Oogenesis in the leech Glossiphonia heteroclita (Annelida, Hirudinea, Glossiphonidae). I. Ovary structure and previtellogenic growth of oocytes

Glossiphonia heteroclita has paired ovaries whose shape and dimensions change as oogenesis proceeds: during early previtellogenesis they are small and club-shaped, whereas during vitellogenesis they broaden and elongate considerably. During early oogenesis (previtellogenesis), each ovary is composed of an outer envelope (ovisac) that surrounds the ovary cavity and is filled with hemocoelomic fluid, in which a single and very convoluted ovary cord is bathed. The ovary cord consists of germline cells, including nurse cells and young oocytes surrounded by a layer of elongated follicle cells. Additionally, follicle cells with long cytoplasmic projections occur inside the ovary cord, where they separate germ cells from each other. The ovary cord contains thousands of nurse cells. Each nurse cell has one intercellular bridge, connecting it to a central anucleate cytoplasmic mass, the cytophore (rachis); it in turn is connected by one intercellular bridge with each growing oocyte. Numerous mitochondria, RER cisternae, ribosomes, and Golgi complexes are transported from the nurse cells, via the intercellular bridge and cytophore, to the growing oocytes. Oogenesis in G. heteroclita is synchronous with all oocytes in the ovary in the same stage of oogenesis. The youngest observed oocytes are slightly larger than nurse cells, and usually occupy the periphery of the ovary cord. As previtellogenesis proceeds, the oocytes gather a vast amount of cell organelles and become more voluminous. As a result, in late previtellogenesis the oocytes gradually protrude into the ovary cavity. Simultaneously with oocyte growth, the follicle cells differentiate into two subpopulations. The morphology of the follicle cells surrounding the nurse cells and penetrating the ovary cord does not change, whereas those enveloping the growing oocytes become more voluminous. Their plasma membrane invaginates deeply, forming numerous broad vesicles that eventually seem to form channels or conducts through which the hemocoelomic fluid can easily access the growing oocytes.     

哺乳动物卵泡卵母细胞发生的分子调控

哺乳动物卵泡卵母细胞发生的研究一直是发育生物学研究的重点之一。简要叙述了哺乳动物卵泡卵母细胞发生的一般过程,重点分析了原始生殖细胞向卵母细胞分化过程中gdf9、c-kti、BMP4及TGF家族关键基因的表达调控对卵母细胞发生的影响,以及卵母细胞与颗粒细胞间的相互调节作用,介绍了卵母细胞体外发生的最新研究进展及面临的难题等,为进一步研究原始生殖细胞向卵母细胞分化以及卵泡生长发育的机制提供了理论基础。     

Structure of the vector tissue in piscicolid leeches (Annelida, Hirudinea, Rhynchobdellida, Piscicolidae)

Hypodermic insemination occurs in piscicolid leeches (Hirudinea, Rhynchobdellida, Piscicolidae). The spermatophore is implanted in a specialized region of the leech body, the copulatory area. Just beneath the copulatory area, there is a specialized connective tissue (vector tissue) that is considered to guide the sperm toward the ovaries. In this study, we show that the vector tissue in the four species of the genus Piscicola is composed of a mass of cells located directly beneath the copulatory area, and two thin strands extend toward the ovaries. The ultrastructure of the vector tissue has been described for the first time. Four cell types were identified, constructing the vector tissue. The envelope of this tissue is made up of extracellular fibrous matrix and two types of cells: vesicular and flat envelope cells, which are embedded within the matrix. The rest of the tissue is formed of granular and plasmatic cells. Both of these last cell types have prominent cytoplasmic projections, filled with a filamentous material. However, only granular cells have numerous small electron-dense granules in their cytoplasm. The vector tissue was described prior, during and following copulation. Sperm passes within free spaces between the granular and plasmatic cells. Characteristic vector tissue cells also occur within the ovary wall and inside the ovary lumen. This supports earlier data, which postulated that the vector tissue appears to be an outgrowth of the ovary wall.     

