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PubMed1973

Gametogenesis in Chlamydomonas eugametos: I. Light Requirements.

Male and female mating types of Chlamydomonas eugametos Moewus show an absolute light requirement for gametogenesis. Increasing light intensity from 0.3 to 1.2 mw cm(-2) during nitrogen starvation (a precondition for gametogenesis) caused an increase in gametogenesis throughout a 28-hour period. Gametogenesis was measured by determining the percentage of paired cells after a 1-hour mixing period. Light requirements for the male and female differed. There was a 9-hour lag period in gametogenesis in the male, but no lag in the female. Gametogenesis was reduced 50% in the female and 90% in the male when 6.0 mum 3-(3,4-dichlorophenyl)-1, 1-dimethyl-urea was in the N-starvation medium. Sodium acetate, 1.8 mm, in the N-starvation medium increased gametogenesis in both mating types and eliminated the 9-hour lag in the male for cells irradiated for 3, 6, 9, 12, 15, 18, or 23 hours during the last part of a 23-hour N-starvation period. Sodium acetate concentrations higher than 1.8 mm inhibited the mating process. 3-(3,4-Dichlorophenyl)-1, 1-dimethylurea inhibition of gametogenesis was decreased in the male but increased in the female, when sodium acetate was added to the N-starvation medium. These results indicate a nonphotosynthetic as well as a photosynthetic role for light in the gametogenesis of both mating types. Also, the male will not undergo gametogenesis unless a required amount of energy is provided either in the medium or through photosynthesis.

Journal Article↗

PubMed2006

The development of an aquatic bivalve model: evaluating the toxic effects on gametogenesis following 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) exposure in the eastern oyster (Crassostrea virginica).

The objective of this study is to develop a gametogenesis protocol to serve as a model for evaluating the toxic effects of chemicals on oogenesis and spermatogenesis in the eastern oyster (Crassostrea virginica). The compound 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) was selected as a "proof of principle" toxicant to examine developmental toxicity in this invertebrate system. The studies were designed to: (1) test the model using 2,3,7,8-TCDD and (2) to use histopathological evaluations to characterize the effects on oocyte and sperm development during stages of gametogenesis. 2,3,7,8-TCDD at 10 pg/g resulted in significant histopathological gonadal lesions by day 14 of gametogenesis in both female and male oysters. These lesions resulted in complete inhibition of gonadogenesis. Studies also showed that a total body dose of 2 and 10 pg/g 2,3,7,8-TCDD caused adverse responses resulting in abnormal gametogenesis in female and male oysters, respectively, such as: (1) incomplete oocyte division, (2) inhibition of oocyte growth and maturation, (3) unsynchronized sperm development, and (4) inhibition of spermatogenesis. The eastern oyster is one of the most responsive invertebrate models tested to date for reproductive effects of chemicals. Therefore, the eastern oyster can be used as a sensitive toxicological model for examining the effects of dioxin-like compounds and other xenobiotics on gametogenesis. The reported studies show that environmentally relevant concentrations of 2,3,7,8-TCDD (2-10 pg/g) have a significant adverse effect on oyster gametogenesis.

Animals↗

PubMed1994

Endocrine regulation of gametogenesis in fish.

The pituitary-gonadal axis plays an important role in regulating gametogenesis in vertebrates. In most cases, gonadotropins act through the biosynthesis of gonadal steroid hormones which in turn mediate various stages of gametogenesis. A series of studies in our laboratory using several species of teleost fishes as experimental animals has provided new information about the endocrine regulation of gametogenesis, including oocyte growth, oocyte maturation, spermatogenesis and sperm maturation. This article briefly reviews our findings on the identification of steroidal mediators involved in each process of gametogenesis, and the sites and mechanisms of action of the mediators. These observations collectively demonstrate the appropriateness of using teleost fishes as valid models for examining hormonal influences on gametogenesis. Such models could also have applications and validity for vertebrates in general.

