The uterovaginal sperm host glands of the quail (Coturnix coturnix japonica): an ultrastructural and ultracytochemical study

Gross and Histomorphological Study of the Ovary and Oviduct of Turkey Hen with Especial Emphasis on the Sperm-Host Gland

Turkey bird is one of the popular poultry species which is reared primarily for meat production and considered as one of the major sources of animal protein. With such importance of this species, this study was designed to investigate the gross and histomorphology of the ovary and oviduct with especial emphasis on sperm-host glands of the turkey hen involving ten mature female turkeys (Meleagris gallopavo). The present study highlighted the distribution pattern of sperm-host glands (SHGs) in the oviduct of turkey hen that has a potential role in producing a fertile egg in poultry industries. The oviduct of turkey consists of the infundibulum, magnum, isthmus, uterus, and vagina which are sole distributors for making nutrition enriched egg. The tissue samples were collected from the ovary, different segments of the oviduct and especially uterovaginal junction (UVJ) and infundiomagnal junction of the oviduct. The ovaries and the oviducts were dissected and fixed in Bouins solution and processed for a light microscopic study. Histologically, the left ovary of turkey consisted of an outer cortex and inner medulla, with different stages of follicles. In all areas of the oviduct except the infundibulum and vagina, the tunica mucosa epithelium was lined with ciliated pseudo stratified columnar epithelium, and the lamina propria-submucosa contained branched tubular glands. Sperm-storage tubules were observed in the uterovaginal junction and infundibulo-magnum junction. These tubules were mostly branched, slightly coiled and extended into the lamina propria from the bases of the mucosal folds. These glands had proximal and distal parts; the proximal part was lined by pseudostratified columnar epithelium and distal part by non-ciliated simple columnar epithelium. The number of sperm host glands was more at uterovaginal junction than infundibulomagnal junction. The sperm-host glands might play a functional role in the storage and release of spermatozoa from the SHGs in response to oviposition or ovulation. The results would help poultry scientists and farmers in developing effective disease control and growth strategies.

Detrimental effects of excessive fatty acid secretion on female sperm storage in chickens

Background

Female sperm storage (FSS), the maintenance of sperm inside the female reproductive tract for an extended period of time, is pervasive among organisms with internal fertilization. Because FSS enables asynchronous mating and fertilization, it could be extremely important to reproduction. However, the physiological mechanisms underlying prolonged preservation and maintenance are poorly understood. Here, we used chicken, a typical oviparous animal, to determine the mechanisms ensuring sperm functionality in sperm storage tubules (SSTs).

Results

We performed an insemination experiment on over two thousand hens at two periods, and found that the FSS capabilities varied widely among individuals. Except for the differences in the SST density between the two groups with distinct FSS abilities, we quantitatively profiled small-molecule metabolites derived from SST cells, and identified 28 metabolites with differential expression. In particular, high levels of lipids, fatty acids and lipid peroxidation product were observed in hens with low FSS capability. Pathway analysis showed that these differential metabolites were significantly enriched in the biosynthesis of unsaturated fatty acids. Moreover, we detected the total antioxidant capacity and lipid peroxidation level of SSTs, and found that chickens with a lower FSS ability had a significantly higher content of lipid peroxidation end-product, which was 2.4-fold greater than chickens with a higher FSS capability, and no significant difference was found in the total antioxidant capacity between these two groups.

Conclusions

Our findings reveal that the long-term storage of sperm and the maintenance of their function in the female reproductive tract require an adequate microenvironment. The superabundance of fatty acids secreted by SST cells had detrimental effects on sperm storage in the female reproductive tract. Lipid peroxidation produces toxic biological substances that may cause irreversible damage to resident spermatozoa, resulting in short-term sperm retention and decreased fertility. Our findings provide new avenues for studying sperm storage and sustaining fertility.

