Ancestral paternal genotype controls body weight and food intake for multiple generations

Khdc3 Regulates Metabolism Across Generations in a DNA-Independent Manner

Genetic variants can alter the profile of heritable molecules such as small RNAs in sperm and oocytes, and in this manner ancestral genetic variants can have a significant effect on offspring phenotypes even if they are not themselves inherited. Here we show that wild type female mice descended from ancestors with a mutation in the mammalian germ cell gene Khdc3 have hepatic metabolic defects that persist over multiple generations. We find that genetically wild type females descended from Khdc3 mutants have transcriptional dysregulation of critical hepatic metabolic genes, which persist over multiple generations and pass through both female and male lineages. This was associated with dysregulation of hepatically-metabolized molecules in the blood of these wild type mice with mutational ancestry. The oocytes of Khdc3-null females, as well as their wild type descendants, had dysregulation of multiple small RNAs, suggesting that these epigenetic changes in the gametes transmit the phenotype between generations. Our results demonstrate that ancestral mutation in Khdc3 can produce transgenerational inherited phenotypes, potentially indefinitely.

Allograft inflammatory factor-1-like is a situational regulator of leptin levels, hyperphagia, and obesity

Mouse models enable the study of genetic factors affecting the complex pathophysiology of metabolic disorders. Here, we identify reductions in leptin levels, food intake, and obesity due to high-fat diet, accompanied by increased leptin sensitivity, in mice that harbor the E2a-Cre transgene within Obrq2, an obesity quantitative trait locus (QTL) that includes the leptin gene. Interestingly, loss of allograft inflammatory factor-1-like (AIF1L) protein in these transgenic mice leads to similar leptin sensitivity, yet marked reversal of the obesity phenotype, with accelerated weight gain and increased food intake. Transgenic mice lacking AIF1L also have low circulating leptin, which suggests that benefits of enhanced leptin sensitivity are lost with further impairment of leptin expression due to loss of AIF1L. Together, our results identify AIF1L as a genetic modifier of Obrq2 and leptin that affects leptin levels, food intake, and obesity during the metabolic stress imposed by HFD.

Effects of non-inherited ancestral genotypes on offspring phenotypes

It is well established that environmental exposures can modify the profile of heritable factors in an individual's germ cells, ultimately affecting the inheritance of phenotypes in descendants. Similar to exposures, an ancestor's genotype can also affect the inheritance of phenotypes across generations, sometimes in offspring who do not inherit the genetic aberration. This can occur via a variety of prenatal, in utero, or postnatal mechanisms. In this review, we discuss the evidence for this process in mammals, with a focus on examples that are potentially mediated through the germline, while also considering alternate routes of inheritance. Non-inherited ancestral genotypes may influence descendant's disease risk to a much greater extent than currently appreciated, and focused evaluation of this phenomenon may reveal novel mechanisms of inheritance.

Genetic control of non-genetic inheritance in mammals: state-of-the-art and perspectives

Thought to be directly and uniquely dependent from genotypes, the ontogeny of individual phenotypes is much more complicated. Individual genetics, environmental exposures, and their interaction are the three main determinants of individual's phenotype. This picture has been further complicated a decade ago when the Lamarckian theory of acquired inheritance has been rekindled with the discovery of epigenetic inheritance, according to which acquired phenotypes can be transmitted through fertilization and affect phenotypes across generations. The results of Genome-Wide Association Studies have also highlighted a big degree of missing heritability in genetics and have provided hints that not only acquired phenotypes, but also individual's genotypes affect phenotypes intergenerationally through indirect genetic effects. Here, we review available examples of indirect genetic effects in mammals, what is known of the underlying molecular mechanisms and their potential impact for our understanding of missing heritability, phenotypic variation. and individual disease risk.

Germline-dependent transmission of male reproductive traits induced by an endocrine disruptor, di-2-ethylhexyl phthalate, in future generations

In males, defective reproductive traits induced by an exposure to an endocrine disruptor are transmitted to future generations via epigenetic modification of the germ cells. Interestingly, the impacted future generations display a wide range of heterogeneity in their reproductive traits. In this study, the role that the Y chromosome plays in creating such heterogeneity is explored by testing the hypothesis that the Y chromosome serves as a carrier of the exposure impact to future generations. This hypothesis implies that a male who has a Y chromosome that is from a male that was exposed to an endocrine disruptor will display a more severe reproductive phenotype than a male whose Y chromosome is from an unexposed male. To test this hypothesis, we used a mouse model in which F1 generation animals were exposed prenatally to an endocrine disruptor, di-2-ethylhexyl phthalate (DEHP), and the severity of impacted reproductive traits was compared between the F3 generation males that were descendants of F1 males (paternal lineage) and those from F1 females (maternal lineage). Pregnant dams (F0 generation) were exposed to the vehicle or 20 or 200 μg/kg/day of DEHP from gestation day 11 until birth. Paternal lineage F3 DEHP males exhibited decreased fertility, testicular steroidogenic capacity, and spermatogenesis that were more severely impaired than those of maternal lineage males. Indeed, testicular transcriptome analysis found that a number of Y chromosomal genes had altered expression patterns in the paternal lineage males. This transgenerational difference in the DEHP impact can be attributed specifically to the Y chromosome.

Intergenerational transmission of paternal trauma among US Civil War ex-POWs

We study whether paternal trauma is transmitted to the children of survivors of Confederate prisoner of war (POW) camps during the US Civil War (1861-1865) to affect their longevity at older ages, the mechanisms behind this transmission, and the reversibility of this transmission. We examine children born after the war who survived to age 45, comparing children whose fathers were non-POW veterans and ex-POWs imprisoned in very different camp conditions. We also compare children born before and after the war within the same family by paternal ex-POW status. The sons of ex-POWs imprisoned when camp conditions were at their worst were 1.11 times more likely to die than the sons of non-POWs and 1.09 times more likely to die than the sons of ex-POWs when camp conditions were better. Paternal ex-POW status had no impact on daughters. Among sons born in the fourth quarter, when maternal in utero nutrition was adequate, there was no impact of paternal ex-POW status. In contrast, among sons born in the second quarter, when maternal nutrition was inadequate, the sons of ex-POWs who experienced severe hardship were 1.2 times more likely to die than the sons of non-POWs and ex-POWs who fared better in captivity. Socioeconomic effects, family structure, father-specific survival traits, and maternal effects, including quality of paternal marriages, cannot explain our findings. While we cannot rule out fully psychological or cultural effects, our findings are most consistent with an epigenetic explanation.

