Distribution of parthenogenetic cells in the mouse brain and their influence on brain development and behavior

Evidence for parent-of-origin effects in autism spectrum disorder: a narrative review

Autism spectrum disorder (ASD) is a heterogeneous group of early-onset neurodevelopmental disorders known to be highly heritable with a complex genetic architecture. Abnormal brain developmental trajectories that impact synaptic functioning, excitation-inhibition balance and brain connectivity are now understood to play a central role in ASD. Ongoing efforts to identify the genetic underpinnings still prove challenging, in part due to phenotypic and genetic heterogeneity.This review focuses on parent-of-origin effects (POEs), where the phenotypic effect of an allele depends on its parental origin. POEs include genomic imprinting, transgenerational effects, mitochondrial DNA, sex chromosomes and mutational transmission bias. The motivation for investigating these mechanisms in ASD has been driven by their known impacts on early brain development and brain functioning, in particular for the most well-documented POE, genomic imprinting. Moreover, imprinting is implicated in syndromes such as Angelman and Prader-Willi, which frequently share comorbid symptoms with ASD. In addition to other regions in the genome, this comprehensive review highlights the 15q11-q13 and 7q chromosomal regions as well as the mitochondrial DNA as harbouring the majority of currently identified POEs in ASD.

Systematic investigation of imprinted gene expression and enrichment in the mouse brain explored at single-cell resolution

BACKGROUND

Although a number of imprinted genes are known to be highly expressed in the brain, and in certain brain regions in particular, whether they are truly over-represented in the brain has never been formally tested. Using thirteen single-cell RNA sequencing datasets we systematically investigated imprinted gene over-representation at the organ, brain region, and cell-specific levels.

RESULTS

We established that imprinted genes are indeed over-represented in the adult brain, and in neurons particularly compared to other brain cell-types. We then examined brain-wide datasets to test enrichment within distinct brain regions and neuron subpopulations and demonstrated over-representation of imprinted genes in the hypothalamus, ventral midbrain, pons and medulla. Finally, using datasets focusing on these regions of enrichment, we identified hypothalamic neuroendocrine populations and the monoaminergic hindbrain neurons as specific hotspots of imprinted gene expression.

CONCLUSIONS

These analyses provide the first robust assessment of the neural systems on which imprinted genes converge. Moreover, the unbiased approach, with each analysis informed by the findings of the previous level, permits highly informed inferences about the functions on which imprinted gene expression converges. Our findings indicate the neuronal regulation of motivated behaviours such as feeding and sleep, alongside the regulation of pituitary function, as functional hotspots for imprinting. This adds statistical rigour to prior assumptions and provides testable predictions for novel neural and behavioural phenotypes associated with specific genes and imprinted gene networks. In turn, this work sheds further light on the potential evolutionary drivers of genomic imprinting in the brain.

Cell-Type Specificity of Genomic Imprinting in Cerebral Cortex

In mammalian genomes, a subset of genes is regulated by genomic imprinting, resulting in silencing of one parental allele. Imprinting is essential for cerebral cortex development, but prevalence and functional impact in individual cells is unclear. Here, we determined allelic expression in cortical cell types and established a quantitative platform to interrogate imprinting in single cells. We created cells with uniparental chromosome disomy (UPD) containing two copies of either the maternal or the paternal chromosome; hence, imprinted genes will be 2-fold overexpressed or not expressed. By genetic labeling of UPD, we determined cellular phenotypes and transcriptional responses to deregulated imprinted gene expression at unprecedented single-cell resolution. We discovered an unexpected degree of cell-type specificity and a novel function of imprinting in the regulation of cortical astrocyte survival. More generally, our results suggest functional relevance of imprinted gene expression in glial astrocyte lineage and thus for generating cortical cell-type diversity.

Placental genotype affects early postpartum maternal behaviour

The mammalian placenta is a source of endocrine signals that prime the onset of maternal care at parturition. While consequences of placental dysfunction for offspring growth are well defined, how altered placental signalling might affect maternal behaviour is unstudied in a natural system. In the cross between sympatric mouse species, Mus musculus domesticus and Mus spretus, hybrid placentas are undersized and show misexpression of genes critical to placental endocrine function. Using this cross, we quantified the effects of placental dysregulation on maternal and anxiety-like behaviours in mice that differed only in pregnancy type. Relative to mothers of conspecific litters, females exposed to hybrid placentas did not differ in anxiety-like behaviours but were slower to retrieve 1-day-old pups and spent less time in the nest on the night following parturition. Early deficits in maternal responsiveness were not explained by reduced ultrasonic vocalization production in hybrid pups and there was no effect of pup genotype on measures of maternal behaviour and physiology collected after the first 24 h postpartum. These results suggest that placental dysregulation leads to poor maternal priming, the effect of which is alleviated by continued exposure to pups. This study provides new insight into the placental mediation of mother-offspring interactions.

Epigenetic and Cellular Diversity in the Brain through Allele-Specific Effects

The benefits of diploidy are considered to involve masking partially recessive mutations and increasing genetic diversity. Here, we review new studies showing evidence for diverse allele-specific expression and epigenetic states in mammalian brain cells, which suggest that diploidy expands the landscape of gene regulatory and expression programs in cells. Allele-specific expression has been thought to be restricted to a few specific classes of genes. However, new studies show novel genomic imprinting effects that are brain-region-, cell-type- and age-dependent. In addition, novel forms of random monoallelic expression that impact many autosomal genes have been described in vitro and in vivo. We discuss the implications for understanding the benefits of diploidy, and the mechanisms shaping brain development, function, and disease.