Role of genome-wide mRNA-seq profiling in understanding the long-term sperm maintenance in the storage tubules of laying hens

Sperm storage function of the sperm storage tubules (SSTs) is directly correlated with the fertility of laying hens. SSTs are located at the utero-vaginal junction (UVJ) and infundibulum of the hen oviduct. However, little is known about the cellular and molecular mechanisms responsible for long-term sperm maintenance in the lumen of the SSTs. In this study, we profiled transcriptomes to detect the different gene expressions between infundibulum and UVJ using RNA-seq. As a result, we identified a total of 1382 differentially expressed genes (DEGs). GO analysis showed that fat acid metabolism, regulation of cell differentiation, regulation of transport, and immune response were enriched for these DEGs, and many of the pH-regulatory functions genes such as CAIV and SLC4A4 were highly expressed in UVJ, which inferred that SSTs could preserve sperm by regulating physiological functions in UVJ. Our results provide new insight to understand the specific function for SSTs to extend sperm life span in the oviduct of laying hens.

Finite cell lines of turkey sperm storage tubule cells: ultrastructure and protein analysis

Cell lines of turkey sperm storage tubule (SST) epithelial cells were established. Turkey SSTs were dissected from freshly obtained uterovaginal junction (UVJ) tissue and placed in explant culture on various substrates and media. Primary cultures of SST epithelium only survived and grew from SST explants that were cultured on inactivated Sandoz inbred strain, thioguanine- and ouabain-resistance (STO) mouse feeder-cell layers in 12% fetal bovine serum-supplemented Dulbecco's Modified Eagle Medium mixed 1:1 with F12 nutrient mixture. Three independent primary colonies gave rise to 3 finite cell lines, SST-1, -2, and -3, which were continuously cultured for 8 to 16 passages at 1:3 passage ratios over a period of 3 to 4 mo. The cells were passaged by pretreatment with Y27632 and dissociation with Accutase. The SST cells grew as tightly knit monolayers on top of the feeder cells at a slow rate (approximately 96 h doubling time) at a medium pH of approximately 6.9. Lipid vacuoles were visible by light microscopy in the cells particularly at the periphery of growth. Transmission electron microscopy revealed the cells to be a polarized epithelium with apical microvilli and to have lateral tight-junction-like unions and associated desmosomes. Numerous secretory vesicles filled the upper portion of the cells’ cytoplasm, and nuclei and other major organelles such as mitochondria, rough endoplasmic reticulum, and Golgi apparatus were distributed somewhat lower in the cytoplasm. The secretory vesicles resembled mucin secretory vesicles. Proteomic analysis by mass spectroscopy of the conditioned medium of the cells, and of the cells themselves, showed the cell lines did not secrete large amounts of any particular protein, and the analysis confirmed their epithelial character. In conclusion, the SST-derived cell lines resembled the mucus-secreting cells found in the epithelium lining the UVJ of the turkey's reproductive tract.

Changes in localization and density of CD63-positive exosome-like substances in the hen oviduct with artificial insemination and their effect on sperm viability

Avian sperm are stored in the sperm storage tubules (SSTs) of the hen oviduct for a prolonged period. However, the precise mechanisms by which sperm are kept alive in the SSTs are still not fully understood. The aim of this study was to determine whether exosomes are secreted by SST cells and play a role in the survival of sperm. Utero-vaginal junction (UVJ) tissue from approximately 50 wk old White Leghorn hens was collected before (control group) and after intravaginal insemination with seminal plasma (SP group) or semen (AI group). The samples were used to prepare frozen sections and total protein extraction. The localization of the CD63, an exosome marker, was determined by immunohistochemistry and its protein level in the UVJ mucosal tissues was examined by Western blot. Exosomes were isolated from the culture media of UVJ and vaginal mucosa cells by ultracentrifugation and characterized by SDS-PAGE and Western blot. The viability and motility of sperm incubated with exosomes were also examined. CD63 was localized in the apical region of UVJ mucosal epithelium cells and SST cells of control, SP, and AI groups. The CD63 protein decreased in SST cells surrounding resident sperm and tended to appear in the SST lumen in the AI group. The protein level of CD63 in UVJ mucosal tissues was significantly higher in the AI group than control. The CD63 protein (approximately 75 kDa) was detected in ultracentrifugation pellets from the culture medium of UVJ and vagina cells. The viability of sperm incubated with 1 μg/μl vaginal exosomes was significantly decreased but was not affected by UVJ exosomes. These results suggest that exosomes were synthesized by SST cells and may be secreted into SST lumen when sperm were stored in SSTs. The role of SST exosomes in sperm storage needs to be examined further.

