Mice lacking paternal expression of imprinted Grb10 are risk-takers

The imprinted genes Grb10 and Nesp influence impulsive behavior on a delay discounting task in an opposite manner. A recently developed theory suggests that this pattern of behavior may be representative of predicted effects of imprinted genes on tolerance to risk. Here we examine whether mice lacking paternal expression of Grb10 show abnormal behavior across a number of measures indicative of risk‐taking. Although Grb10^+/p mice show no difference from wild type (WT) littermates in their willingness to explore a novel environment, their behavior on an explicit test of risk‐taking, namely the Predator Odor Risk‐Taking task, is indicative of an increased willingness to take risks. Follow‐up tests suggest that this risk‐taking is not simply because of a general decrease in fear, or a general increase in motivation for a food reward, but reflects a change in the trade‐off between cost and reward. These data, coupled with previous work on the impulsive behavior of Grb10^+/p mice in the delayed reinforcement task, and taken together with our work on mice lacking maternal Nesp, suggest that maternally and paternally expressed imprinted genes oppositely influence risk‐taking behavior as predicted.

Intragenomic conflict over bet-hedging

Genomic imprinting, where an allele's expression pattern depends on its parental origin, is thought to result primarily from an intragenomic evolutionary conflict. Imprinted genes are widely expressed in the brain and have been linked to various phenotypes, including behaviours related to risk tolerance. In this paper, we analyse a model of evolutionary bet-hedging in a system with imprinted gene expression. Previous analyses of bet-hedging have shown that natural selection may favour alleles and traits that reduce reproductive variance, even at the expense of reducing mean reproductive success, with the trade-off between mean and variance depending on the population size. In species where the sexes have different reproductive variances, this bet-hedging trade-off differs between maternally and paternally inherited alleles. Where males have the higher reproductive variance, alleles are more strongly selected to reduce variance when paternally inherited than when maternally inherited. We connect this result to phenotypes connected with specific imprinted genes, including delay discounting and social dominance. The empirical patterns are consistent with paternally expressed imprinted genes promoting risk-averse behaviours that reduce reproductive variance. Conversely, maternally expressed imprinted genes promote risk-tolerant, variance-increasing behaviours. We indicate how future research might further test the hypotheses suggested by our analysis. This article is part of the theme issue 'Risk taking and impulsive behaviour: fundamental discoveries, theoretical perspectives and clinical implications'.

Analysis of mutation, selection, and epistasis: an informed approach to cancer clinical trials

Currently, drug development efforts and clinical trials to test them are often prioritized by targeting genes with high frequencies of somatic variants among tumors. However, differences in oncogenic mutation rate-not necessarily the effect the variant has on tumor growth-contribute enormously to somatic variant frequency. We argue that decoupling the contributions of mutation and cancer lineage selection to the frequency of somatic variants among tumors is critical to understanding-and predicting-the therapeutic potential of different interventions. To provide an indicator of that strength of selection and therapeutic potential, the frequency at which we observe a given variant across patients must be modulated by our expectation given the mutation rate and target size to provide an indicator of that strength of selection and therapeutic potential. Additionally, antagonistic and synergistic epistasis among mutations also impacts the potential therapeutic benefit of targeted drug development. Quantitative approaches should be fostered that use the known genetic architectures of cancer types, decouple mutation rate, and provide rigorous guidance regarding investment in targeted drug development. By integrating evolutionary principles and detailed mechanistic knowledge into those approaches, we can maximize our ability to identify those targeted therapies most likely to yield substantial clinical benefit.

Live animal assessments of rump fat and muscle score in Angus cows and steers using 3-dimensional imaging

