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

Expression of Epithelial and Mesenchymal Differentiation Markers in the Early Human Gonadal Development

Expressions of cytokeratin 8 (CK8), vimentin, nestin, and alpha-smooth-muscle-actin (alpha-SMA) were analyzed in the developing gonads of 12, 5-9 week old (W) human conceptuses by immunohistochemistry and immunofluorescence. During the investigated period, the number of CK8 positive cells increased from 56% to 92% in the gonadal surface epithelium, from 50% to 60% in the stroma, and from 23% to 42% in the medulla. In the early fetal period, the cell expression of CK8 increased in all gonadal parts, whereas primordial germ cells (PGC) remained negative. The expression of vimentin increased in the gonad stroma (gs) from 73% to 88%, and in the surface epithelium from 18% to 97% until ninth W. The medulla had the highest expression of vimentin in the seventh to eighth W (93%). Vimentin and CK8 colocalized in the somatic cells, while some PGCs showed vimentin expression only. Initially, nestin was positive in the gonad surface epithelium (8%) and stroma (52%), however during further development it decreased to 1% and 33%, respectively. In the early fetal period, the nestin positive cells decreased from 44% to 31% in the gonad medulla. Alpha-SMA was positive only in the blood vessels and mesonephros. The described pattern of expression of intermediate filaments (IF) in developing human gonads suggests their role in the control of PGC apoptosis, early differentiation of gs cells and cell migration. Both epithelial and mesenchymal origins of follicular cells and possible epithelial-to-mesenchymal transition of somatic cells is proposed. Lastly, IF intensity expression varies depending on the cell type and developmental period analyzed. Anat Rec, 300:1315-1326, 2017. © 2017 Wiley Periodicals, Inc.

The balance of proangiogenic and antiangiogenic VEGFA isoforms regulate follicle development

Vascular endothelial growth factor A (VEGFA) has been extensively studied because of its role in follicular development and is a principal angiogenic factor essential for angiogenesis. Since vascularization of the theca layer increases as follicles progress in size through preantral and antral stages, VEGFA might influence follicle growth via the regulation of angiogenesis. However, VEGFA might also influence follicular development through nonangiogenic mechanisms, since its expression has been localized in nonvascular follicles and cells. Alternative mRNA splicing of eight exons from the VEGFA gene results in the formation of various VEGFA isoforms. Each isoform has unique properties and is identified by the number of amino acids within the mature protein. Proangiogenic isoforms (VEGFA_XXX) are encoded by exon 8a, whereas a sister set of isoforms (VEGFA_XXXB) with antiangiogenic properties is encoded by exon 8b. The antiangiogenic VEGFA_XXXB isoforms comprise the majority of VEGFA expressed in most tissues, whereas expression of the proangiogenic VEGFA isoforms is upregulated in tissues undergoing active angiogenesis. Although proangiogenic and antiangiogenic isoforms can now be distinguished from one another, many studies evaluating VEGFA in ovarian and follicular development up to now have not differentiated proangiogenic VEGFA from antiangiogenic VEGFA. Experiments from our laboratory indicate that proangiogenic VEGFA promotes follicle recruitment and early follicular development and antiangiogenic VEGFA inhibits these processes. The balance of proangiogenic versus antiangiognic VEGFA isoforms is thus of importance during follicle development. Further studies are warranted to elucidate the way that this balance regulates follicular formation and progression.

Ovarian granulosa cell lines

The ovary is a complex endocrine gland responsible for production of sex steroids and is the source of fertilizable ova for reproduction. It also produces various growth factors, transcription factors and cytokines that assist in the complex signaling pathways of folliculogenesis. The ovary possesses two primary steroidogenic cell types. The theca cells (and to a lesser extent, the stroma) are responsible for androgen synthesis, and the granulosa cells are responsible for conversion of androgens to estrogens, as well as progesterone synthesis. These cells undergo a transformation in the luteal phase of the menstrual cycle, converting them from estrogen producing, to predominantly progesterone producing cells. Understanding the molecular mechanisms regulating these cells is essential in understanding the regulation of steroidogenesis and reproduction. Creation of appropriate in vitro cell model systems can provide important tools for the study of ovarian function. This has led to the development of ovarian steroidogenic cell lines in several laboratories. Developing theca cell lines has met with limited success. Conversely, numerous human and animal granulosa cell lines have been developed. This review will discuss the existing granulosa cell lines and their characteristics.