Activins↗

PubMed2000

Determination of mosquito bloodmeal pH in situ by ion-selective microelectrode measurement: implications for the regulation of malarial gametogenesis.

Malarial gametocytes circulate in the peripheral blood of the vertebrate host as developmentally arrested intra-erythrocytic cells, which only resume development into gametes when ingested into the bloodmeal of the female mosquito vector. The ensuing development encompasses sexual reproduction and mediates parasite transmission to the insect. In vitro the induction of gametogenesis requires a drop in temperature and either a pH increase from physiological blood pH (ca pH 7.4) to about pH 8.0, or the presence of a gametocyte-activating factor recently identified as xanthurenic acid (XA). However, it is unclear whether either the pH increase or XA act as natural triggers in the mosquito bloodmeal. We here use pH-sensitive microelectrodes to determine bloodmeal pH in intact mosquitoes. Measurements taken in the first 30 min after ingestion, when malarial gametogenesis is induced in vivo, revealed small pH increases from 7.40 (mouse blood) to 7.52 in Aedes aegypti and to 7.58 in Anophĕles stephensi. However, bloodmeal pH was clearly suboptimal if compared to values required to induce gametogenesis in vitro. Xanthurenic acid is shown to extend the pH-range of exflagellation in vitro in a dose-dependent manner to values that we have observed in the bloodmeal, suggesting that in vivo malarial gametogenesis could be further regulated by both these factors.

Aedes↗

PubMed1995

Cloning and characterization of genes expressed during gametogenesis of female and male mice.

Isolation and initial characterization of clones from a mouse fetal ovary cDNA library are reported. In mammals, the development of female gametogenesis, including the prophase of the first meiotic division, begins in the fetus. A parallel conserved process occurs in males, from puberty onwards. We cloned cDNAs preferentially expressed in both sexes during gametogenesis considering both the meiotic programme and the non-germ cells participating in the developmental regulation of gametogenesis. From 183 clones that showed positive hybridization with adult testis and negligible hybridization with somatic probes, 32 clones were selected. After partial sequencing, 16 were found to correspond to known genes that are expressed during other programmes of differentiation and development. Sixteen clones represent novel sequences. The accumulation of corresponding transcripts was analysed by developmental northern blots during spermatogenesis, and genes expressed during gametogenesis were characterized together with others showing pleiotropic expression in different tissues. Additional specific, gametic transcripts were also detected.

Animals↗

PubMed2001

DNA repair mechanisms and gametogenesis.

In mammals, there is a complex and intriguing relationship between DNA repair and gametogenesis. DNA repair mechanisms are involved not only in the repair of different types of DNA damage in developing germline cells, but also take part in the meiotic recombination process. Furthermore, the DNA repair mechanisms should tolerate mutations occurring during gametogenesis, to a limited extent. In the present review, several gametogenic aspects of DNA mismatch repair, homologous recombination repair and postreplication repair are discussed. In addition, the role of DNA damage-induced cell cycle checkpoint control is considered briefly. It appears that many genes encoding proteins that take part in DNA repair mechanisms show enhanced or specialized expression during mammalian gametogenesis, and several gene knockout mouse models show male or female infertility. On the basis of such knowledge and models, future experiments may provide more information about the precise relationship between DNA repair, chromatin dynamics, and genomic stability versus instability during gametogenesis.

Animals↗

PubMed1981

The mat-1 gene in Chlamydomonas regulates DNA methylation during gametogenesis.

