Microscopic structure of the sperm storage tubules in the polygynandrous alpine accentor, Prunella collaris (Aves)

We describe the microscopic structure of the sperm storage tubules (SSTs) of the polygynandrous alpine accentor, Prunella collaris. The SSTs were found at the utero‐vaginal junction of the oviduct and were composed of a single layer of columnar epithelium. The cells of the tubule proper were non‐ciliated and had a round or oval nucleus in their basal portion. Their cytoplasm was finely or coarsely vacuolated due to lipid inclusions. Under the electron microscope, the epithelial cells exhibited a number of mitochondria, Golgi bodies, occasional lysosome‐like dense bodies, granular endoplasmic reticula, junctional complex, and tonofilaments. The apical margin of the cells was fringed with numerous microvilli. The epithelial lining of the SSTs was devoid of mucous cells, but showed occasional infiltration of lymphoid cells. No contractile elements were found in association with the SSTs, but a close apposition of unmyelinated nerve fibres to the basal part of the SST cells was recognized. Intraluminal sperm were arranged in bundles, and their heads were orientated towards the distal portion of the SSTs. Evidence for engulfment of sperm by the SST cells was obtained for the first time. A sign of atrophy or regression of the SSTs was found in one specimen.     

Numbers and size of sperm storage tubules and the duration of sperm storage in birds: a comparative study

Estimates of the numbers of sperm storage tubules (SSTs) in the utero-vaginal junction of 11 bird species are presented. Numbers of SSTs varied by a factor of 40 between species, and ranged from 500 to 20000. Body mass accounted for over 50% of the variation in SST mumbers. SST length was positively correlated with the length of spermatozoa across species. The duration of sperm storage was not correlated with the number of SSTs or the volume of sperm storage tissue. However, the number of 'active' SSTs appears to vary between species and it was not possible to make allowance for this. Sperm storage duration was weakly, positively correlated wth clutch size, but showed a significant positive relationship with the number of days over which laying occurred. The number of SSTs was also positively correlated with the number of sperm per ejaculate. The best predictor of sperm storage duration was a multiple regression equation using the spread of laying and the length of sperm storage tubules. The duration of sperm storage in birds which remain together during the pre-laying period is such that a single insemination immediately before the start of laying could fertilize the entire clutch.     

Ultrastructure of the reproductive system of the black swamp snake (Seminatrix pygaea): Part I. Evidence for oviducal sperm storage

Oviducal sperm storage in the viviparous (lecithotrophic) colubrid snake Seminatrix pygaea was studied by light and electron microscopy. Out of 17 adult snakes examined from May–October, sperm were found in the oviducts of only two specimens. In a preovulatory female sacrificed 14 May, sperm were found in the oviducal lumen and sperm storage tubules (SSTs) of the posterior infundibulum. In a nonvitellogenic female sacrificed 9 June, sperm were found in the lumen and glands of the posterior uterus and anterior vagina, indicating a recent mating. The glands in the posterior infundibulum and vagina were simple or compound tubular, whereas glands in the uterus always were simple tubular. The epithelium of the sperm storage glands was not modified from that lining the rest of the oviduct. The cuboidal or columnar epithelium consisted of alternating ciliated and secretory areas. The secretory product released into the lumen by a merocrine process contained mucoprotein. Lipid droplets also were numerous in the epithelium. Portions of sperm sometimes were embedded in the apical cytoplasm or in secretory material. A carrier matrix containing a mucoid substance, desquamated epithelium, lipids, membranous structures, and possibly phagocytes was found around sperm in the posterior uterus. J. Morphol. 241:1–18, 1999. © 1999 Wiley‐Liss, Inc.     

Morphological identification of sperm receptors above egg microvilli in the polychaete, Neanthes japonica

A fine-structural study of sperm-egg interactions in the polychaete Neanthes japonica was carried out. Unfertilized eggs are surrounded by a chorion 0.6-0.7 micrometers thick. Oocyte microvilli are inserted into the inner layer of the chorion. The outer layers of the chorion are opened just above the tips of the microvilli, where a membrane vesicle (microvillus tip vesicle, about 0.2 micrometers in diameter) plugs the chorion's opening. During fertilization, the acrosomal process of the sperm fuses with an egg microvillus within 1 min of insemination. All the microvillus tip vesicles disappear from the chorion surface within 5 min of insemination. When eggs, which are prefixed with glutaraldehyde, are inseminated, numerous sperm undergoing the acrosome reactions attach to the eggs. In the majority of these sperm, the tip of acrosomal process which is coated with the acrosomal content, adhere to a microvillus tip vesicle. These findings suggest that the microvillus tip vesicle serves as a sperm receptor, which induces the acrosome reactions and adhere to the sperm acrosomal process. The adhesion of the acrosomal process to the microvillus tip vesicle seems to be a prerequisite event for its fusion with the microvillus.     

