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At least 775 records · Page 43Linked to original sources

PubMed2004

Transcriptional programs of early reproductive stages in Arabidopsis.

The life cycle of flowering plants alternates between a diploid sporophytic and a haploid gametophytic generation. After fertilization of each the egg and central cells by one male gamete, the development of both fertilization products occurs coordinated with the maternally derived seed coat and carpel tissues forming the fruit. The reproduction program is likely to involve the concerted activity of many genes. To identify genes with specific functions during reproduction, we have analyzed the expression profile of more than 22,000 genes present on the Arabidopsis ATH1 microarray during three stages of flower and fruit development. We found 1,886 genes regulated during reproductive development and 1,043 genes that were specifically expressed during reproduction. When compared to cells from an Arabidopsis suspension culture, S-phase genes were underrepresented and G2 and M-phase genes were strongly enriched in the set of specific genes, indicating that important functions during reproduction are exerted in the G2 and M phases of the cell cycle. Many potential signaling components, such as receptor-like protein kinases, phosphatases, and transcription factors, were present in both groups of genes. Members of the YABBY, MADS box, and Myb transcription factor families were significantly overrepresented in the group of specific genes, revealing an important role of these families during reproduction. Furthermore, we found a significant enrichment of predicted secreted proteins smaller than 15 kD that could function directly as signaling molecules or as precursors for peptide hormones. Our study provides a basis for targeted reverse-genetic approaches aimed to identify key genes of reproductive development in plants.

Arabidopsis↗

PubMed2002

Patterns of divergence in the effects of mating on female reproductive performance in flour beetles.

Sexual selection can lead to rapid divergence in reproductive characters. Recent studies have indicated that postmating events, such as sperm precedence, may play a key role in speciation. Here, we stress that other components of postmating sexual selection may be involved in the evolution of reproductive isolation. One of these is the reproductive investment made by females after mating (i.e., differential allocation). We performed an experiment designed to assess genetic divergence in the effects of mating on female reproductive performance in flour beetles, Tribolium castaneum. Females were mated to males of three different wild-type genotypes at two different frequencies, in all possible reciprocal combinations. Male genotype affected all aspects of female reproduction, through its effects on female longevity, total offspring production, reproductive rate, mating rate, and fertility. Moreover, male and female genotype interacted in their effects on offspring production and reproductive rate. We use the pattern of these interactions to discuss the evolutionary process of divergence and suggest that the pattern is most consistent with that expected if divergence was driven by sexually antagonistic coevolution. In particular, the fact that females exhibited a relatively weak response to males with which they were coevolved suggests that females have evolved resistance to male gonadotropic signals/stimuli.

Animals↗

PubMed2005

Population structure attributable to reproductive time: isolation by time and adaptation by time.

Many populations are composed of a mixture of individuals that reproduce at different times, and these times are often heritable. Under these conditions, gene flow should be limited between early and late reproducers, even within populations having a unimodal temporal distribution of reproductive activity. This temporal restriction on gene flow might be called "isolation by time" (IBT) to acknowledge its analogy with isolation by distance (IBD). IBD and IBT are not exactly equivalent, however, owing to differences between dispersal in space and dispersal in time. We review empirical studies of natural populations that provide evidence for IBT based on heritabilities of reproductive time and on molecular genetic differences associated with reproductive time. When IBT is present, variation in selection through the reproductive season may lead to adaptive temporal variation in phenotypic traits [adaptation by time (ABT)]. We introduce a novel theoretical model that shows how ABT increases as (i) selection on the trait increases; (ii) environmental influences on reproductive time decrease; (iii) the heritability of reproductive time increases; and (iv) the temporal distribution of reproductive activity becomes increasingly uniform. We then review empirical studies of natural populations that provide evidence for ABT by documenting adaptive temporal clines in phenotypic traits. The best evidence for IBT and ABT currently comes from salmonid fishes and flowering plants, but we expect that future work will show these processes are more widespread.

Adaptation, Physiological↗

PubMed2005

Crossing the taxonomic divide: conflict and its resolution in societies of reproductively totipotent individuals.

