NCAM in developing mouse gonads and ducts

The Loss of Polysialic Acid Impairs the Contractile Phenotype of Peritubular Smooth Muscle Cells in the Postnatal Testis

In the testis, the germinal epithelium of seminiferous tubules is surrounded by contractile peritubular cells, which are involved in sperm transport. Interestingly, in postnatal testis, polysialic acid (polySia), which is also an essential player for the development of the brain, was observed around the tubules. Western blotting revealed a massive decrease of polySia from postnatal day 1 towards puberty, together with a fundamental reduction of the net-like intertubular polySia. Using polysialyltransferase knockout mice, we investigated the consequences of the loss of polySia in the postnatal testis. Compared to postnatal wild-type animals, polySia knockouts showed slightly reduced smooth muscle actin (SMA) immunostaining of peritubular smooth muscle cells (SMCs), while calponin, marking more differentiated SMCs, dramatically decreased. In contrast, testicular SMA and calponin immunostaining remained unchanged in vascular SMCs in all genotypes. In addition, the cGMP-dependent protein kinase PKG I, a key enzyme of SMC relaxation, was nearly undetectable in the peritubular SMCs. Cell proliferation in the peritubular layer increased significantly in the knockouts, as shown by proliferating cell nuclear anti (PCNA) staining. Taken together, in postnatal testis, the absence of polySia resulted in an impaired differentiation of peritubular, but not vascular, SMCs to a more synthetic phenotype. Thus, polySia might influence the maintenance of a differentiated phenotype of non-vascular SMCs.

Polysialylation takes place in granulosa cells during apoptotic processes of atretic tertiary follicles

In the neuronal system, polysialic acid (polySia) is known to be involved in several cellular processes such as the modulation of cell-cell interactions. This highly negatively-charged sugar moiety is mainly present as a post-translational modification of the neural cell adhesion molecule (NCAM). More than 20 years ago, differently glycosylated forms of NCAM were detected in the ovaries. However, the exact isoform of NCAM, as well as its biological function, remained unknown. Our analysis revealed that granulosa cells of feline tertiary follicles express the polysialylated form of NCAM-140. Unexpectedly, polySia was only expressed in the granulosa layers of atretic follicles and not of healthy follicles. By contrast, only the un-polysialylated form of NCAM was present on the membrane of granulosa cells of healthy follicles. To study a possible cellular function of polySia in feline follicles, a primary granulosa cell culture model was used. Interestingly, loss of polySia leads to a significant inhibition of apoptosis, demonstrating that polySia is involved during atretic processes in granulosa cells. Thus, polySia might not only directly influence regeneration processes as shown, for example, in the neuronal system, but also apoptosis.

Polysialylation of NCAM characterizes the proliferation period of contractile elements during postnatal development of the epididymis

Polysialic acid (polySia) attached to the neural cell adhesion molecule (NCAM) regulates inter alia the proliferation and differentiation via the interactions with neurotrophins. Since in postnatal epididymis neurotrophins and their receptors like the Low-Affinity Nerve Growth Factor Receptor p75 and TrK B receptor are expressed, we wanted to analyze if the polysialylation of NCAM is also involved during the development of the epididymis. To this end, we monitored the developmental changes in the expression of the polysialyltransferases and NCAM polysialylation using murine epididymis at different time points during postnatal development. Our results revealed that during postnatal development of the epididymis both polysialyltransferases, ST8SiaII and ST8SiaIV, were expressed and that the expression levels dropped with increasing age. In agreement with the expression levels of the polysialyltransferases the highest content of polysialylated NCAM was present during the first 10 days after birth. Interestingly, proliferating smooth muscle cell populations prevalently expressed polysialylated NCAM. Furthermore, we observed that inverse to the decrease in polysialylation of smooth muscle cells a strong up-regulation of collagen takes place suggesting a functional relationship since collagen was recently described to induce the turnover of polysialylated NCAM via an induction of endocytosis in cellulo. The same time course of polySia and collagen synthesis was also observed in other regions of the male reproductive system e.g. vas deferens and tunica albuginea (testis). Together, we identified a spatio-temporal expression pattern of polySia-NCAM characterized by high proliferation rate of smooth muscle cells and low collagen content.