Mouse Parthenogenetic Embryonic Stem Cells with Biparental-Like Expression of Imprinted Genes Generate Cortical-Like Neurons That Integrate into the Injured Adult Cerebral Cortex

One strategy for stem cell-based therapy of the cerebral cortex involves the generation and transplantation of functional, histocompatible cortical-like neurons from embryonic stem cells (ESCs). Diploid parthenogenetic Pg-ESCs have recently emerged as a promising source of histocompatible ESC derivatives for organ regeneration but their utility for cerebral cortex therapy is unknown. A major concern with Pg-ESCs is genomic imprinting. In contrast with biparental Bp-ESCs derived from fertilized oocytes, Pg-ESCs harbor two maternal genomes but no sperm-derived genome. Pg-ESCs are therefore expected to have aberrant expression levels of maternally expressed (MEGs) and paternally expressed (PEGs) imprinted genes. Given the roles of imprinted genes in brain development, tissue homeostasis and cancer, their deregulation in Pg-ESCs might be incompatible with therapy. Here, we report that, unexpectedly, only one gene out of 7 MEGs and 12 PEGs was differentially expressed between Pg-ESCs and Bp-ESCs while 13 were differentially expressed between androgenetic Ag-ESCs and Bp-ESCs, indicating that Pg-ESCs but not Ag-ESCs, have a Bp-like imprinting compatible with therapy. In vitro, Pg-ESCs generated cortical-like progenitors and electrophysiologically active glutamatergic neurons that maintained the Bp-like expression levels for most imprinted genes. In vivo, Pg-ESCs participated to the cortical lineage in fetal chimeras. Finally, transplanted Pg-ESC derivatives integrated into the injured adult cortex and sent axonal projections in the host brain. In conclusion, mouse Pg-ESCs generate functional cortical-like neurons with Bp-like imprinting and their derivatives properly integrate into both the embryonic cortex and the injured adult cortex. Collectively, our data support the utility of Pg-ESCs for cortical therapy. Stem Cells 2018;36:192-205.

Maternal-fetal conflict, genomic imprinting and mammalian vulnerabilities to cancer

Antagonistic coevolution between maternal and fetal genes, and between maternally and paternally derived genes may have increased mammalian vulnerability to cancer. Placental trophoblast has evolved to invade maternal tissues and evade structural and immunological constraints on its invasion. These adaptations can be co-opted by cancer in intrasomatic selection. Imprinted genes of maternal and paternal origin favour different degrees of proliferation of particular cell types in which they reside. As a result, the set of genes favouring greater proliferation will be selected to evade controls on cell-cycle progression imposed by the set of genes favouring lesser proliferation. The dynamics of stem cell populations will be a particular focus of this intragenomic conflict. Gene networks that are battlegrounds of intragenomic conflict are expected to be less robust than networks that evolve in the absence of conflict. By these processes, maternal-fetal and intragenomic conflicts may undermine evolved defences against cancer.

High Gestational Folic Acid Supplementation Alters Expression of Imprinted and Candidate Autism Susceptibility Genes in a sex-Specific Manner in Mouse Offspring

Maternal nutrients play critical roles in modulating epigenetic events and exert long-term influences on the progeny's health. Folic acid (FA) supplementation during pregnancy has decreased the incidence of neural tube defects in newborns, but the influence of high doses of maternal FA supplementation on infants' brain development is unclear. The present study was aimed at investigating the effects of a high dose of gestational FA on the expression of genes in the cerebral hemispheres (CHs) of 1-day-old pups. One week prior to mating and throughout the entire period of gestation, female C57BL/6J mice were fed a diet, containing FA at either 2 mg/kg (control diet (CD)) or 20 mg/kg (high maternal folic acid (HMFA)). At postnatal day 1, pups from different dams were sacrificed and CH tissues were collected. Quantitative RT-PCR and Western blot analysis confirmed sex-specific alterations in the expression of several genes that modulate various cellular functions (P < 0.05) in pups from the HMFA group. Genomic DNA methylation analysis showed no difference in the level of overall methylation in pups from the HMFA group. These findings demonstrate that HMFA supplementation alters offsprings' CH gene expression in a sex-specific manner. These changes may influence infants' brain development.

Roles of imprinted genes in neural stem cells

Imprinted genes and neural stem cells (NSC) play an important role in the developing and mature brain. A central theme of imprinted gene function in NSCs is cell survival and G1 arrest to control cell division, cell-cycle exit, migration and differentiation. Moreover, genomic imprinting can be epigenetically switched off at some genes to ensure stem cell quiescence and differentiation. At the genome scale, imprinted genes are organized in dynamic networks formed by interchromosomal interactions and transcriptional coregulation of imprinted and nonimprinted genes. Such multilayered networks may synchronize NSC activity with the demand from the niche resembling their roles in adjusting fetal size.

Genomic imprinting, action, and interaction of maternal and fetal genomes

Mammalian viviparity (intrauterine development of the fetus) introduced a new dimension to brain development, with the fetal hypothalamus and fetal placenta developing at a time when the fetal placenta engages hypothalamic structures of the maternal generation. Such transgenerational interactions provide a basis for ensuring optimal maternalism in the next generation. This success has depended on genomic imprinting and a biased role of the matriline. Maternal methylation imprints determine parent of origin expression of genes fundamental to both placental and hypothalamic development. The matriline takes a further leading role for transgenerational reprogramming of these imprints. Developmental errors are minimized by the tight control that imprinted genes have on regulation of downstream evolutionary expanded gene families important for placental and hypothalamic development. Imprinted genes themselves have undergone purifying selection, providing a framework of stability for in utero development with most growth variance occurring postnatally. Mothers, not fathers, take the lead in the endocrinological and behavior adaptations that nurture, feed, and protect the infant. In utero coadaptive development of the placenta and hypothalamus has thus required a concomitant development to ensure male masculinization. Only placental male mammals evolved the sex determining SRY, which activates Sox9 for testes formation. SRY is a hybrid gene of Dgcr8 expressed in the developing placenta and Sox3 expressed in hypothalamic development. This hybridization of genes that take their origin from the placenta and hypothalamus has enabled critical in utero timing for the development of fetal Leydig cells, and hence testosterone production for hypothalamic masculinization.

The mechanisms underlying sexual differentiation of behavior and physiology in mammals and birds: relative contributions of sex steroids and sex chromosomes

From a classical viewpoint, sex-specific behavior and physiological functions as well as the brain structures of mammals such as rats and mice, have been thought to be influenced by perinatal sex steroids secreted by the gonads. Sex steroids have also been thought to affect the differentiation of the sex-typical behavior of a few members of the avian order Galliformes, including the Japanese quail and chickens, during their development in ovo. However, recent mammalian studies that focused on the artificial shuffling or knockout of the sex-determining gene, Sry, have revealed that sex chromosomal effects may be associated with particular types of sex-linked differences such as aggression levels, social interaction, and autoimmune diseases, independently of sex steroid-mediated effects. In addition, studies on naturally occurring, rare phenomena such as gynandromorphic birds and experimentally constructed chimeras in which the composition of sex chromosomes in the brain differs from that in the other parts of the body, indicated that sex chromosomes play certain direct roles in the sex-specific differentiation of the gonads and the brain. In this article, we review the relative contributions of sex steroids and sex chromosomes in the determination of brain functions related to sexual behavior and reproductive physiology in mammals and birds.

