarity during embryonic development. All three members of the CELSR family (CELSR1-3) have large ecto-domains that form homophilic interactions and encompass more than 2000 amino acids. Mutations in the ecto-domain or other gene locations of CELSRs are associated with neural tube defects and other diseases in humans. Celsr knockout (KO) animals have many developmental defects. Therefore, specific agonists or antagonists of CELSR members may have therapeutic potential. Although significant progress has been made regarding the functions and biochemical properties of CELSRs, our knowledge of these receptors is still lacking, especially considering that they are broadly distributed but have few characterized functions in a limited number of tissues. The dynamic activation and inactivation of CELSRs and the presence of endogenous ligands beyond homophilic interactions remain elusive, as do the regulatory mechanisms and downstream signaling of these receptors. Given this motivation, future studies with more advanced cell biology or biochemical tools, such as conditional KO mice, may provide further insights into the mechanisms underlying CELSR function, laying the foundation for the design of new CELSR-targeted therapeutic reagents. The cadherin EGF LAG seven-pass G-type receptors (CELSRs) are a special subgroup of adhesion G protein-coupled receptors (GPCRs), which have large ecto-domains that form homophilic interactions and encompass more than 2000 amino acids. Recent studies have revealed that CELSRs are pivotal regulators of many biological processes, such as neuronal/endocrine cell differentiation, vessel valve formation and the control of planar cell polarity during embryonic development.

SOX8 regulates permeability of the blood-testes barrier that affects adult male fertility in the mouse

Sertoli cells provide nutritional and physical support to germ cells during spermatogenesis. Sox8 encodes a member of the high mobility group of transcription factors closely related to Sox9 and Sox10. Sertoli cells express SOX8 protein, and its elimination results in an age-dependent dysregulation of spermatogenesis, causing adult male infertility. Among the claudin genes with altered expression in the Sox8(-/-) testes, was claudin-3, which is required for the regulation and maintenance of the blood-testes barrier (BTB). Because the BTB is critical in restricting small molecules in the luminal compartment of the seminiferous tubules, the aim of this study was to analyze the level of tight junction proteins (claudin-3, claudin-11, and occludin) and BTB permeability in Sox8(-/-) adult testes. The acetylation level of alpha-tubulin and microtubule organization was also evaluated because microtubules are critical in maintaining the microenvironment of the seminiferous epithelium. Western blot analysis shows that claudin-3 protein is decreased in Sox8(-/-) testes. Chromatin immunoprecipitation confirmed that SOX8 binds at the promoter region of claudin-3. Claudin-3 was localized to the Sertoli cell tight junctions of wild-type testes and significantly decreased in the Sox8(-/-) testes. The use of biotin tracers showed increased BTB permeability in the Sox8(-/-) adult testes. Electron microscopy analysis showed that microtubule structures were destabilized in the Sox8(-/-) testes. These results suggest that Sox8 is essential in Sertoli cells for germ cell differentiation, partly by controlling the microenvironment of the seminiferous epithelium.

Asynchronous expression of the homeodomain protein CUX1 in Sertoli cells and spermatids during spermatogenesis in mice

The homeodomain CUX1 protein exists as multiple isoforms that arise from proteolytic processing of a 200-kDa protein or an alternate splicing or from the use of an alternate promoter. The 200-kDa CUX1 protein is highly expressed in the developing kidney, where it functions to regulate cell proliferation. Transgenic mice ectopically expressing the 200-kDa CUX1 protein develop renal hyperplasia associated with reduced expression of the cyclin kinase inhibitor p27. A 55-kDa CUX1 isoform is expressed exclusively in the testes. We determined the pattern and timing of CUX1 protein expression in developing testes. CUX1 expression was continuous in Sertoli cells from prepubertal testes but became cyclic when spermatids appeared. In testes from mature mice, CUX1 was highly expressed only in round spermatids at stages IV-V of spermatogenesis, in both spermatids and Sertoli cells at stages VI-X of spermatogenesis, and only in Sertoli cells at stage XI of spermatogenesis. While most of the seminiferous tubules in wild-type mice were between stages VI and X of spermatogenesis, there was a significant reduction in the percentage of seminiferous tubules between stages VI and X in Cux1 transgenic mice and a significant increase in the percentage of seminiferous tubules in stages IV-V and XI. Moreover, CUX1 was not expressed in proliferating cells in testes from either wild-type or transgenic mice. Thus, unlike the somatic form of CUX1, which has a role in cell proliferation, the testis-specific form of CUX1 is not involved in cell division and appears to play a role in signaling between Sertoli cells and spermatids.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 5: intercellular junctions and contacts between germs cells and Sertoli cells and their regulatory interactions, testicular cholesterol, and genes/proteins associated with more than one germ cell generation

In the testis, cell adhesion and junctional molecules permit specific interactions and intracellular communication between germ and Sertoli cells and apposed Sertoli cells. Among the many adhesion family of proteins, NCAM, nectin and nectin-like, catenins, and cadherens will be discussed, along with gap junctions between germ and Sertoli cells and the many members of the connexin family. The blood-testis barrier separates the haploid spermatids from blood borne elements. In the barrier, the intercellular junctions consist of many proteins such as occludin, tricellulin, and claudins. Changes in the expression of cell adhesion molecules are also an essential part of the mechanism that allows germ cells to move from the basal compartment of the seminiferous tubule to the adluminal compartment thus crossing the blood-testis barrier and well-defined proteins have been shown to assist in this process. Several structural components show interactions between germ cells to Sertoli cells such as the ectoplasmic specialization which are more closely related to Sertoli cells and tubulobulbar complexes that are processes of elongating spermatids embedded into Sertoli cells. Germ cells also modify several Sertoli functions and this also appears to be the case for residual bodies. Cholesterol plays a significant role during spermatogenesis and is essential for germ cell development. Lastly, we list genes/proteins that are expressed not only in any one specific generation of germ cells but across more than one generation.