Structure of the germinal vesicle during oogenesis in leech Glossiphonia heteroclita (Annelida, Hirudinea, Rhynchobdellida)

Oogenesis in the glossiphoniid leech Glossiphonia heteroclita (Hirudinea, Rhynchobdellida) is nutrimental, i.e., the growing oocyte is supported by specialized germline cells, the nurse cells. The main function of the nurse cells is to provide oocytes with cell organelles and RNAs (mainly rRNA). However, in studied leech species, irrespective of the nutrimental mode of oogenesis, the germinal vesicle (GV = oocyte nucleus) seems to be very active in rRNA production. As shown in the present study, during early previtellogenesis in the GV the meiotic chromosomes and prominent primary nucleoli occur. In late previtellogenesis the chromosomes condense and occupy a limited space of nucleoplasm in close vicinity to primary nucleolus, forming a karyosome. At the onset of vitellogenesis several prominent extrachromosomal DNA bodies appear in close association with the karyosome. At the same time, the primary nucleolus is no longer visible in the GV. As vitellogenesis proceeds the extrachromosomal DNA bodies undergo fragmentation and numerous spherical, RNA- and AgNOR-positive inclusions occur in the nucleoplasm. They are regarded as multiple nucleoli. Finally, in late oogenesis numerous accessory nuclei are formed in close proximity to the nuclear envelope. They usually contain one dense body, morphologically similar to multiple nucleoli. The amplification of rDNA genes, the occurrence of extrachromosomal DNA bodies, as well as the presence of multiple nucleoli and accessory nuclei are described for the first time in the phylum Annelida.     

Environmental factors for establishment of the dormant state in oocytes

Guaranteeing the sustainability of gametogenesis is a fundamental issue for perpetuating the species. In the mammalian ovary, sustainability is accomplished by keeping a number of oocytes “stocked” in the dormant state. Despite the evident importance of this state, the mechanisms underlying the oocyte dormancy are not fully understood, although it is presumed that both intrinsic and extrinsic factors are involved. Here, we review environmental factors involved in the regulation of oocyte dormancy. Consideration of the environmental factors illustrates the nature of the ovarian compartment, in which primordial follicles reside. This should greatly improve our understanding of the mechanisms and also assist in reconstitution of the dormant state in culture. Accumulating knowledge on the dormant state of oocytes will contribute to a wide range of research in fields such as developmental biology, reproductive biology and regenerative medicine.     

Egg-feeding in the freshwater piscicolid leech Cystobranchus virginicus (Annelida, Hirudinea)

Abstract. Leeches are common terrestrial and aquatic annelids, parasitizing or feeding on a wide range of host taxa. Here we report evidence for an unusual feeding behavior of egg‐feeding in the piscicolid leech Cystobranchus virginicus. We identified distended specimens of C. virginicus in the nests of at least 4 different fish species: Campostoma anomalum, Moxostoma carinatum, Moxostoma sp. (either M. anisurum and/or M. breviceps), and Nocomis leptocephalus. We collected a total of 41 leeches from the nests of these host species and documented at least 1 leech in 19 of 55 nests (35%), with many sites containing multiple leeches. Individuals of C. virginicus were not identified feeding on any of the 41 adult specimens of Moxostoma spp. or the 635 adult specimens of Nocomis leptocephalus examined, and were never found in the absence of active host spawning (26 sites). These results are consistent with individuals of C. virginicus being an opportunistic or possibly even an obligate egg‐feeder, potentially timing their own reproductive activities with the spawning of their fish hosts. The current distribution of C. virginicus has been expanded to include North Carolina, South Carolina, and Tennessee. The potential for leech species to induce mortality in developing fish eggs could be a concern for fish conservation and merits further investigation.     

Morphology and ultrastructure of the midgut in Piscicola geometra (Annelida, Hirudinea)

This paper presents information on the organization of the midgut and its epithelium ultrastructure in juvenile and adult specimens of Piscicola geometra (Annelida, Hirudinea), a species which is a widespread ectoparasite found on the body and gills and in the mouth of many types of fish. The analysis of juvenile nonfeeding specimens helped in the explanation of all alterations in the midgut epithelium which are connected with digestion. The endodermal portion (midgut) of the digestive system is composed of four regions: the esophagus, the crop, the posterior crop caecum, and the intestine. Their epithelia are formed by flat, cuboidal, or columnar digestive cells; however, single small cells which do not contact the midgut lumen were also observed. The ultrastructure of all of the regions of the midgut are described and discussed with a special emphasis on their functions in the digestion of blood. In P. geometra, the part of the midgut that is devoid of microvilli is responsible for the accumulation of blood, while the epithelium of the remaining part of the midgut, which has a distinct regionalization in the distribution of organelles, plays a role in its absorption and secretion. Glycogen granules in the intestinal epithelium indicate its role in the accumulation of sugar. The comparison of the ultrastructure of midgut epithelium in juvenile and adult specimens suggests that electron-dense granules observed in the apical cytoplasm of digestive cells take part in enzyme accumulation. Numerous microorganisms were observed in the mycetome, which is composed of two large oval diverticles that connect with the esophagus via thin ducts. Similar microorganisms also occurred in the cytoplasm of the epithelium in the esophagus, the crop, the intestine, and in their lumen. Microorganisms were observed both in fed adult and unfed juvenile specimens of P. geometra, which strongly suggests that vertical transmission occurs from parent to offspring.     