The inheritance of chloroplast genes in Chlamydomonas is regulated by methylation of chloroplast DNA during gametogenesis. The wild-type pattern of maternal inheritance results from the methylation of chloroplast DNA in female (mt+) but not in male (mt-) gametes, leading to preferential degradation of chloroplast DNA of male origin in zygotes. This paper describes the distribution of 5-methyl cytosine residues in restriction fragments of chloroplast DNA sampled during gametogenesis by two methods: ethidium bromide staining of agarose gels, and binding of antibody directed against 5-methyl cytosine onto restriction fragments blotted to nitro-cellulose paper. Methylated cytosines are located in most if not all Eco RI and Msp I fragments, but the extent of methylation is not proportional to fragment size. The mat-1 mutation carried by males converts maternal inheritance. Chloroplast DNA of male gametes carrying the mat-1 mutation becomes methylated during gametogenesis. This methylation protects against restriction enzyme-promoted degradation in zygotes, as shown by physical data demonstrating the transmission to progeny of chloroplast genes carried on chloroplast DNA of the mat-1 male parent. Thus the mat-1 gene, which is linked to the mating-type locus, determines whether or not methylation of chloroplast DNA will occur in males during gametogenesis.

Chlamydomonas↗

PubMed1998

Gametogenesis in yeast is regulated by a transcriptional cascade dependent on Ndt80.

Gametogenesis requires the successful coordination of two key processes, meiotic nuclear division and gamete morphogenesis. A central regulatory step in progression through gametogenesis occurs at the pachytene stage of meiotic prophase. We find that Ndt80 functions at pachytene of yeast gametogenesis (sporulation) to activate transcription of a set of genes required for both meiotic division (e.g., B-type cyclins) and gamete formation (e.g., SPS1). Ectopic synthesis of Ndt80 in vegetative cells induces transcription of these genes, and recombinant Ndt80 protein binds to a conserved sequence in their upstream region. Transcription of NDT80 itself is dependent on Ime1, which activates expression of early sporulation genes. Transcription of the Ndt80-regulated gene CLB1 is mediated by the checkpoint gene RAD17. Thus Ndt80 is a pivotal component of a transcriptional cascade programming yeast gametogenesis and may also be a target of meiotic checkpoint control.

Cyclin B↗

PubMed2006

Cell-cycle regulation and mammalian gametogenesis: a lesson from the unexpected.

The progression of mammalian gametogenesis requires a precise balance between cell-cycle activities and elimination of defective gametogenic cells to ensure the perpetuation of species. Both spermatogonia and oogonia are stem cell populations committed to meiosis with the aim of generating haploid gametes for fertilization. At puberty, mitotically dividing spermatogonial cell cohorts maintain the ability of cell renewal and occupy niches in the seminiferous tubule. In contrast, mitotically dividing oogonial cell cohorts produced in the fetal ovary, are exclusively committed to meiosis and produce primordial follicles housing a primary oocyte surrounded by somatic follicular cells. A consistent physiological event during mammalian gametogenesis is the disposal of spermatogenic cells by apoptosis and ovarian follicles by atresia. Cyclin-dependent kinases (Cdks) and their cyclin partners coordinate the activities of the cell cycle. An additional cell-cycle regulatory component is the centrosome. The centrosome harbors regulatory proteins controlling the normal progression of the cell cycle. Changes in individual centrosome proteins can lead to cell-cycle arrest and a decrease in the genomic protective function of p53 that promotes apoptosis. Disruption of cyclin A1, Cdk2, and Cdk4 expression in transgenic mice results in infertility and gonadal atrophy. Cdk-cyclin complexes interact with regulatory proteins, which may fine-tune the activities of the complex. One of the many regulatory proteins is p12, a 115 amino acid growth suppressor polypeptide designated p12(CDK2AP1), partner of Cdk2 and with binding affinity to DNA polymerase alpha/primase. Overexpression of p12 is associated with testicular and ovarian atrophy without affecting fertility. Ectopic expression of p12 was driven by the keratin 14 promoter. Keratin 14 is the pairing partner of keratin 5 and both keratins are expressed in testis. The efficiency of keratin promoters in driving ectopic gonadal gene expression, the association of gonadal atrophy with the ectopic expression of a Cdk2 regulatory protein and the centrosome, as a reservoir of cell-cycle regulatory proteins, open new experimental opportunities to address still lingering questions concerning cell differentiation and division during mammalian gametogenesis.