Reproduction in groups may be unequal, with one or a few individuals monopolizing direct reproduction assisted by nonbreeding helpers. In social insects this has frequently led to a pronounced queen-worker dichotomy and a loss of reproductive totipotency among workers. However, in some invertebrate and all vertebrate societies, all or most individuals remain reproductively totipotent. In these groups, conflicts of interest over reproduction are potentially greatest. Here, we synthesize previous analyses of reproductive conflict, aggression and breeder replacement in haplodiploid societies of totipotent individuals and extend them to cover diploid (vertebrate) examples. We test predictions arising from this approach using the best-studied invertebrate (Dinoponera queenless ants) and vertebrate (naked mole-rat, Heterocephalus glaber) examples, although in principle our analysis applies to all similar groups. We find that premature replacement of a parent breeder by nonbreeders (overthrow) is rare. Dominant coercive control of nonbreeders by the breeder is often unnecessary and honest signalling of breeder vitality can maintain group stability and resolve conflicts over reproduction. We hope that by providing an explicit transfer of social theory between ants and naked mole-rats we will stimulate further cross-taxonomic studies that will greatly broaden our understanding of sociality.

Aggression↗

PubMed2006

Plant reproductive susceptibility to habitat fragmentation: review and synthesis through a meta-analysis.

The loss and fragmentation of natural habitats by human activities are pervasive phenomena in terrestrial ecosystems across the Earth and the main driving forces behind current biodiversity loss. Animal-mediated pollination is a key process for the sexual reproduction of most extant flowering plants, and the one most consistently studied in the context of habitat fragmentation. By means of a meta-analysis we quantitatively reviewed the results from independent fragmentation studies throughout the last two decades, with the aim of testing whether pollination and reproduction of plant species may be differentially susceptible to habitat fragmentation depending on certain reproductive traits that typify the relationship with and the degree of dependence on their pollinators. We found an overall large and negative effect of fragmentation on pollination and on plant reproduction. The compatibility system of plants, which reflects the degree of dependence on pollinator mutualism, was the only reproductive trait that explained the differences among the species' effect sizes. Furthermore, a highly significant correlation between the effect sizes of fragmentation on pollination and reproductive success suggests that the most proximate cause of reproductive impairment in fragmented habitats may be pollination limitation. We discuss the conservation implications of these findings and give some suggestions for future research into this area.

Conservation of Natural Resources↗

PubMed2001

Implications for evaluating the impact of family planning programs with a reproductive health orientation.

In 1994, Jain and Bruce proposed an index--HARI, an acronym for Helping Individuals Achieve their Reproductive Intentions--to measure success or failure of family planning programs with a reproductive health orientation. HARI applies the principle of individual rights and well-being to the assessment of these programs. The index measures two components: the achievement of an individual's reproductive intentions and the avoidance of severe reproductive health problems associated with an individual's efforts to achieve her stated reproductive intentions. A family planning program can be deemed successful if an individual is able to avoid having an unintended pregnancy (or is able to have a wanted child) within the stipulated period and if she experiences no severe reproductive health problems in the process. If these conditions are not met, the program could be deemed a failure. The HARI index has not yet been applied in field conditions. This report illustrates the procedure for estimating HARI by using data from a panel survey conducted in Peru. It discusses the usefulness and limitations of the index in assessing the success or failure of a family planning program with a reproductive health orientation.

Evaluation Studies as Topic↗

PubMed2000

Differential role of melanocortins in mediating leptin's central effects on feeding and reproduction.

Leptin serves as a humoral link coupling the status of energy reserves to the functional activity of the reproductive system. Leptin is thought to act through melanocortinergic pathways in the brain to regulate ingestive behaviors; however, whether melanocortins mediate leptin's actions on the neuroendocrine-reproductive axis is unknown. We tested this hypothesis first by determining whether the effects of leptin on feeding behavior and reproduction in the ob/ob mouse could be blocked by the melanocortin receptor (MC-R) antagonist SHU9119 and second, by examining the effects of the MC-R agonist MTII on feeding and the endocrine-reproductive system. Administered by intracerebroventricular injections, leptin inhibited food intake, raised plasma gonadotropin levels, and increased seminal vesicle weights compared with controls; SHU9119 (intracerebroventricularly) attenuated leptin's effects on food intake and body weight but did not alter leptin's stimulatory effect on the reproductive axis. MTII (intracerebroventricularly and intraperitoneally) decreased food intake and increased body temperature compared with controls but had no effect on the reproductive-endocrine axis. These results suggest that although leptin acts centrally through melanocortinergic pathways to inhibit ingestive behaviors and stimulate metabolism, leptin's activational effect on the reproductive axis is likely to be mediated by other, unknown neuroendocrine circuits.