Polysialylation of NCAM correlates with onset and termination of seasonal spermatogenesis in roe deer

Roe deer (Capreolus capreolus) are seasonal breeders and cyclic structural changes of roe bucks' testis come along with a totally arrested (winter) and a highly activated spermatogenesis (summer). For this reason, roe buck represents an interesting model to study general mechanisms of initiation and termination of spermatogenesis. We investigated if polysialic acid (polySia)-a linear homopolymer of α2,8-linked sialic acids, which could act as a negative regulator of cell-cell adhesion-might be involved in the activation and/or inactivation of spermatogenesis. To address this point, testis samples of adult male roe deer were collected at different time point of the year. Intriguingly, we observed that polySia attached to the neural cell adhesion molecule was enhanced during the onset of spermatogenesis in April. In addition, polySia was highly expressed in December. Predominantly, polySia was detectable between Sertoli cells and spermatogonia in the basal regions of testicular tubules and in the adluminal part of Sertoli cells. Interestingly, similar polySia distributions were observed during early testis development of other mammalians when gonocytes (pre-spermatogonia) and Sertoli cells represent the only cell populations in tubuli seminiferi. Thus, polySia is expressed during key steps of the "on/off mechanisms" of spermatogenesis and might represent one mediator of the interaction and communication between Sertoli cells and germ cell precursors.

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.

Gonadal development in mammals at the cellular and molecular levels

In mammals, although sex is determined chromosomally, gonads in both sexes begin development as similar structures. Until recently it was widely held that female development constituted a "default" pathway of development, which would occur in the absence of a testis-determining gene. This master gene on the Y chromosome, SRY in the human and Sry in the mouse, is thought to act in a cell-autonomous fashion to determine that cells in the gonadal somatic population develop as pre-Sertoli cells. Triggering of somatic cell differentiation along the Sertoli cell pathway is therefore a key event; it was thought that further steps in gonadal differentiation would follow in a developmental cascade. In the absence of Sertoli cells, the lack of anti-Mullerian hormone would allow development of the female Mullerian duct and absence of Leydig cells would prevent maintenance of the Wolffian duct. Recent findings that female signals not only maintain the Mullerian duct and repress the Wolffian duct but also suppress the development of Leydig cells and maintain meiotic germ cells, together with the finding that an X-linked gene is required for ovarian development and must be silenced in the male, have shown that the female default pathway model is an oversimplification. Morphological steps in gonadal differentiation can be correlated with emerging evidence of molecular mechanisms; growth factors, cell adhesion, and signaling molecules interact together, often acting within short time windows via reciprocal control relationships.

Role of NCAM, cadherins, and microfilaments in cell-cell contact formation in TM4 immature mouse sertoli cells

To determine events that lead to the formation of intercellular contacts, we examined the spatial and temporal distribution of NCAM, cadherins, and F-actin in TM4 cells by immunofluorescence and laser scanning confocal microscopy. TM4 cells exhibited epithelioid characteristics and formed large overlapping lamella-like cell-cell contacts that contained a high concentration of NCAM. NCAM-rich lamellae formed from smaller NCAM patches at the ends of filopodia-like contacts between adjacent cells. Cadherins, as visualized by a pan-cadherin antibody, were present in a pattern distinctly different from that of NCAM. Although in filopodia-like contacts, both cadherins and NCAM were often concentrated at filopodial tips, in the larger lamella-like contacts that developed later, cadherins were located in an irregular punctate pattern only at the distal and more apical margins of the slanted NCAM-rich contact regions. Patterns of NCAM and microfilament (MF) bundle distribution were distinctly different, suggesting that the ends of these MF bundles were not physically linked to NCAM. By contrast, cadherins were concentrated at the ends of MF bundles at all stages of contact formation examined. Interestingly, this association of cadherins with MF bundles was mostly seen at the edge of the overlapping processes. In the lower cell process, MF bundles at the contact site were often arranged in random fashion, indicating an asymmetric distribution of MF in the junctional region. However, N-cadherin was enriched only at sites where MF bundles from both the upper and lower cell processes were aligned and terminated at the junctional membrane. Thus the organization of the actin cytoskeleton at cell-cell contact sites is influenced by the differential localization of different cadherins. These data also suggest that different mechanisms are involved in the accumulation of NCAM and cadherins in cell-cell contact regions.