Sperm storage in the female reproductive tract in birds

The ability to store sperm in the female genital tract is frequently observed in vertebrates as well as in invertebrates. Because of the presence of a system that maintains the ejaculated sperm alive in the female reproductive tract in a variety of animals, this strategy appears to be advantageous for animal reproduction. Although the occurrence and physiological reasons for sperm storage have been reported extensively in many species, the mechanism of sperm storage in the female reproductive tract has been poorly understood until recently. In avian species, the specialized simple tubular invaginations referred to as sperm storage tubules (SSTs) are found in the oviduct as a sperm storage organ. In this review, we summarize the current understanding of the mechanism of sperm uptake into the SSTs, maintenance within it, and controlled release of the sperm from the SSTs. Since sperm storage in avian species occurs at high body temperatures (i.e., 41 C), elucidation of the mechanism for sperm storage may lead to the development of new strategies for sperm preservation at ambient temperatures, and these could be used in a myriad of applications in the field of reproduction.

Sperm activation by heat shock protein 70 supports the migration of sperm released from sperm storage tubules in Japanese quail (Coturnix japonica)

Systems for maintaining the viability of ejaculated sperm in the female reproductive tract are widespread among vertebrates and invertebrates. In birds, this sperm storage function is performed by specialized simple tubular invaginations called sperm storage tubules (SSTs) in the uterovaginal junction (UVJ) of the oviduct. Although the incidence and physiological reasons for sperm storage in birds have been reported extensively, the mechanisms of sperm uptake by the SSTs, sperm maintenance within the SSTs, and control of sperm release from the SSTs are poorly understood. In this study, we demonstrated that the highly conserved heat shock protein 70 (HSP70) stimulates sperm motility in vitro and also that HSP70 expressed in the UVJ may facilitate the migration of sperm released from the SSTs. Quantitative RT-PCR analysis demonstrated that the expression of HSP70 mRNA in the UVJ increases before ovulation/oviposition. Gene-specific in situ hybridization and immunohistochemical analysis with a specific antibody to HSP70 demonstrated that HSP70 is localized in the surface epithelium of the UVJ. Furthermore, injection of anti-HSP70 antibody into the vagina significantly inhibited fertilization in vivo. In addition, we found that recombinant HSP70 activates flagellar movement in the sperm and that the binding of recombinant HSP70 to the sperm surface is mediated through an interaction with voltage-dependent anion channel protein 2 (VDAC2). Our results suggest that HSP70 binds to the sperm surface by interacting with VDAC2 and activating sperm motility. This binding appears to play an important role in sperm migration within the oviduct.

Período de permanência de espermatozoides em glândulas hospedeiras de espermatozoides e glândulas infundibulares em codorna de corte

Para determinar o tempo de permanência de espermatozoides nas glândulas hospedeiras de espermatozoides (GHEs) e nas glândulas infundibulares (GIs) de codorna de corte (Coturnix coturnix coturnix), foram utilizados 12 machos e 66 fêmeas, totalizando 78 codornas em fase reprodutiva. As fêmeas foram distribuídas em 11 grupos e acasaladas por 24 horas em gaiolas individuais. Os machos, utilizados de modo intercalado, foram separados do contato com as fêmeas e colocados em descanso. As aves do grupo-controle (G0 - seis fêmeas) foram abatidas no início do experimento, enquanto as 60 fêmeas acasaladas foram distribuídas em 10 grupos (G1 a G10, com seis fêmeas cada) e abatidas a cada período de 24 horas, de forma sequencial. Fragmentos foram obtidos da região uterovaginal e do infundíbulo e submetidos às análises histológica, histoquímica e histométrica com técnicas de rotina. Os resultados morfométricos mostraram que 46% das GHEs continham espermatozoides em seu lume no primeiro dia após o acasalamento, diminuindo gradativamente nos dias posteriores chegando a 3% no quinto dia. Nesse período, os espermatozoides ascendem em direção às GIs, onde permanecem viáveis e férteis por, pelo menos, 96 horas após deixarem as GHEs, possibilitando a postura de ovos férteis por 10 dias, em média, após o acasalamento.

