Female Oogenesis Research Articles

Collapse of a fish population after exposure to a synthetic estrogen

Municipal wastewaters are a complex mixture containing estrogens and estrogen mimics that are known to affect the reproductive health of wild fishes. Male fishes downstream of some wastewater outfalls produce vitellogenin (VTG) (a protein normally synthesized by females during oocyte maturation) and early-stage eggs in their testes, and this feminization has been attributed to the presence of estrogenic substances such as natural estrogens [estrone or 17beta-estradiol (E2)], the synthetic estrogen used in birth-control pills [17 alpha-ethynylestradiol (EE2)], or weaker estrogen mimics such as nonylphenol in the water. Despite widespread evidence that male fishes are being feminized, it is not known whether these low-level, chronic exposures adversely impact the sustainability of wild populations. We conducted a 7-year, whole-lake experiment at the Experimental Lakes Area (ELA) in northwestern Ontario, Canada, and showed that chronic exposure of fathead minnow (Pimephales promelas) to low concentrations (5-6 ng x L(-1)) of the potent 17 alpha-ethynylestradiol led to feminization of males through the production of vitellogenin mRNA and protein, impacts on gonadal development as evidenced by intersex in males and altered oogenesis in females, and, ultimately, a near extinction of this species from the lake. Our observations demonstrate that the concentrations of estrogens and their mimics observed in freshwaters can impact the sustainability of wild fish populations.

Ras signaling modulates activity of the ecdysone receptor EcR during cell migration in the drosophila ovary

Ecdysone Receptor (EcR) mediates effects of the hormone ecdysone during larval molts, pupal metamorphosis, and adult female oogenesis. In the ovary, egg chamber formation requires interactions between the somatic follicle cell (FC) epithelium and the germ line nurse cell/oocyte cyst. Previous work has shown EcR is required in the germ line for egg chamber maturation, and here we examine EcR requirements in the FC at late stages of oogenesis. EcR protein is ubiquitous in the FC but its activity is restricted, visualized by activity of the "ligand sensor" hs-GAL4-EcR ligand binding domain fusion and EcRE-lacZ reporter gene expression. GAL4-EcR is activated in the FC by an ecdysone agonist and repressed by tissue-specific Ras GTPase signals. To determine the significance of restricted sites of EcR activity in the FC, we used targeted misexpression of the dominant negative EcR (EcR-DN) molecules EcR(F645A) and EcR(W650A). EcR-DN expression at stage 10 reduced EcRE-lacZ expression in the nurse cell FC and resulted in abnormal FC migrations, including aberrant centripetal migration and dorsal appendage tube formation, leading to the formation of cup-shaped eggs with shortened, branched dorsal appendages at stage 14. Clones of FC expressing EcR-DN displayed cell-autonomous increases in DE-cadherin expression and abnormal epithelial junction formation. EcR-DN expression caused thin eggshell phenotypes that correlated with both reduced levels of chorion gene expression and reduction in chorion gene amplification. Our results indicate that tissue-specific modulation of EcR activity by the Ras signaling pathway refines temporal ecdysone signals that regulate FC differentiation and cadherin-mediated epithelial cell shape changes.

Germline X Chromosomes Exhibit Contrasting Patterns of Histone H3 Methylation in Caenorhabditis elegans

In mammals, one of the two somatic X chromosomes in the female is inactivated, thereby equalizing X chromosome-derived transcription in the two sexes, a process known as dosage compensation. In the germline, however, the situation is quite different. Both X chromosomes are transcriptionally active during female oogenesis, whereas the X and Y chromosomes are transcriptionally silent during male spermatogenesis. Previous studies suggest that Caenorhabditis elegans germline X chromosomes might have different transcriptional activity in the two sexes in a manner similar to that in mammals. Using antibodies specific to H3 methylated at either lysine 4 or lysine 9, we show that the pattern of site-specific H3 methylation is different between X chromosomes and autosomes as well as between germline X chromosomes from the two sexes in C. elegans. We show that the pachytene germline X chromosomes in both sexes lack Me(K4)H3 when compared with autosomes, consistent with their being transcriptionally inactive. This transcriptional inactivity of germline X chromosomes is apparently transient in hermaphrodites because both X chromosomes stain brightly for Me(K4)H3 after germ nuclei exit pachytene. The male single X chromosome, on the other hand, remains devoid of Me(K4)H3 staining throughout the germline. Instead, the male germline X chromosome exhibits a high level of Me(K9)H3 that is not detected on any other chromosomes in either sex, consistent with stable silencing of this chromosome. Using mutants defective in the sex determination pathway, we show that X-chromosomal Me(K9)H3 staining is determined by the sexual phenotype, and not karyotype, of the animal. We detect a similar high level of Me(K9)H3 in male mouse XY bodies, suggesting an evolutionarily conserved mechanism for silencing the X chromosome specifically in the male germline.