The imprinted brain: how genes set the balance between autism and psychosis

The imprinted brain theory proposes that autism spectrum disorder (ASD) represents a paternal bias in the expression of imprinted genes. This is reflected in a preference for mechanistic cognition and in the corresponding mentalistic deficits symptomatic of ASD. Psychotic spectrum disorder (PSD) would correspondingly result from an imbalance in favor of maternal and/or X-chromosome gene expression. If differences in gene expression were reflected locally in the human brain as mouse models and other evidence suggests they are, ASD would represent not so much an 'extreme male brain' as an extreme paternal one, with PSD correspondingly representing an extreme maternal brain. To the extent that copy number variation resembles imprinting and aneuploidy in nullifying or multiplying the expression of particular genes, it has been found to conform to the diametric model of mental illness peculiar to the imprinted brain theory. The fact that nongenetic factors such as nutrition in pregnancy can mimic and/or interact with imprinted gene expression suggests that the theory might even be able to explain the notable effect of maternal starvation on the risk of PSD - not to mention the 'autism epidemic' of modern affluent societies. Finally, the theory suggests that normality represents balanced cognition, and that genius is an extraordinary extension of cognitive configuration in both mentalistic and mechanistic directions. Were it to be proven correct, the imprinted brain theory would represent one of the biggest single advances in our understanding of the mind and of mental illness that has ever taken place, and would revolutionize psychiatric diagnosis, prevention and treatment - not to mention our understanding of epigenomics.

Epigenetics and brain evolution

Fundamental aspects of mammalian brain evolution occurred in the context of viviparity and placentation brought about by the epigenetic regulation of imprinted genes. Since the fetal placenta hormonally primes the maternal brain, two genomes in one individual are transgenerationally co-adapted to ensure maternal care and nurturing. Advanced aspects of neocortical brain evolution has shown very few genetic changes between monkeys and humans. Although these lineages diverged at approximately the same time as the rat and mouse (20 million years ago), synonymous sequence divergence between the rat and mouse is double that when comparing monkey with human sequences. Paradoxically, encephalization of rat and mouse are remarkably similar, while comparison of the human and monkey shows the human cortex to be three times the size of the monkey. This suggests an element of genetic stability between the brains of monkey and man with a greater emphasis on epigenetics providing adaptable variability.

Imprinted genes and hypothalamic function

Genomic imprinting is an important and enigmatic form of gene regulation in mammals in which one copy of a gene is silenced in a manner determined by its parental history. Imprinted genes range from those with constitutive monoallelic silencing to those, typically more remote from imprinting control regions, that display developmentally regulated, tissue-specific or partial monoallelic expression. This diversity may make these genes, and the processes they control, more or less sensitive to factors that modify or disrupt epigenetic marks. Imprinted genes have important functions in development and physiology, including major endocrine/neuroendocrine axes. Owing to is central role in coordinating growth, metabolism and reproduction, as well as evidence from genetic and knockout studies, the hypothalamus may be a focus for imprinted gene action. Are there unifying principles that explain why a gene should be imprinted? Conflict between parental genomes over limiting maternal resources, but also co-adaptation between mothers and offspring, have been invoked to explain the evolution of imprinting. Recent reports suggest there may be many more genes imprinted in the hypothalamus than hitherto expected, and it will be important for these new candidates to be validated and to determine whether they conform to current notions of how imprinting is regulated. In fully evaluating the role of imprinted genes in the hypothalamus, much work needs to be done to identify the specific neuronal populations in which particular genes are expressed, establish whether there are pathways in common and whether imprinted genes are involved in long-term programming of hypothalamic functions.

Is there a genomically imprinted social brain?

Imprinted genes (IGs) are expressed or silenced according to their parent-of-origin. These genes are known to play a role in regulating offspring growth, development and infant behaviors such as suckling and ultrasonic calls. In adults, neurally expressed IGs coordinate several behaviors including maternal care, sex, feeding, emotionality, and cognition. However, despite evidence from human psychiatric disorders and evolutionary theory that maternally and paternally expressed genes should also regulate social behavior, little empirical data from mouse research exists. This paper discusses data from a recent study (Garfield et al., 2011) that the IG Grb10 governs unique aspects of mouse social behavior and interprets the relevance of these findings for the future of this field.

Genomic imprinting: the emergence of an epigenetic paradigm

The emerging awareness of the contribution of epigenetic processes to genome function in health and disease is underpinned by decades of research in model systems. In particular, many principles of the epigenetic control of genome function have been uncovered by studies of genomic imprinting. The phenomenon of genomic imprinting, which results in some genes being expressed in a parental--origin-specific manner, is essential for normal mammalian growth and development and exemplifies the regulatory influences of DNA methylation, chromatin structure and non-coding RNA. Setting seminal discoveries in this field alongside recent progress and remaining questions shows how the study of imprinting continues to enhance our understanding of the epigenetic control of genome function in other contexts.

Genomic imprinting and mammalian reproduction

Among animals, genomic imprinting is a uniquely mammalian phenomenon in which certain genes are monoallelically expressed according to their parent of origin. This silencing of certain alleles often involves differential methylation at regulatory regions associated with imprinted genes and must be recapitulated at every generation with the erasure and reapplication of these epigenetic marks in the germline. Imprinted genes encode regulatory proteins that play key roles in fetal growth and development, but they also exert wider effects on mammalian reproduction. Genetic knockout experiments have shown that certain paternally expressed imprinted genes regulate post-natal behavior in offspring as well as reproductive behaviors in males and females. These deficits involve changes in hypothalamic function affecting multiple areas and different neurochemical pathways. Paternally expressed genes are highly expressed in the hypothalamus which regulates growth, metabolism and reproduction and so are well placed to influence all aspects of reproduction from adults to the resultant offspring. Coadaptation between offspring and mother appears to have played an important role in the evolution of some paternally expressed genes, but the influence of these genes on male reproductive behavior also suggests that they have evolved to regulate their own transmission to successive generations via the male germline.

A conceptual contribution to battles in the brain

Badcock and Crespi have advanced the hypothesis that autism and schizophrenia are caused by imbalanced imprinting in the brain. They argue that an imbalance between the effects of paternally and maternally expressed genes on brain development results in either an extreme paternal (autism) or maternal brain (schizophrenia). In this paper their conceptual model is discussed and criticized since it presupposes an incoherent distinction between observable physical and hidden mental phenomena. An alternative model is discussed that may be more fruitful for investigating the possible role of imprinted genes in the development of social behaviour. The development of crying and reactive crying and behaviours necessary for collaborative action are discussed as a promising research area for understanding the effects of imprinted genes.

