Epigenetic control of development and expression of quantitative traits

DNA methylation profile in beef cattle is influenced by additive genetics and age

DNA methylation (DNAm) has been considered a promising indicator of biological age in mammals and could be useful to increase the accuracy of phenotypic prediction in livestock. The objectives of this study were to estimate the heritability and age effects of site-specific DNAm (DNAm level) and cumulative DNAm across all sites (DNAm load) in beef cattle. Blood samples were collected from cows ranging from 217 to 3,192 days (0.6 to 8.7 years) of age (n = 136). All animals were genotyped, and DNAm was obtained using the Infinium array HorvathMammalMethylChip40. Genetic parameters for DNAm were obtained from an animal model based on the genomic relationship matrix, including the fixed effects of age and breed composition. Heritability estimates of DNAm levels ranged from 0.18 to 0.72, with a similar average across all regions and chromosomes. Heritability estimate of DNAm load was 0.45. The average age effect on DNAm level varied among genomic regions. The DNAm level across the genome increased with age in the promoter and 5′ UTR and decreased in the exonic, intronic, 3′ UTR, and intergenic regions. In addition, DNAm level increased with age in regions enriched in CpG and decreased in regions deficient in CpG. Results suggest DNAm profiles are influenced by both genetics and the environmental effect of age in beef cattle.

Chicken embryo as a model in epigenetic research

Epigenetics is defined as the study of changes in gene function that are mitotically or meiotically heritable and do not lead to a change in DNA sequence. Epigenetic modifications are important mechanisms that fine tune the expression of genes in response to extracellular signals and environmental changes. In vertebrates, crucial epigenetic reprogramming events occur during early embryogenesis and germ cell development. Chicken embryo, which develops external to the mother's body, can be easily manipulated in vivo and in vitro, and hence, it is an excellent model for performing epigenetic studies. Environmental factors such as temperature can affect the development of an embryo into the phenotype of an adult. A better understanding of the environmental impact on embryo development can be achieved by analyzing the direct effects of epigenetic modifications as well as their molecular background and their intergenerational and transgenerational inheritance. In this overview, the current possibility of epigenetic changes during chicken embryonic development and their effects on long-term postembryonic development are discussed.

Genetic potential for residual feed intake and diet fed during early- to mid-gestation influences post-natal DNA methylation of imprinted genes in muscle and liver tissues in beef cattle

Discovery of epigenetic modifications associated with feed efficiency or other economically important traits would increase our understanding of the molecular mechanisms underlying these traits. In combination with known genetic markers, this would provide opportunity to improve genomic selection accuracy in cattle breeding programs. It would also allow cattle to be managed to improve favorable gene expression. The objective of this study was to identify variation in DNA methylation between beef cattle of differential pre-natal nutrition and divergent genetic potential for residual feed intake (RFI). Purebred Angus offspring with the genetic potential for either high (HRFI) or low (LRFI) RFI were prenatally exposed to either a restricted maternal diet of 0.5 kg/d average daily gain (ADG) or a moderate maternal diet of 0.7 kg/d ADG from 30 to 150 d of gestation. We performed DNA methylation analysis of differentially methylated regions (DMR) of imprinted genes (Insulin-like growth factor 2 (IGF2) DMR2, IGF2/H19 imprinting control region (ICR) and IGF2 receptor (IGF2R) DMR2) using post-natal samples of longissimus dorsi (LD) muscle taken from male and female calves at birth and weaning, and of LD muscle, semimembranosus (SM) muscle, and liver samples collected from steers at slaughter (17 months of age). Interestingly, for all three DMR investigated in liver, LRFI steers had higher levels of methylation than HRFI steers. In LD muscle, IGF2/H19 ICR methylation differences for heifers at birth were due to pre-natal diet, while for steers at birth they were mostly the result of genetic potential for RFI with LRFI steers again having higher levels of methylation than HRFI steers. While results from repeated measures analysis of DNA methylation in steers grouped by RFI revealed few differences, in steers grouped by diet, we found higher methylation levels of IGF2 DMR2 and IGF2R DMR2 in LD muscle of restricted diet steers at weaning and slaughter than at birth, as well as increased methylation in LD muscle of restricted diet steers compared with moderate diet steers at weaning and/or slaughter. Our results suggest that differential pre-natal nutrition, and divergent genetic potential for RFI, induces tissue- and sex-specific alterations in post-natal IGF2 and IGF2R methylation patterns and that these patterns can vary with age in Angus beef cattle.