Animals↗

PubMed2004

The transcriptional program of synchronous gametogenesis in Chlamydomonas reinhardtii.

Cells of Chlamydomonas reinhardtii undergo gametogenesis to produce sexually competent gametes under nitrogen-starved conditions. By using a synchronized system for gametogenesis of early G1 cells, several previously identified marker genes and 18 novel nitrogen-starved gametogenesis (NSG) genes isolated by macroarray analysis were placed into at least three temporal classes of expression. Early genes are induced transiently in the first 2 h after transfer to nitrogen-free medium. Middle genes are strongly induced between 3 h and 4 h after nitrogen removal, a time corresponding to the acquisition of mating competency, suggesting their involvement in the gamete program. Late genes are induced between 5 h and 8 h after nitrogen removal, a time after the completion of gametic differentiation, suggesting that they are not directly involved in the formation of sexually competent gametes. All of the 18 NSG genes examined are induced in both mating-type plus and minus gametes and about two-thirds of the genes are also expressed in the mitotic cell cycle, especially at S/M phases.

Animals↗

PubMed2003

Developmental estrogenic exposure in zebrafish (Danio rerio): II. Histological evaluation of gametogenesis and organ toxicity.

Aquatic species can be exposed to endocrine disrupting chemicals (EDCs) in wastewater that often includes the weak estrogen, 4-nonylphenol (NP) and the potent estrogen, 17alpha-ethinylestradiol (EE). The goal of the present study was to determine concentration-dependent effects of developmental exposure to NP and EE on gametogenesis, as well as gonad, kidney and liver pathology using quantitative histological evaluation of hematoxylin/eosin-stained saggital sections of zebrafish (Danio rerio). The major finding of the present study was that exposure to NP (>/=100 microg/l nominal) and EE (>/=1 ng/l nominal) from 2 to 60 days post-hatch (dph) caused concentration-dependent suppression of gametogenesis in both male and female zebrafish. Severe kidney pathology was observed in 60 dph zebrafish, specifically glomerular dilation or degeneration, fibrosis, tubule enlargement and tubule necrosis, at a threshold of 10 ng/l EE. However, minor kidney histopathology indicated by increased pyknotic nuclei in kidney tubule and interstitial (hematopoietic) cells was detected at lower estrogenic exposures (>/=10 microg/l NP nominal) than delayed gametogenesis. Considering all histological parameters in the current study, the rank order of potency for pathological effects in 60 dph zebrafish was 10 ng/l EE>1 ng/l EE=100 microg/l NP>30 microg/l NP>10 microg/l NP10 (nominal concentrations). Zebrafish from the same cohort examined in the current study that had been placed in clean water from 60 to 300 dph had histologically normal testes and no kidney or liver histopathology. However, increased ovarian follicle atresia was detected at 300 dph in zebrafish exposed developmentally to 100 microg/l NP. Therefore, we conclude that functional rather than morphological changes may be more important for future evaluations of developmental exposure to estrogens in fish, and that negative effects in female rather than male gonads may contribute to prolonged breeding impairment.

Animals↗

PubMed2003

Toward the genetics of mammalian reproduction: induction and mapping of gametogenesis mutants in mice.

The genetic control of mammalian gametogenesis is inadequately characterized because of a lack of mutations causing infertility. To further the discovery of genes required for mammalian gametogenesis, phenotype-driven screens were performed in mice using random chemical mutagenesis of whole animals and embryonic stem cells. Eleven initial mutations are reported here that affect proliferation of germ cells, meiosis, spermiogenesis, and spermiation. Nine of the mutations have been mapped genetically. These preliminary studies provide baselines for estimating the number of genes required for gametogenesis and offer guidance in conducting new genetic screens that will accelerate and optimize mutant discovery. This report demonstrates the efficacy and expediency of mutagenesis to identify new genes required for mammalian gamete development.

Animals↗

PubMed1990

Expression of inhibin alpha-subunit gene during mouse gametogenesis.