Critical periods and the developmental origins of disease: an epigenetic perspective of schizophrenia

Epigenetics holds promise to explain some puzzles concerning the risk and course of psychiatric disorders. Epigenetic information is essential as a set of operating instructions for the genome, which is heritable with DNA. The epigenetic regulation of gene expression can plausibly be influenced by the environment of one's ancestors, prenatal exposures, and by early life events. Some epigenetic mechanisms may alter neurophysiology throughout life by programming gene expression, perhaps in anticipation of certain life experiences. These epigenetic signals are only meta-stable and may be perturbed by stochastic events, errors, or by environmental toxins. This introduction considers the possibility that epigenetic change that may occur as paternal age advances or during fetal adversity may be causally related to the susceptibility for schizophrenia.

Parent-of-origin and trans-generational germline influences on behavioral development: the interacting roles of mothers, fathers, and grandparents

Mothers and fathers do not contribute equally to the development of their offspring. In addition to the differential investment of mothers versus fathers in the rearing of offspring, there are also a number of germline factors that are transmitted unequally from one parent or the other that contribute significantly to offspring development. This article shall review four major sources of such parent-of-origin effects. Firstly, there is increasing evidence that genes inherited on the sex chromosomes including the nonpseudoautosomal part of the Y chromosome that is only inherited from fathers to sons, contribute to brain development and behavior independently of the organizing effects of sex hormones. Secondly, recent work has demonstrated that mitochondrial DNA that is primarily inherited only from mothers may play a much greater than anticipated role in neurobehavioral development. Thirdly, there exists a class of genes known as imprinted genes that are epigenetically silenced when passed on in a parent-of-origin specific manner and have been shown to regulate brain development and a variety of behaviors. Finally, there is converging evidence from several disciplines that environmental variations experienced by mothers and fathers may lead to plasticity in the development and behavior of offspring and that this phenotypic inheritance can be solely transmitted through the germline. Mechanistically, this may be achieved through altered programming within germ cells of the epigenetic status of particular genes such as retrotransposons and imprinted genes or potentially through altered expression of RNAs within gametes.

High-resolution analysis of parent-of-origin allelic expression in the mouse brain

Genomic imprinting results in preferential expression of the paternal or maternal allele of certain genes. We have performed a genome-wide characterization of imprinting in the mouse embryonic and adult brain. This approach uncovered parent-of-origin allelic effects of more than 1300 loci. We identified parental bias in the expression of individual genes and of specific transcript isoforms, with differences between brain regions. Many imprinted genes are expressed in neural systems associated with feeding and motivated behaviors, and parental biases preferentially target genetic pathways governing metabolism and cell adhesion. We observed a preferential maternal contribution to gene expression in the developing brain and a major paternal contribution in the adult brain. Thus, parental expression bias emerges as a major mode of epigenetic regulation in the brain.

The essence of linkage-based imprinting detection: comparing power, type 1 error, and the effects of confounders in two different analysis approaches

Imprinting is critical to understanding disease expression. It can be detected using linkage information, but the effects of potential confounders (heterogeneity, sex-specific penetrance, and sex-biased ascertainment) have not been explored. We examine power and confounders in two imprinting detection approaches, and we explore imprinting-linkage interaction. One method (PP) models imprinting by maximising lod scores w.r.t. parent-specific penetrances. The second (DRF) approximates imprinting by maximising lods over differential male-female recombination fractions. We compared power, type 1 error, and confounder effects in these two methods, using computer-simulated data. We varied heterogeneity, penetrance, family and dataset size, and confounders that might mimic imprinting. Without heterogeneity, PP had more imprinting-detecting power than DRF. PP's power increased when parental affectedness status was ignored, but decreased with heterogeneity. With heterogeneity, type 1 error increased dramatically for both methods. However, DRF's power also increased under heterogeneity, more than was attributable to inflated type 1 error. Sex-specific penetrance could increase false positives for PP but not for DRF. False positives did not increase on ascertainment through an affected "mother". For PP, non-penetrant individuals increased information, arguing against using affected-only methods. The high type 1 error levels under some circumstances means these methods must be used cautiously.

ATRX partners with cohesin and MeCP2 and contributes to developmental silencing of imprinted genes in the brain

Human developmental disorders caused by chromatin dysfunction often display overlapping clinical manifestations, such as cognitive deficits, but the underlying molecular links are poorly defined. Here, we show that ATRX, MeCP2, and cohesin, chromatin regulators implicated in ATR-X, RTT, and CdLS syndromes, respectively, interact in the brain and colocalize at the H19 imprinting control region (ICR) with preferential binding on the maternal allele. Importantly, we show that ATRX loss of function alters enrichment of cohesin, CTCF, and histone modifications at the H19 ICR, without affecting DNA methylation on the paternal allele. ATRX also affects cohesin, CTCF, and MeCP2 occupancy within the Gtl2/Dlk1 imprinted domain. Finally, we show that loss of ATRX interferes with the postnatal silencing of the maternal H19 gene along with a larger network of imprinted genes. We propose that ATRX, cohesin, and MeCP2 cooperate to silence a subset of imprinted genes in the postnatal mouse brain.

Genomic imprinting of experience-dependent cortical plasticity by the ubiquitin ligase gene Ube3a

A defect in the maternal copy of a ubiqutin ligase gene Ube3a can produce a neurodevelopmental defect in human children known as Angelman syndrome. We investigated the role of the maternally expressed Ube3a gene in experience-dependent development and plasticity of the mouse visual system. As demonstrated by optical imaging, rapid ocular dominance (OD) plasticity after brief monocular deprivation (MD) was severely impaired during the critical period (CP) in the visual cortex (VC) of Ube3a maternal-deficient (m-/p+) mice. Prolonged MD elicited significant plasticity in m-/p+ mice that never matched the level seen in control animals. In older animals after the CP, 7-day MD elicited mild OD shifts in both control and m-/p+ mice; however, the OD shifts in m-/p+ mice lacked the strengthening of visual responses to the two eyes characteristic of normal adult plasticity. Anatomic effects of the maternal deficiency include reduced spine density on basal, but not apical, dendrites of pyramidal neurons in the binocular region of the VC. Imprinting of Ube3a expression was not fully established in the early postnatal period, consistent with the normal development of cortical retinotopy and visual acuity that we observed in m-/p+ mice, but was fully established by the onset of the CP. These results demonstrate that paternal and maternal genomes are not functionally equivalent for cortical plasticity, and that maternally expressed Ube3a is required for normal experience-dependent modification of cortical circuits during and after the CP.

