Functional morphology of the gonoduct of the viviparous teleost Poeciliopsis gracilis (Heckel, 1848) (Poeciliidae)

Female teleosts do not develop Müllerian ducts; consequently, the ovary of teleosts contains two zones: germinal and gonoduct. The gonoduct lacks germinal cells, but has relevant functions in the reproductive process. We describe the functional morphology of the gonoduct in the viviparous teleost Poeciliopsis gracilis during nongestation and gestation stages. This study tests the hypothesis that the gonoduct functions as a barrier between the germinal zone and the exterior. By providing information about morphology and function of the gonoduct we show that this part of the ovary has an essential role in the reproduction of teleosts. The ovaries were processed by histological technique and stained with hematoxylin‐eosin (H‐E), Masson's trichrome, toluidine blue and periodic acid‐Schiff (PAS). The gonoduct is divided into three regions: cephalic, middle, and caudal. In the cephalic and middle regions there are mucosal folds that extend into the gonoductal lumen, forming structures similar to a cervix. The caudal region has two portions: the anterior contains a dorsal invagination and exocrine glands among columnar cells; the posterior has a ventral flexion and stratified epithelium with apical secretory cells. The morphology of this epithelium indicates two functions: (a) secretory by the apical columnar cells, and (b) protection through the stratification. Another peculiarity of the caudal region is that both ducts, reproductive and digestive, converge in a common cavity at their caudal ends, forming a cloacal region. The histology of the gonoduct indicates relevant functions including: (1) the control of the luminal diameter by the muscle and the presence of mucosal folds, like a cervix; (2) the relationship with the spermatozoa during insemination and storing them in mucosal folds; (3) the support of immunological processes; (4) secretory activities; (5) forming the duct during birth; and (6) possibly, acts as a barrier against parasite infestations.     

Structure of the female gonoduct of the viviparous teleost Poecilia reticulata (Poeciliidae) during nongestation and gestation stages

Female teleosts do not have oviducts because Müllerian ducts do not develop. Instead, the caudal region of the ovary, the gonoduct, connects to the exterior. Because of the lack of oviducts in viviparous teleosts, the embryos develop in the ovary, as an intraovarian gestation, unique in vertebrates. This is the first study to address the histology of the gonoduct in a viviparous teleost. The gonoduct of Poecilia reticulata was analyzed during previtellogenesis, vitellogenesis, and gestation. The gonoduct lacks germinal cells. From deep to superficial, the wall has simple cuboidal or columnar epithelium, loose connective tissue, longitudinal layer of smooth muscle, and visceral peritoneum. Cells of the immune system occur in the lumen and in the mucosa. The gonoduct was divided in three regions: 1) cephalic, 2) middle, and 3) caudal. At the initial part of each region, thin mucosal folds extend into the lumen. The cephalic region forms a tubular structure with light and irregular folds. The middle region has a wider lumen and is more irregular due to ventral invaginations and irregular and short mucosal folds; beneath the epithelium there are melano‐macrophage centers. The caudal region is delimited from the middle region by folds; however, they are thinner than these of the other regions. Ventral invaginations form exocrine glands, and the smooth muscle is thicker than in the other regions. During gestation, cells of the immune system are abundant; melano‐macrophage centers become larger and the glands exhibit desquamated cells. These observations suggest roles of the gonoduct in reducing the diameter of the lumen; receiving sperm during vitellogenesis; producing secretions, more abundant during vitellogenesis; and in immunological activity throughout the reproductive cycle. The ciliated epithelium and the thick muscle of the caudal region may be involved during birth. J. Morphol. 275:247–257, 2014. © 2013 Wiley Periodicals, Inc.     