Changes in Age-Related Reproductive Tactics in the Female of the Butterfly, Eurema hecabe

The occurrence of mate solicitation by virgin females was investigated in the butterfly Euremahecabe. Young (1-day-old) virgin females rarely showed mate solicitation to male model, however, old (at least 6-day-old) virgin females frequently showed such flight. The duration of solicitation was significantly longer in older females than in younger ones. The age-related behavioral change occurs with female oogenesis (Hiroki and Kato 1996), and such behavior may thus be a result of female adaptation to maximize their fecundity.

Genetics of the butterfly Danaus chrysippus (L.) in a broad hybrid zone, with special reference to sex ratio, polymorphism and intragenomic conflict

Abstract The aposematic savanna butterfly Danaus chrysippus seems to be an exception to the rule that Batesian models and Mullerian mimics are not polymorphic. Throughout Asia and in much of Africa the species is in fact monomorphic and polytypic, as expected. It is, however, polymorphic for 3–4 colour genes over a large area of central and eastern Africa, where deviant sex ratios and non-Mendelian segregations also occur. All-female broods are widespread and frequent, often outnumbering bisexual progenies and giving rise to heavily female-biased populations. Full and partial sex linkage, which is not controlled from the X or Y chromosomes, and male-biased broods also occur. Genetical analysis for the BC-autosome carrying colour genes suggests there are two, probably mitochondrial, cytotypes (microbe-induced early male death syndrome is considered unlikely) and an autosomal, incompatibility (I) gene, two alleles of which are male-specific killers. F2 and backcross matings by females heterozygous at the I-locus give progenies which are either thelygenic, all males dying at or soon after hatching, or bisexual but showing full or partial sex linkage. Male death is attributed to nuclear-cytoplasmic incompatibility (NCI). Females achieve reversion from a thelygenic to a bisexual line by mating with males of compatible (maternal) cytotype. A second NCI system causes meiotic drive in female oogenesis for a cytoplasmically compatible A-autosome, with no effect on SR. The array of non-Mendelian segregations for sex and two autosomes, with switching between bisexual and unisexual lineages, indicates autosomal intragenomic conflict with the outcome that one autosome is preserved from elimination in females and the other condemned in dead males. The geographical distribution of the colour marker genes suggests that the polymorphisms have a hybrid origin involving several once allopatric subspecies, some of which have divergent cytotypes. Secondary contact probably followed range expansion induced by the periodic spread of savanna during the Pleistocene and massive deforestation by man in recent times. The unusual extent of the hybrid zone is attributed to the large number of subspecies involved in its origin, and to introgression promoted by the butterfly's extensive migratory activity.

The formation, transfer, and fate of spermatophores in Photinus fireflies (Coleoptera: Lampyridae)

Fireflies in the genus Photinus have been assumed previously to be among the many insect species in which males transfer primarily sperm during mating. In this study, male P. ignitus and P. marginellus were found to produce a complex proteinaceous spermatophore in four paired male accessory glands, a major component of the spermatophore being formed within prominent spiral glands. The spermatophore is transferred to the female within the first 40 min of copulation, and sperm bundles are released into the spermatheca. The remainder of the spermatophore subsequently undergoes digestion within a specialized sac in the female reproductive tract. To examine the function of male spermatophores, male P. marginellus were fed rhodamine B, resulting in the production of intensely fluorescent spermatophores. After mating with rhodamine-dyed males, females incorporated material derived from male spermatophores into their oocytes within 58 h post mating. Nutrient donations from males during mating are expected to play particularly important roles in female oogenesis in insects with nonfeeding adults, such as Photinus spp. The presence of spermatophores in Photinus is related to marked differences among species in their life histories, mating systems, and mating behaviors.

Glomus tumours and genomic imprinting: influence of inheritance along the paternal or maternal line.

Two new families with glomus tumours and two additions to earlier publications are presented. The pattern of inheritance is autosomal dominant. Familial glomus tumours are inherited almost exclusively via the paternal line, a finding inconsistent with autosomal dominant transmission. This can be explained by genomic imprinting. The maternally derived gene is inactivated during female oogenesis and can be reactivated only during spermatogenesis. Two different loci have been assigned, one to a 5 cM region of chromosome 11q13.1 and one to 11q22.3-q23.3. Genomic imprinting has already been found for the distal locus and here we demonstrate that the proximal locus is subject to genomic imprinting too. Genomic imprinting has considerable implications for genetic counselling in families with glomus tumours. In addition to this the sex ratio among affected offspring appears to be influenced by the paternal or maternal origin of the gene of the transmitting father.