A new species of marine leech (Hirudinea: Piscicolidae) from the north-eastern Pacific Ocean, parasitic on the English sole, Parophrys vetulus Girard

The marine piscicolid leech Calliobdella knightjonesi sp. nov. from the Oregon coast is described and illustrated. Mature individuals do not exceed 10 mm in length, have faint reddish-brown segmental pigment bands, small pulsatile vesicles, six pairs of testisacs and a well-developed seminal receptacle connected to the posterior portion of the bursa by paired tissue strands. The leech lacks eyes and ocelli.     

Ultrastructure of spermiogenesis in the Cottonmouth,Agkistrodon piscivorus (Squamata: Viperidae: Crotalinae)

To date multiple studies exist that examine the morphology of spermatozoa. However, there are limited numbers of data detailing the ontogenic characters of spermiogenesis within squamates. Testicular tissues were collected from Cottonmouths (Agkistrodon piscivorus) and tissues from spermiogenically active months were analyzed ultrastructurally to detail the cellular changes that occur during spermiogenesis. The major events of spermiogenesis (acrosome formation, nuclear elongation/DNA condensation, and flagellar development) resemble that of other squamates; however, specific ultrastructural differences can be observed between Cottonmouths and other squamates studied to date. During acrosome formation vesicles from the Golgi apparatus fuse at the apical surface of the nuclear membrane prior to making nuclear contact. At this stage, the acrosome granule can be observed in a centralized location within the vesicle. As elongation commences the acrosome complex becomes highly compartmentalized and migrates laterally along the nucleus. Parallel and circum‐cylindrical microtubules (components of the manchette) are observed with parallel microtubules outnumbering the circum‐cylindrical microtubules. Flagella, displaying the conserved 9 + 2 microtubule arrangement, sit in nuclear fossae that have electron lucent shoulders juxtaposed on either side of the spermatids basal plates. This study aims to provide developmental characters for squamates in the subfamily Crotalinae, family Viperidae, which may be useful for histopathological studies on spermatogenesis in semi‐aquatic species exposed to pesticides. Furthermore, these data in the near future may provide morphological characters for spermiogenesis that can be added to morphological data matrices that may be used in phylogenetic analyses. J. Morphol. 2010. © 2009 Wiley‐Liss, Inc.     

Ultrastructure of the ovary and oogenesis in six species of patellid limpets (Gastropoda: Patellogastropoda) from South Africa

Abstract. The ultrastructural features of the ovary and oogenesis have been described in 6 species of patellid limpets from South Africa. The ovary is a complex organ that is divided radially into numerous compartments or lacunae by plate-like, blind-ended, hollow trabeculae that extend from the outer wall of the ovary to its central lumen. Trabeculae are composed of outer epithelial cells, intermittent smooth muscle bands, and extensive connective tissue. Oocytes arise within the walls of the trabeculae and progressively bulge outward into the ovarian lumen during growth while partially surrounded by squamous follicle cells. During early vitellogenesis, the follicle cells lift from the surface of the underlying oocytes and microvilli appear in the perivitelline space. Follicle cells restrict their contact with the oocytes to digitate foot processes that form desmosomes with the oolamina. When vitellogenesis is initiated, the trabecular epithelial cells hypertrophy and become proteosynthetically active. Yolk synthesis involves the direct incorporation of extraoocytic precursors from the lumen of the trabeculae (hemocoel) into yolk granules via receptor-mediated endocytosis. Lipid droplets arise de novo and Golgi complexes synthesize cortical granules that form a thin band beneath the oolamina. A fibrous jelly coat forms between the vitelline envelope and the overlying follicle cells in all species.     