Ultrastructure of sperm and male reproductive system in Lineus viridis (Heteronemertea, Nemertea)

Nemerteans possess serially arranged gonads that lie between the midgut pouches. In both sexes the gonads are lined with an epithelium. During maturity, they gain contact to the exterior by a ciliated duct, which is generally assumed to be a derivative of the gonad. Gonad lining and sperm ultrastructure are little known in heteronemerteans, a group of nemerteans belonging to the Anopla, one of the two large nemertean subgroups. Reproduction biology in heteronemertean Lineus viridis allows predicting a modified sperm type, so-called introsperm for this taxon. Nothing is known on the fate of the testes at the end of the reproductive period of this perennial species. In order to test the predictions and to broaden the data base, males of L. viridis were collected at different times of the year. Histological and ultrastructural data show that the gonad wall is lined with different aciliated endothelial cells and germ cells, while the gonoduct is formed by densely ciliated cells. The testes are completely filled with sperm cells during maturity; there is no hint at ongoing spermiogenesis at this time. The sperm consists of head, midpiece and tail. Externally, head and midpiece cannot be discriminated. The acrosome is cup-shaped and lies anterior to the nucleus which contains 6–8 lateral ridges. Three long mitochondria mark the midpiece. They line the posterior section of the nucleus and extend up to the level of the ciliary basal structures. The sperm morphology corroborates the predictions derived from the mode of reproduction. At the end of the reproductive period the male gonads change cellular composition, while the gonoduct degenerates. Provided that both sexes show the same growth rate, male offspring acquire sexual maturity earlier than female offspring, since L. viridis males are always smaller than the females. In contrast to the males, females keep their gonads and gonoducts during most time of the year. Since large males were never found within the studied population, these data indicate that L. viridis might be a consecutive hermaphrodite.     

Patterns of reproductive morphology in the genus Gobiodon (Teleostei: Gobiidae)

The reproductive system of gobiid fishes (family Gobiidae), especially among hermaphroditic goby species, is morphologically diverse. Two hermaphroditic species in the genus Gobiodon, G. okinawae and G. oculolineatus, have several modifications of the gonoduct and gonad that are associated with secretion production and storage. In this study, an examination of six additional Gobiodon species, G. citrinus, G. fulvus, G. histrio, G. micropus, G. quinquestrigatus and G. rivulatus, revealed similar reproductive modifications. Among these six Gobiodon species, a number of features were found to be shared amongst each other and with G. okinawae and G. oculolineatus. All individuals had either an ovariform gonad or an ovotestis; no individuals had a purely testicular gonad. The gonadal lobes extended caudally past, rather than terminating at, their union with the gonoduct. Accessory secretory structures associated with the reproductive complex, termed accessory gonoduct structures, or AGdS, always originated from the gonoduct. The ovariform gonad was comprised entirely of ovarian tissue, while the ovotestis was divided into three morphologically distinct regions. Only one of the ovotestis regions was strictly gametogenic, consisting of both early stage oocytes and sperm-filled seminiferous lobules. The second region of the ovotestis was made up of stromal tissue surrounding some compressed lumina and a small number of early-stage oocytes. The third region was highly lobulated and acted as a storage region for eosinophilic secretions. Anteriorly, the stromal region of each of the two ovotestis lobes disappeared and the gametogenic and secretory storage regions of the ovotestis separated into two discrete lobes. In all of the examined Gobiodon species, all individuals having an ovotestis also had AGdS. However, AGdS presence among individuals having an ovariform gonad varied in a species-specific manner, with the AGdS being fully differentiated and well-developed in a number of species, and either in a very early stage of development, or absent, in others. The distribution of these AGdS states among Gobiodon species corresponds with that of several other morphological features that have been proposed by Harold et al. (Bull Mar Sci 82:119–136, 2008) as phylogenetically informative for intra-generic clade identification. Reproductive characters may prove informative in the development of hypotheses of relationships among gobiid fishes.     

The Comparative Cellular Architecture of the Female Gonoduct Among Tylenchoidea (Nematoda: Tylenchina)

The cellular architecture of the female gonoduct of 68 nematode populations representing 42 species belonging to Tylenchidae, Belonolaimidae, Hoplolaimidae and Meloinema is shown to have an overall similarity in cellular gonoduct structure. The oviduct consists of two rows of four cells; the spermatheca is comprised of 10 to 20 cells, and the uterus cells, except in the case of Psilenchus, are arranged in four (Tylenchidae) or three (Belonolaimidae, Hoplolaimidae and Meloinema) regular rows. Although the genus Meloinema is classified within Meloidogynidae, its spermatheca is clearly hoplolaimid-like and lacks the spherical shape with lobe-like protruding cells typical of Meloidogyne. Detailed morphology of expelled gonoducts may provide a valuable character set in phylogenetic analysis, and the cellular morphology of the spermatheca appears to be a distinguishing feature at species level, especially in the genera Tylenchus and Geocenamus. Ultrastructural data on the oviduct-spermatheca region of Meloidogyne incognita complement light-microscopic (LM) results. The combination of LM of expelled organs and transmission electron microscopy (TEM) on selected sections is put forward as a powerful tool to combine three-dimensional knowledge with ultrastructural detail.     

