Histochemical investigations of Rotifera Bdelloidea. I. Localization of cholinesterase activity

Summary Cholinesterase activity has been investigated in Rotifera Bdelloidea (Philodina roseola, Philodina tubercolata, Rotaria rotatoria and other unidentified species) by histochemical methods andin vivo observations. Parallel histological studies have been carried out. The enzyme specificity was tested by employing different substrates and inhibitors. The effectsin vivo of tubocurarin, bungarotoxin and acetylcholine were also observed. Acetylcholinesterase activity is localized in the nervous and muscular tissues, in sensory organs and in all the ciliated cells. Secretory cells (subcerebral, salivary and pedal glands) and gonad cells (nuclei of the syncytial vitellarium and follicular layer, oocytes and eggs) show both acetyl-and butyrylcholinesterase activities. The effectsin vivo of cholinesterase inhibitors, as well as those of tubocurarin, bungarotoxin and acetylcholine, are consistent with the histochemical results, indicating a cholinergic system of transmission and acetylcholinesterase, as well as butyrylcholinesterase, activity.This paper is dedicated to my master, the late Professor António Minganti.     

Source of a new crop of oocytes inTilapia mossambica

Summary 1. In the teleostTilapia mossambica (Peters), new crops of oocytes arise from nests of cells of the germinal epithelium as well as from the epithelial strands ramifying into the ovocoel.2. There is no evidence to indicate that degenerating follicle cells form a source for a new crop of oocytes.3. After one spawning is over, the follicular layer of the mature unspawned ova alone undergo atresia.4. Neither immature oocytes nor oocytes in the growth stages undergo degeneration.5. The occurrence of immature, maturing, and fully ripe ova in the ovary at a particular time account for asynchronism inTilapia mossambica.

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Origine des poussées ovocytaires chezTilapia mossambica

Extrait L'ovaire deTilapia mossambica a été étudié dans le but de préciser l'origine des poussées ovocytaires. Après la ponte l'ovaire n'est pas vide pour autant, et il y subsiste des ovocytes à tous les stades du développement. Les replis de l'épithélium germinatif et les tractus épithéliaux ramifiés contiennent des flots de cellules qui produisent des ovogonies primaires, lesquelles se transforment en ovocytes et en cellules folliculaires. Il ne semble pas qu'une nouvelle poussée ovocytaire puisse se faire à partir des résidus des follicules des ovocytes atrétiques. Seuls les ovules mûrs non évacués par la ponte subissent une atrésie et se résorbent; les ovocytes immatures ou en voie de croissance ne dégénèrent pas. L'asynchronisme deT. mossambica se traduit par la présence simultanée, dans l'ovaire, d'ovocytes à tous les stades de croissance et de maturation.

     

Structure of the ovaries and oogenesis in Cixius nervosus (Cixiidae), Javesella pellucida and Conomelus anceps (Delphacidae) (Insecta, Hemiptera, Fulgoromorpha)

Ovary organization in representatives of two families of Fulgoromorpha, Cixiidae (Cixius nervosus) and Delphacidae (Javesella pellucida and Conomelus anceps), was examined by light and transmission electron microscopy. Ovaries of studied fulgoromorphans consist of telotrophic ovarioles. From apex to base individual ovarioles have four well defined regions: a terminal filament, tropharium (trophic chamber), vitellarium and pedicel (ovariolar stalk). Tropharia are not differentiated into distinct zones and consist of syncytial lobes containing multiple trophocyte nuclei embedded in a common cytoplasm. Lobes are radially arranged around a branched, cell-free trophic core. Early previtellogenic (arrested) oocytes and prefollicular cells are located at the base of the tropharium. The vitellarium houses linearly arranged developing oocytes each of which is connected to the trophic core by a broad nutritive cord. Each oocyte is surrounded by a single layer of follicular cells that become binucleate at the beginning of vitellogenesis.     