Barbronia weberi (Clitellata,Hirudinida, Salifidae) has ovary cords of the Erpobdella type

The organization of the ovaries in representative of the Salifidae (Hirudinida, Erpobdelliformes) was studied at the ultrastructural level for the first time. Like in other leeches, the ovaries of Barbronia weberi are composed of an outer envelope (i.e., an ovisac made up of two coelomic epithelia, muscle cells, and connective tissue) and several internal units, which are broadly similar to the ovary cords found in representatives of the Erpobdellidae. There are usually 6–8 ovary cords that are twisted or cambered with a narrow apical part and a broader, irregularly shaped distal end in each ovisac of B. weberi. Each ovary cord is built from somatic and germ‐line cells and the latter tend to form multicellular cysts that are equipped with a central cytoplasmic core (cytophore). There are two morphologically different subpopulations of germ‐line cells: oocytes and more numerous nurse cells. Growing oocytes form protuberances on the ovary cord surface and eventually detach from the cord and float freely in the ovisac lumen, whereas the other components of germ‐line cysts (i.e., nurse cells and cytophore) degenerate. It should be pointed out that there is a prominent gradient of germ‐cell development along the long axis of the cord. The somatic cells form the ovary cord envelope (the so‐called spongiosa cells) and also penetrate the spaces between germ‐line cells. Both kinds of the somatic cells, that is, those forming the cord envelope and the somatic cells that are associated with oocytes (follicular cells) have a well‐developed system of intercellular channels. Additionally, one prominent somatic cell, the apical cell, was found at the apical tip of each ovary cord. Because the aforementioned features of ovary cords found in B. weberi are very similar (with a few minor exceptions) to the ovary cords that have been described in Erpobdella octoculata and E. johanssoni, we propose the term “ovary cords of the Erpobdella type” for them. Our results support a close phylogenetic relationship between Salifidae and Erpobdellidae. J. Morphol. 275:479–488, 2014. © 2013 Wiley Periodicals, Inc.     

Ultrastructure and function of follicle cell in the ovary of Branchiostoma belcheri

The ultrastructure of follicle cells in the ovary at different developmental stages ofBranchiostoma has been observed in detail with a transmission electron microscope. The results indicate that only one kind of follicle cell exists with structural features related to steroid hormone biosynthesis: (i) oval or round mitochondria with tubules; (ii) smooth surfaced endoplasmic reticulum; (iii) several large lipid droplets in the cytoplasm; (iv) a well developed Golgi complex and tubular rough surfaced endoplasmic reticulum, as can be found in mammalian theca interna cells. In addition, as steroid hormone synthesizing cells, they obviously play an important role in the phagocytosis of relict gametes and cellular debris and may have a nutritive function for the oocytes. They can produce abundant secretory granules in stages III-IV ovaries. In mature ovaries they transform into flat epithelial cells with numerous microfilaments which may play a role in ovulation.     

Ultrastructure and function of follicle cell in the ovary of Branchiostoma belcheri

The ultrastructure of follicle cells in the ovary at different developmental stages of Branchiostoma has been observed in detail with a transmission electron microscope. The results indicate that only one kind of follicle cell exists with structural features related to steroid hormone biosynthesis: (i) oval or round mitochondria with tubules; (ii) smooth surfaced endoplasmic reticulum; (iii) several large lipid droplets in the cytoplasm; (iv) a well de-veloped Golgi complex and tubular rough surfaced endoplasmic reticulum, as can be found in mammalian theca interna cells. In addition, as steroid hormone synthesizing cells, they obviously play an important role in the phagocytosis of relict gametes and cellular debris and may have a nutritive function for the oocytes. They can produce abundant secre-tory granules in stages III-IV ovaries. In mature ovaries they transform into flat epithelial cells with numerous micro-filaments which may play a role in ovulation.     

The female gonad in two species of Microplana (Platyhelminthes,Tricladida, Rhynchodemidae): Ultrastructural and cytochemical investigations

The female gonad of the land planarians Microplana scharffi and Microplana terrestris consists of two small germaria located ventrally in the anterior third of the body and of two ventro‐lateral rows of oblong vitelline follicles distributed between the intestinal pouches. Both these structures are enveloped by a tunica composed of an outer extracellular lamina and an inner sheath of accessory cells. Oocyte maturation is characterized by the appearance of chromatoid bodies and the development of endoplasmic reticulum and Golgi complexes. These organelles appear to be correlated with the production of egg granules with a fenestrated/granular content of medium electron density, about 4–5 μm in diameter, which remain dispersed in the ooplasm of mature oocytes. On the basis of cytochemical tests showing their glycoprotein composition, and their localization in mature oocytes, these egg granules have been interpreted as yolk. In the vitelline follicles, vitellocytes show the typical features of secretory cells with well‐developed rough endoplasmic reticulum and Golgi complexes involved in the production of eggshell globules and yolk. The eggshell globules, which appear to arise from repeated coalescences of two types of Golgi‐derived vesicles, contain polyphenols and, when completely mature, they measure about 1–1,2 μm in diameter and show a meandering/concentric content pattern as is typical of the situation observed in most Proseriata and Tricladida. Mature vitellocytes also contain a large amount of glycogen and lipids as further reserve material. On the basis of the ultrastructural features of the female gonad and in relation to the current literature the two species of rhynchodemids investigated appear to be closely related to the freshwater planarians belonging to the family Dugesiidae. J. Morphol. 2009. © 2009 Wiley‐Liss, Inc.     