The objective of this study was to develop a proof of concept for using off-the-shelf Red Green Blue-Depth (RGB-D) Microsoft Kinect cameras to objectively assess P8 rump fat (P8 fat; mm) and muscle score (MS) traits in Angus cows and steers. Data from low and high muscled cattle (156 cows and 79 steers) were collected at multiple locations and time points. The following steps were required for the 3-dimensional (3D) image data and subsequent machine learning techniques to learn the traits: 1) reduce the high dimensionality of the point cloud data by extracting features from the input signals to produce a compact and representative feature vector, 2) perform global optimization of the signatures using machine learning algorithms and a parallel genetic algorithm, and 3) train a sensor model using regression-supervised learning techniques on the ultrasound P8 fat and the classified learning techniques for the assessed MS for each animal in the data set. The correlation of estimating hip height (cm) between visually measured and assessed 3D data from RGB-D cameras on cows and steers was 0.75 and 0.90, respectively. The supervised machine learning and global optimization approach correctly classified MS (mean [SD]) 80 (4.7) and 83% [6.6%] for cows and steers, respectively. Kappa tests of MS were 0.74 and 0.79 in cows and steers, respectively, indicating substantial agreement between visual assessment and the learning approaches of RGB-D camera images. A stratified 10-fold cross-validation for P8 fat did not find any differences in the mean bias ( = 0.62 and = 0.42 for cows and steers, respectively). The root mean square error of P8 fat was 1.54 and 1.00 mm for cows and steers, respectively. Additional data is required to strengthen the capacity of machine learning to estimate measured P8 fat and assessed MS. Data sets for and continental cattle are also required to broaden the use of 3D cameras to assess cattle. The results demonstrate the importance of capturing curvature as a form of representing body shape. A data-driven model from shape to trait has established a proof of concept using optimized machine learning techniques to assess P8 fat and MS in Angus cows and steers.

Impulsive choices in mice lacking imprinted Nesp55

Genomic imprinting is the process whereby germline epigenetic events lead to parent-of-origin specific monallelic expression of a number of key mammalian genes. The imprinted gene Nesp is expressed from the maternal allele only and encodes for Nesp55 protein. In the brain, Nesp55 is found predominately in discrete areas of the hypothalamus and midbrain. Previously, we have shown that loss of Nesp55 gives rise to alterations in novelty-related behaviour. Here, we extend these findings and demonstrate, using the Nesp^m/+ mouse model, that loss of Nesp55 leads to impulsive choices as measured by a delayed-reinforcement task, whereby Nesp^m/+ mice were less willing to wait for a delayed, larger reward, preferring instead to choose an immediate, smaller reward. These effects were highly specific as performance in another component of impulsive behaviour, the ability to stop a response once started as assayed in the stop-signal reaction time task, was equivalent to controls. We also showed changes in the serotonin system, a key neurotransmitter pathway mediating impulsive behaviour. First, we demonstrated that Nesp55 is co-localized with serotonin and then went on to show that in midbrain regions there were reductions in mRNA expression of the serotonin-specific genes Tph2 and Slc6a4, but not the dopamine-specific gene Th in Nesp^m/+ mice; suggesting an altered serotonergic system could contribute, in part, to the changes in impulsive behaviour. These data provide a novel mode of action for genomic imprinting in the brain and may have implications for pathological conditions characterized by maladaptive response control.

Survival of the Curviest: Noise-Driven Selection for Synergistic Epistasis

A major goal of human genetics is to elucidate the genetic architecture of human disease, with the goal of fueling improvements in diagnosis and the understanding of disease pathogenesis. The degree to which epistasis, or non-additive effects of risk alleles at different loci, accounts for common disease traits is hotly debated, in part because the conditions under which epistasis evolves are not well understood. Using both theory and evolutionary simulation, we show that the occurrence of common diseases (i.e. unfit phenotypes with frequencies on the order of 1%) can, under the right circumstances, be expected to be driven primarily by synergistic epistatic interactions. Conditions that are necessary, collectively, for this outcome include a strongly non-linear phenotypic landscape, strong (but not too strong) selection against the disease phenotype, and "noise" in the genotype-phenotype map that is both environmental (extrinsic, time-correlated) and developmental (intrinsic, uncorrelated) and, in both cases, neither too little nor too great. These results suggest ways in which geneticists might identify, a priori, those disease traits for which an "epistatic explanation" should be sought, and in the process better focus ongoing searches for risk alleles.

The evolving landscape of imprinted genes in humans and mice: Conflict among alleles, genes, tissues, and kin

Three recent genome-wide studies in mice and humans have produced the most definitive map to date of genomic imprinting (gene expression that depends on parental origin) by incorporating multiple tissue types and developmental stages. Here, we explore the results of these studies in light of the kinship theory of genomic imprinting, which predicts that imprinting evolves due to differential genetic relatedness between maternal and paternal relatives. The studies produce a list of imprinted genes with around 120-180 in mice and ~100 in humans. The studies agree on broad patterns across mice and humans including the complex patterns of imprinted expression at loci like Igf2 and Grb10. We discuss how the kinship theory provides a powerful framework for hypotheses that can explain these patterns. Finally, since imprinting is rare in the genome despite predictions from the kinship theory that it might be common, we discuss evolutionary factors that could favor biallelic expression.

Genomic imprinting of Grb10: coadaptation or conflict?

