Lectin-binding carbohydrates in sexual differentiation of rat male and female gonads

Histochemical Characterization of Oocytes in the Pink Cuskeel (Genypterus blacodes)

In the present study we histochemically and lectinhistochemically characterized the growing oocytes of the pink cuskeel (Genypterus blacodes). We used histochemical methods for the localization and characterization of glycoconjugates (GCs) and lectin histochemical techniques for the identification of specific sugar residues. We analyzed presence and distribution of GCs in the different structures of the growing follicles (cortical alveoli, globules, yolk granules and zona radiata). During the initial stage of vitellogenesis, the oocytes presented small yolk granules composed of GCs that gradually increased during exogenous vitellogenesis. These GCs contained moderate quantities of α-D-mannose, D-glucose, N-acetylglucosamine and N-acetyl-neuraminic acid. The cortical alveoli contained both neutral and carboxylated GCs, and lectin techniques detected N-acetylgalactosamine, galactose and L-fucose. The zona radiata showed a strong positive reaction to PAS and it reacted weakly with more specific techniques, such as KOH/PA*S and PA/Bh/KOH/PAS. This structure showed GCs with oxidizable vicinal diols, O-acyl sugars and sialic acid residues with different substitution types and presented N-acetylgalactosamine and L-fucose specific residues. The oocytes follicular envelope evidenced neutral and acidic non-sulfated GCs and high concentrations of α-D-mannose, D-glucose, galactose and N-acetylgalactosamine. The intergranular cytoplasmic GCs were mainly rich in α-D-mannose, D-glucose, N-acetylgalactosamine, N-acetylglucosamine and N-acetyl-neuraminic acid. These results enhance the comprehension of the structure and functionality of the pink cuskeel ovarian follicles, and provide a useful tool for the study of this tissue in other teleost species.

Origin and function of embryonic Sertoli cells

In the adult testis, Sertoli cells (SCs) are the epithelial supporting cells of the seminiferous tubules that provide germ cells (GCs) with the required nutrients and structural and regulatory support to complete spermatogenesis. SCs also form the blood-testis barrier, phagocytose apoptotic spermatocytes and cell debris derived from spermiogenesis, and produce and secrete numerous paracrine and endocrine signals involved in different regulatory processes. In addition to their essential functions in the adult testis, SCs play a pivotal role during testis development. They are the first cells to differentiate in the embryonic XY gonadal primordium and are involved in the regulation of testis-specific differentiation processes, such as prevention of GC entry into meiosis, Leydig and peritubular myoid cell differentiation, and regression of the Müllerian duct, the anlagen of the uterus, oviducts, and the upper part of the vagina. Expression of the Y-linked gene SRY in pre-SCs initiates a genetic cascade that leads to SC differentiation and subsequently to testis development. Since the identification of the SRY gene, many Sertoli-specific transcription factors and signals underlying the molecular mechanisms of early testis differentiation have been identified. Here, we review the state of the art of the molecular interactions that commit the supporting cell lineage of the gonadal primordium to differentiate as SCs and the subsequent Sertoli-specific signaling pathways involved in early testis differentiation.

Expression pattern of glycoconjugates in the Bidderian and ovarian follicles of the Brazilian toad Bufo ictericus analyzed by lectin histochemistry

The Bidder's organ and ovary of the Brazilian toad Bufo ictericus were studied by light microscopy, using hematoxylin-eosin (HE) and periodic acid Schiff (PAS) staining. The expression and distribution of carbohydrate moieties was analyzed by lectin histochemistry, using 8 lectins with different carbohydrate specificities: Ulex europaeus (UEA I), Lens culinaris (LCA), Erythrina cristagalli (ECA), Arachis hypogaea (PNA), Ricinus communis (RCA I), Aleuria aurantia (AAA), Triticum vulgaris (WGA), and Glycine maximum (SBA). The results showed that the Bidderian zona pellucida presented alpha-mannose, alpha-L-fucose, beta-D-galactose, N-acetyl-D-glucosamine, and alpha/beta-N-acetyl-galactosamine residues. The Bidderian follicular cells showed the presence of beta-D-galactose and N-acetyl-D-glucosamine. In the extracellular matrix, alpha-mannose and alpha/beta-N-acetyl-galactosamine residues were detected. The ovarian zona pellucida showed alpha-L-fucose, N-acetyl-D-glucosamine, alpha/beta-N-acetyl-galactosamine residues, and alpha-mannose and N-acetyl-D-glucosamine residues were detected in the follicular cells. Thus, the zona pellucida in both organs contains N-acetyl-D-glucosamine, and alpha/beta-N-acetyl-galactosamine residues. alpha-L-fucose residues were detected in the zona pellucida of both organs, using different lectins. Considering that beta-D-galactose residue was absent from ovary but present in the Bidder's organ, this sugar residue may play an important role in follicle development, blocking the Bidderian follicles and preventing further development of the Bidder's organ into a functional ovary.