A study about the Coelom of four Haementeria Filippi, 1849 species (Glossiphoniidae,Rhynchobdellae, Hirudinea)

Six types of coelomic sinuses arranged in five longitudinal stems (one median, two paramedian and two lateral) and a system of transversal branches were observed in adult and young individuals of Haementeria depressa and H. lutzi, and in adult forms only in H. tuberculifera and H. vizottoi. Some information about the relative position of the different sinuses as referred to the body segments and to other systems of organs is given, as well as about the internal structure and the connections linking the sinuses to one another. In H. depressa and H. lutzi, a relationship between the hypodermic sinuses and the circular muscle fibres of the body is reported. An account of the figurative elements of the coelom, and the relationship between acid cell size and organisms maturity is also given.     

栽培甜菜卵细胞、合子及二细胞原胚的超微结构

为丰富被子植物生殖生物学资料, 并为甜菜相关研究提供参考, 应用透射电镜技术研究栽培甜菜（Beta vulgaris）卵细胞、合子和二细胞原胚的超微结构特征。结果如下：在成熟卵细胞中多聚核糖体数量不多, 且细胞代谢活性较弱; 初期合子内, 核仁大量合成核糖体前体物质, 胞质中多聚核糖体数目众多, 细胞代谢活性较强; 休眠期合子的核仁变小, 胞质中核糖体数量急剧减少, 仅有少量多聚核糖体, 细胞代谢活性较弱; 合子分裂前期和二细胞原胚期, 核仁显著, 胞质中核糖体的密度增加, 出现大量多聚核糖体, 细胞代谢活性较强。根据上述结果可以得出, 栽培甜菜从卵细胞成熟→合子初期→合子休眠期→合子分裂前期→二细胞原胚的超微结构变化中多聚核糖体的变化最为显著, 表现为“少→多→少→多”的数量变化过程, 反映出细胞代谢状态也经历了“弱→强→弱→强”的变化过程, 这种变化趋势与配子体世代向孢子体世代转变有关。     

Morphological and quantitative evaluation of the ovarian recrudescence in Nile tilapia (Oreochromis niloticus) after spawning in captivity

The Nile tilapia is one of the most important fish species for aquaculture worldwide. Understanding their reproductive biology is essential for improving their aquaculture methods. The morphological and quantitative dynamics of ovarian recrudescence of Oreochromis niloticus was studied for 21 days postspawning. To accomplish this, breeding females were kept in controlled conditions and ovarian samples were collected weekly for histological, ultrastructural and morphometric analyses. Ovarian follicle morphology revealed an intense synthesis activity of the follicular cells, which actively contributed to formation of the zona radiata and oocyte development following spawning. Recently spawned ovaries contained follicles at all developmental stages, but they were predominantly early primary growth (～42%) and full‐grown follicles (～20%). Remnants of spawning, postovulatory follicle complexes represented approximately 5% of the former ovarian follicles immediately after spawning, and less than 1% after 7 days. Atretic follicles accounted for approximately 2% of the follicles studied during the period. The stock of primary growth follicles was stable during ovarian recrudescence, indicating their availability for continuous recruitment. Only the frequency of full‐grown follicles significantly increased in the ovaries during recrudescence, representing approximately 35% of the follicles 21 days postspawning. The diameters of all follicles were significantly different between the periods analyzed. The ovaries' morphological characteristics, the maintenance of young follicles stocks and the gradual and significant increase in the proportion and diameter of full‐grown follicles showed a rapid ovarian recovery and follicular growth of O. niloticus, in 21 days at 29.5°C, necessary for the next spawning. J. Morphol. 275:348–356, 2014. © 2013 Wiley Periodicals, Inc.