Molecular cloning and expression of a new gene, GON-SJTU1 in the rat testis

BACKGROUND

Spermatogenesis is a complex process involving cell development, differentiation and apoptosis. This process is governed by a series of genes whose expressions are highly regulated. Male infertility can be attributed to multiple genetic defects or alterations that are related to spermatogenesis. The discovery, cloning and further functional study of genes related to spermatogenesis is of great importance to the elucidation of the molecular mechanism of spermatogenesis. It is also physiologically and pathologically significant to the therapy of male infertility.

METHODS

GON-SJTU1 was identified and cloned from rat testis by cDNA library screening and 3'-and 5'-RACE. The products of GON-SJTU1 were assessed by Northern and Western blotting. The expression of GON-SJTU1 was also examined by In situ hybridization and immunohistochemistry.

RESULTS

Here we identified and cloned a new gene, GON-SJTU1, with the biological process of spermatogenesis. GON-SJTU1 is highly expressed in the testis from day 1 to 15 and then decreased, suggesting that GON-SJTU1 might be a time-related gene and involved in the early stage of spermatogenesis. And the expression of GON-SJTU1 in the testis occurred in some male germ cells, particularly in gonocytes and spermatogonial stem cells.

CONCLUSION

GON-SJTU1 may play a role in the biological process of spermatogenesis.

Expression of protocadherin-1 (Pcdh1) during mouse development

Protocadherin-1 (Pcdh1) is a member of the delta-protocadherin subgroup of non-clustered protocadherins. We studied the expression of Pcdh1 from the early embryonic to the adult stage of mouse development by semi-quantitative RT-PCR and in situ hybridization. Pcdh1 can be detected as early as embryonic day 9.5. In early embryogenesis, expression is especially prominent in blood vessels. During later development and in the adult mouse, organs derived from the embryonic gut, such as the esophagus, intestines, liver, lung, and submandibular gland, contain epithelia and other types of tissues that are Pcdh1-positive. Other positive organs include the brain, spinal cord, retina, peripheral ganglia, the inner ear, hair follicles, kidney, vagina, uterus, placenta, testis, prostate, and the seminal gland. The tight spatial and temporal regulation of Pcdh1 expression suggests that this protocadherin plays multiple roles not only during development but also in mature tissues and organs in the mouse.

CDH1 is a specific marker for undifferentiated spermatogonia in mouse testes

In the mammalian testis, spermatogenesis is initiated from a subset of stem cells belonging to undifferentiated type A spermatogonia. In spite of the biologic significance of undifferentiated type A spermatogonia, little is known about their behavior and properties because of a lack of specific cell surface markers. Here we show that CDH1 (previously known as E-cadherin) is expressed specifically in undifferentiated type A spermatogonia in the mouse testis. Histologic analysis showed that CDH1-positive cells had all the characteristics of undifferentiated type A spermatogonia. Whole-mount immunohistochemistry showed that CDH1-positive cells made clusters mainly comprising one, two, four, or eight cells. They survived after administration of the cytotoxic agent busulfan to mice, and then regenerated seminiferous epithelia. Transplantation experiments showed that only CDH1-positive cells had colonizing activity in the recipient testis. Our data clearly demonstrated that spermatogenic stem cells reside among undifferentiated type A spermatogonia, which express CDH1.

Switch of cadherin expression from E- to N-type during the activation of rat hepatic stellate cells

The activation of hepatic stellate cell (HSC) is a common pathway leading to hepatic fibrosis. However, the molecular mechanisms underlying HSC activation remain obscure. To elucidate the nature of the HSC activation, we investigated the expression of E-cadherin and its switch to N-cadherin during rat HSC activation, in vivo and in vitro. Immunohistochemical and immunocytochemical staining were performed to identify the expressions of E-cadherin, N-cadherin, and beta-catenin in rat HSCs, in vivo and in vitro. Serial changes in the expressions of these adhesion molecules during the spontaneous activation of cultured rat HSCs were also demonstrated by RT-PCR and by immunoblotting. E-cadherin and beta-catenin were expressed on opposing cell membranes of GFAP-positive rat HSCs and adjacent hepatocytes in vivo, and between desmin-positive rat HSCs in vitro. With the progression of rat HSC activation in tissue and in culture, E-cadherin disappeared gradually, whereas N-cadherin appeared at the cell periphery. The results of RT-PCR and immunoblotting were concordant with immunocytochemistry findings. In conclusion, resting rat HSCs express E-cadherin and beta-catenin both in vivo and in vitro, and E-cadherin switches to N-cadherin during HSC activation. These results suggest that HSC activation represents transdifferentiation from an epithelial to a mesenchymal phenotype.