Upregulation of imprinted genes in mice: an insight into the intensity of gene expression and the evolution of genomic imprinting

Imprinted genes are expressed monoallelically because one of the two copies is silenced epigentically in a parent-of-origin pattern. This pattern of expression is controlled by differential marking of parental alleles by DNA methylation and chromatin modifications, including both suppressive and permissive histone acetylation and methylation. Suppressive histone modifications mark silenced alleles of imprinted genes, while permissive histone modifications mark the active alleles, suggesting the possibility that imprinted genes would show upregulation in gene expression. However, it is currently unknown whether imprinted genes show such upregulation. To address this question in mice, we estimated the intensity of expression of 59 genes relative to the rest of the genome by analyzing microarray data. Expression levels of 24 genes were validated using quantitative real-time PCR (qPCR). Expression of imprinted genes was found to be upreguled in various adult and embryonic mouse tissues. Consistent with their functions in growth and development, imprinted genes were found to be highly expressed in extraembryonic tissues and progressively upregulated during early embryonic development. In conclusion, upregulation of imprinted genes found in this study is similar to the dosage compensation (twofold upregulation) recently reported for X-linked genes. It has been proposed that the twofold upregulation of X-linked genes has been coupled with low transcriptional variation (noise) which could lead to deleterious effects on the organism. Results of this study suggest a general need for imprinted genes in the mouse to be upregulated to certain levels in order to avoid deleterious effects of variation in gene expression.

THE INHERITANCE OF COGNITIVE SKILLS: DOES GENOMIC IMPRINTING PLAY A ROLE?

Genomic imprinting refers to the differential expression of a gene based on parental origin. Animal and clinical studies have suggested that genomic imprinting is influential in brain development, with the maternal genome playing a disproportionate role in the development of the cortex. The present study investigated this phenomenon in a nonclinical human population, using intrafamilial correlations. Broadly consistent with predictions, it was found that abilities mediated by frontal, parietal, and temporal lobes, but not occipital lobes, were more closely correlated between children and mothers versus fathers. The implications of these findings for the prevailing theory of the evolution of genomic imprinting, and for the general study of genetics and behavior, are discussed.

Genomic imprinting in the development and evolution of psychotic spectrum conditions

I review and evaluate genetic and genomic evidence salient to the hypothesis that the development and evolution of psychotic spectrum conditions have been mediated in part by alterations of imprinted genes expressed in the brain. Evidence from the genetics and genomics of schizophrenia, bipolar disorder, major depression, Prader-Willi syndrome, Klinefelter syndrome, and other neurogenetic conditions support the hypothesis that the etiologies of psychotic spectrum conditions commonly involve genetic and epigenetic imbalances in the effects of imprinted genes, with a bias towards increased relative effects from imprinted genes with maternal expression or other genes favouring maternal interests. By contrast, autistic spectrum conditions, including Kanner autism, Asperger syndrome, Rett syndrome, Turner syndrome, Angelman syndrome, and Beckwith-Wiedemann syndrome, commonly engender increased relative effects from paternally expressed imprinted genes, or reduced effects from genes favouring maternal interests. Imprinted-gene effects on the etiologies of autistic and psychotic spectrum conditions parallel the diametric effects of imprinted genes in placental and foetal development, in that psychotic spectrum conditions tend to be associated with undergrowth and relatively-slow brain development, whereas some autistic spectrum conditions involve brain and body overgrowth, especially in foetal development and early childhood. An important role for imprinted genes in the etiologies of psychotic and autistic spectrum conditions is consistent with neurodevelopmental models of these disorders, and with predictions from the conflict theory of genomic imprinting.

Imprinting and psychiatric genetics: Beware the diagnostic phenotype

Studies of the role of imprinted genes in psychological phenomena are long overdue. The target article is comprehensive, presenting a wealth of important and convergent evidence, and provides an excellent point of departure for further research. However, the authors' evidentiary grasp exceeds the explicatory capacity of the proposed model. Greater genotypic and phenotypic precision would significantly enhance its predictive power.

Is this conjectural phenotypic dichotomy a plausible outcome of genomic imprinting?

What is the status of the dichotomy proposed and the nosological validity of the contrasting pathologies described in the target article? How plausibly can dysregulated imprinting explain the array of features described, compared with other genetic models? We believe that considering alternative models is more likely to lead in the long term to the correct classification and explanation of the component behaviours.

Derivation of human embryonic stem cell lines from parthenogenetic blastocysts

Parthenogenesis is one of the main, and most useful, methods to derive embryonic stem cells (ESCs), which may be an important source of histocompatible cells and tissues for cell therapy. Here we describe the derivation and characterization of two ESC lines (hPES-1 and hPES-2) from in vitro developed blastocysts following parthenogenetic activation of human oocytes. Typical ESC morphology was seen, and the expression of ESC markers was as expected for alkaline phosphatase, octamer-binding transcription factor 4, stage-specific embryonic antigen 3, stage-specific embryonic antigen 4, TRA-1-60, and TRA-1-81, and there was absence of expression of negative markers such as stage-specific embryonic antigen 1. Expression of genes specific for different embryonic germ layers was detected from the embryoid bodies (EBs) of both hESC lines, suggesting their differentiation potential in vitro. However, in vivo, only hPES-1 formed teratoma consisting of all three embryonic germ layers (hPES-2 did not). Interestingly, after continuous proliferation for more than 100 passages, hPES-1 cells still maintained a normal 46 XX karyotype; hPES-2 displayed abnormalities such as chromosome translocation after long term passages. Short Tandem Repeat (STR) results demonstrated that the hPES lines were genetic matches with the egg donors, and gene imprinting data confirmed the parthenogenetic origin of these ES cells. Genome-wide SNP analysis showed a pattern typical of parthenogenesis. All of these results demonstrated the feasibility to isolate and establish human parthenogenetic ESC lines, which provides an important tool for studying epigenetic effects in ESCs as well as for future therapeutic interventions in a clinical setting.