Mammalian development involves significant interactions between offspring and mother. But is this interaction a carefully coordinated effort by two individuals with a common goal--offspring survival? Or is it an evolutionary battleground (a central idea in our understanding of reproduction). The conflict between parents and offspring extends to an offspring's genes, where paternally inherited genes favor demanding more from the mother, while maternally inherited genes favor restraint. This "intragenomic conflict" (among genes within a genome) is the dominant evolutionary explanation for "genomic imprinting." But a new study in PLOS Biology provides support for a different perspective: that imprinting might facilitate coordination between mother and offspring. According to this "coadaptation theory," paternally inherited genes might be inactivated because maternally inherited genes are adapted to function harmoniously with the mother. As discussed in this article, the growth effects associated with the imprinted gene Grb10 are consistent with this idea, but it remains to be seen just how general the pattern is.

Demography, kinship, and the evolving theory of genomic imprinting

Genomic imprinting is the differential expression of an allele based on the parent of origin. Recent transcriptome-wide evaluations of the number of imprinted genes reveal complex patterns of imprinted expression among developmental stages and cell types. Such data demand a comprehensive evolutionary framework in which to understand the effect of natural selection on imprinted gene expression. We present such a framework for how asymmetries in demographic parameters and fitness effects can lead to the evolution of genomic imprinting and place recent theoretical advances in this framework. This represents a modern interpretation of the kinship theory, is well suited to studying populations with complex social interactions, and provides predictions which can be tested with forthcoming transcriptomic data. To understand the intricate phenotypic patterns that are emerging from the recent deluge of data, future investigations of genomic imprinting will require integrating evolutionary theory, transcriptomic data, developmental and functional genetics, and natural history.

Immunization against polyandroalbumin leads to increases in lambing and tailing percentages

A series of 10 farm trials was conducted in which the lambing performance of ewes immunised against polyandroalbumin was compared with that of untreated ewes in the same flock. The trials show that polyandroalbumin treatment is a reliable method of increasing lambing and tailing percentages in New Zealand flocks. An average of 39 extra lambs born per 100 ewes tupped was achieved on farms where ewes were given two treatments about four weeks apart and rams were introduced 18-26 days after the second dose. On farms where rams were introduced less than 12 days after this booster injection an average of 19 extra lambs born per 100 ewes tupped resulted. On farms where rams were introduced at 18-26 days post booster injection an average of 35 extra lambs were tailed for every 100 ewes tupped. The response for immunization increased in direct relation to the liveweight of the ewes at tupping.

Diseases associated with genomic imprinting

Genomic imprinting is the phenomenon where the expression of a locus differs between the maternally and paternally inherited alleles. Typically, this manifests as transcriptional silencing of one of the alleles, although many genes are imprinted in a tissue- or isoform-specific manner. Diseases associated with imprinted genes include various cancers, disorders of growth and metabolism, and disorders in neurodevelopment, cognition, and behavior, including certain major psychiatric disorders. In many cases, the disease phenotypes associated with dysfunction at particular imprinted loci can be understood in terms of the evolutionary processes responsible for the origin of imprinting. Imprinted gene expression represents the outcome of an intragenomic evolutionary conflict, where natural selection favors different expression strategies for maternally and paternally inherited alleles. This conflict is reasonably well understood in the context of the early growth effects of imprinted genes, where paternally inherited alleles are selected to place a greater demand on maternal resources than are maternally inherited alleles. Less well understood are the origins of imprinted gene expression in the brain, and their effects on cognition and behavior. This chapter reviews the genetic diseases that are associated with imprinted genes, framed in terms of the evolutionary pressures acting on gene expression at those loci. We begin by reviewing the phenomenon and evolutionary origins of genomic imprinting. We then discuss diseases that are associated with genetic or epigenetic defects at particular imprinted loci, many of which are associated with abnormalities in growth and/or feeding behaviors that can be understood in terms of the asymmetric pressures of natural selection on maternally and paternally inherited alleles. We next described the evidence for imprinted gene effects on adult cognition and behavior, and the possible role of imprinted genes in the etiology of certain major psychiatric disorders. Finally, we conclude with a discussion of how imprinting, and the evolutionary-genetic conflicts that underlie it, may enhance both the frequency and morbidity of certain types of diseases.