Nutrition of Broodmares

Forage availability should cover most needs for mares bred during spring and summer. Out-of-season breeding, lack of access to pasture, or good quality forage calls for nutritional supplementation. Current evaluations of broodmare needs are based on fetoplacental tissue requirements, but do not consider endocrine changes or that the maternal diet quality affects long-term foal health. This article reviews pregnant mares' current nutritional recommendations. Secondly, fetoplacental developmental stages during gestation are outlined, defining critical periods in the context of the developmental origins of health and disease. Last, examples of how maternal nutrition affects long-term foal health are presented.

Exposure of zebrafish to elevated temperature induces sex ratio shifts and alterations in the testicular epigenome of unexposed offspring

Accumulating evidence shows that environmental changes can affect population sex ratios through epigenetic regulation of gene expression in species where sex depends on both genetic and environmental cues. Sometimes, altered sex ratios persist in the next generation even when the environmental cue is no longer present (a multigenerational effect). However, evidence of transgenerational effects (i.e., beyond the first non-exposed generation), which tend to be paternally transmitted, is scarce and a matter of debate. Here, we used the AB strain of zebrafish, where sex depends on both genetic and environmental influences, to study possible multi- (to the F₁) and transgenerational (to the F₂) effects of elevated temperature during the critical period of sex differentiation. From eight initial different families, five were selected in order to capture sufficient variation between the sex ratio of the control group (28 °C) and the group exposed to elevated (35 °C) temperature only at the parental (P) generation. Results showed a consistent increase in the proportion of males in the P generation in all five families as a result of heat treatment. Sex ratios were then determined in the F₁ and F₂ offspring derived from both above groups, which were all raised at 28 °C. A persisting male-skewed sex ratio in the 35°C-derived, unexposed offspring of the F₁ generation was observed in three families, denoting family-dependent multigenerational effects. However, no transgenerational effects were observed in the F₂ generation of any family. DNA methylation was also assessed in the testis of P, F₁ and F₂ males derived from exposed and non-exposed fathers and grandfathers. DNA methylation was significantly decreased only in the testis of the 35°C-derived males in the F₁ generation but not of the F₂ generation and, surprisingly, neither in the 35°C-exposed males of the P generation. Taken together, our results show great interfamily variation, not only in sex ratio response to elevated temperature, but also on its multigenerational effects, denoting a strong influence of genetics. Alterations in the testicular epigenome in F₁ males calls for attention to possible, previously unnoticed, effects of temperature in the unexposed offspring of heat-exposed parents in a global warming scenario.

Embryonic Exposure to Bisphenol A Impairs Primordial Germ Cell Migration without Jeopardizing Male Breeding Capacity

A large amount of chemicals are released to the environment each year. Among them, bisphenol A (BPA) is of utmost concern since it interferes with the reproductive system of wild organisms due to its capacity to bind to hormone receptors. Additionally, BPA epigenotoxic activity is known to affect basic processes during embryonic life. However, its effects on primordial germ cells (PGCs) proliferation and migration, both mechanisms being crucial for gametogenesis, remain unknown. To investigate the effects of BPA on PGCs migration and eventual testicle development, zebrafish embryos were exposed to 100, 2000 and 4000 µg/L BPA during the first 24 h of development. Vasa immunostaining of PGCs revealed that exposure to 2000 and 4000 µg/L BPA impaired their migration to the genital ridge. Two pivotal genes of PGCs migration (cxcr4b and sdf1a) were highly dysregulated in embryos exposed to these doses, whereas DNA methylation and epigenetic marks in PGCs and their surrounding somatic cells were not altered. Once embryos reached adulthood, the morphometric study of their gonads revealed that, despite the reduced number of PGCs which colonized the genital ridges, normal testicles were developed. Although H3K9ac decreased in the sperm from treated fishes, it did not affect the progeny development.