Structural and regulatory macromolecules in sex differentiation of gonads

The manifestations of sex determination were studied in vivo by detection and localization of structural and regulatory macromolecules (type IV collagen alpha 1, alpha 2, alpha 3, alpha 4, and alpha 5; laminin alpha 5, beta 1, and beta 2; cytokeratins 18 and 19, desmin, vimentin; integrin alpha(6;) anti-Müllerian hormone (AMH); and SOX9 in developing male and female gonads by light and electron microscopy, immunocytochemistry, and protein analysis. The goal has been to find sex-related differences and on this basis to offer new molecules to be tested further for a possible role in sex determination. Specific antibodies for each molecule or for a defined subchain were used to allow tentative correlation with specific genes. Sex-dependent differences in timing and localization were found in laminin alpha 5; collagen, alpha 3, alpha 4, and alpha 5; cytokeratin 19; AMH; and SOX9. On this basis we hypothesize that the transcription factors for the mentioned structural proteins must be directly or indirectly involved in the regulatory chain of gonadal sex differentiation. Especially promising is the finding in the rat that laminin alpha 5 chain disappears from the basement membrane of embryonic testicular cords (Sertoli cells) when AMH secretion by Sertoli cells starts, and that the same chain reappears as the AMH disappears two weeks after birth. Via AMH as an intermediary factor, we now have for the first time a putative cascade of regulatory molecules from SRY, SF1, and SOX9 to a component of a structural protein (laminin alpha 5 chain) which directly participates in the formation of the basement membrane of the testicular cords. J. Exp. Zool. 290:523-528, 2001.

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.

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.

Sex-specific localization of laminin alpha 5 chain in the differentiating rat testis and ovary

The localization of laminin (Ln) alpha 5, beta 1 and beta 2 chains in the differentiating rat testis and ovary was studied by immunolabeling light and electron microscopy. The initial formation of the male and female gonadal blastemas included an emergence of Ln alpha 5 and beta 1 chains, but not of Ln beta 2 chain. The sexual differentiation of the embryonic male gonadal cords included rapid sex-specific disappearance of the incipient Ln alpha 5 chain. The rete testis cords, in contrast, remained positive for Ln alpha 5 chain. In the postnatal testis, the Ln alpha 5 chain reappeared in Ln beta 1 chain-positive cord basement membranes, which also became positive for Ln beta 2 chain. The differentiating myoid cells also gradually became positive for both Ln alpha 5 and Ln beta 1 chains. In the ovary Ln alpha 5 chain persisted in BMs of the cords throughout the fetal phase. Small and newly formed follicles in the early postnatal rat ovary were also positive for Ln alpha 5 chain, whereas growing and large follicles were negative. During the early postnatal phase, Ln beta 1-chain positive follicular BMs became also positive for the Ln beta 2 chain. Basement membranes of testicular and ovarian surface epithelia contained the Ln alpha 5 chain throughout the study. The blood vessels of the male and female gonad showed differentiation-dependent variation in their reactivity for the Ln alpha 5 and beta 2 chains. The present results show that the Ln alpha 5 chain is an early molecular marker for sexual differentiation, which therefore may be regulated by the testis-determining factors. The results also show that in the early postnatal rat ovary, the follicular basement membranes are heterogeneous in their Ln content, which may offer a means to distinguish different follicular populations from each other and to identify the different stages of follicular growth.