Animals↗

PubMedDate not supplied

Nonhuman primate models of skeletal and reproductive aging.

BACKGROUND: Bone loss, osteoarthritis (OA) and age-related changes in reproduction are some of the most apparent and troubling results of advancing age in the human population. The significance of these changes underscores the need for developing appropriate animal models to study aging of bone and the reproductive system. OBJECTIVE: This review surveys the literature regarding the current state of nonhuman primates (NHP) as models for skeletal and reproductive aging in humans. RESULTS: Several species of NHP exhibit age-related bone loss as well as changes in the mineral content and architecture of bone that are similar to those reported in humans. In addition, since aged females of some species of NHP exhibit cessation of menses and serum hormone profiles consistent with those described in peri- and premenopausal women, they provide useful models of postmenopausal bone loss. Sensitivity to surgical estrogen depletion and hormone replacement has also been demonstrated in female NHP. Spontaneous development of degenerative arthritis, analogous to humans in age at onset, joint involvement and histologic changes, suggest that NHP are suitable for the study of human OA. Many similarities exist between female NHPs and women in age-related changes in reproductive function including hormone concentrations, menstrual cycling, fertility and the development of endometriosis. Changes in male sexual behavior and fertility with age are also comparable in men and male NHP. CONCLUSIONS: Genetic similarity, long lives and similar reproductive endocrinology suggest that NHPs are likely candidates as models of skeletal and reproductive aging in humans. Current data confirm that several species of NHP exhibit changes in bone and reproduction that are comparable to those known to occur in humans.

Aging↗

PubMed2006

Tonic activation of brain GnRH immunoreactivity despite reduction of peripheral reproductive parameters in opportunistically breeding zebra finches.

Opportunistically breeding species offer the unique opportunity to understand mechanisms in reproductive physiology that allow for extreme flexibility in the regulation of reproduction. We studied a well-known opportunistic breeder, the zebra finch (Taeniopygia guttata) to test the hypothesis that the reproductive axis of opportunists is in a constant state of 'near-readiness'. In wild zebra finches, reproduction is highly correlated with rainfall, and in the laboratory, water availability and humidity are the strongest cues to affect reproductive activation. We therefore subjected individuals to water restriction for eleven weeks followed by a two week period of ad libitum access to water. The control group had water freely available for the entire experiment. We measured the state of activation of the hypothalamo-pituitary gonad (HPG) axis at three levels: in the hypothalamus by measuring immunoreactive (ir) cGnRH-I and cGnRH-II; in the anterior pituitary gland by measuring plasma luteinizing hormone (LH); and in the gonads by measuring gonadal volume and function. We found that water restriction caused a reduction in circulating LH concentrations and that testis volume was more likely to decrease in water restricted than in control birds. Subsequent short-term return to ad libitum water availability caused LH to return to baseline in water restricted birds. These changes occurred without significant changes in ir-cGnRH-I, ir-cGnRH-II, or in testis function. These data suggest that in these opportunistic breeders, an inhibition of parts of the reproductive axis is not necessarily correlated with full inactivation of reproductive potential. GnRH-ir cells in the hypothalamus appear to remain active and able to respond to subsequent stimulation.

Analysis of Variance↗

PubMed1986

Lifetime reproductive success in female Japanese macaques.

Lifetime reproductive success, measured by the number of offspring surviving to age five, varied from 0 to 10 in a group of 33 provisioned female Japanese macaques. Of the three contributors to reproductive success, the number of reproductive years, fecundity per year and survivorship of offspring to reproductive age, the first accounted for two-thirds of the variation. Fecundity per year and survivorship were negatively correlated, indicating reproductive costs of reducing interbirth interval. No other demographic measure used, nor the behavioral measure 'dominance rank', significantly correlated with lifetime reproductive success or its components. Age-specific changes in fecundity and infant survival were not found for this sample, neither could cessation of reproduction, even in very old females, be demonstrated.