The Red Queen theory of recombination hotspots

Recombination hotspots are small chromosomal regions, where meiotic crossover events happen with high frequency. Recombination is initiated by a double-strand break (DSB) that requires the intervention of the molecular repair mechanism. The DSB repair mechanism may result in the exchange of homologous chromosomes (crossover) and the conversion of the allelic sequence that breaks into the one that does not break (biased gene conversion). Biased gene conversion results in a transmission advantage for the allele that does not break, thus preventing recombination and rendering recombination hotspots transient. How is it possible that recombination hotspots persist over evolutionary time (maintaining the average chromosomal crossover rate) when they are self-destructive? This fundamental question is known as the recombination hotspot paradox and has attracted much attention in recent years. Yet, that attention has not translated into a fully satisfactory answer. No existing model adequately explains all aspects of the recombination hotspot paradox. Here, we formulate an intragenomic conflict model resulting in Red Queen dynamics that fully accounts for all empirical observations regarding the molecular mechanisms of recombination hotspots, the nonrandom targeting of the recombination machinery to hotspots and the evolutionary dynamics of hotspot turnover.

Short-term grazing of lucerne and chicory increases ovulation rate in synchronised Merino ewes

This study evaluated the ability of short-term grazing of live=green pasture to increase ovulation rate during late summer when annual pasture is generally dead and of low quality. Ovulation rates, measured by the number of corpora lutea, were compared between 4 nutritional treatments: senesced phalaris (Phalaris aquatica), phalaris plus 500g lupin grain per day, lucerne (Medicago sativa) or chicory (Chicorum intybus) pastures. The study used 100 Merino ewes per treatment, divided between 2 replicates. The experiment was repeated in 3 years; February 2006, and January 2007 and 2008. Oestrus was synchronised and the ewes grazed the pastures for 9 days prior to ovulation at times corresponding to days 8-17 of the cycle in 2006, and days 6-14 in 2007 and 2008. The proportion of ewes producing multiple ovulations was higher (P<0.05) in the lucerne and chicory (0.36, 0.38) than the phalaris (0.27), and intermediate in the lupin (0.33) treatment. Regression analysis showed that the proportion of ewes with multiple ovulations increased with the quantity of live herbage (P<0.04). Responses were achieved even at low levels of live herbage with 90% of the maximum proportion of multiples occurring at 350kg DM/ha. It is concluded that providing short-term grazing of live chicory or lucerne to ewes can increase ovulation rates relative to ewes grazing senesced phalaris and to levels similar to those achieved by lupin grain supplementation.

Imprinted genes and human disease: an evolutionary perspective

Imprinted genes have been associated with a wide range of diseases. Many of these diseases have symptoms that can be understood in the context of the evolutionary forces that favored imprinted expression at these loci. Modulation of perinatal growth and resource acquisition has played a central role in the evolution of imprinting and many of the diseases associated with imprinted genes involve some sort of growth or feeding disorder. In the first part of this chapter, we discuss the relationship between the evolution of imprinting and the clinical manifestations of imprinting-associated diseases. In the second half, we consider the variety of processes that can disrupt imprinted gene expression and function. We ask specifically if there is reason to believe that imprinted genes are particularly susceptible to deregulation-and whether a disruption of an imprinted gene is more likely to have deleterious consequences than a disruption of an unimprinted gene. There is more to a gene than its DNA sequence. C. H. Waddington used the term "epigenetic" to describe biological differences between tissues that result from the process of development. Waddington needed a new term to describe this variation which was neither the result of genotypic differences between the cells nor well described as phenotypic variation. We now understand that heritable modifications of the DNA--such as cytosine methylation--and aspects of chromatin structure--including histone modifications--are the mechanisms underlying what Waddington called the "epigenotype." Epigenetic modifications are established in particular cell lines during development and are responsible for the patterns of gene expression seen in different tissue types. In contemporary usage, the term epigenetic refers to heritable changes in gene expression that are not coded in the DNA sequence itself. In recent years, much attention has been paid to a particular type of epigenetic variation: genomic imprinting. In the case of imprinting, the maternally and paternally inherited genes within a single cell have epigenetic differences that result in divergent patterns of gene expression. In the simplest scenario, only one of the two alleles at an imprinted locus is expressed. In other cases, an imprinted locus can include a variety of maternally expressed, paternally expressed and biallelically expressed transcripts. Some of these transcripts produce different proteins through alternate splicing, while others produce noncoding RNA transcripts. Genomic imprinting can also interact with the "epigenotype" in Waddington's sense: many genes are imprinted in a tissue-specific manner, with monoallelic expression in some cell types and biallelic expression in others. Other chapters in this volume cover our current understanding of the mechanisms of imprinting, the phenotypic effects of imprinted genes in mammals and what we know about imprinting in plants. In this chapter we discuss the link between imprinted genes and human disease. First, we consider the phenotypes associated with imprinted genes and ask whether the disorders associated with these genes share a common motif. Second, we consider the nature and frequency of mutations of imprinted genes. We ask whether we should expect that imprinted genes are particularly fragile. That is, are they more likely to undergo mutation and/or are mutations of imprinted genes particularly likely to result in human disease? In general we consider how the field of evolutionary medicine--the use of evolution to understand why our body's design allows for the existence of disease at all--might contribute to our comprehension of disorders linked to genomic imprinting.

