Oogonial Cells Research Articles

Cell wall-mediated maternal control of apical-basal patterning of the kelp Undaria pinnatifida.

The role of maternal tissue in embryogenesis remains enigmatic in many complex organisms. Here, we investigate the contribution of maternal tissue to apical-basal patterning in the kelp embryo. Focussing on Undaria pinnatifida, we studied the effects of detachment from the maternal tissue using microsurgery, staining of cell wall modifications, morphometric measurements, flow cytometry, genotyping and a modified kelp fertilisation protocol synchronising kelp embryogenesis. Detached embryos are rounder and often show aberrant morphologies. When a part of the oogonial cell wall remains attached to the zygote, the apical-basal patterning is rescued. Furthermore, the absence of contact with maternal tissue increases parthenogenesis, highlighting the critical role of maternal signals in the initial stages of development. These results show a key role for the connection to the maternal oogonial cell wall in apical-basal patterning in kelps. This observation is reminiscent of another brown alga, Fucus, where the cell wall directs the cell fate. Our findings suggest a conserved mechanism across phylogenetically distant oogamous lineages, where localised secretion of sulphated F2 fucans mediates the establishment of the apical-basal polarity. In this model, the maternal oogonial cell wall mediates basal cell fate determination by providing an extrinsic patterning cue to the future kelp embryo.

Conservation of oocyte development in germline cysts from Drosophila to mouse.

Recent studies show that pre-follicular mouse oogenesis takes place in germline cysts, highly conserved groups of oogonial cells connected by intercellular bridges that develop as nurse cells as well as an oocyte. Long studied in Drosophila and insect gametogenesis, female germline cysts acquire cytoskeletal polarity and traffic centrosomes and organelles between nurse cells and the oocyte to form the Balbiani body, a conserved marker of polarity. Mouse oocyte development and nurse cell dumping are supported by dynamic, cell-specific programs of germline gene expression. High levels of perinatal germ cell death in this species primarily result from programmed nurse cell turnover after transfer rather than defective oocyte production. The striking evolutionary conservation of early oogenesis mechanisms between distant animal groups strongly suggests that gametogenesis and early embryonic development in vertebrates and invertebrates share even more in common than currently believed.

Isolation, culture and bacterial contamination of oogonial stem cells of Brown trout, <em>Salmo trutta macrostigma</em> (Dumeril, 1858)

Increased commercial value of brown trout, Salmo trutta macrostigma has lead to its declined natural stock due to over exploitation, and thereby made it an endangered species. Cryopreservation of spermatogonial and oogonial stem cells may help in protecting this species. In this context, we have earlier isolated and cultured spermatogonial stem cells from male S.t. macrostigma. In this study, we report isolation and culture of oogonial stem cells from brown trout (S. t. macrostigma).In addition, bacterial contamination in oogonial cell culture media were identified and described. Wild females wereobtained from Kılıç Trout Fish Farm (Kahramanmaraş, Turkey). In order to identify the appropriate size, age and ovarystructure for oogonial stem cell isolation and culture, the ovary structure was morphologically and histologically studied.Fish were anesthetized with 0.04% 2-phenoxethanol. The ovary tissue were digested by 0.25% trypsin-EDTA.HBSS, with1.0 μg/mL NaHCO3, antibiotics were used to maintain cells in a viable stage. The concentration of cells was measured byhemocytometer. Antibiogram and Gram staining techniques were applied to the culture media contaminated with bacteria.Appropriate age, size and weight of trout for oogonial stem cell isolation and culture were identified as 7+ month old,14.6±1.6 cm, 28.2±7.7 g, respectively. The highest oogonial stem cells were measured in the perinucleolar stage of theovary. Enterobacter cloacae and Acinetobacter baumannii were identified in the contaminated cell media. Density ofoogonial stem cells were measured as 5.4×105±2.6×105 cells/mL. In this study, germ cell isolation and culture technique wasdeveloped for S. t. macrostigma.