Ultrastructure of the reproductive system of the black swamp snake (Seminatrix pygaea). II. Annual oviducal cycle

This article is the first ultrastructural study on the annual oviducal cycle in a snake. The ultrastructure of the oviduct was studied in 21 females of the viviparous natricine snake Seminatrix pygaea. Specimens were collected and sacrificed in March, May, June, July, and October from one locale in South Carolina during 1998-1999. The sample included individuals: 1) in an inactive reproductive condition, 2) mated but prior to ovulation, and 3) from early and late periods of gravidity. The oviduct possesses four distinct regions from cranial to caudal: the anterior infundibulum, the posterior infundibulum containing sperm storage tubules (SSTs), the uterus, and the vagina. The epithelium is simple throughout the oviduct and invaginations of the lining form tubular glands in all regions except the anterior infundibulum and the posterior vagina. The tubular glands are not alveolar, as reported in some other snakes, and simply represent a continuation of the oviducal lining with no additional specializations. The anterior infundibulum and vagina show the least amount of variation in relation to season or reproductive condition. In these regions, the epithelium is irregular, varying from squamous to columnar, and cells with elongate cilia alternate with secretory cells. The secretory product of the infundibulum consists largely of lipids, whereas a glycoprotein predominates in the vagina; however, both products are found in these regions and elsewhere in the oviduct. In the SST area and the anterior vagina, tubular glands are compound as well as simple. The epithelium of the SST is most active after mating, and glycoprotein vacuoles and lipid droplets are equally abundant. When present, sperm form tangled masses in the oviducal lumen and glands of the SST area. The glands of the uterus are always simple. During sperm migration, a carrier matrix composed of sloughed epithelial cells, a glycoprotein colloid, lipids, and membranous structures surround sperm in the posterior uterus. During gravidity, tubular glands, cilia, and secretory products diminish with increasing development of the fetus, and numerous capillaries abut the basal lamina of the attenuated epithelial lining of the uterus.     

The sperm roller: a modified testicular duct linked to giant sperm transport within the male reproductive tract

The male reproductive tracts of Drosophila display considerable variation in the relative size of their components, notably of the testes, but there are few structural differences between species. Here we report a remarkable coiled structure separating the testes from the seminal vesicles in the giant sperm species Drosophila bifurca. This evolutionary novelty, known as the 'sperm roller', seems to be an exaggeration in the size of the testicular duct as revealed by light and electron microscopic observations. It consists of a tubular monocellular epithelium lying on the basal laminae and muscle and conjunctive cells. The lumen of the roller contains crypts. The apical membrane of the epithelial cells presents numerous long microvilli protruding into the lumen. The sperm roller structure is probably involved in managing sperm during their transit through the male genital tract, because sperm are seen in bundles at the base of the testis, whereas they are singly rolled up by the time they enter the seminal vesicles. The hypercoiling of the individual spermatozoon within the roller probably occurs as the result of an osmotic process produced by features of the epithelial wall and the dramatically increased exchange surface. This is the first report of a specialized device of this type in Drosophila or, more generally, in insects.     