An immunohistochemical study of the rete ovarii and epoophoron

A study to compare the immuno-histochemical profile of the human rete ovarii, and epoophoron, with the Fallopian tube and ovarian surface epithelium was performed with 31 antibodies and antisera. A reaction was present in the epithelial cytoplasm of the rete ovarii and epoophoron of mesonephric origin, for vimentin, GFAP, cytokeratin markers, (AE1/AE3, MNF116; Cam 5.2, 34 beta E12 and for the monospecific antibodies to cytokeratins 7 and 19), heat shock protein 27, in the cell membrane for HBME-1, EMA and in the subepithelial collagen for collagen IV. Reactions were present only in the epithelium in the rete ovarii for EGFR (one case) and CA-125 (four cases). A reaction was present in the epithelium of the epoophoron only for Ber-EP-4 and S100. There was no reaction with antibodies for desmin, neurofilament protein, cytokeratins 20 or 14, actin, calretinin, E-cadherin, C-erb-B2, or CEA (monoclonal and polyclonal reagents). The immuno-histochemical profile of the Fallopian tube was consistent with its para-mesonephric origin and that in the ovarian surface epithelium was consistent with a proposed modified mesothelial origin. This study provides an immunohistochemical profile of these structures with a large panel of commonly available antibodies and antisera, confirming and extending the findings described in previous studies.

Sequences 5' of the basement membrane laminin beta 1 chain gene (LAMB1) direct the expression of beta-galactosidase during development of the mouse testis and ovary

The murine LAMB1 gene encoding laminin beta 1 is expressed in the developing male and female gonads and mesonephros. To identify the cis-acting elements regulating the expression of LAMB1, murine transgenic lines were generated by fusing regions of the LAMB1 gene to the Eschericia coli lacZ gene. The p3.9LAM beta gal construct contained approximately 4 kb of 5' flanking sequence and directed beta-galactosidase expression in many different organs including the kidney, mammary gland, and the male and female genital systems, the focus of this report. In male embryos, between gestational ages E 14.5 and birth beta-galactosidase was transiently expressed in the prospermatogonia cells of the testis and in the differentiating epithelial cells in the ductus deferens, ductus epididymis, and seminal vesicles. In female embryos, beta-galactosidase was not detected in the ovary until about 1 week after birth; at this time, beta-galactosidase was expressed by oocytes of primary and secondary follicles. In contrast, transgenic mice carrying the first 0.7 kb of LAMB1 fused to the lacZ gene expressed beta-galactosidase only in the prospermatogonia cells of the testis. Thus, the cis-acting element(s) necessary for the expression of the LAMB1 gene in prospermatogonia cells are located in the first 0.7 kb of LAMB1 5' flanking sequence; element(s) required for expression of the LAMB1 gene in oocytes and epithelial cells of the mesonephric ducts, mesonephric tubules, the ductus deferens, ductus epididymis, and seminal vesicles are located with 4 kb 5' of the transcription initiation site.

Sex-dependent expression of placental (P)-cadherin during mouse gonadogenesis

BACKGROUND

Placental (P)-cadherin is one of a family of cell adhesion molecules that participate in embryonic sorting and organogenesis. In previous work, P-cadherin was localized to Sertoli cells in the mouse testis as early as postnatal day 1. This early postnatal localization raised questions about when P-cadherin first appeared in the embryonic testis and whether P-cadherin was expressed differentially in the embryonic testis and ovary.