Ovarian structure,folliculogenesis and oogenesis of the annual killifish Millerichthys robustus (Cyprinodontiformes: Cynolebiidae)

Cellular aspects of oocyte development of the Mexican rivulus Millerichthys robustus were morphologically described in order to analyze ovarian function and the cellular recruitment dynamics associating it with life history strategies of annual killifishes. Millerichthys is an iteroparous batch spawner with continuous oocyte recruitment and indeterminate fecundity with asynchronous development of the follicles. It has two ovaries of cystovarian type, with a central lumen, which communicates with the outside through the caudal region of the ovary, that is, the gonoduct. From the walls of the ovary, irregular lamellae composed of germinal epithelium and vascularized stroma project. Oogenesis starts with oogonial proliferation, found alone or in nests within the germinal epithelium. The oogonia come into meiosis becoming oocytes and advancing to the chromatin nucleolus stage and to early primary growth stage. Folliculogenesis is completed in the primary growth stage and cortical alveoli step. Follicles moves toward the stroma, but they continue to be attached to the germinal epithelium through the basement membrane until ovulation. The inclusion of fluid yolk in the follicles during the secondary growth stage was observed. During ovulation, the follicle collapsed, the oocyte was released into the lumen, and the constitutive elements of the post-ovulatory follicle complex remained in the stroma.     

Microscopic Anatomy and Ultrastructure of Nephridium in the Sipunculan Thysanocardia nigra Ikeda, 1904 from the Sea of Japan

The microscopic anatomy and ultrastructure of nephridium have been studied in the sipunculan Thysanocardia nigra Ikeda, 1904 (Sipuncula, Sipunculidea) from the Sea of Japan using histological and electron microscopic techniques (SEM and TEM). This paper describes ultrastructural features of nephridial epithelium, muscle grid, and coelomic epithelium on the surface of the nephridium, the area of the ciliary funnel, and the tongue. Several types of cells were distinguished in the excretory tube of the nephridium: (1) a columnar epithelium of the excretory bunches; (2) a cubical or flattened epithelium of flask-shaped infoldings; and (3) granulocytes that migrate from the coelom to the extracellular matrix of the nephridial wall. The system of podocytes and multiciliary cells were described in the nephridial coelothelium. Two types of secretion of nephridial epithelium have been discovered: a merocrine secretion of columnar cells and an apocrine secretion of cells of the flask-shaped infoldings. Using ultrastructural data, two zones of filtration through the wall of excretory tube have been found, namely (1) the tips of flask-shaped infoldings (via the extracellular matrix and microvillary canals between the epithelial cells) and (2) areas between the flask-shaped infoldings (via the contacts of podocytes, extracellular matrix, and the basal labyrinth of the columnar cells). Unlike previously studied representatives of the genus Phascolosoma, no coelomic epithelium is present on the tips of the flask-shaped infoldings in Th. nigra. This data on the anatomy and histology allow us to conclude that the funnel only works like a gonoduct.     

Comparative study of the olfactory epithelium of the three-spined stickleback (Gasterosteus aculeatus) and the nine-spined stickleback (Pungitius pungitius)

Summary The olfactory epithelium of the three-spined stickleback (Gasterosteus aculeatus) and the nine-spined stickleback (Pungitius pungitius) has been studied with a conventional histochemical and a novel immunological staining technique. In both species, the sensory epithelium is arranged in folds separated by non-sensory epithelial tissue. In the nine-spined stickleback, intrinsic folds consisting of non-sensory cells are found in the apical part of the sensory epithelium where they divide the surface of the sensory epithelium into small islets. These non-sensory cells are non-ciliated, flattened and piled on top of each other; they contain numerous electron-translucent vesicles. The intrinsic folds are absent from the sensory epithelium of the three-spined stickleback. In both species, axons of receptor cells form a layer of fibers in the sensory epithelium immediately above the basal cells. In the three-spined stickleback, thick branches of the olfactory nerve are frequently found in this layer. These branches are only occasionally observed in the sensory epithelium of the nine-spined stickleback. Thus, the three-spined stickleback and the nine-spined stickleback show considerable differences in the organization of the sensory regions of the olfactory epithelium.     