Competitive signal discrimination, methylation reprogramming and genomic imprinting

Genomic imprinting (parent-of-origin-dependent gene regulation) is associated with intra-genomic evolutionary conflict over the optimal pattern of gene expression. Most theoretical models of imprinting focus on the conflict between the maternally and paternally derived alleles at an imprinted locus. Recently, however, more attention has been focused on multi-directional conflicts involving not only the imprinted gene itself, but also the genes that encode the regulatory machinery responsible for establishing and maintaining imprinted gene expression. In this paper, I examine the conflict involved in epigenetic reprogramming of imprinted genes in early mammalian embryonic development. In the earliest phase of development, maternal-store proteins are responsible for most regulatory activity in the embryo. These proteins are under selection to maximize the mother's inclusive fitness, which is not identical to that of either of the sets of genes present in the embryo. Both the maternally and paternally derived genomes in the embryo favor maintenance of the epigenetic modifications established in the female and male germlines, respectively. Maternal-store proteins favor maintenance of some of these modifications, but erasure of others. Here I consider the logical structure of the machinery responsible for these two activities. Methylation maintenance is most effectively performed by AND-linked architectures, which may explain the unusual trafficking behavior of the oocyte-specific DNA methyltransferase, Dnmt1o. By contrast, demethylation is better supported by OR-linked architectures, which may explain the difficulty in identifying the factor(s) responsible for the active demethylation of the paternal genome following fertilization.

Expected coalescence times and segregating sites in a model of glacial cycles

The climatic fluctuations of the Quaternary have influenced the distribution of numerous plant and animal species. Several species suffer population reduction and fragmentation, becoming restricted to refugia during glacial periods and expanding again during interglacials. The reduction in population size may reduce the effective population size, mean coalescence time and genetic variation, whereas an increased subdivision may have the opposite effect. To investigate these two opposing forces, we proposed a model in which a panmictic and a structured phase alternate, corresponding to interglacial and glacial periods. From this model, we derived an expression for the expected coalescence time and number of segregating sites for a pair of genes. We observed that increasing the number of demes or the duration of the structured phases causes an increase in coalescence time and expected levels of genetic variation. We compared numerical results with the ones expected for a panmictic population of constant size, and showed that the mean number of segregating sites can be greater in our model even when population size is much smaller in the structured phases. This points to the importance of population structure in the history of species subject to climatic fluctuations, and helps explain the long gene genealogies observed in several organisms.

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.

Inheritance of proportionate dwarfism in Angus cattle

OBJECTIVE

To determine the mode of inheritance of congenital proportionate dwarfism in Angus and Angus crossbred cattle, initially detected in two commercial beef herds in northern New South Wales.

DESIGN

Matings of normal carrier sires to unrelated cows of diverse breeds, and of one carrier sire to his unaffected daughters. An unrelated Piedmontese bull was also mated to unaffected daughters of the carrier sires.

PROCEDURE

Two carrier Angus bulls and nine unaffected daughters, all of whom were completely indistinguishable from normal animals, were purchased for controlled breeding studies under known nutritional and disease conditions. Affected and carrier individuals were examined for the presence of obvious chromosomal abnormalities.

RESULTS

Angus dwarfism has been successfully reproduced under controlled experimental conditions over successive years using unrelated dams and is undoubtedly heritable. The high frequency of occurrence of affected individuals (23/61 = 0.38 +/- .06) among the progeny of matings of the Angus sires to unrelated females of diverse breeding is not compatible with recessive inheritance, because of the negligible frequency of proportionate dwarfism in the breeds of the dams. Both paternal and maternal transmission of the defect was demonstrated, so that imprinting in the strict sense of a gene that is only expressed when received from the male parent appears not to be involved. Tested individuals showed no evidence of gross chromosomal abnormality. Dominant autosomal inheritance with incomplete penetrance was indicated by the lack of expression of the defective gene in the two Angus sires and in three unaffected daughters who produced dwarf calves from matings to the Piedmontese bull.