Parental obesity leads to metabolic changes in the F2 generation in Drosophila

OBJECTIVE

A significant portion of the heritable risk for complex metabolic disorders cannot be attributed to classic Mendelian genetic factors. At least some of this missing heritability is thought to be due to the epigenetic influence of parental and grandparental metabolic state on offspring health. Previous work suggests that this transgenerational phenomenon is evolutionarily conserved in Drosophila. These studies, however, have all depended on dietary paradigms to alter parental metabolic state, which can have inconsistent heritable effects on the metabolism of offspring.

METHODS

Here we use AKHR null alleles to induce obesity in the parental generation and then score both metabolic parameters and genome-wide transcriptional responses in AKHR heterozygote F1 progeny and genetically wild-type F2 progeny.

RESULTS

Unexpectedly, we observe elevated glycogen levels and changes in gene expression in AKHR heterozygotes due to haploinsufficiency at this locus. We also show that genetic manipulation of parental metabolism using AKHR mutations results in significant physiological changes in F2 wild-type offspring of the grandpaternal/maternal lineage.

CONCLUSIONS

Our results demonstrate that genetic manipulation of parental metabolism in Drosophila can have an effect on the health of F2 progeny, providing a non-dietary paradigm to better understand the mechanisms behind the transgenerational inheritance of metabolic state.

How mice are indispensable for understanding obesity and diabetes genetics

PURPOSE OF REVIEW

The task of cataloging human genetic variation and its relation to disease is rapidly approaching completion. The new challenge is to discover the function of disease-associated genes and to understand the pathways that lead to human disease. We propose that achieving this new level of understanding will increasingly rely on the use of model organisms. We discuss the advantages of the mouse as a model organism to our understanding of human disease.

RECENT FINDINGS

The collection of available mouse strains represents as much genetic and phenotypic variation as is found in the human population. However, unlike humans, mice can be subjected to experimental breeding protocols and the availability of tissues allows for a far greater and deeper level of phenotyping. New methods for gene editing make it relatively easy to create mouse models of known human mutations. The distinction between genetic and epigenetic inheritance can be studied in great detail. Various experimental protocols enable the exploration of the role of the microbiome in physiology and disease.

SUMMARY

We propose that there will be an interdependence between human and model organism research. Technological advances and new genetic screening platforms in the mouse have greatly improved the path to gene discovery and mechanistic studies of gene function.

Epigenetic and genetic components of height regulation

Adult height is a highly heritable trait. Here we identified 31.6 million sequence variants by whole-genome sequencing of 8,453 Icelanders and tested them for association with adult height by imputing them into 88,835 Icelanders. Here we discovered 13 novel height associations by testing four different models including parent-of-origin (|β|=0.4-10.6 cm). The minor alleles of three parent-of-origin signals associate with less height only when inherited from the father and are located within imprinted regions (IGF2-H19 and DLK1-MEG3). We also examined the association of these sequence variants in a set of 12,645 Icelanders with birth length measurements. Two of the novel variants, (IGF2-H19 and TET1), show significant association with both adult height and birth length, indicating a role in early growth regulation. Among the parent-of-origin signals, we observed opposing parental effects raising questions about underlying mechanisms. These findings demonstrate that common variations affect human growth by parental imprinting.

Partitioning the variance in calorie restriction-induced weight and fat loss in outbred mice

OBJECTIVE

An increased understanding of the factors influencing interindividual variation in calorie restriction (CR)-induced weight loss is necessary to combat the current obesity epidemic. This study investigated the partitioning of the phenotypic variation in CR-induced wight loss.

METHODS

Two generations of male and female outbred MF1 mice raised by their biological mother or a foster mother were studied. Mice were exposed to 4 weeks of 30% CR when 6 months old.

RESULTS

Heritability was estimated at 0.43 ± 0.12 for CR-induced changes in body mass and 0.24 ± 0.10 for fat mass using mid-parent-offspring regressions. No significant relationships between weight loss in fathers or foster mothers and offspring were observed. Partitioning of phenotypic variance in weight loss using maximum likelihood modeling indicated 19 ± 17% of the variation could be attributed to additive genetic effects, 8 ± 14% to maternal effects during pregnancy, and <1% to maternal effects during lactation. A narrow-sense heritability around 0.50 was observed for ad libitum food intake and general activity.

CONCLUSIONS

A large part of individual variation in CR-induced weight loss could be attributed to additive genetic and maternal effects during pregnancy, but not to maternal effects in lactation. Genetic differences in food intake and general activity may play a role in determining these effects.

Fetal programming and epigenetic mechanisms in arterial hypertension

PURPOSE OF REVIEW

To provide an overview of available evidence of the potential role of epigenetics in the pathogenesis of hypertension and vascular dysfunction.

RECENT FINDINGS

Arterial hypertension is a highly heritable condition. Surprisingly, however, genetic variants only explain a tiny fraction of the phenotypic variation and the term 'missing heritability' has been coined to describe this phenomenon. Recent evidence suggests that phenotypic alteration that is unrelated to changes in DNA sequence (thereby escaping detection by classic genetic methodology) offers a potential explanation. Here, we present some basic information on epigenetics and review recent work consistent with the hypothesis of epigenetically induced arterial hypertension.

SUMMARY

New technologies that enable the rigorous assessment of epigenetic changes and their phenotypic consequences may provide the basis for explaining the missing heritability of arterial hypertension and offer new possibilities for treatment and/or prevention.

THE GENETICS OF EPIGENETIC INHERITANCE: MODES, MOLECULES, AND MECHANISMS

Organisms adapt developmental and physiological features to local and transient conditions in part by modulating transcription, translation, and protein functions, usually without changing DNA sequences. Remarkably, these epigenetic changes sometimes endure through meiosis and gametogenesis, thereby affecting phenotypic variation across generations, long after epigenetic changes were triggered. Transgenerational effects challenge our traditional understanding of inheritance. In this review, we focus on patterns of inheritance, molecular features, mechanisms that lead from environmental and genetic perturbations to phenotypic variation in later generations, and issues about study design and replication.

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.