Ultrastructure of the metanephridia of Terebratulina retusa and Crania anomala (Brachiopoda)

Adult specimens of Terebratulina retusa and Crania anomala have one pair of metanephridia. Each metanephridium is composed of a ciliated nephridial funnel (nephrostome) and an outleading nephridial canal, thus, these organs are open ducts connecting the metacoel of the animal with the outer medium. In both species, the inner side of a nephrostome is lined by a columnar monociliated epithelium which contacts the coelothel within one of the two ileoparietal bands. The coelothel contains basal filaments (in C. anomala these are definite myofilaments). The canal epithelium also consists of monociliated columnar cells which differ from the nephrostome epithelial cells in size and some cell components. Within the nephropore, the canal epithelium makes contact with the so-called inner mantle epithelium which lines the mantle cavity. The nephrostome epithelial cells and the canal epithelial cells never contain any contractile filaments. There are always continuous transitions between these different epithelia and distinct borders cannot be observed. The present results, especially in comparison to Phoronida, do not contradict the hypothesis of a coelothelially derived nephridial funnel and an ectodermal nephridial duct in Brachiopoda. But with regard to the differences between Phoronida and Brachiopoda (larval protonephridia and podocytes in the adults are unknown in Brachiopoda), further investigations have to be done to test the hypothesis of such heterogeneously assembled metanephridia.     

SCHIZOGENY AND ULTRASTRUCTURE OF DEVELOPING LATEX DUCTS IN MAMMILLARIA GUERRERONIS (CACTACEAE)

The schizo-lysigenous latex ducts of Mammillaria guerreronis, sect. Subhydrochylus, were examined by optical and electron microscopy. These ducts are complex having a distinct outer epithelium without intercellular spaces and an inner epithelium in which schizogenous spaces arise. Schizogeny begins with formation of bulbous pockets and/or production of dark streaks in certain walls. Spaces formed by these processes ultimately contain a combination of electron dense materials, vesicles, and numerous thin, convoluted wall layers. Schizogeny may be responsible for initial formation of lumen and latex and may also separate some inner epithelial cells from the surrounding layers. Lysigeny of the inner epithelial cells contributes materials to the latex and allows enlargement of the duct. The inner epithelial cells contain mitochondria, dictyosomes, apparently functional nuclei, and numerous vesicles. The outer epithelium has fewer vesicles than the inner epithelium. Schizo-lysigeny in the members of sect. Subhydrochylus is considered to be ancestral to the strict lysigeny of the members of sect. Mammillaria. The inner and outer epithelia of M. guerreronis are thought to be homologous to the lumen and epithelium respectively of M. heyderi.     

Trichoplax adhaerens (Phylum Placozoa) has Cells that React with Antibodies Against the Neuropeptide RFamide

Abstract The phylum Placozoa contains the most simply organized multicellular animals: they have a thick lower epithelium and a thin upper epithelium with some single cells sandwiched between these layers. Placozoans are generally considered to have no nerve cells or specialized sensory cells. However, the results of this investigation demonstrate the existence of a specific set of cells which react with antibodies against the neuropeptide family RFamide. The RFamide-positive cells of Trichoplax adhaerens are positioned at some distance along the margin of the animal.     

Role of cell polarity and planar cell polarity (PCP) proteins in spermatogenesis

Abstract

Studies on cell polarity proteins and planar cell polarity (PCP) proteins date back to almost 40?years ago in Drosophila and C. elegans when these proteins were shown to be crucial to support apico-basal polarity and also directional alignment of polarity cells across the plane of an epithelium during morphogenesis. In adult mammals, cell polarity and PCP are most notable in cochlear hair cells. However, the role of these two groups of proteins to support spermatogenesis was not explored until a decade earlier when several proteins that confer cell polarity and PCP proteins were identified in the rat testis. Since then, there are several reports appearing in the literature to examine the role of both cell polarity and PCP in supporting spermatogenesis. Herein, we provide an overview regarding the role of cell polarity and PCP proteins in the testis, evaluating these findings in light of studies in other mammalian epithelial cells/tissues. Our goal is to provide a timely evaluation of these findings, and provide some thought provoking remarks to guide future studies based on an evolving concept in the field.     

