Modulation of the oviductal environment by gametes

The notion of a gamete recognition system that alerts females to the presence of gametes in their reproductive tract profoundly influences our understanding of the physiology of events leading to conception and the bearing of offspring. Here, we show that the female responds to gametes within her tract by modulating the environment in which pregnancy is initially established. We found distinct alterations in oviductal gene expression as a result of sperm and oocyte arrival in the oviduct, which led directly to distinct alterations to the composition of oviductal fluid in vivo. This suggests that either gamete activates a cell-type-specific signal transduction pathway within the oviduct. This gamete recognition system presents a mechanism for immediate and local control of the oviductal microenvironment in which sperm transport, sperm binding and release, capacitation, transport of oocytes, fertilization, and early cleavage-stage embryonic development occur. This may explain the mechanisms involved in postcopulatory sexual selection, where there is evidence suggesting that the female reproductive tract can bias spermatozoa from different males in the favour of the more biologically attractive male. In addition, the presence of a gamete recognition system explains the oviduct's ability to tolerate spermatozoa while remaining intolerant to pathogens.     

The role of glutathione in mammalian gametes

The paper reviews a recent research on the role of glutathione (GSH) in the male and female germ cells as well as during the early stages of embryo development in mammals. In both the male and female gametes, GSH is involved in the protection of these cells against oxidative damage. Glutathione has been implicated in maintaining the meiotic spindle morphology of the oocyte. After fertilization, this thiol plays an active role in the formation of the male pronucleus, and has a beneficial effect on early embryogenesis to the blastocyst stage. GSH concentrations change within the oocytes during meiotic maturation and its synthesis is regulated by gonadotropins. Furthermore, GSH concentrations in the maturing spermatozoa gradually decline during spermatogenesis. This review also addresses the important role of cumulus cells in glutathione synthesis.     

The reproductive biology of the horse mackerel Trachurus trachurs (L.) in the North Sea and English Channel

In the horse mackerel the gametes develop asynchronously and are released in batches. The maturity cycle is characterized by a rapid post-spawning recovery period and a relatively long period of oocyte maturation. Mean gonad weight reached a peak in June and intraovarian hyaline oocytes occurred from May to August. Determination of fecundity was complicated by resorption of oocytes both before and after spawning, and by the fact that resting and developing oocytes were not clearly separated by size. An estimate of'potential fecundity'was obtained by a combination of histology and oocyte measurement. Plankton surveys showed that a major spawning area exists in the Southern Bight of the North Sea, with eggs occurring from May to late August. An estimate of annual egg production was combined with the fecundity data to give an estimate of stock size of about 500 000 tons.     

Resorption of Gametes in the Testes of the Sea Star <Emphasis Type="Italic">Asterina pectinifera</Emphasis> (Mueller et Troschel, 1842)

The process of resorption of spermatozoa is described in the testes of the starfish Asterina pectinifera. It is shown that the mode of resorption of the male gametes in this species is different from that in the starfish Asterias vulgaris (see Walker [17, 18]), A. amurensis, and Aphelasterias japonica (see Kasyanov et al. Original Russian Text Copyright © 2005 by Biologiya Morya, Kalachev, Reunov.     

Parasexually produced hybrids between female and male plants of Griffithsia tenuis C. Agardh,a red alga

Somatic cell fusion between vegetative cells of a male and a female isolate of Griffithsia tenuis, a marine red alga, has been obtained. Hybrid cells have been isolated and they have regenerated new plants. Almost all these hybrid plants made reproductive structures. In nearly half these cases the first 3–10 cells of the hybrid filament produced reproductive structures chracteristic of the tetrasporic (diploid) phase rather than the sexual (haploid) phase of the life cycle of this alga. However as these filaments continued to grow, cells further along the filament began to produce sexual, either female or male, reproductive structures. The observations suggest that the production of tetrasporangial branches does not require the fusion of male and female nucleic; rather, male and female nucleic remaining separate, act in concert to produce these structures, and in subsequent cell divisions the nuclei of one sex may be left behind allowing the nuclei of the remaining sex to direct the production of sexual branches.     