Patterns of keratins 8, 18 and 19 during gonadal differentiation in the mouse: sex- and time-dependent expression of keratin 19

The acidic keratins K18 and K19 have been shown to display a sex-specific expression during gonadal differentiation in the rat. To extend these findings, we have undertaken a study of the expression of genes encoding for K18 and K19 and their basic partner K8 in the mouse from 10.5 days of gestation until adulthood, using immunofluorescence, in situ hybridization, and reverse transcriptase polymerase chain reaction (RT-PCR). In the urogenital ridge at 10.5 days of gestation, K18, K19, and K8 are present, in both sexes, in coelomic epithelium in the area of the prospective gonad. At 11 days and 10 h of gestation, they are detected in differentiating gonadal blastema. In male gonads at 11 days and 16 h of gestation the first Sertoli cells differentiate. They are stained for anti-Müllerian hormone by immunofluorescence and appear as dispersed cells throughout the blastema. Progressively, they adhere to each other and form differentiating seminiferous cords. K19 disappears as Sertoli cells differentiate. K18 and K8 continue to be detected in Sertoli cells during fetal life and after birth until 14 days postpartum. In the adult testis, no keratin is observed. In differentiating ovaries, the three keratins are present in somatic cells of the ovigerous cords during fetal life and in primordial follicles differentiating from 1-2 days postpartum. In the course of follicular development, K19 is no longer detected as primordial follicles differentiate into growing follicles. K18 and K18 are present in all stages of follicular development. These results show both differences and similarities with the results previously obtained in the rat. In the mouse, in contrast to the rat, keratins are detected in adult ovaries, and K18 is found in undifferentiated gonads and in ovaries. K18 is, thus, not specific to the testis in the mouse, as it is in the rat. In both species, K19 ceases to be expressed in male gonads as Sertoli cells differentiate and form seminiferous cords. The present observations confirm that downregulation of K19 gene expression in the fetal testis is one of the earliest molecular events attesting the commitment of the undifferentiated gonad to the male differentiative pathway.

Differential distribution of type IV collagen chains in the developing rat testis and ovary

The localization of type IV collagen alpha 1-alpha 5 chains in the differentiating rat testis and ovary was studied by immunocytochemistry. The initial formation of the testis and ovary included the appearance of collagen alpha 1/alpha 2(IV) chains in the gonadal blastemas. Upon further differentiation of the epithelia of the gonads alpha 1/alpha 2(IV) chains became localized in all of the respective basement membranes (BMs). The alpha 3, alpha 4 and alpha 5 chains of type IV collagen were not detectable in the prenatal rat testis and ovary. With the postnatal differentiation of the rat testis the alpha 3-alpha 5(IV) chains gradually appeared, and were localized in BMs of the testicular cords and seminiferous tubules, rete cords, myoid cells, surface epithelium, Leydig cells, and in some blood vessels. In the postnatal rat ovary, the alpha 3(IV) chain appeared in the BMs of small cortical follicles whereas the BMs of secondary and more deeply localized follicles were devoid of this chain. The alpha 1/alpha 2(IV) chains were abundant in the theca. A reaction for alpha 3-alpha 5(IV) chains also appeared in the BM of the ovarian surface epithelium and of some blood vessels after birth. The present results show that the alpha 3-alpha 5(IV) chains are not only less widely distributed than the alpha 1/alpha 2(IV) chains but are also synthesized much later in development. The late appearance of the alpha 3-alpha 5(IV) chains shows that the development of the mature testicular and ovarian BMs is a long process and that the time schedule for the synthesis of these chains is different from that of many other extracellular matrix proteins. A careful analysis of the expression of alpha 3(IV) chain may be useful in the further study of the kinetics and regulation of ovarian follicular growth.