Mammalian gametogenesis is regulated through complex interactions between germ and somatic cells. To investigate the mechanism underlying the differentiation of functional gametes, some genes specifically expressed during gametogenesis have been isolated and characterized. In a search for further examples of such genes, we have isolated from a newborn mouse testis cDNA library, a clone corresponding to mouse inhibin alpha-subunit. Although it is known that the inhibin alpha-subunit molecule is abundantly produced in ovarian follicle and in testicular Sertoli cells, the spatial and temporal patterns of expression of this gene remain to be elucidated. In this study, the patterns of expression of inhibin alpha-subunit mRNA during mouse gametogenesis were examined by RNA blot, cytoplasmic dot and in situ hybridization techniques. In the testis, the concentration of inhibin alpha-subunit mRNA increased from about 16 dpc (days post coitum), peaked at birth and then gradually decreased, paralleling testicular development. Inhibin alpha-subunit mRNA was localized in Sertoli cells of wild type as well as W/Wv testes. In adult testis, mRNA was restricted to the perinuclear cytoplasm of Sertoli cells. Inhibin alpha-subunit mRNA was expressed in follicle cells of adult ovary more abundantly than in adult testis. Analysis of expression during folliculogenesis showed that the accumulation of this mRNA began in preantrum follicles and the level of expression reached a maximum in Graafian follicles.

Amino Acid Sequence↗

PubMed1992

Evidence for a selective destabilization of an integral membrane protein, the cytochrome b6/f complex, during gametogenesis in Chlamydomonas reinhardtii.

We studied the process of photosynthetic inactivation during gametogenesis of the unicellular green alga Chlamydomonas reinhardtii. We show that it is caused by the selective destabilization of a single transmembrane protein complex, the cytochrome b6/f complex, which is initially accumulated in the thylakoid membranes of vegetative cells. This protein destabilization is controlled by the intracellular energy sources available in the gametes, i.e. the coupled electron flow in the mitochondria and the amount of starch accumulated in the chloroplast. It nevertheless requires the expression of gamete-specific proteins. The loss of cytochrome b6/f complexes during gametogenesis is prevented by the addition of cycloheximide, but is chloramphenicol insensitive. Therefore, it is likely to involve some translation product of nuclear origin, specifically expressed during gametogenesis. Among the new polypeptides specifically found in the gametes, we detected a soluble polypeptide M alpha (approximate molecular mass of 63 kDa), which shared common epitopes with cytochrome f. Its synthesis displays an antibiotic sensitivity typical of a nuclear-encoded polypeptide and is controlled by the same intracellular signals which control the destabilization of the cytochrome b6/f complexes in the thylakoid membranes.

Adenosine Triphosphate↗

PubMed1992

Parental methylation patterns of a transgenic locus in adult somatic tissues are imprinted during gametogenesis.

The methylation status of a mouse metallothionein-I/human transthyretin fusion gene was studied during gametogenesis in transgenic mice. In the adult tissues of this mouse line, the promoter region of the transgene on chromosome 11 is methylated when it is maternally inherited and undermethylated when it is paternally inherited. Germ cells from various developmental stages of gametogenesis were isolated, and their DNAs were assayed using methylation-sensitive restriction endonucleases and the polymerase chain reaction. Only low to nonexistent levels of transgene methylation were detected in germ cells from 14.5-day-old male and female fetuses irrespective of the parental origin of the transgene. This undermethylated state persisted in oocytes from newborn females as well as in testicular spermatogenic cells and sperm. By contrast, the transgene promoter was completely methylated in fully grown oocytes arrested at the first meiotic prophase. The endogenous metallothionein-I gene promoter, located on a different chromosome, remained undermethylated at all stages examined, consistent with previous findings reported for a typical CpG island. Taken together, the results suggest that parental-specific adult patterns of transgene methylation are established during gametogenesis.

Animals↗

PubMed2006

[Seasonal characteristics of gametogenesis in the Corbicula japonica].