Distribution of terminal sugar residues in the testis of the spotted rayTorpedo marmorata

Lectins represent a class of proteins/glycoproteins binding specifically to terminal sugar residues. The present investigation aims to identify lectin-binding sites in testis of Torpedo marmorata. Using a panel of lectins coupled with fluoresceine isothiocyanate, we demonstrated that germ and somatic cells present in Torpedo testis contain glycoconjugates, whose distribution at the level of the surface, the cytoplasm and the nucleus changes during germ cell differentiation. Moreover our observations demonstrate that the germ cells undergoing apoptosis (Prisco et al., 2003a: Mol Reprod Dev 64:341-348) overexpress a residual sugar recognised by WFA lectin that can be considered a specific marker for apoptotic germ cells. Finally, our results indicate that there is a progressive increase in glycosilation during spermatogenesis, especially at the level of the acrosome in the spermatocyte-spermatid step, and that Leydig cells are differently stained in relation to the spermatogenetic cycle.

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.

Expression and action of neurotropin-3 and nerve growth factor in embryonic and early postnatal rat testis development

The current study examines the expression and potential actions of neurotropin-3 (NT3), nerve growth factor (NGF), and their receptors during morphological sex determination (seminiferous cord formation) and perinatal rat testis development. The expression of neurotropins and their receptors was analyzed with immunohistochemistry. Cellular localization of neurotropin ligand and receptor proteins changed during embryonic testis development. Neurotropin-3 was localized to Sertoli cells at Embryonic Day 14 (E14), was present in gonocytes at Postnatal Day 0 (P0), and after birth became localized to the interstitium and Sertoli cells (P3-P5). The expression of trk C (the high affinity receptor for NT3) was localized to mesonephric ducts and cells surrounding the cords (E14-E18). In addition, Sertoli cells and preperitubular cells surrounding the cords at E14 also stained for trk C. Neurotropin-3 was expressed in gonocytes and Sertoli cells at P0-P5. Nerve growth factor was detected in Sertoli cells at E14, was clearly in Sertoli and interstitial cells at E16 and E18, and in Sertoli, germ, and interstitial cells from P0-P5. The expression of trk A (the high affinity receptor for NGF) was located in Sertoli and interstitial cells at E16-P5. To determine the actions of neurotropins during embryonic and perinatal testis development, experiments were conducted on E13 and P0 testis. Antisense oligonucleotide experiments with NT3 were used on E13 testis organ cultures to determine effects on seminiferous cord formation. Cord formation was inhibited in 40% of the organ cultures treated with the antisense NT3 oligonucleotides, while no inhibition was observed with sense oligonucleotides. In P0 testis cultures, both NT3 and NGF alone and in combination stimulated thymidine incorporation into DNA. Therefore, the neurotropins are involved in embryonic morphological events (cord formation; NT3) and in growth of the perinatal testis (P0; NT3 and NGF). To define further the growth effects of neurotropins on testis development, expression of transforming growth factor alpha and beta (TGF alpha and TGF beta) were examined in response to neurotropins. The P0 testis cultures were treated with neurotropins, and expression of mRNA for TGF alpha and TGF beta was analyzed utilizing a quantitative reverse transcription-polymerase chain reaction assay. Nerve growth factor and NT3 alone or in combination inhibited expression of mRNA for TGF alpha while NT3 increased mRNA expression of epidermal growth factor receptor. The combination treatment of neurotropins inhibited expression of TGF beta 1 and increase expression of TGF beta 3. In summary, observations suggest that NT3, NGF, trk A, and trk C are localized to cells critical to seminiferous cord formation and appear to be important regulators of morphological sex determination. In addition to these morphological effects, both NT3 and NGF stimulate P0 testis growth and may elicit their action through altering the expression of locally produced growth factors such as TGF alpha and TGF beta. Taken together these results suggest that neurotropins are regulators of paracrine cell-cell interactions that result in morphological sex determination and perinatal testis growth.