A note on transgenerational epigenetics affecting egg quality traits in meat-type quail

1. The aim of the following experiment was to estimate transgenerational epigenetic variance for egg quality traits using genealogical and phenotypic information in meat-type quail. Measured traits included egg length (EL) and width (EWD), albumen weight (AW), shell weight (SW), yolk weight (YW) and egg weight (EW). 2. A total of 391 birds were evaluated for egg quality by collecting a sample of one egg per bird, during three consecutive days, starting on the 14th d of production. Analyses were performed using mixed models including the random epigenetic effect. Variance components were estimated by the restricted maximum likelihood method. A grid-search for values for the auto-recursive parameter (λ) was used in the variance components estimation. This parameter is directly related to the reset (v) and epigenetic transmissibility (1 - v) coefficients. 3. The epigenetic effect was not significant for any of the egg quality traits evaluated. Direct heritability estimates for egg quality traits ranged in magnitude from 0.06 to 0.33, whereby the higher estimates were found for AW and SW. Epigenetic heritability estimates were low and close to zero (ranging from 0.00 to 0.07) for all evaluated traits. 4. The current breeding strategies accounting for additive genetic effect seem to be suitable for egg quality traits in meat-type quail.

Review: Epigenetics, developmental programming and nutrition in herbivores

Epidemiological studies in humans and animal models (including ruminants and horses) have highlighted the critical role of nutrition on developmental programming. Indeed, it has been demonstrated that the nutritional environment during the periconceptional period and foetal development can altered the postnatal performance of the resultant offspring. This nutritional programming can be exerted by maternal and paternal lineages and can affect offspring beyond the F1 generation. Alterations in epigenetic mechanisms have been proposed as the causative link behind the programming trajectories observed in the offspring. Although a clear cause-effect relationship between epigenetic modifications during early development and later offspring phenotype has not been demonstrated in livestock species, strong associations have been reported for some epigenetic marks (e.g. messenger RNA) that are worth exploring as possible predictors of future offspring phenotype. In this review, we shortly describe the main epigenetic mechanisms studied so far in mammals (i.e. mainly in the mouse) thought to be associated with developmental programming, and discuss the few studies available in mammalian herbivores (e.g. cattle) showing the effect of nutrition on epigenetic marks and the associated phenotype. Clearly, there is a need to develop research on nutritional strategies capable of modulating the epigenetic machinery with positive influence on the phenotype of livestock herbivores. This type of research is needed to alleviate the challenges currently faced by the livestock industry (e.g. impaired fertility of high-yielding dairy cows). This in turn will have a positive influence on animal welfare and productivity of livestock enterprises.

Use of canonical discriminant analysis to study signatures of selection in cattle

BACKGROUND

Cattle include a large number of breeds that are characterized by marked phenotypic differences and thus constitute a valuable model to study genome evolution in response to processes such as selection and domestication. Detection of "signatures of selection" is a useful approach to study the evolutionary pressures experienced throughout history. In the present study, signatures of selection were investigated in five cattle breeds farmed in Italy using a multivariate approach.