Cadherin in developing and maturing cysts of Torpedo Marmorata Testis

We investigated the presence of cadherins, Ca++ dependent cell-cell adhesion molecules, during the development and maturation of cysts in the testis of the spotted ray Torpedo marmorata. Using different anti-cadherin antibodies, we provide evidence by means of immunohistochemistry and immunoblotting that cadherins are involved in the interaction between Sertoli and germ cells. During the development and maturation of cysts, in fact, cadherins occur between Sertoli and germ cells when they begin to interact to build a cyst. Later on, the presence of cadherins between Sertoli and germ cells persists; furthermore, during the formation of spermatoblast, it is also evident at the level of indentations, arising from Sertoli cells and encompassing germ cells. Finally, the present findings strongly suggest that cadherins are also involved in the spermiogenesis as germ cells, when male gamete differentiation starts, are intensively stained, while, when spermiation is completed, the spermatozoa appear unlabeled.

Mono-(2-ethylhexyl) Phthalate Rapidly Increases Celsr2 Protein Phosphorylation in HeLa Cells via Protein Kinase C and Casein Kinase 1

Phthalates are ubiquitous environmental contaminants that target the fetal and pubertal testis and lead to alterations in endocrine and spermatogenic function. Some features of phthalate-induced testicular injury suggest that phthalates alter Sertoli-germ cell adhesion and G protein signaling. Celsr2 is a unique protein that has structural characteristics of both an adhesion molecule and a G protein coupled receptor (GPCR) and has been demonstrated to function in Sertoli-germ cell adhesion. Within 2 h of a 1-g/kg mono-(2-ethylhexyl) phthalate (MEHP) exposure, in vivo Sertoli cell celsr2 localization was altered; celsr2 immunostaining became concentrated in the basal aspect of Sertoli cells, and then a diffuse pattern emerged. Because GPCRs are regulated by phosphorylation, the hypothesis that phthalate exposure induces the phosphorylation of celsr2 was tested by examining phosphorylation in celsr2-transfected HeLa cells treated with MEHP. At concentrations of 1 microM or greater, MEHP transiently increased celsr2 phosphorylation on serine/threonine residues; celsr2 phosphorylation was increased by 15 min of exposure and returned to control levels after 60 min. Cells exposed to the inactive phthalate monoester mono-methyl phthalate showed no change in celsr2 phosphorylation. In addition, phosphorylation of the endogenous HeLa cell GPCR, Chemokine Receptor 4 (CXCR4), was not altered by exposure to MEHP. Inhibition of protein kinase C or casein kinase 1 prevented MEHP-induced celsr2 phosphorylation, while inhibition of protein kinase A or mitogen-activated protein kinase had no effect. These data show that MEHP exposure rapidly alters testicular celsr2 immunolocalization as well as celsr2 posttranslational modification in a model cell line.

Flutamide depresses expression of cortactin in the ectoplasmic specialization between the Sertoli cells and spermatids in the mouse testis

Flutamide (FLUT) has potent anti-androgenic activity and is used in the medical field and in a screening test to detect endocrinologically active compounds. Our previous study demonstrated that FLUT induced histological deformation of spermatids and ultrastructural defects of the apical ectoplasmic specialization (ES) in the mouse testis. The apical ES is an actin-based junctional structure between the Sertoli cells and germ cells. Cortactin, an actin-binding protein, is found in the actin layer of ES. The protein level of cortactin was decreased in FLUT-treated testes as shown by Western blot analysis. The detailed analysis indicated that the protein level was drastically decreased in FLUT-treated seminiferous tubules of stages from VI to IX. Immunohistochemistry and immunoelectron microscopy showed that FLUT depressed cortactin expression in the apical ES. In addition, the effect of FLUT on cortactin localization appeared between 12 h and 8 days (about 180 h) after a one-day treatment. These results suggest that FLUT depressed the expression of cortactin in the apical ES with stage specificity. Therefore, the initial target of FLUT may be the cell-cell interactions between the Sertoli and germ cells. To our knowledge, this study is the first to document the decrease of cortactin expression in the abnormal apical ES following treatment with FLUT.

Gene expression in the spermatogenically inactive "dark" and maturing "light" testicular tissues of the prepubertal colt

In the testis of the 1.5-year-old horse, spermatogenesis initiates locally in grossly light, central areas that contrast with grossly dark, peripheral areas that are as yet inactive in spermatogenesis. Gene expression was compared between "light" and "dark" tissues of 1.5-year-old horse testes to identify mechanisms important to the initiation of spermatogenesis. Microarrays containing human cDNAs were used to assess expression levels of 9132 genes simultaneously in matched pairs of dark and light testis tissues from 3 prepubertal colts. In all 3 analyses, dysferlin (DYS), down-regulated in ovarian cancer 1 (DOC1), and Golgi apparatus protein 1 (GLG1) genes were preferentially expressed in dark tissues, while outer dense fiber of sperm tails (ODF2) and phosphodiesterase 3B (PDE3B) genes were more highly expressed in light testis tissue (>1.7 balanced difference value, Incyte GEM tools software). Expression levels of 88 additional genes appeared to be different between dark and light tissues in 2 of the 3 microarray analyses. The preferential expression of DYS, DOC1, ODF2, and PDE3B genes in dark or light testis tissues was confirmed on Northern blots and localized to cell types by in situ hybridization. Future studies to determine the role of genes regulated during the initiation of spermatogenesis may aid in elucidating molecular mechanisms during this critical time as well as in identifying new therapies for enhancing male fertility.

