Ultrastructural investigations of the ovary and oogenesis in the pycnogonids Cilunculus armatus and Ammothella biunguiculata (Pycnogonida, Ammotheidae)

Abstract. Ovarian ultrastructure and oogenesis in two pycnogonid species, Cilunculus armatus and Ammothella biunguiculata , were investigated. The ovary is morphologically and functionally divided into trunk and pedal parts. The former represents the germarium and contains very young germ cells in a pachytene or postpachytene phase, whereas the latter houses developing previtellogenic and vitellogenic oocytes and represents the vitellarium. Intercellular bridges were occasionally found between young (trunk) germ cells. This indicates that in pycnogonids, as in other animal groups, at the onset of oogenesis clusters of germ cells are generated. As nurse cells are absent in the ovaries of investigated species, the clusters must secondarily split into individual oocytes. In the vitellarium, the oocytes are located outside the ovary. Each oocyte is connected to the ovarian tissue by a stalk composed of several somatic cells. The stalk cells directly associated with the oocyte are equipped with irregular projections that reach the oocyte plasma membrane. This observation suggests that the stalk cells may play a nutritive role. The ooplasm of vitellogenic oocytes comprises mitochondria, free ribosomes, stacks of annulate lamellae, active Golgi complexes, and vesicles derived from these complexes. Within the latter, numerous electron-dense bodies are present. We suggest that these bodies contribute to yolk formation.     

Differentiation of somatic cells in the ovariuteri of the apoikogenic scorpion Euscorpius italicus (Chelicerata,Scorpiones, Euscorpiidae)

In apoikogenic scorpions, growing oocytes protrude from the gonad (ovariuterus) and develop in follicles exposed to the mesosomal (i.e. hemocoelic) cavity. During subsequent stages of oogenesis (previtellogenesis and vitellogenesis), the follicles are connected to the gonad surface by prominent somatic stalks. The aim of our study was to analyze the origin, structure and functioning of somatic cells accompanying protruding oocytes. We show that these cells differentiate into two morphologically distinct subpopulations: the follicular cells and stalk cells. The follicular cells gather on the hemocoelic (i.e. facing the hemocoel) surface of the oocyte, where they constitute a cuboidal epithelium. The arrangement of the follicular cells on the oocyte surface is not uniform; moreover, the actin cytoskeleton of these cells undergoes significant modifications during oocyte growth. During initial stages of the stalk formation the stalk cells elongate and form F-actin rich cytoplasmic processes by which the stalk cells are tightly connected to each other. Additionally, the stalk cells develop microvilli directed towards the growing oocyte. Our findings indicate that the follicular cells covering hemocoelic surfaces of the oocyte and the stalk cells represent two distinct subpopulations of epithelial cells, which differ in morphology, behavior and function.     

Adaptations for matrotrophy in the female reproductive system in the pseudoscorpion Chelifer cancroides (Chelicerata: Pseudoscorpiones,Cheliferidae)

Pseudoscorpiones (pseudoscorpions, false scorpions) is an order of small terrestrial chelicerates. While most chelicerates are lecithotrophic, that is, embryos develop due to nutrients (mostly yolk) deposited in the oocyte cytoplasm, pseudoscorpions are matrotrophic, that is, embryos are nourished by the female. Pseudoscorpion oocytes contain only a small amount of yolk. The embryos develop within a brood sac carried on the abdominal site of the female and absorb nutrients by a pumping organ. It is believed that in pseudoscorpions nutrients for developing embryos are produced in the ovary during a postovulatory (secretory) phase of the ovarian cycle. The goal of our study was to analyze the structure of the female reproductive system during the secretory phase in the pseudoscorpion Chelifer cancroides, a representative of the family Cheliferidae, considered to be one of the most advanced pseudoscorpion taxa. We use diverse microscopic techniques to document that the nutritive fluid is produced not only in the ovaries but also by the epithelial cells in the oviducts. The secretory active epithelial cells are hypertrophic and polyploid and release their content by fragmentation of apical parts. Our observations also indicate that fertilization occurs in the oviducts. Moreover, in contrast to previous findings, we show that secretion of the nutritive material starts when the fertilized oocytes reach the brood sac and thus precedes formation of the pumping organ. Summing up, we show that C. cancroides exhibits traits of advanced adaptations for matrotrophy due to coordinated secretion of the nutritive fluid by the ovarian and oviductal epithelial cells, which substantially increases the efficiency of nutritive fluid formation. Since the secretion of nutrients starts before formation of the pumping organ, we suggest that the embryos are able to absorb the nutritive fluid also in the early embryonic stages.     