Production of anisogametes and gamete motility dimorphism in Monostroma angicava

 The reproductive strategy of a marine alga with a heteromorphic biphasic life cycle was studied by analyzing various sexual reproductive characters in light of the evolution of anisogamy. Gametophytes of Monostroma angicava were dioecious and their gametes were slightly anisogamous. Volume of gametangium, density of gametangia and area of mature gametangial parts on each gametophyte did not differ from male to female. Therefore, the reproductive biomass investment for gamete production was considered to be the same for each sex. Anisogamy in this alga appeared to be derived from the difference in the number of cell divisions during gametogenesis, because the majority of male gametangia each produced 64 (2⁶) gametes and the female produced 32 (2⁵) gametes. This corresponded with measurements of cell size in male and female gametes. Further, the sex ratio was 1:1 for sexually mature plants sampled at Charatsunai. Therefore, it was suggested that in the field twice as many male gametes are released as female gametes. Liberated gametes of both sexes showed positive phototaxis. The swimming velocity of freshly liberated male gametes was a little higher than that of female gametes. Male gametes had the potential to swim for ca. 72 h and female gametes for ca. 84 h. The difference in gamete motility between the two sexes seemed to be related to cell size. Planozygotes were negatively phototactic and swam more rapidly than gametes of either sex. Received: 5 March 1997 / Revision accepted: 18 July 1997     

Reproductive biology of the polychaete Kefersteinia cirrata Keferstein (Hesionidae). I. Ovary structure and oogenesis

The ultrastructure of the ovary and the developing oocytes of the polychaete Kefersteinia cirrata have been described. The paired ovaries occur in all segments from the 11th to the posterior. Each consists of several finger-like lobes around an axial genital blood vessel. Oogenesis is well synchronised, young oocytes start to develop in September and vitellogenesis begins in January and is completed by May.

The young oocytes are embedded among the peritoneal cells of the blood vessel wall which have accumulations of glycogen and other storage products. Each oocyte becomes associated with a follicle cell with abundant rough endoplasmic reticulum. Yolk synthesis involves the accumulation of electron dense granules along the cisternae of the abundant rough endoplasmic reticulum. Active Golgi complexes are present and are involved in the production of cortical alveoli. The oocyte has branched microvilli, which contact the follicle cells or blood sinuses between the follicle cells and peritoneal cells. In post-spawning individuals the lysosome system of the follicle cells is hypertrophied and the cells play a role in oocyte breakdown and resorption.     

Sperm morphology and storage in the female reproductive tract of the fat-tailed dunnart,Sminthopsis crassicaudata (Marsupialia: Dasyuridae)

A study of spermatozoa in the isthmus of the oviduct and of the surrounding epithelial cells in the dasyurid marsupial, Sminthopsis crassicaudata, was carried out. At least 10% of the ejaculated spermatozoa probably populate the isthmus region, where many come to reside in crypts until around the time of ovulation. Ultrastructural observations of spermatozoa in this region indicated that they had intact acrosomes and were identical in their morphology with those in the cauda epididymidis. After ovulation spermatozoa rapidly disappeared, some of which may be phagocytosed by the cells lining the crypts. These epithelial cells were also found to have many large, electron-dense granules at the time of sperm storage, but the contents did not appear to be released until the zygotes passed along the tract. The secretory activity of these cells may thus relate more to the production of the shell membrane that comes to surround the zygote than to the cells performing a nutritive or protective function for the spermatozoa during their period of storage within the female reproductive tract.     

Proteins implicated in sperm capacitation

Spermatozoa after being deposited in the female reproductive tract spend a considerable time in this foreign environment prior to fertilization of the oocyte. Chang and Austin independently observed1,2 that this time spent by the spermatozoa in the female tract is not consequential but a necessary event in the life cycle of the male gamete, and Austin2 first called this maturation period of spermatozoa as 'Capacitation'. Ever since, attempts have been made to understand and unravel the molecular mechanism of capacitation. Based on the results obtained so far, it is clear that capacitation is guided by novel signal transduction pathways influencing varied aspects of spermatozoa. Capacitation could be, thus, defined as the cumulative molecular, cellular and physiological changes that occur in spermatozoa in the female reproductive tract to achieve the final competence to fertilize the oocyte. This review is structured so as to first understand the key features of capacitation and then to survey the players which bring about these changes during capacitation.     