Aging↗

PubMed1996

Seasonal timing of reproduction in a tropical bird, the Seychelles warbler: a field experiment using translocation.

Reproduction of the Seychelles warbler (Acrocephalus sechellensis), a single-island endemic species living close to the equator, is characterized by a pronounced annual rhythm. The bird usually raises only one or two clutches of one egg each per year. Observational data suggest that seasonal changes in feeding conditions are an important proximate factor controlling reproduction. This hypothesis could be tested by transferring breeding pairs from Cousin Island to islands previously unoccupied at the same latitude. These islands, Aride and Cousine, have a higher food supply but similar vegetation and climate. After translocation to Aride Island, with high food availability year-round, individual breeding pairs prolonged their reproductive season (some bred year-round), increased the annual number of broods, and improved the reproductive success per nest-building attempt. Annual production of yearlings per pair on Aride was on average 23 times higher than that of the same pair on Cousin before the transfer. After translocation to Cousine Island, where food availability varied seasonally and was intermediate between Cousin and Aride, individual pairs increased the annual number of broods, but reproductive success per nest-building attempt remained the same. Annual production of yearlings per pair on Cousine was on average 5 times higher than that of the same pair on Cousin before the transfer. Thus the experiments, controlled for group size, breeding partner, breeder age, and experience, showed that food supply can be an important proximate factor in the timing of reproduction in the tropics. The differences in reproductive timing and success by warblers on the three islands are due not to genetic differences but entirely to differences in environmental conditions.

Animal Nutritional Physiological Phenomena↗

PubMed2024

Assessment the carrier frequency of monogenic diseases in populations requiring assisted reproductive technology.

PURPOSE: The objective of this study is to assess the carrier frequency and pathogenic variation of monogenetic diseases in a population of 114 subjects in Han Chinese from Hebei province who are undergoing assisted reproductive technology through the utilization of Expanded Carrier Screening (ECS). METHODS: The study utilized a panel consisting of 155 severe monogenic recessive genetic diseases for ECS. Next-generation sequencing technology was employed to identify specific variants associated with ECS in a cohort of 114 subjects from 97 couples, comprising 97 females and 17 male spouses. RESULTS: A total of 114 individuals received ECS. The carrier rate of pathogenic genes in the enrolled population was 44.74% (51/114). Among the 97 females, the carrier rate of pathogenic genes was higher in those without assisted reproduction indicators than in those with assisted reproduction indicators (59.09% vs. 41.33%). However, the carrier rate of pathogenic genes in males without assisted reproductive technology was slightly lower than that with assisted reproductive technology (40% vs. 41.67%). Among both female and male participants, the carrier rate of pathogenic genes between individuals without indicators of assisted reproduction and those with such indicators was 55.55% vs. 41.38%. In 51 carriers, 72.55% (37/51) carried one genetic variant, 25.49% (13/51) carried two genetic variants, and 1.96% (1/51) carried three genetic variants. A total of 38 pathogenic genes were detected in this study, and GJB2 and MMACHC were most common. The carrier rates of the two genes were both 5.26% (6/114). A total of 55 variations were detected, and c.235delC was most frequently found. The carrier rate was 3.51% (4/114). The incidence of couples carrying the same pathogenic genes was 1.03% (1/97). CONCLUSIONS: The findings elucidate the carrier rate of pathogenic genes among 155 severe monogenic recessive genetic diseases and underscore the significance of ECS as a preventive measure against congenital anomalies. When both partners carry the same genetic mutation for a monogenic disease, preventive strategies can be taken in offspring through preimplantation genetic testing (PGT), prenatal genetic testing, or the utilization of donor gametes. ECS is instrumental in assessing reproductive risk, guiding fertility-related decisions, and reducing the prevalence of monogenic recessive genetic disorders in subsequent generations.