CONCLUSIONS

The mode of inheritance is that of a single autosomal dominant gene with a penetrance coefficient of 0.75 +/- 0.12, estimated from the observed incidence of 23/61 affected offspring of the two carrier Angus bulls mated to unrelated dams. Simple genetic models involving either (i) an unstable mutant which changes at high frequency to the expressed dominant dwarfing allele during gametogenesis, or (ii) a dominant allele with penetrance determined by an unlinked modifying locus, are shown to be compatible with the experimental data. Both models indicate that penetrance of the dwarfing gene may possibly be higher in matings involving carrier daughters of the two Angus bulls.

Sex-biased migration in humans: what should we expect from genetic data?

Different patterns of mitochondrial and Y-chromosome diversity have been cited as evidence of long-term patrilocality in human populations. However, what patterns are expected depends on the nature of the sampling scheme. Samples from a local region reveal only the recent demographic history of that region, whereas sampling over larger geographic scales accesses older demographic processes. A historical change in migration becomes evident first at local geographic scales, and alters global patterns of genetic diversity only after sufficient time has passed. Analysis of forager populations in the ethnographic record suggests that patrilocality may not have predominated among pre-agricultural humans. The higher female migration rate inferred by some genetic studies may reflect a shift to patrilocality in association with the emergence of agriculture. A recent global survey does not show the expected effects of higher female migration, possibly because the sampling scheme used for this study is accessing pre-agricultural human migration patterns. In this paper, we show how the demographic shift associated with agriculture might affect genetic diversity over different spatial scales. We also consider the prospects for studying sex-biased migration using the X-linked and autosomal markers. These multi-locus comparisons have the potential of providing more robust estimates of sex differences than Y-linked and mitochondrial data, but only if a very large number of loci are included in the analysis.

Genomic imprinting and methylation: epigenetic canalization and conflict

Imprinted genes have patterns of expression that depend on the parent of origin of their alleles. Establishment of imprinting at a locus requires that the two alleles be differentially marked in oogenesis and spermatogenesis, that these marks escape reprogramming after fertilization, and that they are reliably transmitted through development. Recent work on the mammalian DNA methyltransferases involved in these processes suggests mechanisms of epigenetic canalization, which might contribute to the stability of epigenetic inheritance. At the same time, the interactions that determine whether a particular modification will be transmitted or reprogrammed are destabilized by evolutionary conflicts, as the genes and gene products controlling these processes are subject to divergent selective forces. This review summarizes many of the recent advances in our understanding of mammalian systems of epigenetic gene regulation in the context of the long-running evolutionary conflicts that have created them.

What good is genomic imprinting: the function of parent-specific gene expression

Parent-specific gene expression (genomic imprinting) is an evolutionary puzzle because it forgoes an important advantage of diploidy--protection against the effects of deleterious recessive mutations. Three hypotheses claim to have found a countervailing selective advantage of parent-specific expression. Imprinting is proposed to have evolved because it enhances evolvability in a changing environment, protects females against the ravages of invasive trophoblast, or because natural selection acts differently on genes of maternal and paternal origin in interactions among kin. The last hypothesis has received the most extensive theoretical development and seems the best supported by the properties of known imprinted genes. However, the hypothesis is yet to provide a compelling explanation for many examples of imprinting.

Inbreeding, maternal care and genomic imprinting

Inactivation of expression of the paternal allele at two maternally silent imprinted loci has recently been reported to diminish the quality of care that female mice lavish on their offspring. This suggests that there can be disagreement between the maternally and paternally derived genomes of mothers over how much care for offspring is appropriate, with the paternally derived genome favoring greater care. The reason for such disagreement is not obvious because the maternally and paternally derived alleles at a locus have equal probabilities of being transmitted to each of the mother's ova and, therefore, would appear to have equal interests in a mother's offspring. However, if a female mates with a related male, her two alleles may have different probabilities of being present in the sperm that fertilize her ova. Natural selection can favor silencing of the maternally derived allele at a locus that enhances the quality of maternal care if the average patrilineal relatedness between a female and her mates decreases more rapidly than the average matrilineal relatedness. Just such an asymmetrical decrease in relatedness over time would be expected in a structured population in which patrilineal inbreeding is more common than matrilineal inbreeding.