METHODS

A total of 4094 bulls from five breeds with different production aptitudes (two dairy breeds: Italian Holstein and Italian Brown Swiss; two beef breeds: Piemontese and Marchigiana; and one dual purpose breed: Italian Simmental) were genotyped using the Illumina BovineSNP50 v.1 beadchip. Canonical discriminant analysis was carried out on the matrix of single nucleotide polymorphisms (SNP) genotyping data, separately for each chromosome. Scores for each canonical variable were calculated and then plotted in the canonical space to quantify the distance between breeds. SNPs for which the correlation with the canonical variable was in the 99th percentile for a specific chromosome were considered to be significantly associated with that variable. Results were compared with those obtained using an FST-based approach.

RESULTS

Based on the results of the canonical discriminant analysis, a large number of signatures of selection were detected, among which several had strong signals in genomic regions that harbour genes known to have an impact on production and morphological bovine traits, including MSTN, LCT, GHR, SCD, NCAPG, KIT, and ASIP. Moreover, new putative candidate genes were identified, such as GCK, B3GALNT1, MGAT1, GALNTL1, PRNP, and PRND. Similar results were obtained with the FST-based approach.

CONCLUSIONS

The use of canonical discriminant analysis on 50 K SNP genotypes allowed the extraction of new variables that maximize the separation between breeds. This approach is quite straightforward, it can compare more than two groups simultaneously, and relative distances between breeds can be visualized. The genes that were highlighted in the canonical discriminant analysis were in concordance with those obtained using the FST index.

Influence of grand-mother diet on offspring performances through the male line in Muscovy duck

Background

In mammals, multigenerational environmental effects have been documented by either epidemiological studies in human or animal experiments in rodents. Whether such phenomena also occur in birds for more than one generation is still an open question. The objective of this study was to investigate if a methionine deficiency experienced by a mother (G0) could affect her grand-offspring phenotypes (G2 hybrid mule ducks and G2 purebred Muscovy ducks), through their Muscovy sons (G1). Muscovy drakes are used for the production of mule ducks, which are sterile offspring of female common duck (Anas platyrhynchos) and Muscovy drakes (Cairina moschata). In France, mule ducks are bred mainly for the production of “foie gras”, which stems from hepatic steatosis under two weeks of force-feeding (FF). Two groups of female Muscovy ducks received either a methionine deficient diet or a control diet. Their sons were mated to Muscovy or to common duck females to produce Muscovy or Mule ducks, respectively. Several traits were measured in the G2 progenies, concerning growth, feed efficiency during FF, body composition after FF, and quality of foie gras and magret.

Results

In the G2 mule duck progeny, grand-maternal methionine deficiency (GMMD) decreased 4, 8, and 12 week body weights but increased weight gain and feed efficiency during FF, and abdominal fat weight. The plasmatic glucose and triglyceride contents at the end of FF were higher in the methionine deficient group. In the G2 purebred Muscovy progeny, GMMD tended to decrease 4 week body weight in both sexes, and decreased weight gain between the ages of 4 and 12 weeks, 12 week body weight, and body weight at the end of FF in male offspring only. GMMD tended to increase liver weight and increased the carcass proportion of liver in both sexes.

Conclusion

Altogether, these results show that the mother’s diet is able to affect traits linked to growth and to lipid metabolism in the offspring of her sons, in Muscovy ducks. Whether this transmission through the father of information induced in the grand-mother by the environment is epigenetic remains to be demonstrated.

Electronic supplementary material

The online version of this article (doi:10.1186/s12863-015-0303-z) contains supplementary material, which is available to authorized users.

Epigenetic marks: regulators of livestock phenotypes and conceivable sources of missing variation in livestock improvement programs