Combined parental obesity augments single-parent obesity effects on hypothalamus inflammation, leptin signaling (JAK/STAT), hyperphagia, and obesity in the adult mice offspring

We aimed to evaluate the effects of maternal and/or paternal obesity on offspring body mass, leptin signaling, appetite-regulating neurotransmitters and local inflammatory markers. C57BL/6 mice received standard chow (SC, lean groups) or high-fat diet (HF, obese groups) starting from one month of age. At three months, HF mice became obese relative to SC mice. They were then mated as follows: lean mother and lean father, lean mother and obese father, obese mother and lean father, and obese mother and obese father. The offspring received the SC diet from weaning until three months of age, when they were sacrificed. In the offspring, paternal obesity did not lead to changes in the Janus kinase (JAK)/signal transducer and activation of the transcription (STAT) pathway or feeding behavior but did induce hypothalamic inflammation. On the other hand, maternal obesity resulted in increased weight gain, hyperleptinemia, decreased leptin OBRb receptor expression, JAK/STAT pathway impairment, and increased SOCS3 signaling in the offspring. In addition, maternal obesity elevated inflammatory markers and altered NPY and POMC expression in the hypothalamus. Interestingly, combined parental obesity exacerbated the deleterious outcomes compared to single-parent obesity. In conclusion, while maternal obesity is known to program metabolic changes and obesity in offspring, the current study demonstrated that obese fathers induce hypothalamus inflammation in offspring, which may contribute to the development of metabolic syndromes in adulthood.

Transgenerational inheritance of metabolic disease

Metabolic disease encompasses several disorders including obesity, type 2 diabetes, and dyslipidemia. Recently, the incidence of metabolic disease has drastically increased, driven primarily by a worldwide obesity epidemic. Transgenerational inheritance remains controversial, but has been proposed to contribute to human metabolic disease risk based on a growing number of proof-of-principle studies in model organisms ranging from Caenorhabditis elegans to Mus musculus to Sus scrofa. Collectively, these studies demonstrate that heritable risk is epigenetically transmitted from parent to offspring over multiple generations in the absence of a continued exposure to the triggering stimuli. A diverse assortment of initial triggers can induce transgenerational inheritance including high-fat or high-sugar diets, low-protein diets, various toxins, and ancestral genetic variants. Although the mechanistic basis underlying the transgenerational inheritance of disease risk remains largely unknown, putative molecules mediating transmission include small RNAs, histone modifications, and DNA methylation. Due to the considerable impact of metabolic disease on human health, it is critical to better understand the role of transgenerational inheritance of metabolic disease risk to open new avenues for therapeutic intervention and improve upon the current methods for clinical diagnoses and treatment.

Contrasting genetic architectures in different mouse reference populations used for studying complex traits

Quantitative trait loci (QTLs) are being used to study genetic networks, protein functions, and systems properties that underlie phenotypic variation and disease risk in humans, model organisms, agricultural species, and natural populations. The challenges are many, beginning with the seemingly simple tasks of mapping QTLs and identifying their underlying genetic determinants. Various specialized resources have been developed to study complex traits in many model organisms. In the mouse, remarkably different pictures of genetic architectures are emerging. Chromosome Substitution Strains (CSSs) reveal many QTLs, large phenotypic effects, pervasive epistasis, and readily identified genetic variants. In contrast, other resources as well as genome-wide association studies (GWAS) in humans and other species reveal genetic architectures dominated with a relatively modest number of QTLs that have small individual and combined phenotypic effects. These contrasting architectures are the result of intrinsic differences in the study designs underlying different resources. The CSSs examine context-dependent phenotypic effects independently among individual genotypes, whereas with GWAS and other mouse resources, the average effect of each QTL is assessed among many individuals with heterogeneous genetic backgrounds. We argue that variation of genetic architectures among individuals is as important as population averages. Each of these important resources has particular merits and specific applications for these individual and population perspectives. Collectively, these resources together with high-throughput genotyping, sequencing and genetic engineering technologies, and information repositories highlight the power of the mouse for genetic, functional, and systems studies of complex traits and disease models.

Epigenetic effects of paternal diet on offspring: emphasis on obesity

Overnutrition, obesity, and the rise in associated comorbidities are widely recognized as preventable challenges to global health. Behavioral, metabolic, and epigenetic influences that alter the epigenome, when passed on to offspring, can increase their risk of developing an altered metabolic profile. This review is focused on the role of paternal inheritance as demonstrated by clinical, epidemiological, and experimental models. Development of additional experimental models that resemble the specific epigenetic sensitive situations in human studies will be essential to explore paternally induced trans-generational effects that are mediated, primarily, by epigenetic effects. Further elucidation of epigenetic marks will help identify preventive and therapeutic targets, which in combination with healthy lifestyle choices, can diminish the growing tide of obesity, type 2 diabetes, and other related disorders.

The biology of developmental plasticity and the Predictive Adaptive Response hypothesis

Many forms of developmental plasticity have been observed and these are usually beneficial to the organism. The Predictive Adaptive Response (PAR) hypothesis refers to a form of developmental plasticity in which cues received in early life influence the development of a phenotype that is normally adapted to the environmental conditions of later life. When the predicted and actual environments differ, the mismatch between the individual's phenotype and the conditions in which it finds itself can have adverse consequences for Darwinian fitness and, later, for health. Numerous examples exist of the long-term effects of cues indicating a threatening environment affecting the subsequent phenotype of the individual organism. Other examples consist of the long-term effects of variations in environment within a normal range, particularly in the individual's nutritional environment. In mammals the cues to developing offspring are often provided by the mother's plane of nutrition, her body composition or stress levels. This hypothetical effect in humans is thought to be important by some scientists and controversial by others. In resolving the conflict, distinctions should be drawn between PARs induced by normative variations in the developmental environment and the ill effects on development of extremes in environment such as a very poor or very rich nutritional environment. Tests to distinguish between different developmental processes impacting on adult characteristics are proposed. Many of the mechanisms underlying developmental plasticity involve molecular epigenetic processes, and their elucidation in the context of PARs and more widely has implications for the revision of classical evolutionary theory.