Ultrastructural studies of the ovary of Palaeococcus fuscipennis (Burmeister) (Insecta, Hemiptera, Coccinea: Monophlebidae)

Ovaries of Palaeocoocus fuscipennis are composed of about 100 telotrophic ovarioles that are devoid of terminal filaments. In the ovariole a tropharium ( = trophic chamber) and vitellarium can be distinguished. The tropharium contains 7 trophocytes. A single oocyte develops in the vitellarium. The oocyte is surrounded by follicular cells that do not undergo diversification into subpopulations. The obtained results are discussed in a phylogenetic context.     

A very simple mode of follicular cell diversification in Euborellia fulviceps (Dermaptera, Anisolabididae) involves actively migrating cells

The ovaries of Euborellia fulviceps are composed of five elongated ovarioles of meroistic-polytrophic type. The individual ovariole has three discernible regions: the terminal filament, germarium, and vitellarium. The terminal filament is a stalk of flattened, disc-shaped somatic cells. In the germarium, germline cells in subsequent stages of differentiation are located, and the vitellarium comprises numerous ovarian follicles arranged linearly. The individual ovarian follicles within the vitellarium are separated by prominent interfollicular stalks. The follicles are composed by two germline cells only: an oocyte and a single, polyploid nurse cell, which are surrounded by a monolayer of somatic follicular cells (FCs). During subsequent stages of oogenesis, initially uniform follicular epithelium begins to diversify into morphologically and physiologically distinct subpopulations. In E. fulviceps, the FC diversification mode is rather simple and leads to the formation of only three different FC subpopulations: (1) cuboidal FCs covering the oocyte, (2) stretched FCs surrounding the nurse cell and (3) FCs actively migrating between oocyte and a nurse cell. We found that FCs from the latter subpopulation send long and thin filopodium-like and microtubule-rich processes penetrating between the oocyte and nurse cell membranes. This suggests that, in E. fulviceps, cells from at least one FCs subpopulation show the ability to change position within an ovarian follicle by means of active migration.     

Morphology of the ovaries of Sphaerodema (Diplonychus) rusticum (Heteroptera,Belostomatidae)

The female reproductive system of Sphaerodema rusticum consists of a pair of ovaries, two lateral oviducts, a median common oviduct, and a median spermatheca. Accessory glands are absent. Each ovary has five free ovarioles branching from the oviduct. Each ovariole consists of a terminal filament, germarium, vitellarium, brown mass, and an exceptionally long pedicel. The terminal filament consists of a central core, interstitial cells, and an outer sheath. In the germarium, which consists of trophic and prefollicular regions, the trophic region or nurse cell chamber is divided into four histologically differentiated zones, distinguished as zones I–IV. Nutritive cords, originating from the posterior end of the trophic core in zone IV extend centrally and join the developing oocytes in the prefollicular chamber and the vitellarium. The compact prefollicular tissue at the base of the trophic core gives rise to prefollicular cells which, after encircling the young oocytes, become modified into follicular epithelial cells, the interfollicular plug, and epithelial plug. The young oocytes descend into the vitellarium and gradually develop into mature oocytes. A compound corpus luteum is observed simultaneously in all the ovarioles of both ovaries after ovulation. Below the epithelial plug there is an accumulation of material, the “brown mass,” which develops cyclically in correlation with the ovulation cycle. Each pedicel stores five mature chorionated eggs ready for oviposition. The epithelium of the anterior region of the pedicel secretes a PAS-positive material. General morphology and histology of the subdivisions of the ovarioles are described.     

Effects of pyrimidine-2-thiol on the ovarian histology of Epilachna vigintioctopunctata (Fabr.) (Coleoptera: Coccinellidae)

The telotrophic ovary of Epilachna vigintioctopunctata is composed of 32-40 ovarioles, each with an apical germarium and a basal vitellarium. The germarium encloses mononucleate and binucleate trophocytes, prefollicular tissue and oogonia, while the vitellarium contains 2-5 oocytes arranged in order of maturity. Definite nutritive cords are absent. When females are exposed to 75 mg 4,4,6-trimethyl-1h, 4H-pyrimidine-2-thiol by contact, the trophocytes and the follicular epithelial cells disintegrate to form dark-staining clumps and thus fail to supply nourishment to the developing oocytes, which consequently remain yolk-less and are ultimately reduced to shrunken masses.     