The ultrastructure of the blood vessels of Branchiostoma lanceolatum (Pallas) (Cephalochordata)

Summary The ultrastructure of the blood vessels of Branchiostoma has been studied using selected characteristic vessels as examples. It is shown that the vessels are a part of the original blastocoelic cavity and are delimited either by the basal laminae of adjacent epithelia or by connective tissue developed in the blastocoelic space. A brief account of the kinds of connective tissue is given. The observed contractility of some vessels depends on two types of contractile filaments situated in the basal part of the surrounding coelomic epithelia. Amoebocytelike cells are present in the blood. They may sometimes lie in contact with the wall of the vessels or with each other, but never form a typical endothelium with junctional complexes and a basal lamina of its own. Actually, there is no endothelium in any part of the vascular system. It is suggested that the term endothelium should be reserved for a closed cellular lining (with junctions) on the luminal side of the vessel wall, standing on a basal lamina of its own and forming a barrier for the exchange between blood and surrounding tissue. It is concluded that the principal structure of the vascular system of Branchiostoma is different from that of vertebrates, but the same as that of other coelomate invertebrates. The blood vessels in these animals are typically delimited directly by a basal lamina secreted by epithelia (epidermal, coelomic or intestinal) lying peripheral to this lamina, and a true endothelium is not present (with a few questionable exceptions).Abbreviations ac atrial cavity - ace atrial epithelium - ao aorta - ap atrial plexus - ax axon bundle - bc blood cell - bl basal lamina - bl ₁ basal lamina of intestinal epithelium - bl ₂ basal lamina of visceral coelomic epithelium - bl ₃ basal lamina of parietal coelomic epithelium - bl ₄ basal lamina of atrial epithelium - bll basement lamella - cf contractile filaments - co coelomic cavity - coe coelomic epithelium - coe _p parietal coelomic epithelium - coe _v visceral coelomic epithelium - ct dense connective tissue - dv longitudinal dorsal vessel - ep epidermis - epe epipharyngeal groove epithelium - epg epipharyngeal groove - fb fibroblast (?) - fi collagen fiber - fl fibril layer - go gonad - hd hemidesmosome - ie intestinal epithelium - in intestine proper - ip intestinal plexus - iv afferent intestinal vessel - ld liver diverticulum - lu vascular lumen - me myocoelic epithelium - ml muscle lamella - mp myoseptal plexus - ms myoseptum - my myomer - myc myocoelic cavity - nc notochord - ns notochordal sheath - ph pharynx - suc subchordal coelom - sv subintestinal vessel - svv segmental ventral vessel - vv longitudinal ventral vessel Supported by a grant from the Danish Natural Science Research Council     

Dynamic changes to claudins in the uterine epithelial cells of the marsupial Sminthopsis crassicaudata (Dasyuridae) during pregnancy

The fluid that surrounds the embryo in the uterus contains important nourishing factors and secretions. To maintain the distinct microenvironment in the uterine lumen, the tight junctions between uterine epithelial cells are remodeled to decrease paracellular movement of molecules and solutes. Modifications to tight junctions between uterine epithelial cells is a common feature of pregnancy in eutherian mammals, regardless of placental type. Here we used immunofluorescence microscopy and western blot analysis to describe distributional changes to tight junctional proteins, claudin‐1, ‐3, ‐4, and ‐5, in the uterine epithelial cells of a marsupial species, Sminthopsis crassicaudata. Immunofluorescence microscopy revealed claudin‐1, ‐3, and ‐5 in the tight junctions of the uterine epithelium of S. crassicaudata during pregnancy. These specific claudins are associated with restricting passive movement of fluid between epithelial cells in eutherians. Hence, their function during pregnancy in S. crassicaudata may be to maintain the uterine luminal content surrounding developing embryos. Claudin‐4 disappears from all uterine regions of S. crassicaudata at the time of implantation, in contrast with the distribution of this claudin in some eutherian mammals. We conclude that like eutherian mammals, distributional changes to claudins in the uterine epithelial cells of S. crassicaudata are necessary to support pregnancy. However, the combination of individual claudin isoforms in the tight junctions of the uterine epithelium of S. crassicaudata differs from that of eutherian mammals. Our findings suggest that the precise permeability of the paracellular pathway of the uterine epithelium is species‐specific.     