How evolutionary principles improve the understanding of human health and disease

An appreciation of the fundamental principles of evolutionary biology provides new insights into major diseases and enables an integrated understanding of human biology and medicine. However, there is a lack of awareness of their importance amongst physicians, medical researchers, and educators, all of whom tend to focus on the mechanistic (proximate) basis for disease, excluding consideration of evolutionary (ultimate) reasons. The key principles of evolutionary medicine are that selection acts on fitness, not health or longevity; that our evolutionary history does not cause disease, but rather impacts on our risk of disease in particular environments; and that we are now living in novel environments compared to those in which we evolved. We consider these evolutionary principles in conjunction with population genetics and describe several pathways by which evolutionary processes can affect disease risk. These perspectives provide a more cohesive framework for gaining insights into the determinants of health and disease. Coupled with complementary insights offered by advances in genomic, epigenetic, and developmental biology research, evolutionary perspectives offer an important addition to understanding disease. Further, there are a number of aspects of evolutionary medicine that can add considerably to studies in other domains of contemporary evolutionary studies.

Stress exposure, food intake and emotional state

This manuscript summarizes the proceedings of the symposium entitled, "Stress, Palatable Food and Reward", that was chaired by Drs. Linda Rinaman and Yvonne Ulrich-Lai at the 2014 Neurobiology of Stress Workshop held in Cincinnati, OH. This symposium comprised research presentations by four neuroscientists whose work focuses on the biological bases for complex interactions among stress, food intake and emotion. First, Dr Ulrich-Lai describes her rodent research exploring mechanisms by which the rewarding properties of sweet palatable foods confer stress relief. Second, Dr Stephanie Fulton discusses her work in which excessive, long-term intake of dietary lipids, as well as their subsequent withdrawal, promotes stress-related outcomes in mice. Third, Dr Mark Wilson describes his group's research examining the effects of social hierarchy-related stress on food intake and diet choice in group-housed female rhesus macaques, and compared the data from monkeys to results obtained in analogous work using rodents. Finally, Dr Gorica Petrovich discusses her research program that is aimed at defining cortical-amygdalar-hypothalamic circuitry responsible for curbing food intake during emotional threat (i.e. fear anticipation) in rats. Their collective results reveal the complexity of physiological and behavioral interactions that link stress, food intake and emotional state, and suggest new avenues of research to probe the impact of genetic, metabolic, social, experiential and environmental factors on these interactions.

Evolution, epigenetics and cooperation

Explanations for biological evolution in terms of changes in gene frequencies refer to outcomes rather than process. Integrating epigenetic studies with older evolutionary theories has drawn attention to the ways in which evolution occurs. Adaptation at the level of the gene is givingway to adaptation at the level of the organism and higher-order assemblages of organisms. These ideas impact on the theories of how cooperation might have evolved. Two of the theories, i.e. that cooperating individuals are genetically related or that they cooperate for self-interested reasons, have been accepted for a long time. The idea that adaptation takes place at the level of groups is much more controversial. However, bringing together studies of development with those of evolution is taking away much of the heat in the debate about the evolution of group behaviour.

Early developmental conditioning of later health and disease: physiology or pathophysiology?

Extensive experimental animal studies and epidemiological observations have shown that environmental influences during early development affect the risk of later pathophysiological processes associated with chronic, especially noncommunicable, disease (NCD). This field is recognized as the developmental origins of health and disease (DOHaD). We discuss the extent to which DOHaD represents the result of the physiological processes of developmental plasticity, which may have potential adverse consequences in terms of NCD risk later, or whether it is the manifestation of pathophysiological processes acting in early life but only becoming apparent as disease later. We argue that the evidence suggests the former, through the operation of conditioning processes induced across the normal range of developmental environments, and we summarize current knowledge of the physiological processes involved. The adaptive pathway to later risk accords with current concepts in evolutionary developmental biology, especially those concerning parental effects. Outside the normal range, effects on development can result in nonadaptive processes, and we review their underlying mechanisms and consequences. New concepts concerning the underlying epigenetic and other mechanisms involved in both disruptive and nondisruptive pathways to disease are reviewed, including the evidence for transgenerational passage of risk from both maternal and paternal lines. These concepts have wider implications for understanding the causes and possible prevention of NCDs such as type 2 diabetes and cardiovascular disease, for broader social policy and for the increasing attention paid in public health to the lifecourse approach to NCD prevention.

Human transgenerational responses to early-life experience: potential impact on development, health and biomedical research

Mammalian experiments provide clear evidence of male line transgenerational effects on health and development from paternal or ancestral early-life exposures such as diet or stress. The few human observational studies to date suggest (male line) transgenerational effects exist that cannot easily be attributed to cultural and/or genetic inheritance. Here we summarise relevant studies, drawing attention to exposure sensitive periods in early life and sex differences in transmission and offspring outcomes. Thus, variation, or changes, in the parental/ancestral environment may influence phenotypic variation for better or worse in the next generation(s), and so contribute to common, non-communicable disease risk including sex differences. We argue that life-course epidemiology should be reframed to include exposures from previous generations, keeping an open mind as to the mechanisms that transmit this information to offspring. Finally, we discuss animal experiments, including the role of epigenetic inheritance and non-coding RNAs, in terms of what lessons can be learnt for designing and interpreting human studies. This review was developed initially as a position paper by the multidisciplinary Network in Epigenetic Epidemiology to encourage transgenerational research in human cohorts.

Genetic determinants of atherosclerosis, obesity, and energy balance in consomic mice

Metabolic diseases such as obesity and atherosclerosis result from complex interactions between environmental factors and genetic variants. A panel of chromosome substitution strains (CSSs) was developed to characterize genetic and dietary factors contributing to metabolic diseases and other biological traits and biomedical conditions. Our goal here was to identify quantitative trait loci (QTLs) contributing to obesity, energy expenditure, and atherosclerosis. Parental strains C57BL/6 and A/J together with a panel of 21 CSSs derived from these progenitors were subjected to chronic feeding of rodent chow and atherosclerotic (females) or diabetogenic (males) test diets, and evaluated for a variety of metabolic phenotypes including several traits unique to this report, namely fat pad weights, energy balance, and atherosclerosis. A total of 297 QTLs across 35 traits were discovered, two of which provided significant protection from atherosclerosis, and several dozen QTLs modulated body weight, body composition, and circulating lipid levels in females and males. While several QTLs confirmed previous reports, most QTLs were novel. Finally, we applied the CSS quantitative genetic approach to energy balance, and identified three novel QTLs controlling energy expenditure and one QTL modulating food intake. Overall, we identified many new QTLs and phenotyped several novel traits in this mouse model of diet-induced metabolic diseases.