Ultra- and microstructure of the female reproductive system of Matsucoccus matsumurae

The ultra- and microstructure of the female reproductive system of Matsucoccus matsumurae was studied using light microscopy, scanning and transmission electron microscopy. The results revealed that the female reproductive system of M. matsumurae is composed of a pair of ovaries, a common oviduct, a pair of lateral oviducts, a spermatheca and two pairs of accessory glands. Each ovary is composed of approximately 50 telotrophic ovarioles that are devoid of terminal filaments. Each ovariole is subdivided into an apical tropharium, a vitellarium and a short pedicel connected to a lateral oviduct. The tropharium contains 8–10 trophocytes and two early previtellogenic oocytes termed arrested oocytes. The trophocytes degenerate after egg maturation, and the arrested oocytes are capable of further development. The vitellarium contains 3–6 oocytes of different developmental stages: previtellogenesis, vitellogenesis and choriogenesis. The surface of the vitellarium is rough and composed of a pattern of polygonal reticular formations with a center protuberance. The oocyte possesses numerous yolk spheres and lipid droplets, and is surrounded by a mono-layered follicular epithelium that becomes binucleate at the beginning of vitellogenesis. Accessory nuclei are observed in the peripheral ooplasm during vitellogenesis.     

Oogenesis in the Polychaete Dipolydora commensalis

Oocytes of the polychaete Dipolydora commensalis develop in the gonad, in close contact with the wall of the genital blood vessel, up to the late stages of vitellogenesis. At the blood vessel wall, between the neighboring vitellogenic oocytes, and sometimes on the apical surface of the oocytes, there are flattened follicular cells. However, no continuous, well-expressed gonad envelope is found. Oogenesis is asynchronous. Gametes at all developmental stages, from oogonia to late vitellogenic oocytes, occur in the gonad. Dividing oogonia vary from 6 to 10 m in diameter. RNA, proteins, glycogen, and lipids accumulate in the oocytes during vitellogenesis. The breakdown of the oocyte germ vesicle occurs in the gonad. Before spawning, gametes accumulate in the coelom and reach 80–90 m in diameter, at which point a new generation appears in the gonad.     

The ovaries of aphids (Hemiptera,Sternorrhyncha, Aphidoidea): morphology and phylogenetic implications

The ovaries of aphids belonging to the families Eriosomatidae, Anoeciidae, Drepanosiphidae, Thelaxidae, Aphididae, and Lachnidae were examined at the ultrastructural level. The ovaries of these aphids are composed of several telotrophic ovarioles. The individual ovariole is differentiated into a terminal filament, tropharium, vitellarium, and pedicel (ovariolar stalk). Terminal filaments of all ovarioles join together into the suspensory ligament, which attaches the ovary to the lobe of the fat body. The tropharium houses individual trophocytes and early previtellogenic oocytes termed arrested oocytes. Trophocytes are connected with the central part of the tropharium, the trophic core, by means of broad cytoplasmic processes. One or more oocytes develop in the vitellarium. Oocytes are surrounded by a single layer of follicular cells, which do not diversify into distinct subpopulations. The general organization of the ovaries in oviparous females is similar to that of the ovaries in viviparous females, but there are significant differences in their functioning: (1) in viviparous females, all ovarioles develop, whereas in oviparous females, some of them degenerate; (2) the number of germ cells per ovariole is usually greater in females of the oviparous generation than in females of viviparous generations; (3) in oviparous females, oocytes in the vitellarium develop through three stages (previtellogenesis, vitellogenesis, and choriogenesis), whereas in viviparous females, the development of oocytes stops after previtellogenesis; and (4) in the oocyte cytoplasm of oviparous females, lipid droplets and yolk granules accumulate, whereas in viviparous females, oocytes accrue only lipid droplets. Our results indicate that a large number of germ cells per ovariole represent the ancestral state within aphids. This trait may be helpful in inferring the phylogeny of Aphidoidea.     