Humans↗

PubMed2001

Longitudinal changes in reproductive hormones and menstrual cyclicity in cynomolgus monkeys during strenuous exercise training: abrupt transition to exercise-induced amenorrhea.

Cross-sectional studies of exercise-induced reproductive dysfunction have documented a high proportion of menstrual cycle disturbances in women involved in strenuous exercise training. However, longitudinal studies have been needed to examine individual susceptibility to exercise-induced reproductive dysfunction and to elucidate the progression of changes in reproductive function that occur with strenuous exercise training. Using the female cynomolgus monkey (Macaca fascicularis), we documented changes in menstrual cyclicity and patterns of LH, FSH, estradiol, and progesterone secretion as the animals developed exercise-induced amenorrhea. As monkeys gradually increased running to 12.3 +/- 0.9 km/day, body weight did not change significantly although food intake remained constant. The time spent training until amenorrhea developed varied widely among animals (7-24 months; mean = 14.3 +/- 2.2 months) and was not correlated with initial body weight, training distance, or food intake. Consistent changes in function of the reproductive axis occurred abruptly, one to two menstrual cycles before the development of amenorrhea. These included significant declines in plasma reproductive hormone concentrations, an increase in follicular phase length, and a decrease in luteal phase progesterone secretion. These data document a high level of interindividual variability in the development of exercise-induced reproductive dysfunction, delineate the progression of changes in reproductive hormone secretion that occur with exercise training, and illustrate an abrupt transition from normal cyclicity to an amenorrheic state in exercising individuals, that is not necessarily associated with weight loss.

Amenorrhea↗

PubMed2004

The bone morphogenetic protein system in mammalian reproduction.

Using molecular, cellular, and genetic approaches, recent studies examining the role of the bone morphogenetic protein (BMP) family of growth factors in the reproductive system have led to significant breakthroughs in our understanding of mammalian reproduction and fertility. Gene expression studies have revealed that key components of the BMP system (ligands, receptors, signaling molecules, and binding proteins) exhibit coordinated spatial and temporal expression patterns in fundamental cell types throughout the reproductive system. Availability of recombinant BMPs has enabled functional studies that have demonstrated important biological activities of BMPs in controlling cellular proliferation, differentiation, and apoptosis in reproductive tissues. The physiological importance of the BMP system for mammalian reproduction has been further highlighted by the elucidation of the aberrant reproductive phenotypes of animals with naturally occurring mutations or targeted deletions of certain BMP family genes. Collectively, these studies have established the concept that the BMP system plays a crucial role in fertility in female and male mammals. The purpose of this article is to review the evidence underpinning the importance of the BMP system in mammalian reproduction.

Animals↗

PubMed2003

Relationship between reproductive success and male plasma vitellogenin concentrations in cunner, Tautogolabrus adspersus.

The gene for vitellogenin, an egg yolk protein precursor, is usually silent in male fish but can be induced by estrogen exposure. For this reason, vitellogenin production in male fish has become a widely used indicator of exposure to exogenous estrogens or estrogen mimics in the aquatic environment. The utility of this indicator to predict impacts on fish reproductive success is unclear because information on the relationship between male plasma vitellogenin and reproductive end points in male and female fish is limited. In the research reported in this article, we investigated whether the presence of male plasma vitellogenin is a reliable indicator of decreased reproductive success in mature fish. Adult and sexually mature male and female cunner (Tautogolabrus adspersus) were exposed to 17ss-estradiol, ethynylestradiol, or estrone, three steroidal estrogens that elicit the vitellogenic response. Data were gathered and pooled on egg production, egg viability, egg fertility, sperm motility, and male plasma vitellogenin concentrations. All males, including two with plasma vitellogenin levels exceeding 300 mg/mL, produced motile sperm. Neither percent fertile eggs nor percent viable eggs produced by reproductively active fish demonstrated a significant correlation with male plasma vitellogenin concentrations. Male gonadosomatic index and average daily egg production by females showed significant, but weak, negative correlation with male plasma vitellogenin concentrations. Results suggest that male plasma vitellogenin expression is not a reliable indicator of male reproductive dysfunction in adult cunner exposed to estrogens for 2-8 weeks during their reproductive season, at least in relation to capacity to produce motile sperm or fertilize eggs. Male plasma vitellogenin expression may serve as an indicator of reduced female reproductive function caused by estrogen exposure.