Improvement in animal productivity has been achieved over the years through careful breeding and selection programs. Today, variations in the genome are gaining increasing importance in livestock improvement strategies. Genomic information alone, however, explains only a part of the phenotypic variance in traits. It is likely that a portion of the unaccounted variance is embedded in the epigenome. The epigenome encompasses epigenetic marks such as DNA methylation, histone tail modifications, chromatin remodeling, and other molecules that can transmit epigenetic information such as non-coding RNA species. Epigenetic factors respond to external or internal environmental cues such as nutrition, pathogens, and climate, and have the ability to change gene expression leading to emergence of specific phenotypes. Accumulating evidence shows that epigenetic marks influence gene expression and phenotypic outcome in livestock species. This review examines available evidence of the influence of epigenetic marks on livestock (cattle, sheep, goat, and pig) traits and discusses the potential for consideration of epigenetic markers in livestock improvement programs. However, epigenetic research activities on farm animal species are currently limited partly due to lack of recognition, funding and a global network of researchers. Therefore, considerable less attention has been given to epigenetic research in livestock species in comparison to extensive work in humans and model organisms. Elucidating therefore the epigenetic determinants of animal diseases and complex traits may represent one of the principal challenges to use epigenetic markers for further improvement of animal productivity.

Placental contribution to nutritional programming of health and diseases: epigenetics and sexual dimorphism

The recent and rapid worldwide increase in non-communicable diseases challenges the assumption that genetic factors are the primary contributors to such diseases. A new concept of the ‘developmental origins of health and disease’ (DOHaD) is at stake and therefore requires a paradigm shift. Maternal obesity and malnutrition predispose offspring to develop metabolic syndrome, a vicious cycle leading to transmission to subsequent generation(s), with differences in response and susceptibility according to the sex of the individual. The placenta is a programming agent of adult health and disease. Adaptations of placental phenotype in response to maternal diet and metabolic status alter fetal nutrient supply. This implies important epigenetic changes that are, however, still poorly documented in DOHaD studies, particularly concerning overnutrition. The aim of this review is to discuss the emerging knowledge on the relationships between the effect of maternal nutrition or metabolic status on placental function and the risk of diseases later in life, with a specific focus on epigenetic mechanisms and sexual dimorphism. Explaining the sex-specific causal variables and how males versus females respond and adapt to environmental perturbations should help physicians and patients to anticipate disease susceptibility.

Birth weight, intrauterine growth retardation and fetal susceptibility to porcine reproductive and respiratory syndrome virus

The severity of porcine reproductive and respiratory syndrome was compared in pregnant gilts originating from high and low birth weight litters. One-hundred and eleven pregnant gilts experimentally infected with porcine reproductive and respiratory syndrome virus on gestation day 85 (±1) were necropsied along with their fetuses 21 days later. Ovulation rates and litter size did not differ between groups, but fetuses from low birth weight gilts were shorter, lighter and demonstrated evidence of asymmetric growth with large brain:organ weight ratios (i.e. brain sparing). The number of intrauterine growth retarded fetuses, defined by brain:organ weight ratios greater than 1 standard deviation from the mean, was significantly greater in low, compared to high, birth weight gilts. Although γδ T cells significantly decreased over time in high compared to low birth weight gilts, viral load in serum and tissues, gilt serum cytokine levels, and litter outcome, including the percent dead fetuses per litter, did not differ by birth weight group. Thus, this study provided no substantive evidence that the severity of porcine reproductive and respiratory syndrome is affected by dam birth weight. However, intrauterine growth retarded fetuses had lower viral loads in both fetal thymus and in endometrium adjacent to the umbilical stump. Crown rump length did not significantly differ between fetuses that survived and those that died at least one week prior to termination. Taken together, this study clearly demonstrates that birth weight is a transgenerational trait in pigs, and provides evidence that larger fetuses are more susceptible to transplacental PRRSv infection.