Genomic imprinting and human psychology: cognition, behavior and pathology

Imprinted genes expressed in the brain are numerous and it has become clear that they play an important role in nervous system development and function. The significant influence of genomic imprinting during development sets the stage for structural and physiological variations affecting psychological function and behaviour, as well as other physiological systems mediating health and well-being. However, our understanding of the role of imprinted genes in behaviour lags far behind our understanding of their roles in perinatal growth and development. Knowledge of genomic imprinting remains limited among behavioral scientists and clinicians and research regarding the influence of imprinted genes on normal cognitive processes and the most common forms of neuropathology has been limited to date. In this chapter, we will explore how knowledge of genomic imprinting can be used to inform our study of normal human cognitive and behavioral processes as well as their disruption. Behavioural analyses of rare imprinted disorders, such as Prader-Willi and Angelman syndromes, provide insight regarding the phenotypic impact of imprinted genes in the brain, and can be used to guide the study of normal behaviour as well as more common but etiologically complex disorders such as ADHD and autism. Furthermore, hypotheses regarding the evolutionary development of imprinted genes can be used to derive predictions about their role in normal behavioural variation, such as that observed in food-related and social interactions.

Genomic imprinting and the evolution of sex differences in mammalian reproductive strategies

Two major developments have occurred that have influenced the evolution of sexually dimorphic reproductive strategies of mammals. Viviparity and development of a placenta is one such development, especially in small-brained rodent lineages, where there has been a major impact of placental hormones on the maternal brain. In the Old World primate/hominoid lineages, the massive expansion of the brain through growth of the neocortex has radically changed how reproductive strategies are determined. Genomic imprinting has played a significant part in both of these developments. Most of the imprinted genes investigated to date are expressed in the placenta and a subset are expressed in both placenta and hypothalamus. Based on phenotypes derived from targeted mutagenesis, a hypothesis is developed for the coadaptive evolution of placenta and hypothalamus, particularly in the context of neurohormonal regulation of maternalism. In small-brained mammals, maternalism places a severe restriction on sexual activity, which in the case of a female rodent is little more than several hours in a lifetime compared with the several weeks given over to maternalism. The consequent sparsity of oestrous, sexually receptive females imposes a rigorous competitive reproductive strategy in males, with the onus being on the male's ability to find oestrous females. This has resulted in a marked sex difference in the chemosensory system, particularly the VNO accessory olfactory system, for the engagement of male sexual behavior in response to oestrous females. Genomic imprinting, together with neonatal androgens, has also played a role in the developing accessory olfactory system and its role in detecting oestrous females. With the evolutionary expansion of the neocortex seen in Old World primates and hominids, reproductive strategies are complex and embedded in the social structure and hierarchies which characterize primate societies. Reproductive strategies depend far more on intelligent behavioral determinants than they do on hormonal determinants. In females, sexual activity is not restricted to oestrous periods, indeed most of the sexual activity is not reproductive. Male Old World primates continue to mate for years after castration, but loss of dominance status leads to a loss of sexual interest within days. The genetic basis for the expansion of neocortical development is complex, but those parts of the brain which have expanded are undoubtedly under the influence of imprinted genes, as studies using parthenogenetic and androgenetic chimeras and allometric analysis of brains across comparative phylogenies have shown. Sex differences in behavior owe much to social structure, social learning, and the deployment of intelligent behavioral strategies. The epigenetic effects of social learning on brain development have become equally as important as the epigenetic effects of hormones on brain development and both contribute to sex differences in behavior in large-brained primates.

Rabbit somatic cell cloning: effects of donor cell type, histone acetylation status and chimeric embryo complementation

The epigenetic status of a donor nucleus has an important effect on the developmental potential of embryos produced by somatic cell nuclear transfer (SCNT). In this study, we transferred cultured rabbit cumulus cells (RCC) and fetal fibroblasts (RFF) from genetically marked rabbits (Alicia/Basilea) into metaphase II oocytes and analyzed the levels of histone H3-lysine 9-lysine 14 acetylation (acH3K9/14) in donor cells and cloned embryos. We also assessed the correlation between the histone acetylation status of donor cells and cloned embryos and their developmental potential. To test whether alteration of the histone acetylation status affects development of cloned embryos, we treated donor cells with sodium butyrate (NaBu), a histone deacetylase inhibitor. Further, we tried to improve cloning efficiency by chimeric complementation of cloned embryos with blastomeres from in vivo fertilized or parthenogenetic embryos. The levels of acH3K9/14 were higher in RCCs than in RFFs (P<0.05). Although the type of donor cells did not affect development to blastocyst, after transfer into recipients, RCC cloned embryos induced a higher initial pregnancy rate as compared to RFF cloned embryos (40 vs 20%). However, almost all pregnancies with either type of cloned embryos were lost by the middle of gestation and only one fully developed, live RCC-derived rabbit was obtained. Treatment of RFFs with NaBu significantly increased the level of acH3K9/14 and the proportion of nuclear transfer embryos developing to blastocyst (49 vs 33% with non-treated RFF, P<0.05). The distribution of acH3K9/14 in either group of cloned embryos did not resemble that in in vivo fertilized embryos suggesting that reprogramming of this epigenetic mark is aberrant in cloned rabbit embryos and cannot be corrected by treatment of donor cells with NaBu. Aggregation of embryos cloned from NaBu-treated RFFs with blastomeres from in vivo derived embryos improved development to blastocyst, but no cloned offspring were obtained. Two live cloned rabbits were produced from this donor cell type only after aggregation of cloned embryos with a parthenogenetic blastomere. Our study demonstrates that the levels of histone acetylation in donor cells and cloned embryos correlate with their developmental potential and may be a useful epigenetic mark to predict efficiency of SCNT in rabbits.

Genomic imprinting mediates sexual experience-dependent olfactory learning in male mice

Mammalian imprinted genes are generally thought to have evolved as a result of conflict between parents; however, recent knockout studies suggest that coadaptation between mother and offspring may have been a significant factor. We present evidence that the same imprinted gene that regulates mammalian maternal care and offspring development also regulates male sexual behavior and olfaction. We have shown that the behavior of male mice carrying a knockout of the imprinted gene Peg3 does not change with sexual experience and that the mice are consequently unable to improve their copulatory abilities or olfactory interest in female odor cues after mating experience. Forebrain activation, as indexed by female odor-induced c-Fos protein induction, fails to increase with sexual experience, providing a neural basis for the behavioral deficits that the male mice display. The behavioral and neural effects of the Peg3 knockout show that this imprinted gene has evolved to regulate multiple and varied aspects of reproduction, from male sexual behavior to female maternal care, and the development of offspring. Moreover, sexual experience-driven behavioral changes may represent an adaptive response that enables males to increase their reproductive potential over their lifespan, and the effects we have found suggest that the evolution of genomic imprinting has been influenced by coadaptation between males and females as well as between females and offspring.