A morphological study of gonads in Corbicula japonica made it possible to distinguish between five stages of gonad maturity. It has been established that stages of active gametogenesis, prespawning and of spawning go almost in parallel and in the shortest time. In July, with the beginning of spawning, gametogenesis does not stop, and oogenesis proceeds up to the end of August. Dynamics of changes of some chemical substances in oocytes was followed. High concentrations of, respectively, RNA, albumens, lipids, glycoproteins and proteoglycans were revealed in oocyte nuclei and nucleoli both at the beginning of the development, and at the stage of active gametogenesis. This testifies in favor of a synthetic activity of these cells.

Animals↗

PubMed1993

The kit-ligand (steel factor) and its receptor c-kit/W: pleiotropic roles in gametogenesis and melanogenesis.

The c-kit receptor tyrosine kinase belongs to the PDGF/CSF-1/c-kit receptor subfamily. The kit-ligand, KL, also called steel factor, is synthesized from two alternatively spliced mRNAs as transmembrane proteins that can either be proteolytically cleaved to produce soluble forms of KL or can function as cell-associated molecules. The c-kit receptor kinase and KL are encoded at the white spotting (W) and steel (Sl) loci of the mouse, respectively. Mutations at both the W and the Sl locus cause deficiencies in gametogenesis, melanogenesis and hematopoiesis. The c-kit receptor is expressed in the cellular targets of W and Sl mutations, while KL is expressed in their microenvironment. In melanogenesis, c-kit is expressed in melanoblasts from the time they leave the neural crest and expression continues during embryonic development and in the melanocytes of postnatal animals. In gametogenesis c-kit is expressed in primordial germ cells, in spermatogonia, and in primordial and growing oocytes, implying a role at three distinct stages of gametogenesis. Many mutant alleles are known at W and Sl loci and their phenotypes vary in the degree of severity in the different cellular targets of the mutations. While many W and Sl alleles severely affect primordial germ cells (PGC), several mild Sl alleles have weak effects on PGCs and exhibit differential male or female sterility. Steel Panda (Sl(pan)) is a KL expression mutation in which KL RNA transcript levels are reduced in most tissues analyzed. In female Sl(pan)/Sl(pan) mice, ovarian follicle development is arrested at the one layered cuboidal stage as a result of reduced KL expression in follicle cells, indicating a role for c-kit in oocyte growth. Wsh is a c-kit expression mutation, which affects mast cells and melanogenesis. While the mast cell defect results from lack of c-kit expression, the pigmentation deficiency appears to stem from ectopic c-kit receptor expression in the somitic dermatome at the time of migration of melanoblasts from the neural crest to the periphery. It is proposed that the ectopic c-kit expression in Wsh mice affects early melanogenesis in a dominant fashion. The "sash" or white belt of Wsh/+ animals and some other mutant mice is explained by the varying density of melanoblasts along the body axis of wild-type embryos.

Animals↗

PubMed2001

Behavior of plastid nucleoids during male gametogenesis in Plumbago auriculata.

We characterized the behavior of plastid (pt) and mitochondrial (mt) nucleoids during male gametogenesis in Plumbago auriculata in three dimensions. The behavior of pt-nucleoids and mt-nucleoids differed throughout male gametogenesis. Pt-nucleoids were distributed in a characteristic manner in three stages: in the early microspore, pt-nucleoids assemble around cell nucleus; in the mid-generative cell, pt-nucleoids gather at the internal side of the pollen; in the late-generative cell, pt-nucleoids aggregation turns its pole to the external side of the pollen. We also studied organelle nucleoids in the egg and the central cell by a method in which semi-thick sections of resin-embedded anthers and ovaries were observed by confocal laser scanning microscopy. The number of pt-nucleoids in the sperm cell did not differ significantly from that in the egg. These results suggest that the behavior of DNA-containing organelles is regulated strictly during male gametogenesis in P. auriculata, and that a biparental inheritance of plastids in the Plumbago embryo is more favored than was previously thought.

Cell Nucleus↗