Animals↗

PubMed1988

Male reproductive toxicology: comparison of the human to animal models.

The human male is of relatively low fertility and thus may be at greater risk from reproductive toxicants than are males of the common laboratory animal model species. Lack of knowledge of the physiological differences that contribute to interspecies variation between man and animals can prevent the effective application of animal data to the assessment of human reproductive risk. Evaluation of spermatogenesis from testicular histology, while uncommon, can provide valuable information about human reproductive risk. The measurement of sperm count or concentration has long been the most feasible approach for human semen evaluation, but may be an insensitive indicator of reproductive function because of high sample-to-sample variability. Interspecies extrapolation factors can be calculated by comparing the reduction in sperm count in humans and test species after exposure to drugs or chemicals. These factors can provide a realistic assessment of relative risk, provided that the sperm are counted at the appropriate time after exposure. However, the degree to which extrapolation factors derived for one agent, and only from sperm counts, can be generalized is not known. Monitoring of sperm motility and morphology parameters is also a common means of evaluating human semen quality, but these techniques are also hampered by the relatively high interindividual and intersample variability. Computer-assisted and morphometric approaches show promise of decreasing the subjective nature of these evaluations and increasing their value in risk assessment procedures. Improvements in predicting human reproductive risk can be expected to come from increased knowledge about reproductive mechanisms in man and animals, together with the utilization of objective measures of cellular indicators of male reproductive function.

Animals↗

PubMed1991

Selection of reproductive health end points for environmental risk assessment.

In addition to the challenges inherent in environmental health risk assessment, the study of reproductive health requires thorough consideration of the very definition of reproductive risk. Researchers have yet to determine which end points need to be considered to comprehensively evaluate a community's reproductive health. Several scientific issues should be considered in the selection of end points: the severity of the outcomes, with a trade-off between clinical severity and statistical or biological sensitivity; the relative sensitivity of different outcomes to environmental agents; the interrelationship among adverse outcomes; the baseline frequency of the adverse outcome; evidence from reproductive toxicology; and specificity of reproductive effects from the environmental agent. Simultaneously, practical concerns should be addressed: frequency of occurrence of an event and consequent statistical power to evaluate changes; frequency of prerequisites (e.g., pregnancy) that are necessary to be at risk; time and money resource requirements for measuring the outcome; amenability of the end point to retrospective measurement; and burden of measurement on the population being studied. In this article, we discuss these scientific and practical considerations and recommend that reproductive risk assessment include measures of fecundability (menstrual function, time to pregnancy), fetal loss (clinically recognized miscarriage), and infant health (birth weight, gestational age). Additional methodological research is needed to refine the array of reproductive health measures that need to be examined as a consequence of environmental exposures.

Environmental Exposure↗

PubMed2002

Insulin-like growth factor-I as a possible hormonal mediator of nutritional regulation of reproduction in cattle.

The current review aims to establish insulin-like growth factor-1 (IGF-I) as the factor that signals nutritional status to the reproductive axis, and show that assessment of IGF-I in blood early postpartum during the negative energy balance (NEB) period could be used to predict both nutritional and reproductive status in dairy cattle. The review also explores the effect of nutritional status on circulating IGF-I concentrations and the endocrine role of IGF-I on the reproductive axis. IGF-I plays an important role in gonadotropin-induced folliculogenesis, ovarian steroidogenesis and corpus luteum (CL) function. It also modulates pituitary and hypothalamus function. IGF-I clearly has an endocrine role on the reproductive axis. Severe under nutrition significantly reduces plasma IGF-I concentrations. During the critical period of NEB in high yielding dairy cattle early postpartum, IGF-I concentrations are low in blood and its levels are positively correlated to energy status and reproductive function during this period. Changes in circulating IGF-I immediately postpartum may help predict both nutritional and reproductive status in dairy cattle. IGF-I is therefore one of the long sought factors that signal nutritional status to the reproductive axis.

Animal Nutritional Physiological Phenomena↗