Spatiotemporal changes in cytokeratin expression in the neonatal rat ovary

Ovarian granulosa cells are derived embryologically from two keratin-positive epithelia of mesodermal origin, the ovarian rete and the ovarian surface epithelium. In the rat, presumptive granulosa cells still express keratin at birth but as they acquire functions related to oocyte support and steroidogenesis in the maturing ovary they lose this epithelial differentiation marker. Using double-label immunofluorescence microscopy, we examined the distribution of keratin-expressing granulosa cells in rat ovaries on days 1-10 postpartum in relation to (i) laminin and collagen type IV in follicular basement membranes, (ii) the zona pellucida, and (iii) 3β-hydroxysteroid dehydrogenase activity. Keratin was present in most (pre)granulosa cells on days 1-3. As the cells became multilayered in growing follicles, keratin was retained by granulosa cells adjacent to follicular basement membranes but disappeared from cells that were displaced towards follicular centers. From day 7 on, large follicles lacked keratin altogether. Laminin was a consistent component of follicular basement membranes at all ages, while collagen IV varied and diminished in parallel with keratin. 3β-Hydroxysteroid dehydrogenase was demonstrable in stromal interstitial cells from day 7 on. Zona pellucida first appeared in primary follicles adjacent to keratin-positive cells and subsequently became surounded with keratin-negative granulosa cells in growing follicles. The results suggest different roles for laminin and collagen IV in follicular basement membranes and support the hypothesis that keratin expression by granulosa cells depends on paracrine interactions with the ovarian stroma. In early growing follicles, these interactions may be interrupted by physical removal from the vicinity of the basement membranes as the granulosa cells become multilayered. In the more mature follicles, the loss of keratin from all granulosa cells suggests that the required stromal signals cease, perhaps as the perifollicular stroma differentiates into the theca.Key words: ovary, differentiation, keratin, basal membrane, development.

Cytokeratin cytoskeleton in the differentiating ovarian follicle of the lizard Podarcis sicula Raf

By immunoblotting and immunocytochemical techniques, we characterized the cytokeratins previously localized by us in the previtellogenic ovarian follicle of Podarcis sicula. Our results show that these cytokeratins correspond to those expressed in the monolayered epithelia. In fact, the immunoblotting analysis showed that the NCL-5D3 antibody, specific for human low molecular weight cytokeratins expressed in monolayered epithelia, reacted with the cytokeratins extracted both from the ovary and from the monolayered intestinal mucosa of Podarcis sicula. Furthermore, this antibody, in this reptile as in humans, clearly immunolabeled sections of corresponding tissues. The organization of the cytokeratin cytoskeleton in the main steps of the ovarian follicle differentiation was also clarified. The reported observations suggest that in Podarcis sicula, the cytokeratin cytoskeleton is absent in the early oocytes. It first appears in the growing oocytes as a thin cortical layer in concomitance with its becoming visible also in the enlarging follicle cells. In the larger follicles, this cytoskeleton appears well organized in intermediate cells and in particular in fully differentiated pyriform cells. In both these cells a cytokeratin network connects the cytoplasm to the oocyte cortex through intercellular bridges. At the end of the previtellogenic oocyte growth, the intense immunolabeling of the apex in the regressing pyriform cells suggests that the cytokeratin, as other cytoplasmic components, may be transferred from these follicle cells to the oocyte. At the end of the oocyte growth, in the larger vitellogenic oocytes surrounded by a monolayer of follicle cells, the cytokeratin constitutes a heavily immunolabeled cortical layer thicker than in the previous stages.

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.

Ultrastructural and immunocytochemical analysis of diploid germ cells isolated from fetal rabbit gonads

Germ cells were isolated from rabbit fetal gonads between 18 and 22 days post coitum and examined morphologically, ultrastructurally and for immunocytochemical and cytochemical characteristics. Observations were compared with the information available from the corresponding cells of other mammalian species. The general morphology and ultrastructure of healthy isolated rabbit fetal germ cells were found to be very similar to those of the rabbit and mouse diploid germ cells in situ. Moreover, rabbit fetal germ cells shared common immunocytochemical characteristics with mouse undifferentiated embryonic stem cells or embryonic carcinoma cells, such as the presence of TEC-1 (SSEA-1) antigens, a peripheral network of F-actin, the absence of cytokeratins 8/18 and lamins A/C and an alkaline phosphatase activity. No difference between the sexes was observed. Morphological and physiological similarities with the migrating and cultured primordial germ cells of the mouse also suggest that diploid rabbit germ cells would be good candidates for deriving pluripotential embryonic germ cells (EG cells) if favourable culture conditions could be found. In conclusion, the rabbit may be a suitable model for investigations on EG cells in domestic mammals with delayed meiosis.