Sex steroid profile during oocyte development and maturation in the intertidal worm Marphysa madrasi (Polychaeta: Eunicidae) from the east coast of India

Marphysa madrasi is a commercially valuable maturation diet in crustacean aquaculture. This study presents the first detailed investigation of oogenesis in the intertidal polychaete worm M. madrasi and reports the steroid profile during oocyte growth and development. Oogenesis is extraovarian type I, originating from coelomic epithelial cells, with four stages of development - primary growth, early vitellogenic, late vitellogenic, and maturation. The primary growth phase contains oogonial cells and previtellogenic oocyte clusters in the early, mid, and late stages of development form a dispersed ovary attached to blood vessels. The late previtellogenic oocytes detach from the ovary at the onset of vitellogenesis. The detached oocytes complete vitellogenesis and final maturation in the coelomic fluid as solitary free-floating cells without any connection with follicle cells. The worms display asynchronous reproduction with a heterogeneous population of developing oocytes. Steroid extracts from the polychaete homogenates in different stages of oogenesis were identified by HPLC and confirmed by LC-MS/MS. In M. madrasi, two vertebrate-type steroids, pregnenolone (P5) and 17α-hydroxyprogesterone (17-OHP) were detected and quantified. The P5 levels were low in immature worms but increased significantly by ∼ 8.3-fold in the previtellogenic stage and peaked during oocyte maturation. 17-OHP levels were low in immature worms but gradually increase as the oogenesis progress to the primary growth and early vitellogenic phase, with a significant increase (p < 0.001) during the late vitellogenic phase. Although an increase in the concentration of P5 and 17-OHP during vitellogenesis and maturation of oocytes points to a possible role in reproduction, the absence of other vertebrate-type steroids in the investigated polychaete signifies a plausible uptake of P5 and 17-OHP from the environment.

Cryopreservation and Flow Cytometric Analysis of Ovarian Tissue in Murray River Rainbowfish, Melanotaenia fluviatilis.

Simple SummaryFreshwater fish populations are in global decline, with many Australian freshwater species expected to become extinct in the next twenty years. The storage of reproductive cells and tissues at extremely cold temperatures in bio-banks known as “Frozen Zoos”, allows for the indefinite storage of genetic material, meaning that in the event of an extinction, we have a genetic blueprint available to produce new individuals and reintroduce a species into the wild. Here we have developed a cryopreservation protocol for the storage of ovarian tissue from the threatened Murray River Rainbowfish. Many Australian freshwater fish species are threatened with extinction, our methodology provides a framework for the conservation of other fish species in Australia and globally.Freshwater fish populations are declining with many small, Australian fish species at risk of extinction within the next twenty-years. Cryopreservation of reproductive cells and tissues makes it possible to reproduce individuals from a species even after they are extinct in the wild. We describe the successful cryopreservation of ovarian tissue in the Murray River Rainbowfish, Melanotaenia fluviatilis (Order: Atheriniformes). Histology showed that oogonia are 13.70 µm ± 1.75 µm in size, stain positive for germ-line marker Vasa, and represent approximately 2.29 ± 0.81% of cells in the ovary. Flow cytometry was used to analyse ovarian cell suspensions, requiring an optimised tissue digestion protocol. We found that 0.25% trypsin with 1.13 mM EDTA produced cell suspensions with the highest viability (76.28 ± 4.64%) and the highest number of cells recovered per gram of tissue (1.2 × 108 ± 4.4 × 107 cells/g). Subsequent sorting of ovarian cell suspensions by flow cytometry increased oogonial cells in suspension from 2.53 ± 1.31% in an unsorted sample to 5.85 ± 4.01% in a sorted sample (p = 0.0346). Cryopreservation of ovarian tissue showed DMSO-treated samples had higher cell viability post-thaw (63.5 ± 18.2%) which was comparable to fresh samples (82.5 ± 7.1%; p = 0.36). Tissue cryopreserved in 2.0 M DMSO had the highest cell viability overall (76.07 ± 3.89%). This protocol could be applied to bio-banking programs for other species in the Melanotaeniidae, and perhaps species in other families and orders of Australian fish.