Ultrastructural investigation of the ovary structure ofOphyiulus pilosus (Myriapoda,Diplopoda)

Summary Histological and ultrastructural investigations of diplopod ovary structure have revealed that oogonia and early meiotic oocytes develop only in the laterodorsal parts of the ovarian wall, where they form groups called germ nests. Euplasmic growth forces diplotene oocytes out of the ovarian wall and into the lumen of the ovary, which leads to the formation of ovarian sacs. Ovarian sacs constitute separate structural-functional units built of a centrally situated oocyte and the epithelial cover. Being turned with their basal parts to the surface of the oocyte and showing no signs of any synthetic nor secretory activity, the epithelial cells of the ovarian sac wall cannot be referred to as typical follicular cells. That is why oogenesis of diplopods must be regarded as solitary.     

Ultrastructure of Follicular Epithelia in the Ovary of Lepidochitona cinerea (L.) (Mollusca: Polyplacophora)

In the sac-like ovary of the polyplacophoran mollusc, Lepidochitona cinerea , nutritive tissue arises from the ventral gonadal wall of the organ as prominent folds which support the oocytes during the various stages of their development. Each oocyte is enveloped by the follicular epithelium. Approximately twenty follicle cells surround one full-grown oocyte and by this late stage are connected to it and to each other by desmosomes. The follicle cells contain glycogen, Golgi dictyosomes, mitochondria, lipid droplets, numerous cisternae and vesicles of the rough endoplasmic reticulum, and various kinds of lysosomes. The nutritional function of these cells and their possible role forming the oocytic hulls is discussed.     

Absence of ribosomal DNA amplification in the meroistic (telotrophic) ovary of the large milkweed bug Oncopeltus fasciatus (Dallas) (Hemiptera: Lygaeidae)

In the typical meroistic insect ovary, the oocyte nucleus synthesizes little if any RNA. Nurse cells or trophocytes actively synthesize ribosomes which are transported to and accumulated by the oocyte. In the telotrophic ovary a morphological separation exists, the nurse cells being localized at the apical end of each ovariole and communicating with the ooocytes via nutritive cords. In order to determine whether the genes coding for ribosomal RNA (rRNA) are amplified in the telotrophic ovary of the milkweed bug Oncopeltus fasciatus, the percentages of the genome coding for ribosomal RNA in somatic cells, spermatogenic cells, ovarian follicles, and nurse cells were compared. The oocytes and most of the nurse cells of O. fasciatus are uninucleolate. DNA hybridizing with ribosomal RNA is localized in a satellite DNA, the density of which is 1.712 g/cm(-3). The density of main-band DNA is 1.694 g/cm(-3). The ribosomal DNA satellite accounts for approximately 0.2% of the DNA in somatic and gametogenic tissues of both males and females. RNA-DNA hybridization analysis demonstrates that approximately 0.03% of the DNA in somatic tissues, testis, ovarian follicles, and isolated nurse cells hybridizes with ribosomal RNA. The fact that the percentage of DNA hybridizing with rRNA is the same in somatic and in male and female gametogenic tissues indicates that amplification of ribosomal DNA does not occur in nurse cells and that if it occurs in oocytes, it represents less than a 50-fold increase in ribosomal DNA. An increase in total genome DNA accounted by polyploidization appears to provide for increasing the amount of ribosomal DNA in the nurse cells.     