Hematopoietic reconstitution with androgenetic and gynogenetic stem cells

Parthenogenetic embryonic stem (ES) cells with two oocyte-derived genomes (uniparental) have been proposed as a source of autologous tissue for transplantation. The therapeutic applicability of any uniparental cell type is uncertain due to the consequences of genomic imprinting that in mammalian uniparental tissues causes unbalanced expression of imprinted genes. We transplanted uniparental fetal liver cells into lethally irradiated adult mice to test their capacity to replace adult hematopoietic tissue. Both maternal (gynogenetic) and paternal (androgenetic) derived cells conveyed long-term, multilineage reconstitution of hematopoiesis in recipients, with no associated pathologies. We also establish that uniparental ES cells can differentiate into transplantable hematopoietic progenitors in vitro that contribute to long-term hematopoiesis in recipients. Hematopoietic tissue in recipients maintained fidelity of parent-of-origin methylation marks at the Igf2/H19 locus; however, variability occurred in the maintenance of parental-specific methylation marks at other loci. In summary, despite genomic imprinting and its consequences on development that are particularly evident in the androgenetic phenotype, uniparental cells of both parental origins can form adult-transplantable stem cells and can repopulate an adult organ.

The Odyssey of MeCP2 and parental imprinting

DNA methylation in mammals has long been implicated in the epigenetic mechanism of parental imprinting, in which selective expression of one allele of specific genes is based on parental origin. Methyl CpG binding protein 2 (MeCP2) selectively binds to methylated DNA and mutations in the MECP2 cause the autism-spectrum neurodevelopmental disorder Rett syndrome. This review outlines the emerging story of how MeCP2 has been implicated in the regulation of specific imprinted genes and loci, including UBE3A and DLX5. The story of MeCP2 and parental imprinting has unfolded with some interesting but unexpected twists, revealing new insights on the function of MeCP2 in the process.

Epigenetics of Complex Diseases: From General Theory to Laboratory Experiments

Despite significant effort, understanding the causes and mechanisms of complex non-Mendelian diseases remains a key challenge. Although numerous molecular genetic linkage and association studies have been conducted in order to explain the heritable predisposition to complex diseases, the resulting data are quite often inconsistent and even controversial. In a similar way, identification of environmental factors causal to a disease is difficult. In this article, a new interpretation of the paradigm of "genes plus environment" is presented in which the emphasis is shifted to epigenetic misregulation as a major etiopathogenic factor. Epigenetic mechanisms are consistent with various non-Mendelian irregularities of complex diseases, such as the existence of clinically indistinguishable sporadic and familial cases, sexual dimorphism, relatively late age of onset and peaks of susceptibility to some diseases, discordance of monozygotic twins and major fluctuations on the course of disease severity. It is also suggested that a substantial portion of phenotypic variance that traditionally has been attributed to environmental effects may result from stochastic epigenetic events in the cell. It is argued that epigenetic strategies, when applied in parallel with the traditional genetic ones, may significantly advance the discovery of etiopathogenic mechanisms of complex diseases. The second part of this chapter is dedicated to a review of laboratory methods for DNA methylation analysis, which may be useful in the study of complex diseases. In this context, epigenetic microarray technologies are emphasized, as it is evident that such technologies will significantly advance epigenetic analyses in complex diseases.

Imbalanced genomic imprinting in brain development: an evolutionary basis for the aetiology of autism

We describe a new hypothesis for the development of autism, that it is driven by imbalances in brain development involving enhanced effects of paternally expressed imprinted genes, deficits of effects from maternally expressed genes, or both. This hypothesis is supported by: (1) the strong genomic-imprinting component to the genetic and developmental mechanisms of autism, Angelman syndrome, Rett syndrome and Turner syndrome; (2) the core behavioural features of autism, such as self-focused behaviour, altered social interactions and language, and enhanced spatial and mechanistic cognition and abilities, and (3) the degree to which relevant brain functions and structures are altered in autism and related disorders. The imprinted brain theory of autism has important implications for understanding the genetic, epigenetic, neurological and cognitive bases of autism, as ultimately due to imbalances in the outcomes of intragenomic conflict between effects of maternally vs. paternally expressed genes.

Chromatin remodeling and neuronal function: exciting links

Regulation of gene expression occurs at different levels, from DNA to protein, and through various mechanisms. One of them is modification of the chromatin structure, which is involved in the definition of transcriptional active and inactive regions of the chromosomes. These phenomena are associated with reversible chemical modifications of the genetic material rather than with variability within the DNA sequences inherited by the individual and are therefore called 'epigenetic' modifications. Ablation of the molecular players responsible for epigenetic modifications often gives rise to neurological and behavioral phenotypes in humans and in mouse models, suggesting a relevant function for chromatin remodeling in central nervous system function, particularly in the adaptive response of the brain to stimuli. We will discuss several human disorders that are due to altered epigenetic mechanisms, with special focus on Rett syndrome.

Tissue-specific reactivation of gene expression at an imprinted locus

Genomic imprinting is the phenomenon where the expression pattern of an allele at a locus differs depending on the allele's parent of origin. In most cases, one of the two alleles is transcriptionally silent. Recent empirical work has shown some genes to be imprinted in a tissue-specific manner, where the silenced allele becomes reactivated in particular cell lineages during development. Here I describe an evolutionary model of tissue-specific transcriptional reactivation. The model describes the relationships among various inclusive fitness functions and phenotypic effects necessary for natural selection to favor the epigenetic reprogramming required for this sort of reactivation, and makes predictions regarding the nature and magnitude of phenotypic and fitness consequences of mutations in particular somatic tissues. In particular, if an imprinted gene is reactivated in one of two tissues that interact in producing a particular phenotype, expression of the gene in those two tissues is expected to have opposite phenotypic effects. The model predicts that in some cases, mutations affecting the silenced allele at an imprinted locus may be phenotypically more severe than those affecting the expressed allele. These predictions are contrasted with those of an alternative explanation for reactivation: protection against deleterious recessive somatic mutations. The inclusive-fitness model of reactivation indicates that the intragenomic conflicts present in the parental germ lines and developing embryo persist though adult life, and can have complex effects on phenotypes and patterns of gene expression in somatic tissues.

Looking for trouble: a search for developmental defects of the hypothalamus

The hypothalamus is a critical integrator of several homeostatic processes that are required for the survival of vertebrates. Disruption of the development of the hypothalamus thus has the potential of perturbing important physiological processes with lifelong consequences. We review current knowledge about how cell types are specified and circuits are formed within the developing hypothalamus. We emphasize the potential clinical impact of the perturbations of these pathways using the regulation of energy balance as a model. We predict that disruption of hypothalamic development is a common, previously unsuspected cause of disorders of homeostatic processes such as obesity and high blood pressure.