A phase overshadowed by mitotic division: interphase

ABSTRACT This study aims to determine misconceptions about interphase, a basic phase in the cell cycle and to address those misconceptions. Meristem cells in plants, stem cells in animals, spermatogonia and oogonia cells, and some cells with partial regeneration ability do not lose dividing ability. However, normal tissue cells other than these are in the G0 stage and do not divide after maturation. Therefore, a maturing cell is restricted again in the G0 phase of interphase and does not re-divide. For this reason, it is not valid to describe interphase as the preparation stage for division in general. This research is planned to emphasise this difference. This quasi-experimental descriptive study is conducted with science teacher candidates. The misunderstanding rate, which decreased after the course designed to resolve the misunderstanding, was not permanent and it was found that the participants remembered prior knowledge one year later. Misunderstanding can be an obstacle for data transfer considering that students whose misunderstandings are resolved are successful in data transfer.

&lt;p&gt;&lt;strong&gt;Two new &lt;em&gt;Pythium&lt;/em&gt; species from southern China based on morphological and &lt;/strong&gt;&lt;strong&gt;molecular characters&lt;/strong&gt;&lt;/p&gt;

Two new species of Pythium, namely P. subinflatum and P. xuzhouense, from soybean (Glycine max) in southern China are described based on their morphology and molecular phylogenetic analyses inferred from the internal transcribed spacer region of the ribosomal RNA gene and mitochondrial cytochrome c oxidase subunit I gene. Pythium subinflatum is characterized by globose to sub-globose or ovoid hyphal swellings, filamentous inflated sporangia, smooth oogonia, mostly diclinous antheridia, elongated along the oogonial stalk, subcircular, subglobose or fist-shaped antheridial cells, and aplerotic and slightly thick-walled oospores (2–3.5 µm); P. xuzhouense differs from other species in the genus by filamentous or lobulated sporangia, smooth oogonia, mostly diclinous, sometimes monoclinous antheridia, subclavate, falcate or semicircle to subcircular antheridial cells, and plerotic or nearly plerotic and thin-walled oospores (0.5–1.5 µm). In addition, the two new species are compared to closely related Pythium species regarding their phylogenetic positions and morphological features.

Correction for: Resveratrol alleviates chemotherapy-induced oogonial stem cell apoptosis and ovarian aging in mice.

Correction for: Resveratrol alleviates chemotherapy-induced oogonial stem cell apoptosis and ovarian aging in mice.

Ultrastructural study of the ovary and oogenesis of Polyonchobothrium clarias Woodland, 1925 (Cestoda: Bothriocephalidea) infecting Clarias gariepinus from Egypt.

The ovarian tissues and different stages of oocytes development of Polyonchobothrium clarias Woodland, 1925 recovered from the intestine of Clarias gariepinus Burchell, 1822 fish was investigated by transmission electron microscope (TEM). The ovarian follicles are enveloped by compressed epithelial sheath lying on basal layer that shows epithelial projection into the lumen of each follicle. The epithelial sheath filled with glycogen, mitochondria and solitary lipid droplets. The epithelial nuclei are appeared closed to the basal part of the ovarian follicle. Numerous heterogeneous electron dense myelin-like bodies observed within the ovarian cytoplasm they appeared different irregular shaped. Each ovarian follicle contains number of oocytes loosely packed within the follicle at different stages of differentiation developmental stages starting with oogonial cells, primary, secondary and mature oocytes. The Oogonia were undergoing characteristic cytological changes that lead to oocyte maturation. Vitelline material appears in early stages of primary oocytes. Lipid droplets appeared in late stages of secondary oocyte. Mature oocytes are filled with clusters of cortical granules adjacent to the oocyte plasma membrane. Syncytial interstitial tissue and number of myelin-like bodies are observed in the ovarian cytoplasm and they fill the cytoplasmic spaces. The results of the present study were compared with the previous reports in other cestode taxa, to define the ultrastructural observations of the female reproductive tissues for clarification the reproductive fecundity of the parasite.