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.

Desmin expressing nonhematopoietic liver cells during rat liver development: an immunohistochemical and morphometric study

The expression and cellular distribution of desmin, alpha-smooth muscle actin (A-SMA) and cytokeratin no. 8 (CK-8) and no. 18 (CK-18) in normal adult, neonatal and fetal rat liver were examined immunohistochemically on cryostat sections. At days 14 and 15 of gestation, nonhematopoietic cells in embryonic liver were strongly desmin-positive, and some of the cells, mainly located in the periphery, were also stained with anti-A-SMA. Desmin immunoreactivity gradually decreased from day 16 of gestation. A close association of desmin-positive cell processes with hematopoietic cells was observed during fetal and early neonatal development. From day 16 of gestation the pre-hepatocytes became desmin-negative, remained CK-8 and CK-18 positive. Desmin-expressing cells were numerous in the liver from the embryonic period to the neonatal age. However, their absolute number per unit area, as well as their number relative to hepatocytes, decreased with age. We suggest that desmin-positive cells in embryonic liver may act as stromal cells in the hepatic hematopoietic microenvironment and support hepatocyte development.

Keratin expression and steroidogenesis in rat granulosa cells, transformed with the Kirsten-ras and SV40 oncogenes singly and in combination

The keratins are a component of the cytoskeleton that is present in fetal and neonatal rat granulosa cells (ROG), but disappears as the cells undergo postnatal steroidogenic differentiation. Steroidogenesis is initiated in the fetus as a low level constitutive function which is cAMP responsive, but becomes responsive to gonadotrophic hormones only after birth. ROG from PMSG-primed immature rats, like mature ROG, are keratin negative, highly steroidogenic and gonadotrophin-responsive, but rapidly lose their steroidogenic capacity in culture. In such cultured cells, transformation with the Kirsten-ras oncogene (v-Ki-ras) maintains low levels of constitutive steroidogenesis and responsiveness to cAMP, and induces the expression of keratin. To determine whether similar changes would occur in cells expressing both the SV40 and v-Ki-ras, cultured ROG were transformed with SV40 early genes, with Kirsten murine sarcoma virus (KiMSV), or with both agents concurrently. Keratin was demonstrated by fluorescence microscopy and Western blots, and progesterone production by RIA. ROG transformed with SV40 alone became immortalized but secreted little steroid and lacked keratin. In contrast, three cell lines, co-transformed with SV40 plus KiMSV, acquired keratin as well as the capacity to secrete progesterone in response to cAMP, closely resembling cells transformed with Ki-ras alone. KiMSV-transformed muscle fascia fibroblasts lacked both steroidogenic potential and keratin. The results show that the complex, v-Ki-ras-induced changes in steroidogenesis and keratin expression are reproducible and tissue specific. The phenotypic resemblance between singly and doubly transformed ROG indicates that the v-Ki-ras oncogene does not act by overcoming SV40-mediated inhibition of differentiation.(ABSTRACT TRUNCATED AT 250 WORDS)

Switch in the expression of the K19/K18 keratin genes as a very early evidence of testicular differentiation in the rat

It has been shown previously that acidic K18 and K19 keratins display a differential immunohistochemical pattern of expression during sexual differentiation of the gonads in the rat (Fridmacher et al. (1992) Development 115, 503-517). The present results indicate that K18 and K19 gene expression is regulated at the transcriptional level. The analysis was performed by Northern Blot, reverse transcriptase polymerase chain reaction (RT-PCR) and in situ hybridization. PCR products were cloned, sequenced and used as species-specific K18 and K19 riboprobes for in situ hybridization. K19 mRNA but not K18 mRNA was detected in undifferentiated gonads and in somatic cells of ovarian cords throughout the fetal ovary development. K18 mRNA expression appeared in male gonads, at 13.5 days of gestation, at the onset of testicular differentiation, as the first Sertoli cells differentiated and aggregated to form seminiferous cords. As testicular differentiation progressed, K19 mRNA disappeared and, from 14.5 days of gestation on, fetal Sertoli cells expressed exclusively K18 mRNA. The changes in the transcriptional activity of K19 and K18 genes, observed in male gonads, occur characteristically at the very beginning of testicular differentiation. In the male pathway of sexual differentiation, the switch in K19/K18 gene expression is, in addition to the activation of the anti-Müllerian hormone gene, the most precocious regulative event occurring after the expression of the testis determining factor SRY.