Structure of the ovary and the differentiation of follicular epithelium in the pig louse, Haematopinus suis (Insecta: Phthiraptera)

The female reproductive system of the pig louse, Haematopinus suis (Insecta: Phthiraptera) is composed of paired ovaries, lateral oviducts, and a common oviduct that leads into a vagina. Clusters of mycetocytes (= cells filled with symbiotic organisms) are associated with lateral oviducts. Each ovary is composed of five loosely arranged ovarioles of the polytrophic-meroistic type. An individual ovariole is covered by a basal lamina and is composed of a terminal filament, germarium, and vitellarium. The terminal filament is composed of large, disc-shaped cells that are orientated perpendicularly to the long axis ofthe ovariole. The basal part of the terminal filament is separated from the germarium by a well-developed transverse septum. The germarium is short and filled with clusters of oogonial cells. In each cluster the cells arejoined by intercellular bridges, filled with fusomal material. Within the cluster, only one cell, the future oocyte, enters the prophase of the first meiotic division; the other cells differentiate into nurse cells. The basal part ofthe germarium is filled with the somatic prefollicular cells. The boundary between the germarium and the vitellarium is not distinct. The vitellarium contains linearly arranged ovarian follicles in subsequent stages of oogenesis (previtellogenesis, vitellogenesis and choriogenesis). Each follicle consists of an oocyte and 7 nurse cells and is surrounded by follicular cells. During oogenesis the follicular cells diversify, so that ultimately, five morphologically distinct subpopulations of these cells can be distinguished: (1) cells in contact with the nurse cells, (2) anterior cells, (3) mainbody cells, (4) posterior cells, and (5) interfollicular cells. Interestingly, the follicular cells associated with the anterior part of the oocyte, i.e. located in space at the oocyte/nurse cell border (fold cells) are mitotically active throughout previtellogenesis. It might be suggested, in this context, that the separation of the oocyte from the nurse cell compartment is brought about by mitotic divisions, consequent multiplication and centripetal migration of these cells.     

Etude cytochimique et ultrastructurale de l'évolution ovocytaire de Nereis pelagica L. (Annélide Polychète)

Résumé En l'absence d'hormone cérébrale, les ovocytes de N. pelagica subissent un accroissement rapide de taille. Ils présentent dans les grandes lignes une évolution cytologique parallèle à celle de l'ovogenèse naturelle. Ces ovocytes acquièrent en particulier des mucopolysaccharides acides qui se répartissent en fin d'évolution en une gangue corticale. Ce matériel toutefois est moins abondant que dans le cas de l'ovogenèse naturelle.A l'échelle de la microscopie électronique, diverses particularités caractérisent les ovocytes ayant évolué en condition anhormonale. Elles sont d'autant plus notables que le diamètre initial des ovocytes en expérimentation est plus faible. On note en particulier un accroissement des formations de reticulum et une augmentation considérable du nombre et de l'importance des lamelles annelées cytoplasmiques et intra-nucléaires. Enfin, la structure des lobules vitellins se caractérise par la présence de formations vésiculaires et lamellaires. La signification de ces modifications ultrastructurales est discutée.

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Cytochemical and ultrastructural study of oocyte development in Nereis pelagica L.II. Development in the absence of brain hormone

Summary In the absence of brain hormone, the oocytes of N. pelagica undergo a fast growth. They show a cytologic development parallel to that of natural oogenesis. In particular, these oocytes acquire acid mucopolysaccharides which finally form a cortical layer. However, this material is less abundant than in natural oogenesis.Electron microscopic investigation reveals some pecularities in oocytes growing under these abnormal conditions. The smaller the initial diameter of the oocytes, the more pronounced are these special traits. Most evident is an increase of the endoplasmic reticulum and a large augmentation in the number of cytoplasmic and intranuclear annulate lamellae. Moreover, the structure of the yolk bodies shows characteristic vesicular and membranous formations.The significance of these ultrastructural modifications is discussed.