Forty years of embryo transfer in cattle: a review focusing on the journal Theriogenology, the growth of the industry in North America, and personal reminisces

After the first successful transfer of mammalian embryos in 1890, it was approximately 60 years before significant progress was reported in the basic technology of embryo transfer (ET) in cattle. Starting in the early 1970s, technology had progressed sufficiently to support the founding of commercial ET programs in several countries. Today, well-established and reliable techniques involving superovulation, embryo recovery and transfer, cryopreservation, and IVF are utilized worldwide in hundreds, if not thousands, of commercial businesses located in many countries. The mean number of embryos produced via superovulation has changed little in 40 years, but there have been improvements in synchrony and hormonal protocols. Cryopreservation of in vivo-derived embryos is a reliable procedure, but improvements are needed for biopsied and in vitro-derived embryos. High pregnancy rates are achieved when good quality embryos are transferred into suitable recipients and low pregnancy rates are often owing to problems in recipient management and not technology per se. In the future, unanticipated disease outbreaks and the ever-changing economics of cattle and milk prices will continue to influence the ET industry. The issue of abnormal pregnancies involving in vitro embryos has not been satisfactorily resolved and the involvement of abnormal epigenetics associate with this technology merits continued research. Last, genomic testing of bovine embryos is likely to be available in the foreseeable future. This may markedly decrease the number of embryos that are actually transferred and stimulate the evolution of more sophisticated ET businesses.

Early detection and staging of spontaneous embryo resorption by ultrasound biomicroscopy in murine pregnancy

BACKGROUND

Embryo resorption is a major problem in human medicine, agricultural animal production and in conservation breeding programs. Underlying mechanisms have been investigated in the well characterised mouse model. However, post mortem studies are limited by the rapid disintegration of embryonic structures. A method to reliably identify embryo resorption in alive animals has not been established yet. In our study we aim to detect embryos undergoing resorption in vivo at the earliest possible stage by ultra-high frequency ultrasound.

METHODS

In a longitudinal study, we monitored 30 pregnancies of wild type C57BI/6 mice using ultra-high frequency ultrasound (30-70 MHz), so called ultrasound biomicroscopy (UBM). We compared the sonoembryology of mouse conceptuses under spontaneous resorption and neighbouring healthy conceptuses and correlated the live ultrasound data with the respective histology.

RESULTS

The process of embryo resorption comprised of four stages: first, the conceptus exhibited growth retardation, second, bradycardia and pericardial edema were observed, third, further development ceased and the embryo died, and finally embryo remnants were resorbed by maternal immune cells. In early gestation (day 7 and 8), growth retardation was characterized by a small embryonic cavity. The embryo and its membranes were ill defined or did not develop at all. The echodensity of the embryonic fluid increased and within one to two days, the embryo and its cavity disappeared and was transformed into echodense tissue surrounded by fluid filled caverns. In corresponding histologic preparations, fibrinoid material interspersed with maternal granulocytes and lacunae filled with maternal blood were observed. In later stages (day 9-11) resorption prone embryos were one day behind in their development compared to their normal siblings. The space between Reichert's membrane and inner yolk sac membrane was enlarged The growth retarded embryos exhibited bradycardia and ultimately cessation of heart beat. Corresponding histology showed apoptotic cells in the embryo while the placenta was still intact. In the subsequent resorption process first the embryo and then its membranes disappeared.

CONCLUSIONS

Our results provide a temporal time course of embryo resorption. With this method, animals exhibiting embryo resorption can be targeted, enabling the investigation of underlying mechanisms before the onset of total embryo disintegration.

Histone post-translational modifications in preimplantation mouse embryos and their role in nuclear architecture

In mammals, epigenetic modifications are globally rearranged after fertilization, when gametes fuse to form the embryo. While gametes carry special epigenetic signatures and a unique nuclear organization, they attain embryo-specific patterns after fertilization. This "reprogramming" is promoted by intimate contact between the parental inherited genomes and the oocyte cytoplasm over the first cell cycles of development. Although the mechanisms of this reprogramming remain poorly understood, it appears that the particular epigenetic landscape established after fertilization is essential for further development. This review looks at histone post-translational modifications, focusing on their functions in chromatin organization and their role in nuclear architecture during mouse embryonic development. Epigenetic changes linked to the use of assisted reproductive technologies are also considered.