Fine Structure of the Retinal Pigment Epithelium of the River Lamprey (Lampetra fluviatilis,Cyclostomi)

The retinal pigment epithelium of Lampetra fluviatilis was studied by electron microscopy. The epithelial cells differ in many details from those of gnathostomes. The lateral cell membranes are difficult to distinguish. The smooth endoplasmic reticulum is well developed; in some animals undulated membrane complexes, comprising systems of tightly fused double membrane plates, are related to the endoplasmic reticulum. Myeloid bodies are common and well developed, but pigment granules are comparatively sparse. The intercellular space between pigment epithelium and photoreceptors is rather wide. There are only a few inclusion bodies with membranous contents. The importance of the pigment epithelium in the retinal metabolic exchange is discussed in view of the fine structure of the cells. Compared with that of hagfishes, the lamprey retina is well developed. However, any comparison must be made against the background of a diphyletic development of the two groups.     

Structure of the Digestive Tube in the Holothurian Eupentacta fraudatrix (Holothuroidea: Dendrochirota)

In the holothurian Eupentacta fraudatrix,the gut wall exhibits trilaminar organization. It consists of an inner digestive epithelium, a middle layer of connective tissue, and an outer mesothelium (coelomic epithelium). The pharynx, esophagus, and stomach are lined with a cuticular epithelium composed of T-shaped cells. The lining epithelium of the intestine and cloaca lacks a cuticle and consists of columnar vesicular enterocytes. Mucocytes are also encountered in the digestive epithelium. The connective tissue layer is composed of a ground substance, which houses collagen fibers, amoebocytes, morula cells, and fibroblasts. The gut mesothelium is a pseudostratified epithelium, which is dominated by peritoneal and myoepithelial cells and also includes the perikarya and processes of the neurons of the hyponeural plexus and vacuolated cells.     

Fine structure of the abdominal epidermis of the adult mudpuppy,Necturus maculosus (Rafinesque)

Summary The ventral epidermis of adult Necturus maculosus has been studied using electron and light microscopy. Many larval characteristics of amphibian epidermal structure are retained in adult Necturus. The epidermis is a stratified epithelium consisting of four cell layers and five cell types. Major differences compared with other adult amphibians are: (1) the absence of a well defined moulting cycle together with an apparently diminished synthetic and mitotic activity in the stratum germinativum; (2) an outermost cell layer (stratum mucosum) that is unkeratinized and appears to synthesize a mucous layer; and (3) numerous large club-shaped Leydig cells which span the epidermis between the cells of the stratum germinativum and stratum mucosum. The apical region of the stratum granulosum and stratum mucosum cells shows evidence of extensive synthesis. The stratum mucosum appears to be involved in the secretion of vesicular contents onto the outermost surface of the epithelium. The external surfaces of the stratum mucosum cells possess numerous microridges which are supported by an intricate network of cytofilaments in the apical region of these cells. The significance of these features is discussed in relation to the physiology and ecology of this species.     

Anatomy and ultrastructure of the proboscis in Mesorhynchus terminostylis (Platyhelminthes,Rhabdocoela)

The ultrastructural organization of the proboscis in Mesorhynchus terminostylis is distinctly different from that in other members of the Polycystididae in which it is currently classified. The sheath epithelium is formed by three belts, all with intra-epithelial nuclei. The apical belt of the bipartite cone epithelium has a single intrabulbar nucleus, and the basal belt possesses five insunk nucleiferous cell parts behind the bulb. Six types of glands surface through the epithelia; the three types emerging through the cone epithelium can be homologized with those described for Polycistis naegelii. Only uniciliary receptors are found in the epithelium. The musculature in the bulb has a very loose appearance, and the bulbar septum appears to be a bipartite basement membrane. The septum can be considered the basement membrane of the cone epithelium as if the contractile portion of the inner longitudinal muscles have invaded the epithelium and come to lie between the epithelial cells and the basement membrane. Thus the inner musculature of the bulb is entirely intraepithelial as is the case for Psammorhynchus tubulipenis and Cytocystis clitellatus. The systematic position of M. terminostylisremains uncertain but seems to lie between Psammorhynchus and Cytocystis on one hand and Koinocystididae and Polycystididae on the other.