In Vitro Generation of Oocytes from Ovarian Stem Cells (OSCs): In Search of Major Evidence.

The existence of ovarian stem cells (OSCs) in women as well as their physiological role in post-menopausal age are disputed. However, accumulating evidence demonstrated that, besides the animal models including primarily mice, even in adult women putative OSCs obtained from ovarian cortex are capable to differentiate in vitro into oocyte-like cells (OLCs) expressing molecular markers typical of terminal stage of oogonial cell lineage. Recent studies describe that, similarly to mature oocytes, the OSC-derived OLCs also contain haploid karyotype. As proof of concept of their stem commitment, OSCs from mice differentiated to oocytes in vitro are suitable to be fertilized and implanted in sterilized animals resulting in embryo development. Despite enthusiasm for these data, which definitely require extended confirmation before considering potential application in humans for treatment of ovarian insufficiency, OSCs appear suitable for other clinical uses, restoring the endocrine derangements in premature ovarian failure or for fertility preservation in oncologic patients after anti-cancer treatments. In this context, the selection of viable oocytes generated from OSCs before chemotherapy protocols would overcome the potential adjunct oncogenic risk in women bearing hormone-dependent tumors who are repeatedly stimulated with high dose estrogens to induce oocyte maturation for their egg recruitment and cryopreservation.

The molecular characterization of porcine egg precursor cells.

Female-factor infertility can be caused by poor oocyte quality and depleted ovarian reserves. Egg precursor cells (EPCs), isolated from the ovarian cortex, have the potential to be used to overcome female infertility. We aimed to define the origins of EPCs by analyzing their gene expression profiles and mtDNA content using a mini-pig model. We characterized FAC-sorted DDX4+-derived porcine EPCs by performing RNA-sequencing and determined that they utilize pathways important for cell cycle and proliferation, which supports the existence of adult mitotically active oogonial cells. Expression of the pluripotent markers Sox2 and Oct4, and the primitive germ cell markers Blimp1 and Stella were not detected. However, Nanog and Ddx4 were expressed, as were the primitive germ cell markers Fragilis, c-Kit and Tert. Moreover, porcine EPCs expressed self-renewal and proliferation markers including Myc, Esrrb, Id2, Klf4, Klf5, Stat3, Fgfr1, Fgfr2 and Il6st. The presence of Zp1, Zp2, Zp3 and Nobox were not detected, indicating that porcine EPCs are not indicative of mature primordial oocytes. We performed mitochondrial DNA Next Generation Sequencing and determined that one mtDNA variant harbored by EPCs was present in oocytes, preimplantation embryos and somatic tissues over three generations in our mini-pig model indicating the potential germline origin of EPCs.

Histology Biomarkers in Muscle and Ovary of Mangrove Crab, &amp;lt;i&amp;gt;Perisesarma bidens&amp;lt;/i&amp;gt; Exposed to Profenofos

The purpose of the present study is to afford information on the outcome of profenofos on the crab, <i>Perisesarma bidens</i>, a biologically momentous mangrove crab. The crabs were exposed to profenofos concentrations of 0.038ppm and 0.076 ppm (sublethal) for 28 days. The muscle tissue showed disintegrated epidermis with vacuolation, gap formation in between the muscle bundles, necrosis, marked thickening and separation of muscle bundle and pronounced intramuscular oedema with minor dystrophic changes. The histopathological changes in the ovary are destruction of epithelial layer with oocytes degeneration and disorganization of nucleus, pycnosis of nutritive cells and oogonial cells, loosely arranged epithelial cells and vacuolization. The histopathological changes induce toxicity at cellular level and hence all possible measures should be taken to prevent the occurrence of profenofos toxicity in the aquatic environment and crustaceans.