EFFECTS OF MALE REPRODUCTIVE TOXICANTS ON GENE EXPRESSION IN RAT TESTES

Predictive biomarkers of testicular toxicity are needed for an efficient development of drugs. The purpose of the present study was to obtain further insight into the toxicity mechanisms of various male reproductive toxicants and to detect genomic biomarkers for rapid screening of testicular toxicity. Four reproductive toxicants, 2,5-hexanedione (Sertoli cells toxicant), ethylene glycol monomethyl ether (EGME; spermatocytes toxicant), cyclophosphamide (spermatogonia toxicant) and sulfasalazine, were orally administered to male rats once. Six hours after the single dosing, gene expression in the testes was monitored by cDNA microarray and real-time RT-PCR and the testes were histopathologically examined. No histopathological abnormality was detected except for slight degeneration of spermatocytes in the EGME-treated testes. cDNA microarray analysis revealed differential gene expression profiles, and it was possible based on the profiles to characterize the action of the compounds in the testes. Interestingly, 3 spermatogenesis-related genes -- heat shock protein 70-2, insulin growth factor binding protein 3 and glutathione S transferase pi -- were affected by all the compounds. The above changes of gene expression were detectable within a short period after the dosing prior to the appearance of obvious pathological changes. These data suggest that cDNA microarray is a useful technique for evaluation of primary testicular toxicity. Furthermore, we propose the above 3 spermatogenesis-related genes as potential biomarkers of testicular toxicity.

Sertoli-Sertoli and Sertoli-germ cell interactions and their significance in germ cell movement in the seminiferous epithelium during spermatogenesis

Spermatogenesis is the process by which a single spermatogonium develops into 256 spermatozoa, one of which will fertilize the ovum. Since the 1950s when the stages of the epithelial cycle were first described, reproductive biologists have been in pursuit of one question: How can a spermatogonium traverse the epithelium, while at the same time differentiating into elongate spermatids that remain attached to the Sertoli cell throughout their development? Although it was generally agreed upon that junction restructuring was involved, at that time the types of junctions present in the testis were not even discerned. Today, it is known that tight, anchoring, and gap junctions are found in the testis. The testis also has two unique anchoring junction types, the ectoplasmic specialization and tubulobulbar complex. However, attention has recently shifted on identifying the regulatory molecules that "open" and "close" junctions, because this information will be useful in elucidating the mechanism of germ cell movement. For instance, cytokines have been shown to induce Sertoli cell tight junction disassembly by shutting down the production of tight junction proteins. Other factors such as proteases, protease inhibitors, GTPases, kinases, and phosphatases also come into play. In this review, we focus on this cellular phenomenon, recapping recent developments in the field.

Identification of tissue-restricted transcripts in human islets

The purpose of our study was to identify transcripts specific for tissue-restricted, membrane-associated proteins in human islets that, in turn, might serve as markers of healthy or diseased islet cell masses. Using oligonucleotide chips, we obtained gene expression profiles of human islets for comparison with the profiles of exocrine pancreas, liver, and kidney tissue. As periislet presence of type 1 interferon is associated with the development of type 1 diabetes, the expression profile of human islets treated ex vivo with interferon-alpha2beta (IFNalpha2beta) was also determined. A set of genes encoding transmembrane- or membrane-associated proteins with novel islet-restricted expression was resolved by determining the intersection of the islet set with the complement of datasets obtained from other tissues. Under the influence of IFNalpha2beta, the expression levels of transcripts for several of the identified gene products were up- or down-regulated. One of the islet-restricted gene products identified in this study, vesicular monoamine transporter type 2, was shown to bind [3H]dihydrotetrabenazine, a ligand with derivatives suitable for positron emission tomography imaging. We report here the first comparison of gene expression profiles of human islets with other tissues and the identification of a target molecule with possible use in determining islet cell masses.

Protocadherin α3 Acts at Sites Distinct from Classic Cadherins in Rat Testis and Sperm1

The testis expresses a variety of cadherin superfamily members including classic cadherins and protocadherins. This report describes the first localization of a protocadherin protein in testis and sperm. After cloning rat cDNAs for protocadherin alpha3 and alpha4, isoform-specific polyclonal antibodies were generated against protocadherin alpha3. Western blotting of rat testis showed that protocadherin alpha3 was solubilized completely by Triton X-100, in contrast to the adhesion junction components N-cadherin, beta-catenin, and p120 catenin. Corroborating this data, protocadherin alpha3 was immunolocalized to the spermatid acrosomal area, intercellular bridge, and flagellum, but not classic cadherin-based adhesion junctions. Acrosome-associated protocadherin alpha3 was first detected at step 8 of spermiogenesis, and this association remained on cauda epididymal sperm. Acrosome immunostaining was reduced, but present, in acrosome-reacted sperm. Spermatid intercellular bridges became positive for protocadherin alpha3 coincident with the appearance of plectin, occurring at spermiogenic steps 8 to 9, and elongate spermatid bridges remained positive throughout spermatogenesis. The developing flagellum was uniformly immunostained for protocadherin alpha3 up to approximately spermiogenic step 17. Subsequently, flagellar immunostaining was confined to the principal piece, and this pattern continued in cauda epididymal sperm. These data show that protocadherin alpha3 performs functions unique from classic cadherins in spermatogenesis and suggest a role for protocadherin alpha3 in organizing germ cell-specific structures including the intercellular bridge, flagellum, and acrosome.