Parental modifiers, antisense transcripts and loss of imprinting

The kinship theory of genomic imprinting has explained parent-specific gene expression as the outcome of an evolutionary conflict between the two alleles at a diploid locus of an offspring over how much to demand from parents. Previous models have predicted that maternally derived (madumnal) alleles will be silent at demand-enhancing loci, while paternally derived (padumnal) alleles will be silent at demand-suppressing loci, but these models have not considered the evolution of trans-acting modifiers that are expressed in parents and influence imprinted expression in offspring. We show that such modifiers will sometimes be selected to reactivate the silent padumnal allele at a demand-suppressing locus but will not be selected to reactivate the silent madumnal allele at a demand-enhancing locus. Therefore, imprinting of demand-suppressing loci is predicted to be less evolutionarily stable than imprinting of demand-enhancing loci.

The coalescent in a continuous, finite, linear population

In this article we present a model for analyzing patterns of genetic diversity in a continuous, finite, linear habitat with restricted gene flow. The distribution of coalescent times and locations is derived for a pair of sequences sampled from arbitrary locations along the habitat. The results for mean time to coalescence are compared to simulated data. As expected, mean time to common ancestry increases with the distance separating the two sequences. Additionally, this mean time is greater near the center of the habitat than near the ends. In the distant past, lineages that have not undergone coalescence are more likely to have been at opposite ends of the population range, whereas coalescent events in the distant past are biased toward the center. All of these effects are more pronounced when gene flow is more limited. The pattern of pairwise nucleotide differences predicted by the model is compared to data collected from sardine populations. The sardine data are used to illustrate how demographic parameters can be estimated using the model.

Genomic imprinting of two antagonistic loci

We present a model that considers the coevolution of genomic imprinting at a growth factor locus and an antagonistic growth suppressor locus. With respect to the two loci considered independently, our model makes the familiar predictions that an imprinted growth factor locus will only be expressed from the paternally derived allele and an imprinted growth suppressor locus only from the maternally derived allele. In addition, our coevolutionary model allows us to make predictions regarding the sequence of evolutionary events necessary for generating such a system. We conclude that imprinting at the growth factor locus preceded the evolution of growth suppressor function at the second locus, which in turn preceded imprinting at that locus. We then discuss the consistency of these predictions with currently available comparative data on the insulin-like growth factor 2 insulin-like growth factor 2 receptor system of mammals.

Genomic imprinting, sibling solidairity and the logic of collective action

Genomic imprinting has been proposed to evolve when a gene's expression has fitness consequences for individuals with different coefficients of matrilineal and patrilineal relatedness, especially in the context of competition between offspring for maternal resources. Previous models have focused on pre-emptive hierarchies, where conflict arises with respect to resource allocation between present and future offspring. Here we present a model in which imprinting arises from scramble competition within litters. The model predicts paternal-specific expression of a gene that increases an offspring's fractional share of resources but reduces the size of the resource pool, and maternal-specific expression of a gene with opposite effects. These predictions parallel the observation in economic models that individuals tend to underprovide public goods, and that the magnitude of this shortfall increases with the number of individuals in the group. Maternally derived alleles are more willing than their paternally derived counterparts to contribute to public goods because they have a smaller effective group size.

Synchronization of estrus and fertility in zebu beef heifers treated with three estrus synchronization protocols

The effects on estrus and fertility of 3 estrus synchronization protocols were studied in Brahman beef heifers. In Treatment 1 (PGF protocol; n=234), heifers received 7.5 mg, i.m. prostianol on Day 0 and were inseminated after observed estrus until Day 5. Treatment 2 (10-d NOR protocol; n = 220) consisted of norgestomet (NOR; 3 mg, s.c. implant and 3 mg, i.m.) and estradiol valerate (5 mg, i.m.) treatment on Day -10, NOR implant removal and 400 IU, i.m. PMSG on Day 0, and AI after observed estrus through to Day 5. Treatment 3 (14-d NOR+PGF protocol; n = 168) constituted a NOR implant (3 mg, sc) on Day -14, NOR implant removal on Day 0, PGF on Day 16, and AI after observed estrus through to Day 21. All heifers were examined for return to estrus at the next cycle and inseminated after observed estrus. The heifers were then exposed to bulls for at least 21 d. During the period of estrus observation (5 d) after treatment, those heifers treated with the PGF protocol had a lower (P<0.01) rate of estrual response (58%) than heifers treated with the 10-d NOR (87%) or 14-d NOR+PGF (88%) protocol. Heifers treated with the 10-d NOR protocol displayed estrus earlier and had a closer synchrony of estrus than heifers treated with either the PGF or the 14-d NOR+PGF protocol. Heifers treated with the 14-d NOR+PGF protocol had higher (P<0.05) conception and calving rates (51 and 46%) to AI at the induced estrus than heifers treated with the PGF (45 and 27%) or the 10-d NOR (38 and 33%) protocol. Calving rate to 2 rounds of AI was greater (P<0.05) for heifers treated with the 14-d NOR-PGF (50%) protocol than heifers treated with the 10-d NOR (38%) but not the PGF (43%) protocol. Breeding season calving rates were similar among the 3 protocols. The results show that the 14-d NOR+PGF estrus synchronization protocol induced a high incidence of estrus with comparatively high fertility in Brahman heifers.