     

Sterility of the coffee berry borer,Hypothenemus hampei (Coleoptera: Curculionidae), caused by the nematode Metaparasitylenchus hypothenemi (Tylenchidae: Allantonematidae)

Metaparasitylenchus hypothenemi is an endoparasitic nematode that causes partial or total sterility of coffee berry borer (Hypothenemus hampei) females, although the causes are unknown. Fecundity and the average size of the common and lateral oviduct, vitellarium, and germarium in the four ovarioles (I, II, III and IV) were compared between parasitised and non-parasitised insects to determine the causes of sterility. The nematode significantly lowers the number of oocytes and 86% of parasitised insects (24 out of 28 insects) were sterile, while fecundity in the remaining 13% was non-significantly different to that in non-parasitised insects. No significant differences were recorded in the size of the common oviduct, lateral oviduct, vitellarium, and germarium between parasitised and non-parasitised insects and the nematode does not cause any apparent damage on the surface of the ovary.     

Correlation between the presence of a bacterial symbiont in oocytes of Parcellio dilatatus petiti, and the sterility of the cross: P.d. petiti male x P.d. dilatatus female]

A symbiotic bacteroid matroclinously transmitted is present in the ovocytes and the follicular cells of the sub-species Porcellio dilatatus petiti of the Saint-Honorat island, as well as in all hybrid females born from a petiti mother. It is absent in the Porfellio dilatatus dilatatus females (population of Poitiers) and this seems to cause the lithality in the periblastula stage -- as a result of abnormal anaphases--of practically all the embryos of the crossing : male petiti x female dilatatus.     

Mayflies (ephemeroptera), the most “primitive” winged insects,have telotrophic meroistic ovaries

Germ line cell cluster formation in ovarioles of three different stages, each from a different mayfly species, was studied using ultra-thin serial sectioning. In the analysed ovariole of Cloeön sp., only one linear, zigzag germ line cell cluster was found, consisting of sibling cells connected by intercellular bridges which represent remnants of preceding synchronized mitotic cycles followed by incomplete cytokinesis. A polyfusome stretched through all sibling cells. At the tip of the ovariole, cytokinesis occurred without preceding division of nuclei; thus, intercellular bridges were lined up but the remaining cytoplasm between the bridges had no nuclei. The analysed Siphlonurus armatus vitellarium contained five oocytes at different stages of development. Each oocyte in the vitellarium was connected via a nutritive cord to the linear cluster of its sibling cells in the terminal trophic chamber. Each cluster had the same architecture as was found in Cloëon. The 3-dimensional arrangement and distribution of closed intercellular bridges strongly suggest that all five clusters are derived from a single primary clone. The position of oocytes within each cluster is random. However, each oocyte is embraced by follicular or prefollicular cells whilst all other sibling cells are enclosed by somatic inner sheath cells, clearly distinguishable from prefollicular cells. In the analysed ovariole of Ephemerella ignita, two small linear clusters were found in the tropharium beside two single cells, two isolated cytoplasmic bags with intercellular bridges but no nuclei, and some degenerating aggregates. One cluster was still connected to a growing oocyte via a nutritive cord. In all species the nurse cells remained small and no indications of polyploidization were found. We suggest that this ancient and previously unknown telotrophic meroistic ovary has evolved directly from panoistic ancestors.     

Allassogonoporus callosciuri n. sp. (Digenea: Allassogonoporidae) from the plantain squirrel Callosciurus notatus (Boddaert) (Rodentia: Sciuridae) in Borneo

A new digenean, Allassogonoporus callosciuri n. sp. from the plantain squirrel Callosciurus notatus from the Malaysian state of Sarawak, Borneo, is described. The new species differs from: A. amphoraeformis by the size of the ventral sucker and the position of the vitellarium and uterus; and from A. marginalis by the smaller oral sucker, the position of the testes and vitellarium; from A. vespertilionis by the position of the vitellarium, testes and ovary; from A. asymmetrica by the position of the testes and uterus. Gilford's (1955) and Dubois' (1963) opinions on the synonymy of Allassogonoporus and Myotitrema is supported. No representatives of the family Allassogonoporidae have been reported previously from sciurids or South-East Asia.     