Fer kinase/FerT and adherens junction dynamics in the testis: an in vitro and in vivo study

Fer kinase is a 94-kDa cytoplasmic cell-cell actin-based adherens junction (AJ)-associated nonreceptor protein tyrosine kinase (PTK) found in multiple epithelia including the testis, whereas FerT kinase (51 kDa) is the truncated testis-specific form of Fer kinase, lacking the Fps/Fes/Fer/CIP4 (products of oncogenes identified in avian and feline sarcoma, encoding tyrosine protein kinases) and the three coiled-coil domains versus Fer kinase. Yet the role(s) of Fer kinase in AJ dynamics in the testis remains largely unexplored. We have used an in vitro model of AJ assembly with Sertoli-germ cell cocultures and an in vivo model of AJ disassembly in which adult rats were treated with 1-(2,4-dichlorobenzyl)-indazole-3-carbohydrazide (AF-2364) to study changes in the expression and/or localization of Fer kinase during AJ restructuring. Fer kinase/FerT was expressed by Sertoli and germ cells when cultured in vitro. Using an antibody prepared against a synthetic peptide, NH2-SAPQNCPEEIFTIMMKCWDYK-COOH, corresponding to residues 779-799 of Fer kinase in the rat, which failed to cross-react with FerT kinase, for immunohistochemistry, Fer kinase was detected in the seminiferous epithelium in virtually all stages of the epithelial cycle. At stages XIII-VI, Fer kinase was associated largely with round and elongating spermatids. At stages VII-VIII, Fer kinase associated almost exclusively with round spermatids with very weak staining associated with elongated spermatids. This stage-specific localization of Fer kinase in the epithelium was confirmed by using staged tubules for semiquantitative reverse transcription-polymerase chain reaction. Studies by immunoprecipitation revealed that Fer kinase associated with N-cadherin, gamma-catenin, p120ctn, c-Src (a putative PTK and the product of the transforming, sarcoma-inducing gene of Rous sarcoma virus), Rab 8 (a GTPase), actin, vimentin, but not E-cadherin, afadin, nectin-3, and integrin beta1, suggesting Fer kinase associates not only with the actin-based cell-cell AJ structures, such as the N-cadherin/catenin complex (but not the alpha6beta1 integrin/laminin and the afadin/nectin complex), but also with intermediate filament-based cell-cell desmosomes. An induction in Fer kinase expression was detected during Sertoli-germ cell AJ assembly in vitro but not during AF-2364-induced AJ disruption in vivo. Yet this AF-2364-induced Fer kinase plummeting associated with an induction in N-cadherin, beta-catenin, and p120ctn, particularly at the base of the seminiferous epithelium. In summary, Fer kinase structurally associates with the N-cadherin/catenin protein complex in the testis and can possibly be used to mediate signaling function via the cadherin/catenin protein complex.

gamma-Tubulin overexpression in Sertoli cells in vivo: I. Localization to sites of spermatid head attachment and alterations in Sertoli cell microtubule distribution

Sertoli cells play a number of roles in supporting spermatogenesis, including structural organization, physical and paracrine support of germ cells, and secretion of factors necessary for germ cell development. Studies with microtubule disrupting compounds indicate that intact microtubule networks are crucial for normal spermatogenesis. However, treatment with toxicants and pharmacologic agents that target microtubules lack cell-type selectivity and may therefore elicit direct effects on germ cells, which also require microtubule-mediated activities for division and morphological transformation. To evaluate the importance of Sertoli cell microtubule-based activities for spermatogenesis, an adenoviral vector that overexpresses the microtubule nucleating protein, gamma-tubulin, was used to selectively disrupt microtubule networks in Sertoli cells in vivo. gamma-Tubulin overexpression was observed to cause redistribution of Sertoli cell microtubule networks, and overexpression of a gamma-tubulin-enhanced green fluorescent protein fusion protein was observed to localize to the site of elongate spermatid head attachment to the seminiferous epithelium.

Neonatal hypothyroidism alters the localization of gap junctional protein connexin 43 in the testis and messenger RNA levels in the epididymis of the rat

The objectives of this study were to determine the effects of propylthiouracil (PTU)-induced neonatal hypothyroidism on the gap junctional protein Cx43 in rat testis and epididymis. PTU (0.02%) was administered via lactation from birth to Day 30, and the rats were sampled at 14, 18, 22, 26, 30, and 91 days of age. Testicular Cx43 was localized along the plasma membranes and cytoplasm of Sertoli cells until Day 22. At Day 30, the immunostaining was localized exclusively along the plasma membrane of Sertoli cells. In PTU-treated rats, Cx43 did not localize to the plasma membrane and was still cytoplasmic at 30 days of age. Occludin was present in tubules of treated rats, but was not localized to the blood-testis barrier in 30-day-old rats, as in controls. There were no differences in Cx43 immunostaining in the adult testis. In the proximal epididymis (initial segment, caput, corpus), Cx43 mRNA levels were lower in PTU-treated rats at 14, 18, and 22 days of age, but no differences were observed in the distal (cauda) epididymis at these ages. In 22- and 30-day-old rats, Cx43 was localized along the plasma membrane between principal and basal cells throughout the epididymis. In PTU-treated rats, Cx43 was not detectable in initial segment, caput, or corpus epididymidis. In the cauda epididymidis, however, Cx43 immunostaining in PTU-treated rats was similar to controls. These data suggest that thyroid hormones regulate Cx43-dependent gap junctional communication in the testis and epididymis.

Is the cadherin/catenin complex a functional unit of cell-cell actin-based adherens junctions in the rat testis?