METHODS

The localization of P-cadherin, epithelial (E)-cadherin, and Müllerian inhibiting substance was determined in frozen sections of mouse gonads between embryonic days 10.5 and 18 using indirect immunohistochemistry. Alkaline phosphatase reactivity was used to identify germ cells.

RESULTS

The expression of P-cadherin was traced back to the indifferent stage of gonadogenesis where uniform distribution was observed in the indifferent gonad of both sexes. However, after sexual differentiation, the expression of P-cadherin in the testis was localized to Sertoli cells in the testicular cords, while its expression in the ovary fell below detectable levels.

CONCLUSIONS

The localization of P-cadherin in the male and female indifferent gonad is similar and cannot be used to distinguish the future testis and ovary. The localization of P-cadherin in the testis after sexual differentiation suggests a role for P-cadherin in testicular cord formation. The common temporal pattern of P-cadherin and Müllerian inhibiting substance expression in Sertoli cells is consistent with a shared regulatory mechanism.

Alpha 6 subunit of integrins in the development and sex differentiation of the mouse ovary

The localization of the alpha 6 subunit of integrins in the ovary was studied by conventional and immunolabeling light and electron microscopy starting from the pregonadal embryonic phase until adulthood. The formation of gonadal blastema cells included an initial expression of the alpha 6 subunit on the plasma membranes of all blastema cells. Subsequently the reaction for the alpha 6 subunit became restricted in groups of these cells, which differentiated into gonadal cord cells, the precursors of follicular cells. The alpha 6 subunit was also found in the cells of the mesonephric duct, mesonephric tubules, and the ovarian rete. Reorganization of the gonadal cords into follicles at birth was accompanied with strong and uniform re-expression of the alpha 6 subunit on the surface of the cord cells. Vascular endothelial cells and the cells of the postnatal surface epithelium remained positive for the alpha 6 integrin subunit. In larger follicles, the intensity of the reaction for the integrin subunit varied. The theca cells of growing follicles contained the alpha 6 subunit. The results show that this subunit of integrins is present in phases of increased adhesion and aggregation, and that its expression probably is involved in the regulation of ovarian epithelial differentiation. The distribution of alpha 6 integrin in ovarian cells shows potentially important sex-specific and developmental differences in epithelial organization when compared with respective changes found earlier by us in the male gonad.

The ability to re-express polysialylated NCAM in soleus muscle after denervation is reduced in aged rats compared to young adult rats

The neural cell-adhesion molecule, NCAM, contains an unusual homopolymer of sialic acid units, polysialic acid. This carbohydrate seems to be involved in neurite outgrowth, bundling and branching, processes which are important during reinnervation. In aged rats, reinnervation of denervated muscle fibres is incomplete. In this study, age-related changes in the degree of polysialylation of NCAM re-expressed after denervation were examined using a monoclonal antibody recognizing polysialic acid and a polyclonal antibody recognizing NCAM. The results show that, after denervation, the degree of polysialylation on NCAM was clearly reduced in rat soleus muscle of aged, compared to young, adult rats. This age-related change in expression of polysialic acid probably influences the reinnervation process in aged muscle.

Expression of the Neural Cell Adhesion Molecule NCAM by Peptide- and Steroid-Producing Endocrine Cells and Tumors: Alternatively Spliced Forms and Polysialylation

The adhesive properties of neural cell adhesion molecules (NCAMs) can be modified by alternative splicing of the primary transcript or by posttranslational modifications, such as sialylation. In this article, we describe distinct forms of alternative splicing and posttranslational modification of the extracellular domain of NCAM of various endocrine tissues and derived tumor cells of the rat and of steroid- and peptide-hormone producing endocrine cells in humans. NCAM-140 is the major isoform expressed in the rat adrenal gland, adenohypophysis, and in granulosa and granulosa-lutein cells. NCAM-180 is predominant in the neurohypophysis. Polysialylated NCAM is expressed in different endocrine tissues and tumor cells of the rat. Different amounts of NCAM mRNA containing the "extra-exon" VASE at the exon 7/8 splice boundary were detected in endocrine cells of rats. Human granulosa cells in culture undergo luteinization. During this process, the VASE-containing NCAM isoform is supplemented by an alternatively spliced isoform without this insert. Thus, modifications of NCAM may be important for adhesive interactions in normal and neoplastic endocrine cells. In addition, the differential expression and the alternative splicing of NCAM during luteinization of granulosa cells raise the possibility that NCAM could be involved in folliculogenesis and the formation of the corpus luteum in humans.