Effect of diets on growth and reproductive development of juvenile pikeperch, Stizostedion lucioperca (L.), reared under intensive culture conditions

Juvenile pikeperch 3.66 ± 0.23 cm total length (TL) and 0.32 ± 0.05 g were reared in water at 22 ± 0.5°C and fed with live zooplankton or alternatively a commercial trout feed. Fish fed with dry diet grew faster and had higher condition factor than fish fed live zooplankton. Sex differentiation in pikeperch was visible at different stages of ontogenesis, but was related to the fish growth rate. The gonads offish that were 3.43-5.69 cm TL revealed undifferentiated characteristics. Clear indication of oogenesis in females was observed in pikeperch at 7.9 cm TL and 3.47 g, whereas evident spermatogenesis was not observed till the end of the experiment.

GENOMIC IMPRINTING IN HEREDITARY GLOMUS TUMOURS: EVIDENCE FOR NEW GENETIC THEORY

A study based on fifteen pedigrees showed that familial glomus tumours are inherited almost exclusively via the paternal line, a finding inconsistent with autosomal dominant transmission. The results can be explained in terms of the genomic imprinting hypothesis—the maternally derived gene is inactivated during female oogenesis and can be reactivated only during spermatogenesis. Genomic imprinting may have considerable implications for genetic counselling with respect to glomus tumours and also for the understanding of other hereditary diseases.

Prospects of the Reproductive Toxicology: With Special Reference to the Developmental Hazards Due to the Treatment at the Stages from Prefertilization to Implantation*

ABSTRACT With the definition of teratogenicity was expanded in terms of developmental stages when the agent acts and types of developmental anomalies induced, the concept of reproductive toxicity or developmental toxicity has been established. These new terms are essentially the synonym; the former gives the prime emphasis on the parent generation while the latter on the longer phase of developmental stage of the offspring.It has been generally stated that the environmental agents which act before the onset of organogenesis will bring the embryo either death or normal growth. However, some affect the preimplantation embryos with resultant congenital anomalies. Moreover, it has been demonstrated that various developmental defects can be induced by a premating treatment to males, some of which may have been caused by mechanisms other than mutagenicity. On the other hand, oogenesis in females takes a very long time and it is often difficult to determine when these environmental agents act before or after pregnancy. Recent episodes of herbicides (Agent Orange) and vaginal spermicides were introduced as examples.Pharmaceutical drugs, chemicals given to humans intentionally at a relatively large amount in a limited duration, have been requested to be tested in laboratory animals on the possible developmental defects in offspring even when given prior to organogenesis. In Japan, at the test administered prior to and in the early stages of pregnancy (segment I study), it is recommended not only to examine fertility of the parent generation but also to observe the development of offspring as long as practically possible.In the symposium held at the 24th Annual Meeting of the Japanese Teratology Society, significance of developmental failures of the offspring induced by environmental factors given to the parents and during the preimplantation period was critically discussed.

Sterilizing effects of trimethylphosphate in Drosophila melanogaster.

Trimethylphosphate (TMP) causes aspermia in D. melanogaster males. If larvae are allowed to develop on standard maize-meal medium containing 0.002 M TMP or greater, the enclosing adult males, when placed on uncontaminated medium, exhibit a period of temporary sterility. Between test groups the period of sterility is most variable at the doses of 0.002-0.004 M, but at 0.005 M or greater is approximately 11-12 days. Near-lethal doses of about 20 g/kg by abdominal injection produces a temporary sterility in adults, whereas oral doses up to 0.02 M are ineffective. Oogenesis in females is not affected by doses which cause temporary sterility in males. In adult male D. melanogaster, which were treated as larvae with 0.01 M TMP in the food medium, the basal region of testes and seminal vesicles do not contain spermatozoa. Cytological examinations of the spermatids reveal ultrastructural changes which are characteristic of those seen in X/O and sterile-mutant males; they contain incomplete axial fibre complexes, abnormal development of the mitochondrial derivatives, and nuclei which fail to elongate and condense. Evidence from cytological studies of larval testes suggests that the chemosterilizing effect of TMP is upon early primary spermatocytes. This is also supported by mating data.