Aspectos morfológicos, morfométricos e histoquímicos dos túbulos armazenadores de espermatozoides da fêmea do peru Meleagris gallopavo

Fragmentos da junção uterovaginal de 16 exemplares de fêmeas adultas de peru foram examinados, com o objetivo de determinar as modificações morfométricas e histológicas dos túbulos armazenadores de espermatozoides (SST), durante os períodos de atividade e repouso reprodutivo. Os estudos foram realizados a partir de dissecações do oviduto esquerdo, utilizando-se técnicas histológicas, histoquímica e histométricas de rotina. Essas estruturas originam-se de invaginações do epitélio das pregas da região uterovaginal e apresentam-se tubulosas, simples e não ramificadas, com epitélio formado por células prismáticas estreitas, claras e escuras, com núcleo vesiculoso basal e microvilos apicais. As secreções dessas células apresentaram reações negativas para PAS e Alcian Blue, indicando ausência de mucossubstâncias. Os parâmetros morfométricos utilizados mostraram que há diferenças significativas entre os períodos de atividade reprodutiva e de repouso. Na fase de atividade reprodutiva, o comprimento tubular, o volume tubular, o volume do lume, o número de SST na junção uterovaginal, o diâmetro externo e interno, a altura celular e o número de células por túbulos estão aumentados, e observam-se espermatozoides agrupados na luz do lume e células claras e escuras nos túbulos com vesículas supranucleares no citoplasma das células tubulares. Na fase de repouso, os parâmetros morfológicos estão reduzidos e não são encontrados espermatozoides na luz do lume. Nesta fase, não são evidenciadas as células escuras nem as vesículas supranucleares no citoplasma celular.

Development of sperm storage tubules in the quail during sexual maturation

The development of the utero-vaginal sperm storage tubules (SST) in the quail during sexual maturation was studied using light microscopy and image analysis. SST development starts at around 28 days with low columnar cells, 10.9 +/- 0.7 microm high, found at the base of mucosal folds in the distal uterus. Seven days later, small bud-like invaginations consisting of columnar, 16.4 +/- 1.1 microm high cells with basal nuclei were found in this region. An extremely rapid growth of the oviduct occurred at approximately 40-42 days of age with considerable variation in oviductal length between birds, coefficient of variation (CV) 64.8% and 66.2%, respectively. Two of these birds had SST containing spermatozoa but were not laying. At 49 days, oviductal length was 24 +/- 0.5 cm (CV 2.0%), and all birds had functional SST with spermatozoa and had started to lay. Mature SST consist of columnar, nonciliated cells, 19.8 +/- 0.7 microm high. Although development of SST in the quail, to a large extent, coincides with the development of the rest of the oviduct, the present findings suggest that utero-vaginal sperm storage is possible before the complete maturation of the oviduct and subsequent onset of lay.

Immunolocalization of progesterone and estrogen receptors in the sperm storage tubules of laying and diethylstilbestrol-injected immature hens

The goal of this study was to determine whether sperm storage tubules (SST) in the uterovaginal junction (UVJ) contain receptors for progesterone and estrogen (PR and ER) and whether estrogenic stimulation induces activation of these receptors in the SST. Frozen sections of UVJ obtained from immature chicks treated with or without diethylstilbestrol (DES), which is an estrogenic substance, and those from laying hens were immunostained for PR and ER. In laying hens, immunoreactions for PR were observed in the SST cells and on the surface epithelium of UVJ; the strongest reactions appeared in the SST cells. In contrast, ER immunoreactions were localized in the SST cells but not in the other cells. Immunoreactions for PR and ER were negligible in the UVJ of control immature birds that received only the oil vehicle. However, in the DES-treated birds, PR immunoprecipitates were localized in the surface epithelium and SST cells, and there were ER in the SST cells. These results suggest that the SST cells in the UVJ contain PR and ER, and estrogenic stimulation may play a significant role in inducing activation of these receptors.