Epigenetic inheritance of metabolic state

As the incidence of complex metabolic disease increases in developed countries, so too does the need to understand the causes and risk factors for these disorders. In addition to the well-known contribution of genetics and environment to metabolic dysfunction, many studies have demonstrated that a significant degree of non-genetic heritable risk can be transmitted from parents to offspring over multiple generations. Understanding the mechanisms by which this occurs could change how we study and treat complex metabolic disorders. In this review, we summarize recent advances in this field utilizing Drosophila, mice, and humans, and propose potential molecular mechanisms that underlie the transgenerational inheritance of metabolic state.

Pathways by which the interplay of organismic and environmental factors lead to phenotypic variation within and across generations

The range of responses made to environmental exigencies by animals, including humans, may be impacted by the experiences of their progenitors. In mammals, pathways have been documented ranging from transactions between a mother and her developing fetus in the womb through continuity of parenting practices and cultural inheritance. In addition, phenotypic plasticity may be constrained by factors transmitted by the gametes that are involved in the regulation of gene expression rather than modifications to the genome itself. Possible mediators for this kind of inheritance are examined, and the conditions that might have led to the evolution of such transmission are considered. Anticipatory adjustments to possible environmental exigencies are likely to occur when such conditions recur regularly, but intermittently across generations and endure for substantial periods of time, and when adjusting to them after the fact is likely to be biologically costly, even life-threatening. It appears that physical growth and responses to nutrient availability are domains in which anticipatory, epigenetically inherited adjustments occur. In addition, given the fact that humans have oppressed one another repeatedly and for relatively long periods of time, such behavioral tendencies as boldness or innovativeness may be behavioral traits subject to such effects. The implications of these factors for research and policy are discussed.

Intergenerational programming of metabolic disease: evidence from human populations and experimental animal models

We are in the midst of unparalleled epidemics of obesity and type 2 diabetes-complex phenotypes originating at the intersection of genetic and environmental risk. As detailed in other chapters, evidence indicates that non-genetic, or environmental, risk may initiate during prenatal and early postnatal life [1]. Striking examples in humans include the association of low birth weight (LBW) and/or accelerated early growth with increased risk of insulin resistance, obesity, type 2 diabetes (T2DM), and cardiovascular disease (CVD), and the close relationship between maternal obesity or diabetes with childhood obesity. In this chapter, we will focus on the intriguing emerging data from both human and animal models that indicate that intrauterine and childhood exposures can also influence risk for diabetes and cardiovascular disease in subsequent generations. Understanding the mechanisms responsible for these effects is critical in order to develop effective metabolic and nutritional interventions to interrupt such vicious intergenerational cycles potentiating risk for metabolic disorders.

What obesity research tells us about epigenetic mechanisms

The pathophysiology of obesity is extremely complex and is associated with extensive gene expression changes in tissues throughout the body. This situation, combined with the fact that all gene expression changes are thought to have associated epigenetic changes, means that the links between obesity and epigenetics will undoubtedly be vast. Much progress in identifying epigenetic changes induced by (or inducing) obesity has already been made, with candidate and genome-wide approaches. These discoveries will aid the clinician through increasing our understanding of the inheritance, development and treatment of obesity. However, they are also of great value for epigenetic researchers, as they have revealed mechanisms of environmental interactions with epigenetics that can produce or perpetuate a disease state. Here, we will review the evidence for four mechanisms through which epigenetics contributes to obesity: as downstream effectors of environmental signals; through abnormal global epigenetic state driving obesogenic expression patterns; through facilitating developmental programming and through transgenerational epigenetic inheritance.

Genetic susceptibility to hypertensive renal disease

Hypertensive renal disease occurs at increased frequency among the relatives of patients with this disease compared to individuals who lack a family history of disease. This suggests a heritable risk in which genetic variation may play a role. These observations have motivated a search for genetic variation contributing to this risk in both experimental animal models and in human populations. Studies of animal models indicate the capacity of natural genetic variants to contribute to disease risk and have produced a few insights into the disease mechanism. In its current phase, human population genetic studies have sought to associate genetic variation with disease in large populations by testing genotypes at a large number of common genetic variations in the genome, expecting that common genetic variants contributing to renal disease risk will be identified. These genome-wide association studies (GWAS) have been productive and are a clear technical success; they have also identified narrowly defined loci and genes containing variation contributing to disease risk. Further extension and refinement of these GWAS are likely to extend this success. However, it is also clear that few additional variants with substantial effects accounting for the greatest part of heritability will be uncovered by GWAS. This raises an interesting biological question regarding where the remaining unaccounted heritable risk may be located. At present, much consideration is being given to this question and to the challenge of testing hypotheses that lead from the various alternative mechanisms under consideration. One result of the progress of GWAS is likely to be a renewed interest in mechanisms by which related individuals can share and transmit traits independently of Mendelian inheritance. This paper reviews the current progress in this area and considers other mechanisms by which familial aggregation of risk for renal disease may arise.

Limited evidence for parent-of-origin effects in inflammatory bowel disease associated loci

Background

Genome-wide association studies of two main forms of inflammatory bowel diseases (IBD), Crohn’s disease (CD) and ulcerative colitis (UC), have identified 99 susceptibility loci, but these explain only ∼23% of the genetic risk. Part of the ‘hidden heritability’ could be in transmissible genetic effects in which mRNA expression in the offspring depends on the parental origin of the allele (genomic imprinting), since children whose mothers have CD are more often affected than children with affected fathers. We analyzed parent-of-origin (POO) effects in Dutch and Indian cohorts of IBD patients.

Methods

We selected 28 genetic loci associated with both CD and UC, and tested them for POO effects in 181 Dutch IBD case-parent trios. Three susceptibility variants in NOD2 were tested in 111 CD trios and a significant finding was re-evaluated in 598 German trios. The UC-associated gene, BTNL2, reportedly imprinted, was tested in 70 Dutch UC trios. Finally, we used 62 independent Indian UC trios to test POO effects of five established Indian UC risk loci.

Results

We identified POO effects for NOD2 (L1007fs; OR = 21.0, P-value = 0.013) for CD; these results could not be replicated in an independent cohort (OR = 0.97, P-value = 0.95). A POO effect in IBD was observed for IL12B (OR = 3.2, P-value = 0.019) and PRDM1 (OR = 5.6, P-value = 0.04). In the Indian trios the IL10 locus showed a POO effect (OR = 0.2, P-value = 0.03).