Deduction of a model for sperm storage in the oviduct of the domestic fowl (Gallus domesticus)

The mechanism of sperm storage in the fowl oviduct has remained a mystery since the 1960s, when sperm storage tubules (SST) were discovered between the shell gland and vagina. Previously, it was known that only motile sperm could ascend the vagina and enter these tubules. However, the means by which sperm resided therein was not clear. Research with computer-assisted sperm motion analysis has demonstrated that 1) seminal plasma glutamate acts as a motility agonist via N-methyl-d-aspartate receptors; 2) motility depends on extracellular Ca2+ and Na+; 3) straight-line velocity is a variable with a skewed distribution; 4) sperm cell trajectory is a function of straight-line velocity; and 5) specific inhibition of phospholipase A2 renders sperm immotile. An additional experiment demonstrated that Ca2+ acts as a second messenger and thereby modulates the content of long-chain acylcarnitine within sperm. Therefore, it is proposed that 1) the release of endogenous fatty acids fuels sperm as they ascend the vagina; (2) on entering the SST, motile sperm maintain position against a fluid current generated by SST epithelial cells; 3) resident sperm metabolize exogenous fatty acids released from lipid-laden epithelial cells; (4) motile sperm emerge from the SST when their velocity declines to a threshold at which retrograde movement begins; and 5) the skewed distribution of straight-line velocity accounts for the exponential pattern of sperm emergence from the SST. In summary, sperm residence within and emergence from the SST are phenomena most likely explicable in terms of sperm cell motility.     

Spermathecae of Salamandrina terdigitata (Amphibia: Salamandridae): Patterns of sperm storage and degradation

The spermathecae of female Salamandrina terdigitata were observed using light and transmission electron microscopy during the fallspring period of sperm storage and secretory activity and during the summer stasis. When sperm are stored inside the spermathecae, the product synthesized by spermathecal epithelial cells is exported into the lumen, where it bathes the sperm. During sperm storage some spermatozoa undergo degradation by the spermathecal epithelium. This process, which includes sperm capture by the apical microvilli, formation of endocytic vacuoles and production of lysosomes, becomes prominent shortly after oviposition. In many instances, cells filled with vacuolized spermatozoa and/or residual bodies undergo desquamation from the spermathecal epithelium and enter the lumen together with residual sperm. Desquamated cells, together with residual sperm, are a common feature in the spermathecal lumina at the end of the egg-laying season. Concomitant to the activity of the spermathecal epithelium, macrophages move into the spermathecae from the stroma and contribute to the degradation of both the residual sperm and desquamated epithelial cells. As a result of this degradation activity, spermathecae observed during the short summer stasis appear devoid of secretory product and sperm. By late summer, however, the spermathecae already show early signs of an imminent resumption of biosynthetic activity. © 1995 Wiley-Liss, Inc.     

The morphology and fine structure of the larval midgut of a moth (Manduca sexta) in relation to active ion transport.

Light and electron microscopic examination of the midgut of Manduca sexta has shown that the organization of this tissue is more complex than was originally believed. The midgut can be divided into anterior, middle and posterior regions on the basis of the pattern of folding of the epithelial sheet, and variations in the structure of goblet and columnar cells which occur along its length. The columnar cells show gradual structural changes form the anterior to the posterior end of the midgut. For example, the microvilli in the anterior region form a dense, interconnecting network from which vesicles break off. This organization becomes less obvious through the middle region, until by the posterior region each microvillus is unconnected to adjacent microvilli along its entire length and vesicles are no longer produced. Two distinct types of goblet cells are found. In the anterior and middle regions the goblet cells have a large basally located cavity, but in the posterior region the cavity occupies only the apical half of the cell. In both cases the cavity is formed by invagination of the apical membrane, which is studded with small particles implicated in active ion transport. In the anterior and middle regions this membrane is closely associated with mitochondria, but not in the posterior region. The significance of the observed structural differences is discussed in relation to active ion transport.     