Structure of ovaries in ensign scale insects,the most primitive representatives of Coccomorpha (Insecta,Hemiptera)

The ovaries of Orthezia urticae and Newsteadia floccosa are paired and composed of numerous short ovarioles. Each ovariole consists of an anterior trophic chamber and a posterior vitellarium that contains one developing oocyte. The trophic chamber contains large nurse cells (trophocytes) and arrested oocytes. The total number of germ cells per ovariole (i.e., cluster) is variable, but it is always higher than 32 and less than 64. This suggests that five successive mitotic cycles of a cystoblast plus additional divisions of individual cells are responsible for the generation of the cluster. Cells of the trophic chamber maintain contact with the oocyte via a relatively broad nutritive cord. The trophic chamber and oocyte are surrounded by somatic cells that constitute the inner epithelial sheath around the former and the follicular epithelium around the latter. Anagenesis of hemipteran ovarioles is discussed in relation to the findings presented. © 1995 Wiley-Liss, Inc.     

Fine structure of the subitaneous eggshell of the sessile rotifer Stephanoceros millsii (Monogononta) with observations on vesicle trafficking in the integument during ontogeny

Rotifers that engage in cyclical parthenogenesis produce two types of eggs: subitaneous eggs that hatch as clonal females and meiotic eggs that hatch as haploid males, or if fertilized, as females after a period of diapause (resting eggs). The ultrastructure of resting eggshells is known for some motile species, but there are limited data on subitaneous eggshells, and no data on any eggshells of sessile rotifers. Here, we investigated the ultrastructure of the subitaneous eggshell of the sessile rotifer Stephanoceros millsii and its potential origins of secretion, the maternal vitellarium and embryonic integument. We also explored secretory activity in the larval and adult integuments to determine whether activity changes during ontogeny. The eggshell consists of a single layer with two sublayers: an external granular sublayer apparently derived from the maternal vitellarium, and an internal flocculent sublayer secreted by the embryonic integument that may form a hatching membrane or glycocalyx. Secretory activity remains high in both the larva and adult and appears to be the source of the thickening glycocalyx. Altogether, the subitaneous eggshell of S. millsii is the thinnest among monogonont rotifers. Thin eggshells may have evolved in response to the added protection provided by the mother’s extracorporeal tube.     

An electron microscopic study of early gonadogenesis in the hermaphroditic appendicularian Oikopleura gracilis (Tunicata,Oikopleuridae)

The postembryonic development of the gonad in the hermaphroditic appendicularian O. gracilis was studied using transmission electron microscopy. The primordial germ cells were detected first in 10-h-old larvae and represent migrating primordial germ syncytium (mPGS) localized in the hemocoel of the tail/trunk junction and several haemocoel areas of the digestive compartment. The mPGS consisted of primordial germ nuclei (PGN) 2 μm in diameter, and elongate somatic-line nuclei 1.8 μm in diameter. In 12.5-h-old juveniles the gonad primordium 40 × 90 μm in size, was separated by a narrow space of haemocoel between the gut and the epidermis of the reproductive compartment. The gonad primordium consisted of the central syncytial part of primordial germ nuclei (PGN), enclosing a single layer of somatic epithelium. In 3-day-old juveniles, the gonad was differentiated into testis and ovary. The testis, 400 × 550 μm in size, is a syncytium of spermatogonial nuclei, covered by a single layer of somatic epithelium. The ovaries, 350 × 850 μm in size, consist of a syncytium with nurse nuclei and meiotic nuclei. The hermaphroditic gonad originates from extragonadal mPGS. Early gonadogenesis in appendicularians has ultrastructural features in common with early gonadogenesis in ascidians.