Conclusions

Little is known about the effect of genomic imprinting in complex diseases such as IBD. We present limited evidence for POO effects for the tested IBD loci. POO effects explain part of the hidden heritability for complex genetic diseases but need to be investigated further.

Chromosome substitution strains: gene discovery, functional analysis, and systems studies

Laboratory mice are valuable in biomedical research in part because of the extraordinary diversity of genetic resources that are available for studies of complex genetic traits and as models for human biology and disease. Chromosome substitution strains (CSSs) are important in this resource portfolio because of their demonstrated use for gene discovery, genetic and epigenetic studies, functional characterizations, and systems analysis. CSSs are made by replacing a single chromosome in a host strain with the corresponding chromosome from a donor strain. A complete CSS panel involves a total of 22 engineered inbred strains, one for each of the 19 autosomes, one each for the X and Y chromosomes, and one for mitochondria. A genome survey simply involves comparing each phenotype for each of the CSSs with the phenotypes of the host strain. The CSS panels that are available for laboratory mice have been used to dissect a remarkable variety of phenotypes and to characterize an impressive array of disease models. These surveys have revealed considerable phenotypic diversity even among closely related progenitor strains, evidence for strong epistasis and for heritable epigenetic changes. Perhaps most importantly, and presumably because of their unique genetic constitution, CSSs, and congenic strains derived from them, the genetic variants underlying quantitative trait loci (QTLs) are readily identified and functionally characterized. Together these studies show that CSSs are important resource for laboratory mice.

Transgenerational epigenetic effects of the Apobec1 cytidine deaminase deficiency on testicular germ cell tumor susceptibility and embryonic viability

Environmental agents and genetic variants can induce heritable epigenetic changes that affect phenotypic variation and disease risk in many species. These transgenerational effects challenge conventional understanding about the modes and mechanisms of inheritance, but their molecular basis is poorly understood. The Deadend1 (Dnd1) gene enhances susceptibility to testicular germ cell tumors (TGCTs) in mice, in part by interacting epigenetically with other TGCT modifier genes in previous generations. Sequence homology to A1cf, the RNA-binding subunit of the ApoB editing complex, raises the possibility that the function of Dnd1 is related to Apobec1 activity as a cytidine deaminase. We conducted a series of experiments with a genetically engineered deficiency of Apobec1 on the TGCT-susceptible 129/Sv inbred background to determine whether dosage of Apobec1 modifies susceptibility, either alone or in combination with Dnd1, and either in a conventional or a transgenerational manner. In the paternal germ-lineage, Apobec1 deficiency significantly increased susceptibility among heterozygous but not wild-type male offspring, without subsequent transgenerational effects, showing that increased TGCT risk resulting from partial loss of Apobec1 function is inherited in a conventional manner. By contrast, partial deficiency in the maternal germ-lineage led to suppression of TGCTs in both partially and fully deficient males and significantly reduced TGCT risk in a transgenerational manner among wild-type offspring. These heritable epigenetic changes persisted for multiple generations and were fully reversed after consecutive crosses through the alternative germ-lineage. These results suggest that Apobec1 plays a central role in controlling TGCT susceptibility in both a conventional and a transgenerational manner.

The influence of DNA sequence on epigenome-induced pathologies

Clear cause-and-effect relationships are commonly established between genotype and the inherited risk of acquiring human and plant diseases and aberrant phenotypes. By contrast, few such cause-and-effect relationships are established linking a chromatin structure (that is, the epitype) with the transgenerational risk of acquiring a disease or abnormal phenotype. It is not entirely clear how epitypes are inherited from parent to offspring as populations evolve, even though epigenetics is proposed to be fundamental to evolution and the likelihood of acquiring many diseases. This article explores the hypothesis that, for transgenerationally inherited chromatin structures, "genotype predisposes epitype", and that epitype functions as a modifier of gene expression within the classical central dogma of molecular biology. Evidence for the causal contribution of genotype to inherited epitypes and epigenetic risk comes primarily from two different kinds of studies discussed herein. The first and direct method of research proceeds by the examination of the transgenerational inheritance of epitype and the penetrance of phenotype among genetically related individuals. The second approach identifies epitypes that are duplicated (as DNA sequences are duplicated) and evolutionarily conserved among repeated patterns in the DNA sequence. The body of this article summarizes particularly robust examples of these studies from humans, mice, Arabidopsis, and other organisms. The bulk of the data from both areas of research support the hypothesis that genotypes predispose the likelihood of displaying various epitypes, but for only a few classes of epitype. This analysis suggests that renewed efforts are needed in identifying polymorphic DNA sequences that determine variable nucleosome positioning and DNA methylation as the primary cause of inherited epigenome-induced pathologies. By contrast, there is very little evidence that DNA sequence directly determines the inherited positioning of numerous and diverse post-translational modifications of histone side chains within nucleosomes. We discuss the medical and scientific implications of these observations on future research and on the development of solutions to epigenetically induced disorders.

The juxtaparanodal proteins CNTNAP2 and TAG1 regulate diet-induced obesity

Despite considerable effort, the identification of genes that regulate complex multigenic traits such as obesity has proven difficult with conventional methodologies. The use of a chromosome substitution strain-based mapping strategy based on deep congenic analysis overcame many of the difficulties associated with gene discovery and led to the finding that the juxtaparanodal proteins CNTNAP2 and TAG1 regulate diet-induced obesity. The effects of a mild Cntnap2 mutation on body weight were highly dependent on genetic background, as both obesity-promoting and obesity-resistant effects of Cntnap2 were observed on different genetic backgrounds. The more severe effect of complete TAG1 deficiency, by decreasing food intake, completely prevented the weight gain normally associated with high-fat-diet feeding. Together, these studies implicate two novel proteins in the regulation of diet-induced obesity. Moreover, as juxtaparanodal proteins have previously been implicated in various neurological disorders, our results suggest a potential genetic and molecular link between obesity and diseases such as autism and epilepsy.