Much controversy exists regarding the presence of the cadherin/catenin complex and its intracellular attachment site in the testis, which is the functional unit for actin-based cell-cell adherens junctions (AJs) in multiple epithelia. Furthermore, whether germ and Sertoli cells are equipped with the necessary AJ-associated signaling molecules to regulate this cadherin/catenin complex during spermatogenesis is not known. In the present study, it was shown that both Sertoli and germ cells indeed express N-cadherin, E-cadherin, alpha-catenin, beta-catenin, and p120(ctn) by semiquantitative reverse transcription-polymerase chain reaction and immunoblotting. Furthermore, the assembly of AJs between Sertoli and germ cells was associated with a transient induction in the steady-state mRNA and protein levels of cadherins and catenins. These analyses reveal, to our knowledge for the first time, that the testis may indeed be using the cadherin/catenin complex as one of the functional units to regulate AJ dynamics between Sertoli and germ cells in addition to alpha(6)beta(1) integrin and the nectin/afadin complex. To further confirm the existence of such a complex between Sertoli and germ cells, immunoprecipitation experiments were performed using Sertoli-germ cell lysates during AJ assembly. An anti-N-cadherin antibody can pull out beta-catenin, whereas N-cadherin can also be pulled out using an anti-beta-catenin antibody. To further expand and validate these in vitro biochemical studies, immunofluorescent histochemistry was performed, which colocalized N-cadherin and beta-catenin to the same site of Sertoli-Sertoli and Sertoli-germ cell AJs, possibly ectoplasmic specializations near the basal compartment, at the lower third of the seminiferous epithelium in vivo as well as between Sertoli cells cultured in vitro. Furthermore, studies by cross-linking using dithiobis(succinimidylpropionate) confirmed that the cadherin/catenin complex between Sertoli cells as well as between Sertoli and germ cells indeed structurally linked to actin but not to vimentin (an intermediate filament protein) or to tubulin (a microtubule protein). These results thus unequivocally demonstrate that the cadherin/catenin complex, which can be up-regulated by testosterone, is indeed present between Sertoli and germ cells and is used for the assembly of functional AJs.

Stage-specific expression of genes associated with rat spermatogenesis: characterization by laser-capture microdissection and real-time polymerase chain reaction

Spermatogenesis in the rat consists of 14 unique morphologic cellular associations between Sertoli cells and developing germ cells within the seminiferous epithelium. The complexity of the cellular associations leads to difficulty in the isolation of individual cells at a defined stage of development for the study of their unique patterns of gene or protein expression. Thus, laser-capture microdissection is an ideal technique to permit such analysis. This study used laser-capture microdissection and real-time reverse transcription-polymerase chain reaction (RT-PCR) to quantitate the stage-specific expression of a series of genes of functional significance in hormonal regulation and cell-cell interactions in spermatogenesis, including cathepsin-L, CREM-tau, transition protein-1, androgen receptor, beta1-integrin, N-cadherin, and hypoxanthine phosphoribosyltransferase (HPRT). Frozen sections (10 micro m) were obtained from normal adult rat testes. Laser-capture microdissection (LCM) was used to capture all cells in cross-sections of seminiferous tubules that were grouped into stages I-V, VII-VIII, and IX-XIII. Transition protein-1 expression was lowest during stages I-V and increased 5.9-fold during stages VII-VIII and IX-XIII (P < 0.01). Cathepsin-L expression was highest during stages I-V and VII-VIII, falling 4.9-fold during stages IX-XIII (P < 0.05). Similarly, CREM-tau expression was highest during stages I-V and VII-VIII, falling 1.6-fold during stages IX-XIII (P < 0.05). A novel CREM-tau isoform lacking the phosphorylation domain was also characterized but was not stage-specific. beta1-Integrin, N-cadherin, and androgen receptor expression did not change between the spermatogenic stages examined. HPRT housekeeper expression was lowest during stages I-V but increased 1.5-fold during stages VII-VIII and IX-XIII (P < 0.05). This study is the first to apply LCM and real-time RT-PCR analysis to quantitate stage-specific changes in the expression of multiple genes in the seminiferous epithelium.

Molecular mechanisms governing Pcdh-gamma gene expression: evidence for a multiple promoter and cis-alternative splicing model

The genomic architecture of protocadherin (Pcdh) gene clusters is remarkably similar to that of the immunoglobulin and T cell receptor gene clusters, and can potentially provide significant molecular diversity. Pcdh genes are abundantly expressed in the central nervous system. These molecules are primary candidates for establishing specific neuronal connectivity. Despite the extensive analyses of the genomic structure of both human and mouse Pcdh gene clusters, the definitive molecular mechanisms that control Pcdh gene expression are still unknown. Four theories have been proposed, including (1) DNA recombination followed by cis-splicing, (2) single promoter and cis-alternative splicing, (3) multiple promoters and cis-alternative splicing, and (4) multiple promoters and trans-splicing. Using a combination of molecular and genetic analyses, we evaluated the four models at the Pcdh-gamma locus. Our analysis provides evidence that the transcription of individual Pcdh-gamma genes is under the control of a distinct but related promoter upstream of each Pcdh-gamma variable exon, and posttranscriptional processing of each Pcdh-gamma transcript is predominantly mediated through cis-alternative splicing.

Expression and potential function of Rho family small G proteins in cells of the mammalian seminiferous epithelium

Dynamic cellular rearrangements involving the actin cytoskeleton are required of both Sertoli and germ cells during spermatogenesis. Rho family small G proteins have been implicated in the control of the actin cytoskeleton in numerous cell types. Therefore, RhoA and Rac1 were investigated in Sertoli and germ cells. RhoA and Rac1 have been detected at both the mRNA and protein levels in these cells. In addition, Sertoli cell L-selectin is shown to interact with actin binding proteins, potentially providing a link between L-selectin and Rac1 signaling. Finally, inactivation of Sertoli cell Rho family proteins yields disruption of the actin cytoskeleton.