Initiation of two ovarian cell lines from Fugu rubripes (Temminck et. Schlegel)

The ovary is an excellent system for studying stem cell renewal and differentiation, which is under the control of ovarian somatic cells. In order to understand oogenesis in Fugu rubripes (Temminck et. Schlegel) as a marine fish model of aquaculture importance, we established cell lines called TSOC1 and TSOC2 from a juvenile ovary of this organism. TSOC1 is composed of spindle epithelial-like cells, while the other is cobblestone-like cells. Therefore, TSOC1 and TSOC2 appear to consist of ovarian somatic cells. Growth requirement condition was investigated including temperature, concentration of FBS and pH. Significant fluorescent signals were observed after TSOC1 and TSOC2 cells were transfected with pEGFP-N3 vector, indicating its potential utility for genetic manipulation such as gene function studies. It is shown that these cell lines are effective for infection by the turbot reddish body iridovirus and flounder lymphosystis disease virus as evidenced by the appearance of cytopathic effect and virus propagation in the virus-infected cells, and most convincingly, the observation of viral particles by electron microscopy, demonstrating that TSOC1 and TSOC2 are suitable to study interactions between virus and host cells. It is believed that TSOC1 and TSOC2 will be useful tools to study sex-related events and interactions between primordial germ cells and oogonia cells during oogenesis. Therefore, establishment of ovary cell lines from Fugu rubripes seems to be significant for those research areas.

Structural alterations in Gills, Liver and Ovaries of Tilapia Fish (Saratherodon galilaeus) as a Biomarker for Environmental Pollution in Ismalia Canal

The present work studied the histological changes in gills, liver and ovaries of Tilapia fish (Saratherodon galilaeus) subjected to disturbed urban stream (sewage and industrial contamination) of two sites (EL-aakada and EL-amerya) on Ismailia Canal during summer season. The most common lesions in gills were epithelial lifting, hyperplasia and hypertrophy of the respiratory epithelium, and lamellar fusion. Liver hepatocytes showed hypertrophied, cytoplasmic and nuclear degeneration, inflammatory cells aggregates and focal areas of necrosis. The ovary showed widened vitellogenic space filled with huge debris, the oogonial cells and immature oocytes were in the process of degeneration particularly at the ooplasmic level. The most sever lesions were comparatively in the liver. It is concluded that histopathology can used as a biomarker for study the effect of pollutants in organs of fish.

Surrogate production of eggs and sperm by intrapapillary transplantation of germ cells in cytoablated adult fish.

Germ cell transplantation (GCT) is a promising assisted reproductive technology for the conservation and propagation of endangered and valuable genetic resources. In teleost fish, GCT in adult gonads has been achieved only in male recipients, limiting greatly the usefulness of this technique in situations where both sexes need equal and timely attention for conservation and/or propagation. Here we describe a simplified GCT approach that ultimately leads to production of donor-derived eggs and sperm in considerably short time. Donor germ cells isolated from young pejerrey Odontesthes bonariensis (Atherinopsidae) were transplanted non-surgically through the genital papilla into the sexually mature gonads of Patagonian pejerrey O. hatcheri recipients whose gonads have been depleted of endogenous GCs by heat (26°C) and chemical treatment (four doses of Busulfan at 30 mg/kg and 40 mg/kg for females and males, respectively). Transplanted spermatogonial and oogonial cells were able to recolonize the recipients' gonads and produce functional donor origin eggs and sperm within 7 months from the GCT. We confirmed the presence of donor-derived gametes by PCR in 17% and 5% of the surrogate O. hatcheri fathers and mothers, respectively. The crosses between surrogate fathers and O. bonariensis mothers yielded 12.6–39.7% pure O. bonariensis and that between a surrogate mother and an O. bonariensis father yielded 52.2% pure O. bonariensis offspring. Our findings confirm that transplantation of germ cells into sexually competent adult fish by non-surgical methods allows the production of functional donor-derived eggs and sperm in a considerably short time. The methods described here could play a vital role in conservation and rapid propagation of endangered fish genetic resources.