Phylogenetic significance of the structure of adult ovary and oogenesis in a primitive chilognathan diplopod,Hyleoglomeris japonica Verhoeff (Glomerida,Diplopoda)

Some histological details of the adult ovary of Hyleoglomeris japonica are described for the first time in the glomerid diplopods. The ovary is a single, long sac-like organ extending from the 4th to the 12th body segment along the median body axis, lying between the alimentary canal and the ventral nerve cord. The ovarian wall consists of a layer of thin ovarian epithelium which surrounds a wide ovarian lumen. A pair of longitudinal “germ zones,” including female germ cells, runs in the lateral ovarian wall. Each germ zone consists of two types of oogenetic areas: 1) 8–12 narrow patch-shaped areas for oogonial proliferation, arranged metamerically in a row along each of the dorsal and ventral peripheries, and 2) the remaining wide area for oocyte growth. Oogonial proliferation areas include oogonia, very early previtellogenic oocytes, and young somatic interstitial cells, among the ovarian epithelial cells. The larger early previtellogenic oocytes in the oogonial proliferation areas are located nearer to the oocyte growth area, and migrate to the oocyte growth area. They are surrounded by a layer of follicle cells and are connected with the ovarian epithelium of the oocyte growth area by a portion of their follicles. They grow into the ovarian lumen, but their follicles are still connected with the oocyte growth area. Various sizes of the previtellogenic and vitellogenic oocytes in the ovarian lumen are connected with the oocyte growth area; the smaller oocytes are connected nearer to the dorsal and ventral oogonial proliferation areas, while the larger ones are connected nearer to the longitudinal middle line of the oocyte growth area. Following the completion of vitellogenesis and egg membrane formation in the largest primary oocytes, the germinal vesicles break down. Ripe oocytes are released from their follicles directly into the ovarian lumen to be transported into the oviducts. Ovarian structure and oogenesis of H. japonica are very similar to those of other chilognathan diplopods. At the same time, however, some characteristic features of the ovary of H. japonica are helpful for understanding the structure and evolution of the diplopod ovaries. Some aspects of the phylogenetic significance in the paired germ zones of H. japonica are discussed. J. Morphol 231:277–285, 1997. © 1997 Wiley-Liss, Inc.     

Structure of the adult ovary and oogenesis in Argulus japonicus thiele (Crustacea: Branchiura)

The adult ovary of the branchiuran Argulus japonicus is a single, median, long sac-like organ located in the thorax above the alimentary canal. A long germarium, including oogonia, very early previtellogenic oocytes, and young somatic cells (interstitial cells), is embedded in the dorsal ovarian wall along the median longitudinal line of the ovary. The ovarian wall, consisting of a layer of the ovarian epithelial cells, is folded repeatedly and distinctively in the lateral and ventral portions of the ovary. Growing oocytes, previtellogenic and vitellogenic, occur on the outer surface of the ovarian wall, not in the ovarian lumen. The smaller oocytes are located nearer to the germarium and the larger ones on the more ventral surface of the ovary. These structural features of the branchiuran ovary are compared with those of other crustaceans and the pentastomids to consider their phylogenetic implications. J. Morphol. 231:29–39, 1997. © 1997 Wiley-Liss, Inc.     

Ovary cord structure and oogenesis in Hirudo medicinalis and Haemopis sanguisuga (Clitellata, Annelida): remarks on different ovaries organization in Hirudinea

In Hirudo medicinalis and Haemopis sanguisuga, two convoluted ovary cords are found within each ovary. Each ovary cord is a polarized structure composed of germ cells (oogonia, developing oocytes, nurse cells) and somatic cells (apical cell, follicular cells). One end of the ovary cord is club-shaped and comprises one huge apical cell, numerous oogonia, and small cysts (clusters) of interconnected germ cells. The main part of the cord contains fully developed cysts composed of numerous nurse cells connected via intercellular bridges with the cytophore, which in turn is connected by a cytoplasmic bridge with the growing oocyte. The opposite end of the cord degenerates. Cord integrity is ensured by flattened follicular cells enveloping the cord; moreover, inside the cord, some follicular cells (internal follicular cells) are distributed among germ cells. As oogenesis progresses, the growing oocytes gradually protrude into the ovary lumen; as a result, fully developed oocytes arrested in meiotic metaphase I float freely in the ovary lumen. This paper describes the successive stages of oogenesis of H. medicinalis in detail. Ovary organization in Hirudinea was classified within four different types: non-polarized ovary cords were found in glossiphoniids, egg follicles were described in piscicolids, ovarian bodies were found characteristic for erpobdellids, and polarized ovary cords in hirudiniforms. Ovaries with polarized structures equipped with apical cell (i.e. polarized ovary cords and ovarian bodies) (as found in arhynchobdellids) are considered as primary for Hirudinea while non-polarized ovary cords and the occurrence of egg follicles (rhynchobdellids) represent derived condition.     