斑衣蜡蝉雌性生殖系统超微结构

【目的】明确斑衣蜡蝉Lycorma delicatula雌成虫生殖系统整体形态及超微结构特征,为蜡蝉总科昆虫分类及系统发育探讨提供更多形态学证据。【方法】采用光学显微镜与透射电子显微镜,观察斑衣蜡蝉雌成虫生殖系统整体形态和各主要器官的超微结构。【结果】斑衣蜡蝉雌成虫生殖系统主要包括1对卵巢、1个中输卵管、1个交配囊、1个交配囊管、1个前阴道、1个后阴道、1个受精囊、1个受精管和2根受精囊附腺。卵巢为端滋式,由14根卵巢小管组成,卵室由固有膜、滤泡细胞和卵细胞组成,卵巢小管中的滋养细胞清晰可见;中输卵管位于前阴道基部,由中输卵管腔、上皮细胞、肌肉鞘和基膜组成;交配囊膨大呈圆球状,囊壁由上皮细胞、肌肉层和基膜组成;交配囊管呈圆柱状,连接交配囊和后阴道,由肌肉鞘、上皮细胞层和管腔组成;前、后阴道超微结构相似,主要由肌肉鞘、基膜、上皮细胞和管腔组成,但后阴道上皮细胞细胞核周围存在分泌颗粒,且管腔内有大量微绒毛,而前阴道壁内包含有大量囊泡结构;受精管从中输卵管末端延伸至受精囊,由基膜、厚层肌肉鞘和管腔组成;受精囊为受精管近末端略膨大的囊状结构,由肌肉鞘、基膜、上皮细胞和囊腔构成;雌性受精囊附腺着生于受精囊末端,为均匀的螺旋管状,主要由肌肉层、上皮细胞层和附腺中心管腔组成。【结论】斑衣蜡蝉雌性生殖系统与已报道的蜡蝉总科其他类群的雌性生殖系统结构相似,但卵巢小管数目有差异;蝉亚目中不同总科雌成虫雌性附腺与受精囊附腺的形态特征存在明显区别;斑衣蜡蝉雌性生殖系统超微结构与叶蝉总科和沫蝉总科昆虫也存在部分差异。这些差异是否可以作为头喙亚目高级阶元的划分依据仍有待于进一步研究。     

Female sperm storage in reptiles.

Internal fertilization and oviparity most likely are symplesiomorphies for modern reptiles, and viviparity has evolved independently numerous times in Sauria and Serpentes. Oviducal sperm storage is known in females of all taxa except Amphisbaenia. However, in Rhynchocephalia and Crocodilia, sperm storage is poorly studied, and specialized sperm storage tubules (Ssts) are unknown. We use the molecular phylogenetic hypothesis [(Chelonia+Archosauria) (Squamata)] to trace evolution of sperm storage characters. Ssts arose independently in Chelonia and Squamata. Turtles possess albumen-secreting glands in the anterior half of the oviduct (the tuba or isthmus), and the most distal of these glands also serve as Ssts; in addition, some turtles possess Ssts in the adjacent segment of the oviduct, the uterus. Squamates lack albumen-secreting glands, and the ancestral state is possession of Ssts in the posterior infundibulum (uterine tube). Secondarily, iguanids have evolved vaginal Ssts. In this paper, we present the first ultrastructural observations on vaginal Ssts in lizards, using Anolis sagrei (Polychrotidae). Proximally, the neck of these simple tubular glands continues the alternation of ciliated and secretory cells lining the lumen of the vagina. However, the epithelial cells of the distal sperm storage area are neither secretory nor ciliated. The Ssts of Anolis are more similar to those of birds more than to infundibular receptacles in snakes and lizards.     

Z-protein, a component of the skeletal muscle Z-line, is located at the apical tips of microvilli of chicken intestinal epithelial cells

Antiserum against Z-protein, which is one of the components of myofibrillar Z-lines, strongly stained the epithelial cells of chicken small intestine at the apical tips of the microvilli and the junctional complexes. Immunoblot tests with anti-Z-protein antiserum showed that there is a peptide of the same antigenicity as myofibrillar Z-protein in the components of the epithelial cells of chicken small intestine. Hence it seems that the apical tip of the microvillus contains a constituent corresponding to the Z-protein of myofibrillar Z-line.     

Exocytotic shedding and glial uptake of photoreceptor membrane by a salticid spider.

Receptors in the anterior lateral eyes of salticid spiders possess paired rhabdomeres. The tips of the rhabdomeral microvilli lie adjacent to non-pigmented glial processes. Photoreceptor membrane is lost during turnover by a hitherto undescribed process: individual microvilli lengthen at their tips, taper, and are received by corresponding, coated endocytotic pits in the glial membrane. Pits detach as coated vesicles with coherent fragments of microvilli within them, lose their coats, and accumulate in the glial processes as disorderly membranous detritus. Some microvillus membrane disintegrates before local endocytosis, and appears to get into the glial arms distant from the parent rhabdomere by invaginations which are either endocytotic clefts or a tubulo-cisternal system, but whose precise nature is not yet clear. No photoreceptor membrane is lost by pinocytosis into the receptor cytoplasm. Analogies between the behaviour of this system and the phagocytosis of shed vertebrate photoreceptor membrane are briefly discussed.     