Ovarian maturation and oogenesis in the blue swimmer crab, Portunus pelagicus (Decapoda: Portunidae)

AbstractThe study was aimed at understanding the process of reproduction and the changes happening in the ovary of Portunus pelagicus during maturation, which would be useful for its broodstock development for hatchery purposes. For that, tissue samples from different regions of the ovary at various stages of maturation were subjected to light and electron microscopy, and based on the changes revealed and the differences in ovarian morphology, the ovary was divided into five stages such as immature (previtellogenic oocytes), early maturing (early vitellogenic oocytes), late maturing (late vitellogenic oocytes), mature (vitellogenic oocytes), and spent (resorbing oocytes). The ovarian wall comprised of an outermost thin pavement epithelium, a middle layer of connective tissue, and an innermost layer of germinal epithelium. The oocytes matured as they moved from the centrally placed germinal zone toward the ovarian wall. The peripheral arrangement of nucleolar materials and the high incidence of cell organelles during the initial stages indicated vitellogenesis I. Movement of follicle cells toward oocytes in the early maturing stage and low incidence of mitochondria and endoplasmic reticulum in the ooplasm during late vitellogenic stage marked the commencement and end of vitellogenesis II, respectively. Yolk granules at various stages of development were seen in the ooplasm from late vitellogenic stage onwards. The spent ovary had an area with resorbing oocytes and empty follicle cells denoting the end of one reproductive cycle and another area with oogonial cells and previtellogenic oocytes indicating the beginning of the next.

Ovary architecture of two branchiobdellid species and Acanthobdella peledina (Annelida, Clitellata)

The aim of this study was to present data about ovary organization and oogenesis in two small groups of clitellate annelids, i.e. in representatives of Acanthobdellida (Acanthobdella peledina) and Branchiobdellida (Branchiobdella pentodonta and Branchiobdella parasitica), and to compare them to ovaries known from true leeches and oligochaetous clitellates. In A. peledina, the ovaries have the form of elongated cords, termed ovary cords, and are enveloped by coelomic sacs, the so-called ovisacs. The ovisacs are paired and each one contains only one ovary cord. The morphology and structure of the ovary cords depend on the maturity level of the animal. In young specimens the ovary cords are short and contain mainly oogonial cells and germ cells entering meiosis. Oogonia divide mitotically without full cytokineses, and as a result germ-line cysts are formed. As the animals grow, the cords become more elongated and the germ cells within the cords differentiate into nurse cells and oocytes. Oocytes gather cell organelles and, finally, detach from the ovary cord and float freely in the ovisac lumen.In both examined branchiobdellidans the ovaries are also paired. They are short and conical and are not enclosed within ovisacs. The narrow end of each ovary is connected to the intersegmental septum via a ligament, whereas the outermost (broad) end of the ovary extends freely into the coelom. The ovaries are polarized. Their narrow ends contain oogonia, whereas nurse cells and growing oocytes, gradually projecting from the ovary, can be found in their middle and outermost parts. Early vitellogenic oocytes detach from the ovary and float freely in the coelom.In all of the species studied, the ovaries are made up of germ-line cysts associated with somatic (follicular) cells. The architecture of a germ-line cyst is exactly the same as in other clitellate annelids that have been studied to date. Each germ cell in a cyst has one stable cytoplasmic bridge connecting it with a central anuclear cytoplasmic mass, a cytophore. The fate of germ cells constituting cysts is diverse. The majority of the cells withdraw from meiosis and become nurse cells; only a few continue meiosis, grow and become oocytes. The meroistic mode of oogenesis is suggested. We suggest also that the formation of germ-line cysts and ovary meroism should be regarded as basal conditions for all Clitellata. The occurrence of ovisacs enveloping the ovaries in A. peledina and Hirudinida is regarded as a synapomorphy of both groups, whereas ovaries found in B. pentodonta and B. parasitica have no ovisacs and resemble ovaries described in Oligochaeta sensu stricto.