Lectinhistochemical and cytometrical evaluation of the corpus luteum of the rat at the end of pregnancy

Most studies on the biochemistry and structure of the corpus luteum have focused on elucidating the processes of progesterone synthesis and release. In the present work, the histochemical composition of the corpus luteum of the rat was evaluated using lectinhistochemistry on rats at the end of pregnancy (days 18-23). We also analysed the morphology of the luteal cells, to characterize the changes attributable to regression in this organ. Seven biotinylated lectins were used (CON-A, WGA, DBA, SBA, PNA, RCA and UEA-I) following pre-set protocols (ABC method). The average diameter and area of the cells and their nuclei were measured. High reactivity of the luteal cells was observed with CON-A and a lower reactivity with WGA. The capillary endothelium gave positive reactivity with WGA and to a certain extent with SBA, PNA and RCA. Vesicular structures were intensely stained with DBA, and were more abundant in sections from animals with more advanced pregnancy, which could be attributable to cellular debris, on the basis of their morphologic characteristics. There were no significant differences among the cytometric variables analysed in comparisons of the values corresponding to the different days of gestation. These observations, together with previous research, suggest that, on the day of delivery, the corpus luteum of the rat is in the very early stages of structural regression, with no changes at the morphological level, but with changes at the molecular level.

Extracellular matrix in ovarian follicles

A lot is known about the control of the development of ovarian follicles by growth factors and hormones, but less is known about the roles of extracellular matrix in the control of follicular growth and development. In this review we focus on the specialized extracellular matrix of the basal laminas that are present in ovarian follicles. These include the follicular basal lamina itself, the Call-Exner bodies of the membrana granulosa, the subendothelial and arteriole smooth muscle basal laminas in the theca, and the basal lamina-like material of the thecal matrix. We discuss the evidence that during follicle development the follicular basal lamina changes in composition, that many of its components are produced by the granulosa cells, and that the follicular basal laminas of different follicles have different ultrastructural appearances, linked to the shape of the aligning granulosa cells. All these studies suggest that the follicular basal lamina is extremely dynamic during follicular development.

The intermediate filament protein nestin occurs transiently in differentiating testis of rat and mouse

Nestin is an intermediate filament (IF) protein (IFP) which occurs during early developmental stages and during regenerative processes in muscle and neuronal cells. The spatial and temporal localization of nestin in the developing testis of rat and mouse was studied by immunolabeling light and electron microscopy and by immunoblotting. Nestin localization was related to the localization of the other major IFPs specific for this tissue, i.e. cytokeratins, vimentin and desmin. Laminin immunocytochemistry and conventional microscopy were used to identify tissues and cells. With the incipient differentiation of the gonadal anlage, the reaction for nestin was weak in the gonadal ridge, whereas the cells of the mesonephric mesenchyme showed a prominent reaction for this IFP. The nestin-specific reaction in the epithelial mesonephric duct and tubules was weak and disappeared at an early phase of differentiation. With the development of the testis proper, nestin was transiently found in several cell types. Nestin was found as well as vimentin and cytokeratins in the Sertoli cells. In the interstitial cells nestin was found together with vimentin and desmin IFPs, and was most prominent in the differentiating myoid cells. After birth, nestin gradually disappeared from the testicular cells and in the rat at puberty was found only in the endothelial cells of some blood vessels. The abolished nestin synthesis in the testis was confirmed by immunoblotting. These results suggest that nestin is required transiently during the development of the testis and mesonephros. The temporary presence of nestin, and several other IFPs during these phases, coincides with key phases of urogenital sex differentiation. This may imply that the orchestrated synthesis of the IFPs nestin, cytokeratins, vimentin and desmin is likely to be linked with the genes regulating sex differentiation.

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.

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)

Intermediate filament proteins and epithelial differentiation in the embryonic ovary of the rat

The development and sexual differentiation of gonads in female rat embryos and fetuses between the ages of 11 and 17 days was studied by immunocytochemical analysis of intermediate filament proteins and laminin by light and electron microscopy. In the 11-day-old pregonadal embryo, the surface epithelial cells in the ventral cortex of the mesonephros contained desmin but not cytokeratin or vimentin. The development of the gonad began on the following day by proliferative growth of the mesonephric surface cells, which like the subepithelial cells soon expressed vimentin in addition to desmin. The differentiation continued by formation of separate epithelial cell clusters, which joined into cords, irregular in shape and size. Desmin disappeared from the cord cells and cytokeratins appeared while vimentin remained in all somatic cell types. Desmin was especially abundant in some stromal cells adjacent to the epithelial tissues. After the segration of the basic ovarian tissues, vimentin and desmin decreased and cytokeratins appeared in the surface epithelial cells. New changes in cytokeratin expression appeared with the differentiation of the embryonic cords in a sex-specific manner with gradual decrease of reactivity for cytokeratin 18. No immunoreaction to the neurofilament proteins was found at the present ages, and the germ cells were negative for intermediate filaments. The results show that desmin is expressed in several primitive ovarian and mesonephric cells even though they are not myogenic.(ABSTRACT TRUNCATED AT 250 WORDS)