Fine structure of the larval midgut of the fly Rhynchosciara and its physiological implications

The midgut of Rhynchosciara americana larvae consists of a cylindrical ventriculus from which protrudes two gastric caeca formed by polyhedral cells with microvilli covering their apical faces. The basal plasma membrane of these cells is infolded and displays associated mitochondria which are, nevertheless, more conspicuous in the apical cytoplasm. The anterior ventricular cells possess elaborate mitochondria-associated basal plasma membrane infoldings extending almost to the tips of the cells, and small microvilli disposed in the cell apexes. Distal posterior ventricular cells with long apical microvilli are grouped into major epithelial foldings forming multicellular crypts. In these cells the majority of the mitochondria are dispersed in the apical cytoplasm, minor amounts being associated with moderately-developed basal plasma membrane infoldings. The proximal posterior ventriculus represents a transition region between the anterior ventriculus and the distal posterior ventriculus. The resemblance between the gastric caeca and distal posterior ventricular cells is stressed by the finding that their microvilli preparations display similar alkaline phosphatase-specific activities. The results lend support to the proposal, based mainly on previous data on enzyme excretion rates, that the endo-ectoperitrophic circulation of digestive enzymes is a consequence of fluid fluxes caused by the transport of water into the first two thirds of midgut lumen, and its transference back to the haemolymph in the gastric caeca and in the distal posterior ventriculus.     

Scanning electron-microscopic study of sperm retention and migration in the vagino-cervical region of the rabbit

Summary The pattern of sperm retention and migration in the vagino-cervical region of rabbit was studied by means of scanning electron microscopy. The following phenomena were observed: 1) Spermatozoa located in the vagina and at the orifice of the ectocervix are usually distributed diffusely. They appear to be resting on the epithelial surface; many are structurally abnormal or decapitated. 2) The great majority of spermatozoa, however, seems to be anchored or retained in narrow epithelial channels with their heads in close file formations. This phenomenon was observed particularly in the fornix vaginae as late as 24 h post coitum. 3) A great number of spermatozoa invading the cervix evidently migrates in groups along the mucosal surface. Their heads are oriented toward the uterus and contact the epithelial cells. Spermatozoa that migrate beyond the cervico-uterine junction are distributed in the same manner. 4) Spermatozoa colonizing the cervical crypts appear to be attached via the anterior margins of their heads to the epithelial cells or to the tips of kinocilia. Their tails project into the crypt lumen. It is suggested that mainly three factors may be responsible for these phenomena: (i) the fact that only motile spermatozoa overcome the vagino-cervical barrier; (ii) the tendency of spermatozoa to move along the mucosa in close vicinity to the epithelial cells; and (iii) the inability to recognize mechanical barriers on the migration route (e.g., cervical crypts) and to overcome them quickly. This may be one of many possible causes leading to sperm retention in the vagino-cervical region.Supported by a grant from the Deutsche Forschungsgemeinschaft     

Sperm aggregations in female Agkistrodon piscivorus (Reptilia:Squamata): a histological and ultrastructural investigation

Upon copulation in female Agkistrodon piscivorus, sperm migrate up the oviduct to sperm storage tubules (SSTs) in the posterior infundibulum. The epithelium of the SSTs is composed of ciliated and secretory cells and differs ultrastructurally from that of the epithelium lining the lumen of the posterior infundibulum. Sperm pass through an area composed primarily of ciliated cells at the opening of each gland before aligning themselves in parallel arrays with their nuclei facing an area composed primarily of secretory cells at the base of the tubules. Sperm are also found embedded inter- and intracellularly in the SSTs. The secretory vacuoles in the SSTs become highly electron dense after the start of the fall mating season along with the synthesis of lipid droplets. Histochemical analysis reveals that the alteration in secretory material density is caused by the production of neutral carbohydrates. Some sperm remain in aggregates in the nonglandular section of the posterior uterus until the time of ovulation. However, ultrastructural evidence indicates these sperm degrade before ovulation. Therefore, sperm in posterior aggregates have no role in fertilization of ovulated ova. The data presented here support the hypothesis that infundibular sperm storage is the mode that snakes utilize to sequester viable sperm until ovulation.     