Expression and alternative splicing of the neural cell adhesion molecule NCAM in human granulosa cells during luteinization

Freshly aspirated human granulosa cells from pre-ovulatory follicles and granulosa cells luteinized in culture possess the neural cell adhesion molecule (NCAM) of approximate molecular mass of 140,000 and NCAM mRNA as confirmed by S1-nuclease protection assays and RT-PCR. Moreover, in the process of luteinization the NCAM isoform pattern is modified. Isoforms containing an insert of 10 amino acids (termed VASE) in the extracellular domain of NCAM were supplemented by alternatively spliced isoforms without this insert. NCAM immunoreactivity, at light and electron microscope levels, was associated with the cell membrane of most granulosa cells which formed clusters. During time in culture an increasing subpopulation of granulosa cells, devoid of NCAM immunoreactivity, spread out and formed monolayers. This differential expression and the alternative splicing of NCAM during luteinization of granulosa cells raise the possibility that NCAM could be involved in folliculogenesis and the formation of the corpus luteum in the human.

Differential distribution of the alpha 6 subunit of integrins in the development and sexual differentiation of the mouse testis

The distribution of the alpha 6 subunit of integrins in the development and sexual differentiation of mouse testis was analyzed by light and electron microscopy during the embryonic, fetal and early postnatal periods. At the pregonadal phase only the epithelial cells of the mesonephric duct and of the distal mesonephric tubules showed a reaction to alpha 6, whereas the surface epithelium and the mesenchyme of the mesonephros were negative or contained only a rudimentary amount of the alpha 6 subunit. With the formation of the gonadal ridge and the testicular blastema, the gonadal cells became positive for the alpha 6 subunit. This expression remained in embryonic cord cells and in the vascular endothelial cells, whereas the differentiating cells of the surface epithelium, tunica albuginea, the Leydig cells, and the interstitial mesenchymal cells were negative. With the fetal and postnatal differentiation, the expression of the alpha 6 subunit gradually diminished in the cord cells, and by the prepubertal phase, alpha 6 was found only at adhesion sites between some Sertoli cells. Similar changes were seen in the mesonephric duct and tubules, and in the rete cords. The presence of alpha 6 in regions undergoing developmental cell aggregation processes and their disappearance during tissue maturation, suggest that alpha 6 plays a specific but transient role in gonadal cell adhesion necessary for the histogenetic organization of the testis. In addition to its role in developing and organizing cells, alpha 6 integrin was also a prominent component in degenerating cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Carbohydrate antigen expression in murine embryonic stem cells and embryos. II. Sialylated antigens and glycolipid analysis

A mouse embryonic stem (ES) cell line E14 and early mouse embryos were stained with a panel of 15 monoclonal antibodies recognizing sialylated or potentially sialylated carbohydrate determinants. Sialyl Le-x and sialyl Le-a were detected on the pre-implantation embryo from the 8-cell stage, and sialyl Le-a weakly on undifferentiated ES cells. Changes in cell surface carbohydrates occurred after induction of ES cell differentiation with retinoic acid (RA) and dibutyryl cAMP. Qualitative analysis of the neutral glycolipids of untreated and RA-treated ES cells using high-performance thin-layer chromatography (HPTLC) revealed few differences between the two types of culture. The major gangliosides in both cultures were indicative of an active 'a' ganglioside synthesis pathway. GD3, a precursor of the 'b' synthesis pathway, previously reported to be characteristic of embryonal carcinoma (EC) cells, was absent. RA-induced differentiation caused a shift in the spectrum to more complex gangliosides. Application of fast atom bombardment mass spectrometry (FAB-MS) to permethylated derivatives of individual bands permitted partial characterization of an unusual sialylated glycolipid and a rare ganglioside with the suggested structure of GalNAc-GD1a.