Imprinted gene expression in the brain

In normal mammals, autosomal genes are present in duplicate (i.e. two alleles), one inherited from the father, and one from the mother. For the majority of genes both alleles are transcribed (or expressed) equally. However, for a small subset of genes, known as imprinted genes, only one allele is expressed in a parent-of-origin dependent manner (note that the 'imprint' here refers to the epigenetic mechanism through which one allele is silenced, and is completely unrelated to classical 'filial imprinting' manifest at the behavioural level). Thus, for some imprinted genes expression is only (or predominantly) seen from the paternally inherited allele, whilst for the remainder, expression is only observed from the maternally inherited allele. Early work on this class of genes highlighted their importance in gross developmental and growth phenotypes. Recent studies in mouse models and humans have emphasised their contribution to brain function and behaviour. In this article, we review the literature concerning the expression of imprinted genes in the brain. In particular, we attempt to define emerging organisation themes, especially in terms of the direction of imprinting (i.e. maternal or paternal expression). We also emphasise the likely role of imprinted genes in neurodevelopment. We end by pointing out that, so far as discerning the precise functions of imprinted genes in the brain is concerned, there are currently more questions than answers; ranging from the extent to which imprinted genes might contribute to common mental disorders, to wider issues related to how easily the new data on brain may be accommodated within the dominant theory regarding the origins and maintenance of imprinting, which pits the maternal and paternal genomes against each other in an evolutionary battle of the sexes.

Conservation of genomic imprinting at the XIST, IGF2, and GTL2 loci in the bovine

Genomic imprinting is theorized to exist in all placental mammals and some marsupials; however, extensive comparative analysis of animals aside from humans and mice remains incomplete. Here we report conservation of genomic imprinting in the bovine at the X chromosome inactivation-specific transcript (XIST), insulin-like growth factor 2 (IGF2), and gene trap locus 2 (GTL2) loci. Coding single nucleotide polymorphisms (SNPs) between Bos gaurus and Bos taurus were detected at the XIST, IGF2, and GTL2 loci, which have previously been identified as imprinted in either humans, mice, or sheep. Expression patterns of parental alleles in F1 hybrids indicated preferential paternal expression at the XIST locus solely in the chorion of females, whereas analysis of the IGF2 and GTL2 loci indicated preferential paternal and maternal expression of alleles, respectively, in both fetal and placental tissues. Comparative sequence analysis of the XIST locus and adjacent regions suggests that repression of the maternal allele in the bovine is controlled by a different mechanism than in mice, further reinforcing the importance of comparative analysis of imprinting.

Paternal contribution to fetal alcohol syndrome

Maternal alcohol use during pregnancy is associated with a wide range of adverse outcomes for the child. Many women who drink during pregnancy also have male partners who abuse alcohol. Existing data on paternal effects of alcohol abuse during the preconceptual period and at the time of conception are reviewed. Epidemiological data offer some support for a paternal influence on birth weight, congenital heart defects, and some evidence of mild cognitive impairments. Animal data have demonstrated decreased litter size, increased prevalence of low birth weight fetuses and mixed data on risk of malformations. Increased susceptibility to Pseudomonas bacterial infection has been reported. Cognitive and behavioral findings are the most robust effects. These include learning and memory deficits, hyperactivity, and poor stress tolerance. Multiple causal mechanisms for a paternal effect have been suggested, but none seems satisfactory to explain all findings. Further research is needed on paternal effects in animals and human populations. The results of this research may influence prevention activities.

Just how happy is the happy puppet? An emotion signaling and kinship theory perspective on the behavioral phenotype of children with Angelman syndrome

The favored level of parental investment in a child may differ for genes of maternal and paternal origin in the child. This conflict can be expressed in the phenomenon of genomic imprinting that refers to situations in which the same gene is differentially expressed depending on its parent of origin. Two disorders that show the effects of genomic imprinting--both at 15q11-q13--are Angelman Syndrome (AS) which is due to the absence of expression of maternally-inherited genes and Prader-Willi syndromes (PWS) which is due to the absence of expression of paternally-inherited genes. However, although both disorders can arise from the deletion of the same genetic region, the gustatory, behavioral, and affective characteristics of AS and PWS children are remarkably distinct. Recent research inspired by kinship theory has suggested the origins of these phenotypic differences may lie in the differential investment of each parent's genome in the AS or PWS child. Specifically, it is thought that each set of parental genes have different 'ideas' regarding how the child should behave towards the mother and how much investment they should look to extract. In normal cases, the trade-off between the competing parental genomes produces a behavioral equilibrium in the child. However, in pathological instances, particularly where gene expression is one-sided, the evolved behavioral strategies favored by the contributing genome will dominate the child's behavior. To date, research in the area of genomic conflict in AS and PWS children has primarily focusing on differences in post-natal nutrition-related behaviors. The current paper extends this framework by offering an emotion and evolutionary signaling interpretation of the affective characteristics of AS children. A review of the affective characteristics of the two syndromes (PWS and AS) is presented before kinship and emotions theory are used to examine the functions that differential affect expression may serve in altering maternal investment. We expected that because the ultimate goal of paternal genes is to increase the child rearing burden of mothers, the Angelman behavioral phenotype should exhibit the emotion signaling characteristics that elicit levels of investment more consistent with paternal genetic interests. AS children display more positive, relative to negative, affect expressions (i.e. AS children laugh and smile more frequently than PWS children). In affect signaling theories, positive affect signals (i.e., smiling, laughing) have evolved to manipulate the sensory systems of receivers to increase social resources. In contrast, because the expression of some negative affects may indicate to the mother that the infant is not viable, negative affect expression is characteristically low among AS children. However, AS children may nonetheless have high levels of non-expressed anxiety because of its role in assisting the child (and its paternal genome) to maintain vigilance for changes in investment on the part of the mother. Overall, our kinship and emotion signaling analysis of AS children suggests that their global pattern of affect signaling represents one manifestation of an array of possible evolved strategies within the parental genome. Specifically, because AS exhibits the effects of paternally-inherited genes unhindered by the expression of maternally-inherited genes, the AS infant manifests a pattern of expression and non-expression that maximize maternal investment and thus paternal fitness. This theory is a significant departure from the standard but erroneous conjecture that a mother and child's inclusive fitness interests are one and the same.