Gonads in Histiostoma mites (Acariformes: Astigmata): Structure and development

The development of male and female gonads in arrhenotokous and thelytokous species of Histiostoma was studied using transmission electron microscopy (TEM). All instars were examined: larvae, protonymphs, facultative heteromorphic deutonymphs (=hypopi), tritonymphs, and adults. In testis primordium, spermatogonia surrounding a testicular central cell (TCC) with a gradually enlarging, branched nucleus are present already at the larval stage. Spermatogonia and the TCC are connected via narrow, tubular intercellular bridges revealing that the TCC is a germline cell. Spermatocytes appear at the protonymphal stage. At the heteromorphic deutonymph stage, the testis primordium is similar to that of the protonymph, but in the tritonymph it is much larger and composed as in the adult: spermatids as well as sperm cells are present. The latter are congregated ventrally in the testis at the entrance of the deferent duct.In the larval ovary, an eccentrically located ovarian nutritive cell (ONC) is surrounded by oogonia which are connected with the ONC via tubular intercellular bridges. In later stages, the ovary grows and oocytes appear in the protonymph. Meiotic synaptonemal complexes in oocytes occur from the tritonymph stage. At about the time of the final molting, tubular intercellular bridges transform into peculiar diaphragm-crossed bridges known only in Histiostoma mites. In the adult female, growing oocytes at the end of previtellogenesis lose intercellular bridges and move ventro-laterally to the ovarian periphery towards the oviduct entrance. Vitellogenesis occurs in oviducts.Germinal cells in both the testis and ovary are embedded in a few somatic stroma cells which may be well discernible already in the larval ovary; in the testis, somatic stroma cells are evident not earlier than the end of the tritonymphal stage. The ovary has a thin wall of flat somatic cells, whereas the testis is covered by a basal lamina only.The obtained results suggest that gonads in Histiostoma and other Astigmata originate from two primordial cells only.     

The organization of the female reproductive system in the parasitic mite Myobia murismusculi (Trombidiformes: Myobiidae)

The general morphology of the internal genital organs in Myobia murismusculi females have been studied by means of light and electron microscopy. It is shown, that their reproductive system is composed of the single ovary, long complex oviduct, cuticular vagina and receptaculum seminis. The apical region of the ovary is formed by the numerous processes of gonadian somatic cells. These cells generate the ovarian sheath and probably take place in oocyte's metabolism. Any nutritive cells in the Myobia ovary are absent. The vitellogenetic oocytes develop in the ovarian pouches like in other trombidiform mites. The oviduct consists of three parts, each of them has a specific ultrastructure and type of secretory product. Two proximal parts of the oviduct produce the egg-shell components, while the third distal part never contains oocytes. It could be suggested that this part produces a special secret onto the oocyte surface to glue the oocytes to the hairs of host.     

Interrelationships between developing oocytes and ovarian tissues in the chiton Sypharochiton septentriones (Ashby) (Mollusca, Polyplacophora)

Oogenesis and the relationships between oocytes and other ovarian tissues have been studied in Sypharochiton septentriones. The ovarian tissues were examined by electron microscopy and by histochemical methods. The sac-like ovary is dorsal, below the aorta, and opens to the exterior by two posterior oviducts. Ventrally, the ovarian epithelium is folded inwards to form a series of plates of tissue, which support the developing ova. Each ovum is attached to a tissue plate by a stalk, the plasma membrane of which is bathed by the blood in the tissue plate sinus. Dorsally, ciliated vessels from the aorta enter the ovary and open into blood sinuses in the top of the plates. After each germinal epithelial cell rounds up to become a primary oogonium, it undergoes four mitotic divisions to give rise to a cluster of 16 secondary oogonia. Of these, the outer ones become follicle cells and the inner ones become oocytes. As in other molluses, the increases in nuclear and nucleolar volume are relatively greatest towards the end of previtellogenesis, when chromosomal and nucleolar activity are most intense. This phase of activity is accompanied by a great increase in cytoplasmic basophilia. Subsequently this basophilia is decreased during vitellogenesis, when chromosomal and nucleolar activity diminish. Fluid filled interstices appear in the cytoplasm during early vitellogenesis. Protein yolk deposition is associated with these interstices, but the lipid yolk appears to arise de novo. The follicle cells do not appear to be directly involved in oocyte nutrition. At times during oogenesis, certain manifestations of polarity can be found in the oocyte. This polarity is based on an apical-basal axis and can be related to the nutritive source of the oocyte, namely the blood which bathes the plasma membrane of the oocyte in the stalk. Numerous granulated cells are present in the ovarian tissue plates and ventral epithelium as storage cells containing lysosomes, and they are capable of phagocytosis and micropinocytosis of extracellular material. A scheme is outlined whereby reserves in these cells may be incorporated into the oocyte cytoplasm. Lysosomal activity is responsible for autolysis of the cells as well as resorption of unspawned ova.     