Sertoli cell vacuolization and abnormal germ cell adhesion in mice deficient in an inositol polyphosphate 5-phosphatase

The dynamic nature of cellular interactions during differentiation of germ cells and their translocation from the basement membrane to the lumen of the seminiferous tubules requires the existence of complex and well-regulated cellular adhesion mechanisms in the testis. Successful migration of the developing germ cells is characterized by dynamic breakage and reformation of cadherin-containing adherens junctions between the germ cells and Sertoli cells, the polarized somatic cells of the testis that support and nourish the developing gametes. Here, we demonstrate the accumulation of abnormally swollen, actin-coated, endosome-like structures that contain intact adherens junctions and stain positive for N-cadherin and beta-catenin in the Sertoli cell cytosol of mice deficient in Inpp5b, an inositol polyphosphate 5-phosphatase. Simultaneous to the formation of these abnormal structures, developing germ cells are prematurely released from the seminiferous epithelium and sloughed into the epididymis. Our results demonstrate a role for Inpp5b in the regulation of cell adhesion in the testis and in the formation of junctional complexes with neighboring cells, and they emphasize the important and essential role of phosphoinositides in spermatogenesis.

Dynamic testicular adhesion junctions are immunologically unique. I. Localization of p120 catenin in rat testis

In the seminiferous epithelium, morphologically diverse junctions mediate inter-Sertoli and Sertoli-germ cell adhesive contact, but the molecular composition of such junctions is not well known. At prototypical adherens junctions, proteins termed catenins bind to the intracellular domain of classic cadherins and regulate the strength of adhesion. Using a panel of monoclonal antibodies (5A7, 8D11, and 15D2), p120 catenin (p120) was localized in postnatal and adult rat testis cryosections and touch preparations by immunofluorescence. Immunoprecipitation of testis homogenates showed that at least four p120 isoforms were expressed from Postnatal Day 7 through adulthood. Both inter-Sertoli and Sertoli-germ cell junctions were p120-positive, however, individual p120 monoclonals were localized to specific junctions. The 5A7 and 8D11 antibodies colocalized with beta-catenin and plectin at inter-Sertoli and Sertoli-spermatocyte junctions. At inter-Sertoli junctions, p120 was juxtaposed to but did not colocalize with f-actin. Thus, p120 is likely a component of inter-Sertoli desmosome-like junctions. In contrast, the 15D2 monoclonal antibody specifically immunostained Sertoli-round spermatid and inter-Sertoli cell junctions in a dynamic pattern. From the time that round spermatids form to their differentiation into elongate spermatids, Sertoli-round spermatid 15D2 immunostaining cycled from a single mass to a curvilinear pattern, and finally to punctate structures scattered throughout the epithelium. This localization and stage-specific immunostaining pattern indicated that 15D2 recognized Sertoli-round spermatid desmosome-like junctions. Between Sertoli cells, 15D2 immunostained newly formed junctions (at Postnatal Days 21 through 43), but not mature junctions in the adult. From these data, we conclude that p120 is a component of most, if not all, desmosome-like junctions, and that desmosome-like junctions between different cell types contain a unique molecular composition.

Dynamic testicular adhesion junctions are immunologically unique. II. Localization of classic cadherins in rat testis

In the seminiferous epithelium, morphologically diverse junctions mediate inter-Sertoli and Sertoli-germ cell adhesive contact and likely transmit signals between contacting cells. Defining the molecular composition of testicular cell-cell junctions is an important step in determining their function. Proteins belonging to the cadherin superfamily are important mediators of cell-cell adhesion, as well as cell signaling. Here, we determined the spatial and temporal protein expression of four classic cadherins in rat testis: N-cadherin, cadherin-6, cadherin-11, and a cadherin defined by an antiserum generated against a conserved classic cadherin peptide (L4). Through Western blot analysis, all antibodies recognized unique proteins. Similarly, each cadherin displayed unique, cell-type specific immunostaining patterns. Whereas N-cadherin, cadherin-11, and L4-positive cadherin were expressed from Postnatal Day 7 through adulthood, cadherin-6 protein was not present at Postnatal Day 7 and first appeared at Day 21. Immunostaining of testis cryosections on Postnatal Days 7, 21, 31, 43, and those of adults indicated that cadherin-11 localized to peritubular cell junctions. N-cadherin immunostaining localized to basal inter-Sertoli junctions, Sertoli-spermatocyte junctions, and at about stages I-VII in Sertoli-elongate spermatid junctions. Cadherin-6 immunostaining was restricted to Sertoli-round spermatid and in Sertoli-elongate spermatid junctions at approximately stages XII-I. Finally, L4-positive immunostaining also detected Sertoli-round spermatid junctions in addition to Sertoli-elongate spermatid junctions at approximately stages XII-I. These data show that the various testicular cell-cell junctions are molecularly unique and dynamic complexes.