Localization of carbonic anhydrase in the sperm-storing regions of the turkey and quail oviduct

The localization of carbonic anhydrase in the sperm storage regions of turkey and quail was investigated using a histochemical method showing the activity of all the isozymes present. Intense carbonic anhydrase activity was found in the turkey sperm storage tubules and infundibular storage glands, whereas no activity could be detected in the quail at these sites. Both species did, however, show strong membrane-bound and cytoplasmic activity in the non-ciliated cells of the utero-vaginal surface epithelium and scattered cells of the vaginal epithelium. The enzyme catalyses the reaction CO2 + H2O <--> H+ + HCO3-, and the presence of carbonic anhydrase in these regions makes rapid changes in pH possible. It is suggested that increasing pH and/or the addition of bicarbonate stimulates sperm motility needed during transfer of the oviducal lumen. A lowering of the pH would keep the sperm quiescent during storage. The duration of sperm storage is considerably longer in the turkey than in the quail. The high quantity of carbonic anhydrase in the turkey sperm storage tubules may, thus, play a role in the duration of sperm storage.

Effect of the ovulatory cycle on oviductal sperm storage in the domestic fowl

Anovulatory domestic hens (pregnant mare serum-treated) and normally cyclic domestic hens were artificially inseminated with 0.034 ml of pooled semen. A subsequent microscopic assessment of the uterovaginal sperm storage glands on days 1, 3, 6, 9 and 12 post-insemination indicated that the sperm glands emptied over time in the normally cyclic hens, but not in the anovulatory hens. The data suggest that events associated with ovulation and/or oviposition are important to the sperm gland emptying process.

Ultrastructural analyses of uterovaginal sperm storage glands in fertile and infertile turkey breeder hens

The ultrastructure of the uterovaginal (UV) sperm storage glands of fertile turkey breeder hens was characterized. Sperm glands were also studied over the course of an entire egg-laying season to determine if changes in ultrastructure occurred with time. In addition, ultrastructural comparisons were made between glands from fertile and infertile hens. Protein synthesis by the sperm gland epithelial cells appeared to be limited. The rough endoplasmic reticulum was not well developed. Intracellular glycogen storage was also minimal. However, lipid stores within the epithelial cells were relatively elevated. The degree of development of the apical microvilli and the presence of baso-lateral plasma membrane folds suggested that a primary function of the glandular epithelium was absorption. The length of time that a hen had been producing eggs did not influence the ultrastructure of UV gland epithelial cells. The morphology of glands from hens collected immediately prior to the commencement of egg production was similar to that of glands taken from hens that had completed an entire season of egg production. Aside from the observation that very few spermatozoa were found in the UV sperm glands of infertile hens, no detectable ultrastructural differences were observed between glands from fertile and infertile hens. Furthermore, there was no ultrastructural evidence of a microbial infection, nor was there evidence of an immunological response at the level of the sperm glands in the infertile hens.

Storage and evacuation of spermatozoa from the uterovaginal sperm-host glands in domestic fowl

Autoradiography with 3H-labeled spermatozoa was utilized to study spermatozoal oviductal interrelationships. Results demonstrated that sperm displacement from the uterovaginal sperm-host glands did not occur in domestic fowl. Furthermore, there was no indication that phagocytosis of labeled spermatozoa by sperm gland epithelium occurred. Associated studies demonstrated that extensive head-to-head agglutination occurred between freshly ejaculated spermatozoa, but the ability to agglutinate was lost as the sperm cells aged. On the basis of these observations, it was proposed that agglutination may be the basic mechanism controlling sperm storage and release from the uterovaginal sperm-host glands. A working model to this effect was presented.