Ovary structure and early oogenesis in the remipede, Godzilliognomus frondosus (Crustacea, Remipedia): phylogenetic implications

Remipedia are enigmatic crustaceans of uncertain phylogenetic position with the general consensus that they are crucial for understanding the crustacean/arthropod evolution. It has been demonstrated previously that the features of the ovary organization and subcellular aspects of oogenesis are useful in resolving phylogenetic relationships in arthropods such as hexapods and onychophorans. The structure of the female gonads in Remipedia remains largely unknown; therefore, we examined the gross morphology and ultrastructural details of the ovary in a remipede, Godzilliognomus frondosus, with special emphasis on characters relevant to phylogenetic reconstructions. The ovaries of G. frondosus are located in the anterior part of the body and are composed of a single anterior proliferative zone (the germarium) and paired ovarian tubes (the vitellarium). The oocytes undergo subsequent stages of development within the lumen of the ovarian tubes, hence the remipede ovaries can be classified as endogenous. During oogenesis, each oocyte is enveloped by a set of characteristic somatic follicular cells, which results in the formation of distinct ovarian follicles. Here, we demonstrate that Remipedia share significant similarities in the ovary organization with Cephalocarida, including the anterior location of the ovary, the anterior-most position of the germarium and the endogenous type of oocyte development. Phylogenetic implications of our findings are discussed.     

Fxna, a novel gene differentially expressed in the rat ovary at the time of folliculogenesis, is required for normal ovarian histogenesis

In rodents, the formation of ovarian follicles occurs after birth. In recent years, several factors required for follicular assembly and the growth of the newly formed follicles have been identified. We now describe a novel gene, Fxna, identified by differential display in the neonatal rat ovary. Fxna encodes an mRNA of 5.4 kb, and a protein of 898 amino acids. Fxna is a transmembrane metallopeptidase from family M28, localized to the endoplasmic reticulum. In the ovary, Fxna mRNA is expressed in granulosa cells; its abundance is maximal 48 hours after birth, i.e. during the initiation of follicular assembly. Reducing Fxna mRNA levels via lentiviral-mediated delivery of short hairpin RNAs to neonatal ovaries resulted in substantial loss of primordial, primary and secondary follicles, and structural disorganization of the ovary, with many abnormal follicles containing more than one oocyte and clusters of somatic cells not associated with any oocytes. These abnormalities were not attributable to either increased apoptosis or decreased proliferation of granulosa cells. The results indicate that Fxna is required for the organization of somatic cells and oocytes into discrete follicular structures. As an endoplasmic reticulum-bound peptidase, Fxna may facilitate follicular organization by processing precursor proteins required for intraovarian cell-to-cell communication.     