Epigenetics and phenotypic variability: some interesting insights from birds

Little is known about epigenetic mechanisms in birds with the exception of the phenomenon of dosage compensation of sex chromosomes, although such mechanisms could be involved in the phenotypic variability of birds, as in several livestock species. This paper reviews the literature on epigenetic mechanisms that could contribute significantly to trait variability in birds, and compares the results to the existing knowledge of epigenetic mechanisms in mammals. The main issues addressed in this paper are: (1) Does genomic imprinting exist in birds? (2) How does the embryonic environment influence the adult phenotype in avian species? (3) Does the embryonic environment have an impact on phenotypic variability across several successive generations? The potential for epigenetic studies to improve the performance of individual animals through the implementation of limited changes in breeding conditions or the addition of new parameters in selection models is still an open question.

Hosting the preimplantation embryo: potentials and limitations of different approaches for analysing embryo - endometrium interactions in cattle

Ongoing detailed investigations into embryo–maternal communication before implantation reveal that during early embryonic development a plethora of events are taking place. During the sexual cycle, remodelling and differentiation processes in the endometrium are controlled by ovarian hormones, mainly progesterone, to provide a suitable environment for establishment of pregnancy. In addition, embryonic signalling molecules initiate further sequences of events; of these molecules, prostaglandins are discussed herein as specifically important. Inadequate receptivity may impede preimplantation development and implantation, leading to embryonic losses. Because there are multiple factors affecting fertility, receptivity is difficult to comprehend. This review addresses different models and methods that are currently used and discusses their respective potentials and limitations in distinguishing key messages out of molecular twitter. Transcriptome, proteome and metabolome analyses generate comprehensive information and provide starting points for hypotheses, which need to be substantiated using further confirmatory methods. Appropriate in vivo and in vitro models are needed to disentangle the effects of participating factors in the embryo–maternal dialogue and to help distinguish associations from causalities. One interesting model is the study of somatic cell nuclear transfer embryos in normal recipient heifers. A multidisciplinary approach is needed to properly assess the importance of the uterine milieu for embryonic development and to use the large number of new findings to solve long-standing issues regarding fertility.

Cytoplasmic inheritance redux

Since the early twentieth century, inheritance was seen as the inheritance of genes. Concurrent with the acceptance of the genetic theory of inheritance was the rejection of the idea that the cytoplasm of the oocyte could also play a role in inheritance and a corresponding devaluation of embryology as a discipline critical for understanding human development. Development, and variation in development, came to be viewed solely as matters of genetic inheritance and genetic variation. We now know that inheritance is a matter of both genetic and cytoplasmic inheritance. A growing awareness of the centrality of the cytoplasm in explaining both human development and phenotypic variation has been promoted by two contemporaneous developments: the continuing elaboration of the molecular mechanisms of epigenetics and the global rise of artificial reproductive technologies. I review recent developments in the ongoing elaboration of the role of the cytoplasm in human inheritance and development.

Humans, fruit flies, and automatons

My response is divided into four sections: (1) is devoted to a potpourri of commentaries that are essentially in agreement with the substance of my target article (with one exception); in (2) I address, in response to one of the commentaries, several issues relating to the use of candidate gene association studies in behavior genetics (in particular those proposing a specific G×E interaction); in (3) I provide a detailed response to several defenses of the twin study methodology; and in (4) I conclude with several reflections on that methodology and the conception of human nature it has fostered.

Integrative control of energy balance and reproduction in females

There is a strong association between nutrition and reproduction. Chronic dietary energy deficits as well as energy surpluses can impair reproductive capacity. Metabolic status impacts reproductive function at systemic level, modulating the hypothalamic GnRH neuronal network and/or the pituitary gonadotropin secretion through several hormones and neuropeptides, and at the ovarian level, acting through the regulation of follicle growth and steroidogenesis by means of the growth hormone-IGF-insulin system and local ovarian mediators. In the past years, several hormones and neuropeptides have been emerging as important mediators between energy balance and reproduction. The present review goes over the main sites implicated in the control of energy balance linked to reproductive success and summarizes the most important metabolic and neuroendocrine signals that participate in reproductive events with special emphasis on the role of recently discovered neuroendocrine peptides. Also, a little overview about the effects of maternal nutrition, affecting offspring reproduction, has been presented.