Differentiated gonochorism in Nile perch Lates niloticus from Lake Victoria, Uganda

Gonadal development and structure were examined in 317 Nile perch, Lates niloticus, of 4 to 157 cm SL taken from Lake Victoria, Uganda, in 2005–2006. Macroscopic and histological investigation showed a differentiated gonochoristic pattern, with no juvenile intersexuality. Oogonial cells (9.8 ± 3.0 μm) developed through six distinct stages: chromatin nucleolar oocyte (16.2 ± 3.3 μm), perinucleolar oocyte (33.8 ± 12.1 μm), late perinucleolar oocyte (74.8 ± 16.5 μm), cortical alveolar oocyte (122.6 ± 38.8 μm), secondary oocyte (260.9 ± 61.2 μm) and tertiary oocyte (475.5 ± 70.7 μm). L. niloticus was found to be an asynchronous spawner. The collection of female brood fish for induced spawning should aim at fish with an oocyte size of 475.5 ± 70.7 μm. Four main developmental stages were identified in the testis: spermatogonia (A and B), primary and secondary spermatocytes, spermatids and spermatozoa. Testicular structure conformed to the lobular and cystic type. Copious amounts of sperm were exuded from ripe males when slight pressure was applied on the belly. Milt could therefore be obtained by stripping.

Isolation of oogonia from ovaries of the sea urchin Strongylocentrotus nudus

The presence of oogonia in the ovaries of adult females is typical in species with a broadcast spawning reproductive strategy, including invertebrates and lower vertebrates. In sea urchins, difficulties in the study of oogonia arise from the small number of these cells and the lack of specific markers for their identification. Therefore, more reliable methods are needed for identifying and manipulating oogonial cells in quantities sufficient for experimentation. Homologs of the DEAD-box RNA helicase vasa expressed in germline cells have been proposed for use as markers to detect germline cells in diverse species. We have developed a method for the isolation of sea urchin oogonia by using immunocytochemistry with vasa antibodies, together with reverse transcription and the polymerase chain reaction to detect the expression of Sp-vasa and Sp-nanos2 homologs and a morphological approach to identify germline cells in sea urchin ovaries and cell fractions isolated from the ovarian germinal epithelium. This method has allowed us to obtain 15%-18% of small oogonia with 70%-75% purity from the total amount of isolated germ cells. Our findings represent the first methodological basis for obtaining cell populations containing sea urchin oogonia; this method might be useful as a tool for further investigations of the early stages of sea urchin oogenesis.

Karyology of parthenogenetic weevils (Coleoptera, Curculionidae): Do meiotic prophase stages occur?

We investigated the cytological mechanism of parthenogenesis by analyzing the chromosomes in five weevil species. All examined species are polyploids, four of which: Otiorhynchus ovatus, Simo variegates, Cathormiocerus aristatus, and Tropiphorus elevatus possess three haploid sets of chromosomes (3 n = 33), whereas the fifth, Trachyphloeus parallelus, is tetraploid with 44 chromosomes (4 n = 44). The plates contained 27–31 chromosomes in triploid species and 38, 39, 41 and even 44 in tetraploid T. parallelus. In all species single clusters of metaphase plates with a haploid number of n = 11 were visible. Some oogonial cells showed nuclei configurations resembling the stages of diplotene and diakinesis. The spiralized chromosomes in these nuclei may have been connected by chiasmata resulting in rods figures and ring-shaped bivalents. Occurrence of the remnants of meiosis could suggest some degree of recombination in parthenogenetic lineages of weevils.