Distribution and possible roles of the highly polysialylated neural cell adhesion molecule (NCAM-H) in the developing and adult central nervous system

The neural cell adhesion molecule (NCAM) is a cell surface glycoprotein which is thought to mediate cell adhesion and recognition. During developmental stages, NCAM is highly polysialylated (NCAM-H) by a unique alpha-2,8-linked polysialic acid chain (PSA), and this PSA portion of NCAM-H has been found to be closely associated with various developmental processes of the nervous system. Further, recent immunohistochemical investigations have revealed that even in the adult nervous system, a persistent PSA expression has been found confined to several regions: the olfactory bulb, the piriform cortex, the hippocampal dentate gyrus, the hypothalamus, some nuclei of the medulla and the dorsal horn of the spinal cord, which are related directly or indirectly to sensory systems. Moreover, in the dentate gyrus and olfactory bulb the expression is connected with adult neurogenesis that may add new neuronal circuits to the adult neural tissue. Therefore, the possible role of NCAM-H in the central nervous system may be associated not only with neural development, but also with adult functions, such as the processing system of sensory information and neuronal plasticity.

The Leydig cell of the human testis--a new member of the diffuse neuroendocrine system

A number of marker substances for neuronal and neuroendocrine cells have been demonstrated in the cytoplasm of the interstitial Leydig cells of human testes using basic immunocytochemical methods and some of their modifications. We were able to reveal immunoreactivity for enzymes involved in the synthesis of the catecholamines dopamine and noradrenaline (tyrosine hydroxylase, aromatic L-amino acid decarboxylase, dopamine-beta-hydroxylase), for the indolamine 5-hydroxytryptamine (serotonin), as well as for a number of well-known neuronal markers such as the neurofilament protein 200, synaptophysin, chromogranin A + B, the neural cell-adhesion molecule (N-CAM), the microtubule-associated protein (MAP-2), and the calcium-binding proteins: S-100, calbindin and parvalbumin. Immunoreactivity for these substances was found in the majority of the interstitial cells although differences in the staining intensity among the individual Leydig cells and among Leydig cells from different patients were observed. At the electron-microscopic level the Leydig cell cytoplasm was seen to contain microtubules, intermediate- and microfilaments as well as clear (40-60 nm) and dense-core (100-300 nm) vesicles, providing a morphological correlate for some of the immunocytochemical results. Although individual marker substances are not absolutely specific for nerve and neuroendocrine cells, the results obtained, together with the already established neuron-specific enolase-, substance P-, methionine-enkephalin- and proopiomelanocortin (POMC)-derived peptide-like immunoreactivity, provide strong evidence for the neuroendocrine (paraneuronal, APUD-like) nature of the Leydig cells of the human testis.

Cultured microvascular endothelial cells derived from the bovine corpus luteum possess NCAM-140

Previously, five phenotypically different, stable types of microvascular endothelial cells (MVE) were isolated from the bovine corpus and cultured successfully. We found that three out of these five types of MVE express the neural cell adhesion molecule (NCAM). As shown by immunocytochemistry, weak NCAM immunoreactivity occurred mainly in the perinuclear area of cell type 1. Monolayers of types 2 and 5 revealed heavy NCAM immunoreactivity, which was localized predominantly at the lateral cell surface outlining the contact zones of adjacent cells. In contrast, cell types 3 and 4 were not NCAM immunoreactive. Western blot analyses substantiated these results: While cell type 1 showed a weak immunoreactive band, cell types 2 and 5 displayed strong NCAM-immunoreactive bands of a molecular weight of approximately 140 kDa (NCAM-140), which was absent in cell types 3 and 4. These results reveal for the first time that NCAM can be expressed by cultured MVE and may serve in mediating endothelial cell contacts. Since luteal cells also express NCAM-140, this adhesion molecule could in addition be involved in the interactions of luteal cells with MVE.