Growth and insulin dynamics in two generations of female offspring of mothers receiving a single course of synthetic glucocorticoids

OBJECTIVE

Synthetic glucocorticoid administration to women threatening preterm delivery increases neonatal survival. However, mounting evidence shows that fetal exposure to glucocorticoid levels higher than appropriate for current maturation adversely programs offspring development. We examined fetal synthetic glucocorticoid multigenerational metabolic effects on F1 and F2 female offspring.

STUDY DESIGN

At 0.7 gestation, pregnant F0 ewes received 4 injections of dexamethasone (2 mg, approximately 60 ug.kg(-1) day(-1) 12 hours apart) or saline (control). F1 female offspring were bred to produce F2 female offspring. Postpubertal pancreatic β-cell function was tested in F1 and F2 by intravenous glucose tolerance test.

RESULTS

F1 and F2 ewe lambs showed reduced birthweight and morphometrics, and similar increased fasting glucose and decreased intravenous glucose tolerance test β-cell response.

CONCLUSION

This is the first demonstration of multigenerational programming of later life β-cell response by clinically relevant doses of synthetic glucocorticoid indicating the need for study of long-term effects of fetal exposure to synthetic glucocorticoid.

Novel aspects of endometrial function: a biological sensor of embryo quality and driver of pregnancy success

Successful pregnancy depends on complex biological processes that are regulated temporally and spatially throughout gestation. The molecular basis of these processes have been examined in relation to gamete quality, early blastocyst development and placental function, and data have been generated showing perturbations of these developmental stages by environmental insults or embryo biotechnologies. The developmental period falling between the entry of the blastocyst into the uterine cavity to implantation has also been examined in terms of the biological function of the endometrium. Indeed several mechanisms underlying uterine receptivity, controlled by maternal factors, and the maternal recognition of pregnancy, requiring conceptus-produced signals, have been clarified. Nevertheless, recent data based on experimental perturbations have unveiled unexpected biological properties of the endometrium (sensor/driver) that make this tissue a dynamic and reactive entity. Persistent or transient modifications in organisation and functionality of the endometrium can dramatically affect pre-implantation embryo trajectory through epigenetic alterations with lasting consequences on later stages of pregnancy, including placentation, fetal development, pregnancy outcome and post-natal health. Developing diagnostic and prognostic tools based on endometrial factors may enable the assessment of maternal reproductive capacity and/or the developmental potential of the embryo, particularly when assisted reproductive technologies are applied.

Evidence for similar changes in offspring phenotype following either maternal undernutrition or overnutrition: potential impact on fetal epigenetic mechanisms

The goal of this review is to shed light on the role of maternal malnutrition in inducing epigenetic changes in gene expression, leading to alterations in fetal growth and development, and to altered postnatal phenotype and the development of metabolic disease. We present evidence supporting the concept that both maternal undernutrition and overnutrition can induce the same cadre of fetal organ and tissue abnormalities and lead to the same postnatal metabolic changes in the resulting offspring. Furthermore, we present evidence that in both overnourished and undernourished ovine pregnancies, fetuses experience a period of nutrient restriction as a result of alterations in placental delivery of maternal nutrients into the fetal compartment. We argue that this bout of reduced fetal nutrition in undernourished and overnourished pregnancies leads to the development of a thrifty phenotype in which the fetus attempts to alter the function of its tissues and organs to maximise its chances of survival in a postnatal environment that is deficient in nutrients. Importantly, we present evidence to support the concept that these phenotypic changes in offspring quality resulting from maternal malnutrition are transmitted to subsequent generations, independent of their maternal nutritional inputs.