In vitro inhibition of oocyte and follicular maturation and spawning in starfish (Asterias forbesi) by 2-4-dinitrophenol

The in vitro effects of 2-4-dinitrophenol (DNP) on spawning and follicular and oocyte maturation in starfish ovaries and its various cellular components were investigated. Spawning and oocyte and follicular maturation induced by starfish gonadotropin radial nerve factor (RNF) in isolated ovarian fragments were all inhibited by appropriate doses of DNP. DNP inhibits processes which occur shortly after addition of the gonadotropin; in ovarian fragments insensitivity to DNP inhibition occurred shortly after addition of RNF but prior to initiation of spawning. Spontaneous follicular and oocyte maturation which occurred following release of ovarian follicles into sea water was prevented by DNP. In non-spontaneously maturing follicles released from the ovary, DNP inhibited both follicle and oocyte maturation induced by the secondary stimulator of spawning and maturation, 1-methyladenine (1-MA). DNP also inhibited 1-MA induced meiotic maturation in isolated immature oocytes incubated in the absence of follicle cells. Inhibition of oocyte maturation was not associated with inhibition of 3H-1-MA incorporation by isolated oocytes. Immature oocytes incubated in the presence of DNP underwent maturation following washing and subsequent exposure to 1-MA. Immature oocytes initially exposed to both 1-MA and DNP, however, showed decreased maturation responsiveness following washing and re-exposure to 1-MA. The results suggest that the inhibitory effects of DNP on spawning and oocyte maturation are the result of direct effects on the oocytes and possibly other cells and tissues within the ovary.     

In vitro Inhibition of Oocyte and Follicular Maturation and Spawning in Starfish (Asterias forbesi) by 2-4-Dinitrophenol

The in vitro effects of 2-4-dinitrophenol (DNP) on spawning and follicular and oocyte maturation in starfish ovaries and its various cellular components were investigated. Spawning and oocyte and follicular maturation induced by starfish gonadotropin radial nerve factor (RNF) in isolated ovarian fragments were all inhibited by appropriate doses of DNP. DNP inhibits processes which occur shortly after addition of the gonadotropin; in ovarian fragments insensitivity to DNP inhibition occurred shortly after addition of RNF but prior to initiation of spawning. Spontaneous follicular and oocyte maturation which occurred following release of ovarian follicles into sea water was prevented by DNP. In non-spontaneously maturing follicles released from the ovary, DNP inhibited both follicle and oocyte maturation induced by the secondary stimulator of spawning and maturation, 1-methyladenine (1-MA). DNP also inhibited 1-MA induced meiotic maturation in isolated immature oocytes incubated in the absence of follicle cells. Inhibition of oocyte maturation was not associated with inhibition of ³H-1-MA incorporation by isolated oocytes. Immature oocytes incubated in the presence of DNP underwent maturation following washing and subsequent exposure to 1-MA. Immature oocytes initially exposed to both 1-MA and DNP, however, showed decreased maturation responsiveness following washing and re-exposure to 1-MA. The results suggest that the inhibitory effects of DNP on spawning and oocyte maturation are the result of direct effects on the oocytes and possibly other cells and tissues within the ovary.     

Evidence for Follicle Wall Involvement in Ovulation and Progesterone Production by Frog (Rana pipiens) Follicles in vitro

Involvement of different cellular investments of the amphibian ovarian follicle wall in the ovulatory process, progesterone production, and oocyte maturation was investigated. Following microdissection, to selectively remove one or more layers (surface epithelium, theca, follicle cells) of the follicle wall, dissected and undirected ovarian follicles were treated with frog pituitary homogenate (FPH) or progesterone. Intact follicles ovulated in response to pituitary homogenate and this was associated with contractions of the follicle wall. Ovulation and follicular contractions were not observed following removal of the surface epithelium without removing the thecal layer. Oocyte maturation occured in response to FPH following removal of the surface epithelium alone or together with the theca, but not in the absence of the follicle cells. Intact follicles were most responsive to FPH with respect to progesterone production, and removal of all somatic cells from oocytes obliterated FPH stimulated progesterone production. Oocytes, regardless of wether any or all follicular wall layers were removed, matured but did not ovulate following exposure to progesterone. The results suggest that the surface epithelium, but not the theca, is required for FPH-induced extrusion (ovulation) of the oocyte from ovarian follicle wall. Additionally, the somatic tissue rather than the oocyte appears to be the cells producing progesterone following FPH treatment. The results indicate that separate cellular layers (individually and/or as a result of interactions) of the follicle wall carry out different functions during follicular differentiation and mediation of ovulation. Data provide functional evidence for a role of the surface epithelium in controlling the process of ovulation and follicular contraction.     