Epigenetics and eating disorders

PURPOSE OF REVIEW

Eating disorders are complex psychiatric disorders in which genes, environment, and gene-environment interactions (G×E) have a role. Such G×E may occur in adulthood or during development. They may also be modified by factors such as (mal)nutrition or stress and this may result in acute or long-term epigenetic modifications. This review discusses the potential for recent developments in epigenetics to address ongoing aetiological issues in eating disorders.

RECENT FINDINGS

Epigenetic studies in eating disorders have focussed on the DNA methylation status of promoter regions of candidate genes: differences have been reported between people with eating disorders and healthy controls, and between subtypes of eating disorders. Animal studies related to eating disorders have focussed on understanding the acute and long-term effects of environmental manipulation on epigenetic changes and on the resultant phenotypes: these studies are promising, but they have also identified some of the complexity of epigenetic processing.

SUMMARY

Because of the difficulties in obtaining brain samples, epigenetic studies in eating disorders (like in other psychiatric illnesses) have used peripheral tissues, usually blood: this raises various problems. It is likely, therefore, that in the immediate future, animal, rather than human studies will guide the progress in epigenetics studies of eating disorders and other psychiatric disorders.

Paternal body mass index (BMI) is associated with offspring intrauterine growth in a gender dependent manner

BACKGROUND

Environmental alternations leading to fetal programming of cardiovascular diseases in later life have been attributed to maternal factors. However, animal studies showed that paternal obesity may program cardio-metabolic diseases in the offspring. In the current study we tested the hypothesis that paternal BMI may be associated with fetal growth.

METHODS AND RESULTS

We analyzed the relationship between paternal body mass index (BMI) and birth weight, ultrasound parameters describing the newborn's body shape as well as parameters describing the newborns endocrine system such as cortisol, aldosterone, renin activity and fetal glycated serum protein in a birth cohort of 899 father/mother/child triplets. Since fetal programming is an offspring sex specific process, male and female offspring were analyzed separately. Multivariable regression analyses considering maternal BMI, paternal and maternal age, hypertension during pregnancy, maternal total glycated serum protein, parity and either gestational age (for birth weight) or time of ultrasound investigation (for ultrasound parameters) as confounding showed that paternal BMI is associated with growth of the male but not female offspring. Paternal BMI correlated with birth parameters of male offspring only: birth weight; biparietal diameter, head circumference; abdominal diameter, abdominal circumference; and pectoral diameter. Cortisol was likewise significantly correlated with paternal BMI in male newborns only.

CONCLUSIONS

Paternal BMI affects growth of the male but not female offspring. Paternal BMI may thus represent a risk factor for cardiovascular diseases of male offspring in later life. It remains to be demonstrated whether this is linked to an offspring sex specific paternal programming of cortisol secretion.

Developmental plasticity and epigenetic mechanisms underpinning metabolic and cardiovascular diseases

The importance of developmental factors in influencing the risk of later-life disease has a strong evidence base derived from multiple epidemiological, clinical and experimental studies in animals and humans. During early life, an organism is able to adjust its phenotypic development in response to environmental cues. Such developmentally plastic responses evolved as a fitness-maximizing strategy to cope with variable environments. There are now increasing data that these responses are, at least partially, underpinned by epigenetic mechanisms. A mismatch between the early and later-life environments may lead to inappropriate early life-course epigenomic changes that manifest in later life as increased vulnerability to disease. There is also growing evidence for the transgenerational transmission of epigenetic marks. This article reviews the evidence that susceptibility to metabolic and cardiovascular disease in humans is linked to changes in epigenetic marks induced by early-life environmental cues, and discusses the clinical, public health and therapeutic implications that arise.

Transgenerational genetic effects

Since Mendel, studies of phenotypic variation and disease risk have emphasized associations between genotype and phenotype among affected individuals in families and populations. Although this paradigm has led to important insights into the molecular basis for many traits and diseases, most of the genetic variants that control the inheritance of these conditions continue to elude detection. Recent studies suggest an alternative mode of inheritance where genetic variants that are present in one generation affect phenotypes in subsequent generations, thereby decoupling the conventional relations between genotype and phenotype, and perhaps, contributing to 'missing heritability'. Under some conditions, these transgenerational genetic effects can be as frequent and strong as conventional inheritance, and can persist for multiple generations. Growing evidence suggests that RNA mediates these heritable epigenetic changes. The primary challenge now is to identify the molecular basis for these effects, characterize mechanisms and determine whether transgenerational genetic effects occur in humans.

Transgenerational genetic effects of the paternal Y chromosome on daughters' phenotypes

AIMS

Recent evidence suggests that transgenerational genetic effects contribute to phenotypic variation in complex traits. To test for the general occurrence of these effects and to estimate their strength, we took advantage of chromosome substitution strains (CSSs) of mice where the Y chromosome of the host strain has been replaced with the Y chromosome of the donor strain. Daughters of these CSS-Y males and host strain females are genetically identical and should be phenotypically indistinguishable in the absence of transgenerational genetic effects of the fathers' Y chromosome on daughters' phenotypes.

MATERIALS & METHODS

Assay results for a broad panel of physiological traits and behaviors were compared for genetically identical daughters of CSS-Y males and host strain females from the B6-Chr(A/J) and B6-Chr(PWD) panels of CSSs. In addition, behavioral traits including specific tests for anxiety-related behaviors were tested in daughters of B6-Chr(129) and 129-Chr(B6) CSS-Y males.

RESULTS

Across a panel of 41 multigenic traits assayed in the B6-Chr(A/J) panel of CSSs females and 21 multigenic traits in the B6-Chr(PWD) panel females, the frequency and strength for transgenerational genetic effects were remarkably similar to those for conventional inheritance of substituted chromosomes. In addition, we found strong evidence that the Y chromosome from the 129 inbred strain significantly reduced anxiety levels among daughters of B6-Chr(129) CSS-Y males.

CONCLUSION

We found that transgenerational genetic effects rival conventional genetic effects in frequency and strength, we suggest that some phenotypic variation found in conventional studies of complex traits are attributable in part to the action of genetic variants in previous generations, and we propose that transgenerational genetic effects contribute to 'missing heritability'.

Understanding transgenerational epigenetic inheritance via the gametes in mammals

It is known that information that is not contained in the DNA sequence - epigenetic information - can be inherited from the parent to the offspring. However, many questions remain unanswered regarding the extent and mechanisms of such inheritance. In this Review, we consider the evidence for transgenerational epigenetic inheritance via the gametes, including cases of environmentally induced epigenetic changes. The molecular basis of this inheritance remains unclear, but recent evidence points towards diffusible factors, in particular RNA, rather than DNA methylation or chromatin. Interestingly, many cases of epigenetic inheritance seem to involve repeat sequences.