Cytokeratin expression in the developing vagina of the postnatal gerbil (Meriones unguiculatus)

During postnatal development the vaginal epithelium of the Mongolian gerbil is transformed from two to three layers into a stratified, first mucified subsequently keratinized squamous epithelium. Changes in the expression of cytokeratins were studied and the immunohistochemical results compared with the ultrastructural findings at the corresponding stage. The first 10 postnatal days (days pn) were characterized by a moderate, positive immunoreaction for pancytokeratin in all vaginal cell layers. A faint reaction was caused by mAB CK 18.01 against CK 1, 5, 6 and 8. The appearance of mucous granules in the luminal cells after 15 pn seemed to coincide with an increase in cytokeratins. The immunoresponse for pancytokeratin in these cells was very intense compared with the reaction in the basal cell layers. Mucocytes during development and at proestrus were the only cells which reacted faintly positive with mAB against CK 18 alone. The keratinizing epithelium, which differentiates after day 40 pn, reacted strongly positive for pancytokeratin in the keratinizing layers, desquamating, fully keratinized cells, however, showed a negative reaction. The data indicate that mucocytes are not transformed squamous keratinized cells, but represent a cell category with its individual differentiation potential. Vimentin was not expressed. Neither the epithelium of the sinus vagina nor of the Müllerian vagina displayed any response.

Sex-dependent expression of tenascin-C in the differentiating fetal rat testis and ovary

The cellular mechanisms controlling sexual differentiation of fetal gonads are poorly understood. By examining the protein and mRNA expression of tenascin-C in correlation with the immunocytochemical detection of alpha-smooth muscle actin (alpha-SMA) and basement membrane heparan sulfate proteoglycan (HSPG) we demonstrate a clear-cut sex-and development-dependent expression pattern of tenascin-C in the rat testis, ovary and mesonephros. Immunocytochemistry and in situ hybridization of tenascin-C in 15-day-pc fetal testis and ovary showed protein and mRNA accumulation within the mesenchyme of the mesogonadal connection. In addition to the male and female mesonephros, some labeling could also be seen within the testicular tunica albuginea and intraovarian mesenchymal septa. In the 17-day-pc testis abundant accumulation of tenascin mRNA and protein appeared in the tunica and mediastinum testis, but not at all in the intratesticular mesenchyme. A similar pattern was still seen in the newborns where, however, a decrease in the anti-tenascin immunoreactivity of the tunica and mediastinum could be demonstrated. In contrast to the testis, expression of tenascin in 17-day-pc ovaries was widespread within the hilus and the entire intragonadal mesenchyme where it continued to accumulate also in newborns. Northern blot analysis of tenascin-C mRNAs showed one message of 8.0 kb in the 15-day-pc male and female gonads. An additional weak signal of 6.5 kb was seen in the female mesonephros. In the 18-day-pc testis, the 6.5-kb signal appeared stronger than the 8.0-kb signal. In contrast to the testis, the 6.5-kb message was weak in the developing ovary where the 8.0-kb signal had an intense peak on the day 18 pc. Further, in the ovary, mesenchymal accumulation of HSPG coincided with the spatial distribution of tenascin. In the testicular tunica and in the mesenchyme of the male and female genital ducts expression of tenascin was parallel with the differentiation of smooth muscle tissue, detected by labeling for alpha-SMA, which also indicated the tenascin-negative myoid cells of the testis. Our results indicate that tenascin expression in the fetal rat internal genitalia is involved in the differentiation of smooth muscle cells but not intratesticular myoid cells. In the ovarian mesenchyme, tenascin-C may have a specific function in the dynamic remodeling of the ovarian cords.

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)