Ovary cords organization in Hirudo troctina Johnson, 1816 and Limnatis nilotica (Savigny, 1822) (Clitellata,Hirudinea)

In both examined species of Hirudinea there are paired spheroid ovisacs, and within each ovisac two convoluted ovary cords occur. The morphology of the cords is characteristic: their apical end is club-shaped, the central part is narrow and may contain developing oocytes, whereas the basal end of the cord is irregularly shaped and composed of degenerating cells. The ovary cords are built of somatic and germ-line cells; the latter are united into syncytial cysts. Each germ cell in such a cyst has only one stable cytoplasmic bridge connecting it to the central anuclear cytoplasmic mass, the cytophore. Initially all germ-line cells in a given cyst are morphologically identical, then the fates of cells diversify. Most of them become nurse cells and eventually degenerate; the rest continue meiosis, gather macromolecules, cell organelles and nutritive material and become oocytes. The oogenesis found in the species studied should be regarded as meroistic. Previtellogenic oocytes protrude from the cord into the ovisac lumen, whereas the vitellogenic ones float freely in the ovisac lumen. The somatic cells found in the ovary cords are: follicular cells which form the envelope of the cord and are also found among germ cells inside the cord, and one, huge apical cell that always is located at the top of the club-shaped end of the ovary cord. The apical cell has several characteristic features, e.g., it forms long cytoplasmic projections filled with intermediate filaments and it is connected to the neighbouring cells (both somatic and germ-line) via hemidesmosomes. We suggest that the apical cell forms the niche for maintaining germ and somatic stem cells. Generally, the organization of the ovary cords found in both studied species is broadly similar to those described in other hirudiniform leeches studied to date.     

Differential expression of ZPC in the bovine ovary,oocyte, and embryo

Using nonradioactive in situ hybridization (ISH), the mRNA encoding the zona glycoprotein bZPC was localized in bovine ovaries, oocytes, and embryos. In the ovary, the distribution of the mRNA was correlated with the developmental stage of the follicle. Whereas in primordial and primary follicles the mRNA was predominantly seen in the oocyte, it was found in both the oocyte and the follicle cells of secondary and tertiary follicles. In 2-day-old embryos produced by in vitro fertilization (IVF), no mRNA encoding ZPC could be demonstrated. Immunoblotting using monospecific polyclonal antibodies against porcine ZPC revealed a distinct band at a molecular weight of 47 kD in the ovarian cortex of cows, calves, and fetuses as well as in bovine follicle cells. Immunohistochemistry using the ZPC antibody displayed a strong signal in the zona pellucida of bovine oocytes and 2- to 6-day-old embryos as well as in the follicle cells. Our results show that during follicular development bovine ZPC is synthesized by the oocyte of the primary follicle and by both the oocyte and the follicle cells of the secondary and tertiary follicle. After fertilization, the synthesis of the zona protein is finished. Mol. Reprod. Dev. 49:435–443, 1998. © 1998 Wiley-Liss, Inc.     

Ultrastructure of somatic tissues in the ovaries of a chaetognath (Ferosagitta hispida)

Transmission electron microscopy reveals that the ovaries of Ferosagitta hispida contain four somatic tissues. A myoepithelial ovary wall, continuous with a thin layer of peritoneocytes lining the coelomic cavity, encloses a fluid-filled ovarian space in which oocytes develop. Lamellar extensions of a “follicular reticulum” branch throughout the ovarian space and ensheath developing oocytes. This tissue has been overlooked in most previous studies of chaetognath ovaries. A bipartite oviductal complex extends the length of each ovary just within the lateral ovary wall. It consists of a flattened, blindly ending cellular tube, herein referred to as the cellular sheath, and an enclosed syncytium. Sheath cells secrete an electron-dense product into the ovarian space. Those sheath cells directly bordering the syncytium are contractile and are joined to the to the syncytium by gap junctions and microvillar interdigitations. The syncytium contains a complex of membrane-bounded lumina. The latter sometimes enclose sperm received during mating or ovulated eggs. Thus the syncytium serves both as a seminal receptacle and as a duct for passage of eggs to the outside. Contrary to several classical reports, the cellular sheath and syncytium of the oviductal complex do not separate at ovulation to form a temporary oviductal lumen.