Assisted reproduction treatment and epigenetic inheritance

BACKGROUND

The subject of epigenetic risk of assisted reproduction treatment (ART), initiated by reports on an increase of children with the Beckwith–Wiedemann imprinting disorder, is very topical. Hence, there is a growing literature, including mouse studies.

METHODS

In order to gain information on transgenerational epigenetic inheritance and epigenetic effects induced by ART, literature databases were searched for papers on this topic using relevant keywords.

RESULTS

At the level of genomic imprinting involving CpG methylation, ART-induced epigenetic defects are convincingly observed in mice, especially for placenta, and seem more frequent than in humans. Data generally provide a warning as to the use of ovulation induction and in vitro culture. In human sperm from compromised spermatogenesis, sequence-specific DNA hypomethylation is observed repeatedly. Transmittance of sperm and oocyte DNA methylation defects is possible but, as deduced from the limited data available, largely prevented by selection of gametes for ART and/or non-viability of the resulting embryos. Some evidence indicates that subfertility itself is a risk factor for imprinting diseases. As in mouse, physiological effects from ART are observed in humans.

In the human, indications for a broader target for changes in CpG methylation than imprinted DNA sequences alone have been found. In the mouse, a broader range of CpG sequences has not yet been studied. Also, a multigeneration study of systematic ART on epigenetic parameters is lacking.

CONCLUSIONS

The field of epigenetic inheritance within the lifespan of an individual and between generations (via mitosis and meiosis, respectively) is growing, driven by the expansion of chromatin research. ART can induce epigenetic variation that might be transmitted to the next generation.

Neuro-Genetics of Reward Deficiency Syndrome (RDS) as the Root Cause of "Addiction Transfer": A New Phenomenon Common after Bariatric Surgery

Now after many years of successful bariatric (weight-loss) surgeries directed at the obesity epidemic clinicians are reporting that some patients are replacing compulsive overeating with newly acquired compulsive disorders such as alcoholism, gambling, drugs, and other addictions like compulsive shopping and exercise. This review article explores evidence from psychiatric genetic animal and human studies that link compulsive overeating and other compulsive disorders to explain the phenomenon of addiction transfer. Possibly due to neurochemical similarities, overeating and obesity may act as protective factors reducing drug reward and addictive behaviors. In animal models of addiction withdrawal from sugar induces imbalances in the neurotransmitters, acetylcholine and dopamine, similar to opiate withdrawal. Many human neuroimaging studies have supported the concept of linking food craving to drug craving behavior. Previously our laboratory coined the term Reward Deficiency Syndrome (RDS) for common genetic determinants in predicting addictive disorders and reported that the predictive value for future RDS behaviors in subjects carrying the DRD2 Taq A1 allele was 74%. While poly genes play a role in RDS, we have also inferred that disruptions in dopamine function may predispose certain individuals to addictive behaviors and obesity. It is now known that family history of alcoholism is a significant obesity risk factor. Therefore, we hypothesize here that RDS is the root cause of substituting food addiction for other dependencies and potentially explains this recently described Phenomenon (addiction transfer) common after bariatric surgery.

The impact of the organism on its descendants

Historically, evolutionary biologists have taken the view that an understanding of development is irrelevant to theories of evolution. However, the integration of several disciplines in recent years suggests that this position is wrong. The capacity of the organism to adapt to challenges from the environment can set up conditions that affect the subsequent evolution of its descendants. Moreover, molecular events arising from epigenetic processes can be transmitted from one generation to the next and influence genetic mutation. This in turn can facilitate evolution in the conditions in which epigenetic change was first initiated.

Maternal obesity and developmental programming of metabolic disorders in offspring: evidence from animal models

The incidence of obesity and overweight has reached epidemic proportions in the developed world as well as in those countries transitioning to first world economies, and this represents a major global health problem. Concern is rising over the rapid increases in childhood obesity and metabolic disease that will translate into later adult obesity. Although an obesogenic nutritional environment and increasingly sedentary lifestyle contribute to our risk of developing obesity, a growing body of evidence links early life nutritional adversity to the development of long-term metabolic disorders. In particular, the increasing prevalence of maternal obesity and excess maternal weight gain has been associated with a heightened risk of obesity development in offspring in addition to an increased risk of pregnancy-related complications. The mechanisms that link maternal obesity to obesity in offspring and the level of gene-environment interactions are not well understood, but the early life environment may represent a critical window for which intervention strategies could be developed to curb the current obesity epidemic. This paper will discuss the various animal models of maternal overnutrition and their importance in our understanding of the mechanisms underlying altered obesity risk in offspring.

Heritability of ocular component dimensions in mice phenotyped using depth-enhanced swept source optical coherence tomography

The range of genetic and genomic resources available makes the mouse a powerful model for the genetic dissection of complex traits. Because accurate, high-throughput phenotypic characterisation is crucial to the success of such endeavours, we recently developed an optical coherence tomography (OCT) system with extended depth range scanning capability for measuring ocular component dimensions in mice. In order to test whether the accuracy and reproducibility of our OCT system was sufficient for gene mapping studies, we carried out an experiment designed to estimate the heritability of mouse ocular component dimensions. High-resolution, two dimensional tomograms were obtained for both eyes of 11 pairs of 8 week-old outbred MF1 mice. Subsequently, images were obtained when their offspring were aged 8 weeks. Biometric data were extracted after image segmentation, reconstruction of the geometric shape of each surface, and calculation of intraocular distances. The repeatability of measurements was evaluated for 12 mice scanned on consecutive days. Heritability estimates were calculated using variance components analysis. Sets of tomograms took ∼2 s to acquire. Biometric data could be obtained for 98% of the 130 eyes scanned. The 95% limits of repeatability ranged from ±6 to ±16 μm for the axial ocular component dimensions. The heritability of the axial ocular components was 0.6-0.8, except for corneal thickness, which had a heritability not significantly different from zero. In conclusion, axial ocular component dimensions are highly heritable in mice, as they are in humans. OCT with extended depth range scanning can be used to rapidly phenotype individual mice with sufficient accuracy and precision to permit gene mapping studies.