Cell Junction Dynamics in the Testis: Sertoli-Germ Cell Interactions and Male Contraceptive Development

Spermatogenesis is an intriguing but complicated biological process. However, many studies since the 1960s have focused either on the hormonal events of the hypothalamus-pituitary-testicular axis or morphological events that take place in the seminiferous epithelium. Recent advances in biochemistry, cell biology, and molecular biology have shifted attention to understanding some of the key events that regulate spermatogenesis, such as germ cell apoptosis, cell cycle regulation, Sertoli-germ cell communication, and junction dynamics. In this review, we discuss the physiology and biology of junction dynamics in the testis, in particular how these events affect interactions of Sertoli and germ cells in the seminiferous epithelium behind the blood-testis barrier. We also discuss how these events regulate the opening and closing of the blood-testis barrier to permit the timely passage of preleptotene and leptotene spermatocytes across the blood-testis barrier. This is physiologically important since developing germ cells must translocate across the blood-testis barrier as well as traverse the seminiferous epithelium during their development. We also discuss several available in vitro and in vivo models that can be used to study Sertoli-germ cell anchoring junctions and Sertoli-Sertoli tight junctions. An in-depth survey in this subject has also identified several potential targets to be tackled to perturb spermatogenesis, which will likely lead to the development of novel male contraceptives.

Structure and control of a cell-cell adhesion complex associated with spermiation in rat seminiferous epithelium

Spermiation, the release of late spermatids from the Sertoli cell, is disrupted by a number of toxicants. Control of the spermiation process, and the proteins that interact to adhere mature spermatids to Sertoli cells, is poorly understood. In these studies we used immunohistochemistry, coimmunoprecipitation/Western blotting, and mass spectrometry to refine an earlier model of sperm adhesion proposed by our laboratory. We have identified specific proteins linked together as part of a multiprotein complex, as well as several additional proteins (cortactin, ERK1/2, and 14-3-3 zeta) that may be functioning in both structural and signal transduction roles. The current and prior data suggest that protein phosphorylation is central to the control of spermiation. We also present and characterize an in vitro tubule culture system that allowed functional testing of the spermiation model by pharmacologic manipulation, and yielded data consistent with the importance of protein phosphorylation in spermiation.

N-cadherin is regulated by gonadal steroids in adult sexually dimorphic spinal motoneurons

Gonadal steroids influence the morphology and function of neurons in the adult spinal cord through cellular and molecular mechanisms that are largely unknown. The cadherins are cell adhesion molecules that participate in the formation and organization of the CNS during embryonic development, and recent evidence suggests that the cadherins continue to regulate neural structure and function in adulthood. Using degenerate oligonucleotides coding conserved regions of the catenin-binding domain of classical cadherins in a RT-PCR cloning strategy, we identified several cadherin subtypes, the most frequently cloned being N-, E-, and R-cadherin, suggesting that these are the major classical cadherin subtypes present in the adult male rat lumbosacral spinal cord. We then examined cadherin expression levels of these cadherin subtypes under steroid conditions known to induce plastic changes in spinal motoneurons. Semiquantitative PCR revealed that mRNA levels of N-cadherin, but not E-cadherin or R-cadherin, are elevated in castrated rats treated with testosterone, 17 beta-estradiol, or dihydrotestosterone relative to castrate rats not treated with steroids. Immunolocalization of N-cadherin revealed that steroid treatment increased N-cadherin expression levels in functionally related neural populations whose morphology and function are regulated by steroids. These results suggest a role for N-cadherin in steroid-induced neuroplastic change in the adult lumbar spinal cord.

Rat seminiferous epithelium contains a unique junction (Ectoplasmic specialization) with signaling properties both of cell/cell and cell/matrix junctions

The seminiferous epithelium contains unique actin related cell-cell junctions, termed ectoplasmic specializations (ESs). Turnover of these junctions is fundamental to sperm release and to movement of spermatocytes from basal to adluminal compartments of the epithelium during spermatogenesis. In this study we report several novel observations related to the spatial and temporal distribution of integrin-related signaling molecules at ESs. We confirm the presence of beta(1)-integrin at these sites and further demonstrate co-localization of integrin linked kinase (ILK). beta(1)-Integrin and ILK were shown by immunoprecipitation to associate in whole cell lysates of seminiferous epithelium. This observation provides the first evidence for a direct beta(1)-integrin/ILK interaction in noncultured epithelium. Pan-cadherin and beta-catenin antibodies did not react at ESs. Rather, antibodies reacted with desmosome-like junctions that are present both at basal junctional complexes between Sertoli cells and at sites of attachment to spermatogenic cells. Focal adhesion kinase (FAK), a known integrin-associated molecule, did not codistribute with beta(1)-integrins and did not associate with these adhesion molecules in immunoprecipitation studies. Although FAK was expressed in the epithelium, it appeared to be limited to the cytoplasm of early spermatogenic cells. Significantly, polyclonal antibodies against phosphotyrosine-containing residues reacted strongly at ESs, with highest levels detected during sperm release and turnover of basal junction complexes. Our observations indicate that ESs share cell signaling features both of cell-cell junctions and of cell-extracellular matrix junctions.

Role of Sertoli cells in injury-associated testicular germ cell apoptosis

This review examines experimental models of Sertoli cell injury resulting in germ cell apoptosis. Since germ cells exist in an environment created by Sertoli cells, paracrine signaling between these intimately associated cells must regulate the process of germ cell death. Germ cell apoptosis may be signaled by a decrease in Sertoli cell pro-survival factors, an increase in Sertoli cell pro-apoptotic factors, or both. The different models of Sertoli cell injury indicate that spermatogenesis is susceptible to disruption, and that targeting critical Sertoli cell functions can lead to rapid and massive germ cell death.