Functional and morphological diversity of sperm in Drosophila

Unlike mammals, where the males produce huge quantities of tiny spermatozoa, insects, and Drosophila in particular, exhibit a wide range of reproductive strategies. Sperm gigantism in Drosophila deviates from the rules that normally govern anisogamy, i.e. differences in the size and quantity of male and female gametes. Sperm gigantism has driven anatomical, physiological and cytological adaptations that affect the correlated evolution of the male and female reproductive systems, and has led to the evolution of a new structure, the roller, located between the testis and the seminal vesicle, and to sperm coiling to form pellets. The diversification of sperm strategy is investigated in the light of sexual selection processes that occur in the female genital tract after copulation. These processes, which bias paternity, result from interactions either between spermatozoa from different males, or between the spermatozoa and the environment within the female reproductive tract. In Drosophila, increased sperm size does not confer any reproductive advantage on the male. The evolution of sperm gigantism does not seem to be attributable to competition between spermatozoa from different males, as has been shown to occur in some vertebrate species. Alternative mechanisms, such as interactions between spermatozoa and the female reproductive system, are therefore currently viewed as being more likely explanations. In particular, the impact of sperm size on female reproductive physiology is being investigated to find out whether having large spermatozoa increases the likelihood of male reproductive success. Correlated adaptations of the spermatozoa and female storage organs also seem to be a major factor in determining sperm success, and their role in male-female conflicts is discussed briefly.     

Expression of a cell surface protein during morphogenesis of the reproductive system in Manduca sexta embryos

New antibody markers have allowed more refined examinations of embryogenesis. Features are being found that were overlooked in whole and sectioned embryos stained with traditional histochemical labels. Two monoclonal antibodies that recognize two different cell surface proteins in Manduca sexta label cells of the developing reproductive system. These specific immunolabels reveal that during a brief period of Manduca embryogenesis, rudiments of both male and female genital ducts are present in a single embryo. This transient phase of genital differentiation parallels the transient indifferent stage known to occur during development of reproductive systems in many vertebrate embryos. At the end of this indifferent stage, one of the two pairs of genital ducts retracts and degenerates. The dynamic expression of the two surface proteins on cells involved in morphogenesis of both the female and male reproductive systems also suggests that these proteins are important in orchestrating the specific cellular interactions that occur between mesodermal cells of the genital ducts and the nearby ventral ectoderm.     

Notes on gamete production in Lanice conchilega (Annelida,Polychaeta, Terebellidae)

Summary

Male and female gametogenesis in Lanice conchilega are described and illustrated as seen by light microscopy. There is no evidence for size-selectivity in the uptake of male gametes by the hypertrophied reproductive nephromixia, since undissociated motile sperm platelets as well as spermatozoa appear to be taken up by the genital funnels, and such funnels show no sexual dimorphism. Maturation of the coelomic oocytes is marked by a change in shape and the appearance of a surface reticulum of ridges.     

Role of signaling pathways in regulating the capacitation of mammalian spermatozoa.

Mammalian testicular spermatozoa are immotile and incompetent for fertilization. They acquire motility during epididymal maturation and fertilizing ability during a second phase of maturation in the female reproductive tract, termed as capacitation. Capacitation was discovered independently by Austin and Cang in early 1950s and was defined as the obligate period of residency of spermatozoa in the female reproductive tract, which confers on the spermatozoa the ability to fertilize an oocyte. Over the years, the definition of capacitation has changed and it has been recognized as a complex phenomenon, which is correlated with changes associated with the spermatozoa in the female tract. These alterations in metabolism, intracellular ion concentration, membrane fluidity, intracellular pH, cAMP concentration and concentration of reactive oxygen species, ultimately make the spermatozoa fertilization-competent. The molecular basis of capacitation is poorly understood despite the fact that it is an important event preceding fertilization. This review presents our current understanding of the signaling events involved in the process of capacitation.     