Myosin-1a powers the sliding of apical membrane along microvillar actin bundles

Microvilli are actin-rich membrane protrusions common to a variety of epithelial cell types. Within microvilli of the enterocyte brush border (BB), myosin-1a (Myo1a) forms an ordered ensemble of bridges that link the plasma membrane to the underlying polarized actin bundle. Despite decades of investigation, the function of this unique actomyosin array has remained unclear. Here, we show that addition of ATP to isolated BBs induces a plus end-directed translation of apical membrane along microvillar actin bundles. Upon reaching microvillar tips, membrane is "shed" into solution in the form of small vesicles. Because this movement demonstrates the polarity, velocity, and nucleotide dependence expected for a Myo1a-driven process, and BBs lacking Myo1a fail to undergo membrane translation, we conclude that Myo1a powers this novel form of motility. Thus, in addition to providing a means for amplifying apical surface area, we propose that microvilli function as actomyosin contractile arrays that power the release of BB membrane vesicles into the intestinal lumen.     

Oviductal sperm storage in the ground skink Scincella laterale holbrook (Reptilia: Scincidae)

The reproductive tracts of female ground skinks, Scincella laterale, collected at various times throughout their reproductive cycle were examined by light and transmission electron microscopy. Examination of the tracts revealed that sperm are retained in the posterior vagina after mating but prior to the ovulation of oocytes. The sperm are not sequestered in specialized glands but occur in scattered clusters in the lumen or among the deep, narrow rugae. The simple columnar lining of the vagina consists mostly of ciliated cells interspersed with occasional secretory cells. After ovulation, as indicated by the presence of eggs in the uterus, sperm are not found in the vagina. No sperm or sperm storage tubules occur in the infundibulum, the characteristic location for sperm storage in scleroglossid squamates that have been studied. Our results are a further indication that too few species have been examined to construct a rigorous phylogenetic hypothesis about the occurrence of sperm storage tubules in lizards.     

Ultrastructure of the endolymphatic sac in the larva of the Japanese red-bellied newt Cynops pyrrhogaster

The ultrastructure of the endolymphatic sac (ES) of the late stage larva of the Japanese red-bellied newt, Cynops pyrrhogaster (stage 57), was examined by light and transmission electron microscopy. The two endolymphatic sacs are located at the dorsal-medial side of the otic vesicle on the dorsal-lateral side of the midbrain in the cranial cavity. The wall of the sac is composed of a layer of cubical epithelial cells with loose, interposed intercellular spaces. The sac contains a large luminal cavity, in which endolymph and numerous otoconia are present. The epithelial cells of different portions of the sac have a similar structure. These cells contain an abundance of cytoplasmic organelles, including ribosomes, Golgi complexes, and numerous vesicles. Two types of vesicles are found in the epithelial cells: the “floccular” vesicle and the “granular” vesicle. The floccular vesicles are located in the supra- and lateral-nuclear cytoplasm and contain flocccular material. The granular vesicles have a fine granular substance and are usually situated apposed to the apical cell membrane. The granular vesicles are suggested to be secreted into the lumen, while the floccular vesicles are thought to be absorbed from the lumen and conveyed to the intercellular spaces by the epithelial cells. The apical surfaces of the epithelial cells bear numerous microvilli. Apparently floating cells, which bear long microvilli on the free surfaces, are observed in the lumen of the ES. Based on the fine structure, the function of the endolymphatic sac of the newt Cynops pyrrhogaster is discussed.     

Lack of sperm production and sperm storage by arctic-nesting shorebirds during spring migration

Birds nesting at high latitudes may copulate during migration to arrive on the nesting grounds ready to breed. We surveyed 12 species of shorebirds during spring migration to determine whether (1) males produced abundant sperm and (2) females harboured functional sperm storage tubules (SSTs). Sperm production by males on migration was rare. Only four of seven species (9.8% of 41 males) of long-distance migrants harboured sperm, whereas all four species (100% of eight males) of short-distance migrants held sperm. In females, no long-distance migrants held sperm in their SSTs ( n  = 28 females) and SSTs were small compared to long-distance migrants collected on their breeding grounds. Our results indicate that shorebirds nesting at high latitudes were generally not reproductively active during migration and that any sexual behaviour on migration is unlikely to lead directly to fertilizations.