Morphology of female reproductive system of Mediterranean flatheaded peachborer,Capnodis tenebrionis (Linnaeus, 1761) (Coleoptera: Buprestidae)

Capnodis tenebrionis causes damage in many species of Rosaceae. The present study investigates on the morphology of the female reproductive system of C. tenebrionis. The female reproductive system of C. tenebrionis has a pair of ovaries, lateral oviducts, a common oviduct, spermatheca, and bursa copulatrix. Each ovary in C. tenebrionis consists of approximately 24 telotrophic meroistic type ovarioles. The ovarioles of C. tenebrionis have four regions (terminal filament, tropharium, vitellarium, and pedicel). Tropharium have trophocytes, young oocytes, and prefollicular cells. Vitellarium consists of previtellogenic, vitellogenic, and choriogenic oocytes. Previtellogenic oocyte is surrounded by cylindrical epithelial cells. Its ooplasm is homogeneous and basophilic. In vitellogenic oocyte, there are intercellular spaces between monolayered follicle cells. Its ooplasm has yolk granules and lipid droplets. Choriogenic oocyte are surrounded by chorion and single-layered cylindrical cells. There are yolk granules and lipid droplets in its ooplasm which is asidophilic. In C. tenebrionis female, spermatheca and bursa copulatrix wall is surrounded by thin cuticular intima, monolayer epithelial, glandular cells, and muscle layer. Spermatheca lumen contains a large number of spermatozoa. Bursa copulatrix lumen is filled with secretory material. This study may be useful in terms of the morphology of mature female reproductive organs of Buprestidae and other coleopteran species.     

Gonad characterization and reproductive seasonality in Siphonaria lessonii (Gastropoda: Heterobranchia) from the southwestern Atlantic Ocean

Histological characterization of the hermaphroditic gonad (HG) and seasonality of gametogenesis were investigated in a population of Siphonaria lessonii from the coast of Buenos Aires Province (37°16′S, 56°58′W). Monthly analysis of the frequency of gametogenic stages, as well as the number and mean size of oocytes, were used to determine reproductive events over a 2‐year period (June 2012–May 2014). Female and male gametes were observed simultaneously within acini of adult individuals and continuously throughout the period studied. Oogenesis commenced in the beginning of austral autumn, with gonads characterized mainly by proliferation of female cells. From this moment, oocytes gradually increased in number and area until spring, when a large number of individuals were found in the evacuation stage. The same trend was observed from early gonad maturation to advanced stages, indicating that gonad development was closely related to the frequency of oocyte stages and to the area (size) of oocytes. Spermatogenesis was also observed as a continuous process throughout the year, although spent acini were more frequent from November until February. Reproductive seasonality and gametogenesis were associated with changes in temperature and day length.     

The annual reproductive pattern of the Antarctic clam, <Emphasis Type="Italic">Laternula elliptica</Emphasis> from Marian Cove,King George Island

The annual reproductive cycle of the Antarctic soft-shelled clam, Laternula elliptica, in Marian Cove, King George Island was studied over a 2-year period from February 1998 to January 2000. Annual changes in the gametogenesis were investigated by measuring the percentage of area occupied by oocytes in a follicle [follicle index (FI)] and the oocyte size. In 1998, the monthly mean FI increased significantly from October to November, peaked in December, and decreased rapidly from December to January. In February and March 1999, degenerated eggs were observed in the spent follicles. Degeneration and resorption of residual eggs by phagocytosis occurred mostly in February and March in both 1998 and 1999, although the resorption process was observed year-round. The histology indicated that complete vitellogenic growth of L. ellpitica at Marian Cove takes at least a year and the clams spawn annually during the austral summer. The ripening and subsequent spawning of clams at Marian Cove in 1998 and 1999 coincided with the algal blooming (September–October 1998 and December and January 1999–2000) suggesting that in coastal Antarctica food supply is a crucial factor that governs gonad maturation and subsequent spawning along with the water temperature.     

A comparative study on the arginine degradation cascade for sperm maturation ofBombyx mori andDrosophila melanogaster

Summary The spermatophore of the silkmoth,Bombyx mori, is a reactor with a specific energy-yielding system for sperm maturation, the arginine degradation cascade. On mating, the highly viscous secretions from various glands in the male reproductive tract, which contain many enzymes and their substrates, are transferred to the female bursa (b.) copulatrix to form the spermatophore. In the spermatophore, transferred arginine-rich proteins are digested by initiatorin, an Arg-C endopeptidase of serine-protease type, and a carboxypeptidase. The produced free arginine is then hydrolyzed to urea and ornithine by arginase. Ornithine is metabolized to glutamate, follwed by forming alanine and 2-oxoglutarate. The latter, as a member of TCA-cycle, is a preferred respiratory substrate for spermatozoa and accelerates the post-testicular sperm maturation.In contrast toBombyx mori, Drosophila melanogaster produces only eupyrene spermatozoa and does not form the spermatophore. The sperm of this dipteran insect acquire motility in the v. seminalis of males. As reported forDrosophila, a high glutamate-pyruvate aminotransferase activity was found in the spermatophore as well as the v. seminalis of the silkmoth. The value in the latter organ reaches 58.3% of the whole male reproductive tract that participates in transfer of the seminal fluid.In the male reproductive system ofDrosophila, the concentration of arginine is low, whereas those of urea and ammonia are high. The accessory gland secretion contains much phosphoserine. Theses substances are transferred to female uterus with spermatozoa during mating. Most amino acids increase distinctly at 30 min after the termination of mating (ATM) and then decline, suggesting active degradation of transferred proteins in the uterus. As found inBombyx, urea increases at the post-mating period, while ornithine shows a rather low concentration. Ornithine must be converted to glutamate. In this connection, it is notable that alanine rises markedly at 30 min following mating. As in the silkmoth, the energy metabolism of the fruit fly spermatozoa involves also arginine, ornithine, urea, and proline. These findings suggest that the occurrence of the arginine degradation cascade or related metabolic pathway in this insect.Abbreviations ATM after the termination of mating - Arg-C arginine-carbon - b. bursa - d. ductus - g. glandula - GPA l-glutamate-pyruvate aminotransferase - NADH₂ reduced nicotinamide-adenine dinucleotide - TCA tricarbonic acid - v. vesicula     

Morphology and histology of male and female reproductive systems in the inseminating species Scoloplax distolothrix (Ostariophysi: Siluriformes: Scoloplacidae)

The morphology and histology of male and female reproductive systems were examined in Scoloplax distolothrix. Internal insemination was documented in this species by the presence of sperm within the ovaries. Mature males and females have elongated genital papillae, exhibiting a tubular shape in males and a plain heart‐shape with two median protuberances in females. The testes are two elongated structures that converge ventrally, under the intestine, towards the genital papilla. They are joined at the caudal end, forming an ovoid single chamber for sperm storage. Secretory regions were not observed. In the lumen of the testicular tubules, spermatozoa can be tightly packed along their lengths, but do not constitute a spermatozeugmata. The lumen of the sperm storage chamber and spermatic duct are filled with free spermatozoa without the accompanying secretions. The ovaries are bird‐wing shaped, saccular structures that converge ventrally under the intestine, towards the genital papilla. They are joined at the caudal end, forming a tubular chamber possibly destined for oocyte storage. An oviduct with an irregular outline connects the chamber to the tubular region of the genital papilla. No distinct sperm storage structure was found in the ovaries. The unique male and female genital papillae suggest that these structures are associated with the reproductive mode in scoloplacids, representing evidence for insemination. The occurrence of free spermatozoa, without the accompanying secretions and not arranged in a spermatozeugmata can be associated with the presence of a tubular male genital papilla for sperm transfer to the female genital tract. This reinforces the idea that sperm packets are not necessary for all inseminating species. The male reproductive system in scoloplacids is very different from that in auchenipterids, a second catfish family with insemination, which indicates that the occurrence of insemination is not connected to the internal morphology of reproductive organs. J. Morphol., 2008. © 2008 Wiley‐Liss, Inc.