Development and testing of a bacterial biosensor for toluene-based environmental contaminants

A bacterial biosensor for benzene, toluene, and similar compounds has been constructed, characterized, and field tested on contaminated water and soil. The biosensor is based on a plasmid incorporating the transcriptional activator xylR from the TOL plasmid of Pseudomonas putida mt-2. The XylR protein binds a subset of toluene-like compounds and activates transcription at its promoter, Pu. A reporter plasmid was constructed by placing the luc gene for firefly luciferase under the control of XylR and Pu. When Escherichia coli cells were transformed with this plasmid vector, luminescence from the cells was induced in the presence of benzene, toluene, xylenes, and similar molecules. Accurate concentration dependencies of luminescence were obtained and exhibited K1/2 values ranging from 39.0 +/- 3.8 microM for 3-xylene to 2,690 +/- 160 microM for 3-methylbenzylalcohol (means +/- standard deviations). The luminescence response was specific for only toluene-like molecules that bind to and activate XylR. The biosensor cells were field tested on deep aquifer water, for which contaminant levels were known, and were able to accurately detect toluene derivative contamination in this water. The biosensor cells were also shown to detect BETX (benzene, toluene, and xylene) contamination in soil samples. These results demonstrate the capability of such a bacterial biosensor to accurately measure environmental contaminants and suggest a potential for its inexpensive application in field-ready assays.

Method of stimulating ovulation rate in Merino ewes may affect conception but not embryo survival

Efficiency in breeding flocks can be improved by increasing twinning rate. While this can be achieved by several methods that stimulate ovulation rate, there is considerable variation in the number of extra lambs produced by alternative treatments. Variations in ovulation rate following stimulation treatments are well documented, but the subsequent processes of conception and embryo survival leading to extra lambs are not. Differences in lambs produced by four alternative stimulation treatments examined in the following experiments were not significantly affected by embryo survival. The stimulation treatments examined were: improved nutrition for several weeks pre-mating (N); lupins (L) as stubble or standing crop, or fed as grain; grazed tagasaste forage (T); Fecundin immunisation (F). Ovulation rates were measured using laparoscopy and viability of embryos monitored using ultrasound. Ovulation rates in treated groups were increased by up to 0.66 (L), 0.20 (T), 0.10 (N) and 0.36 (F) ova per ewe. Survival of twin ova in pregnant ewes ranged from 81 to 93% across treatments and flocks, but did not differ significantly between treatments within flocks. Proportions of ewes pregnant in the first cycle of mating were depressed by 8-11% in F and L treatments. Conception rates were higher (by 7-16%) in twin rather than single ovulating ewes, and, in one flock, higher (by 15%) following bilateral rather than unilateral twin-ovulations. All stimulation treatments increased numbers of lambs conceived, lupins being the most efficient. Differences between treatments in lambs conceived were dependent on ovulation and conception rates but not embryo survival. Rates of embryo survival that were similar between treatments, but differed between flocks, indicated failure due to maternal factors rather than the embryos themselves. The mechanism(s) responsible could not be determined in these experiments, but genetic differences between flocks are suggested.

Regulation of the kinetics of phosducin phosphorylation in retinal rods

Phosducin (Pd) is a widely expressed phosphoprotein that regulates G-protein (G) signaling. Unphosphorylated Pd binds to Gbetagamma subunits and blocks their interaction with Galpha. This binding sequesters Gbetagamma and inhibits both receptor-mediated activation of Galpha and direct interactions between Gbetagamma and effector enzymes. When phosphorylated by cAMP-dependent protein kinase, Pd does not affect these functions of Gbetagamma. To further understand the role of Pd in regulating G-protein signaling in retinal rod photoreceptor cells, we have measured the abundance of Pd in rods and examined factors that control the rate of Pd phosphorylation. Pd is expressed at a copy number comparable to that for the rod G-protein, transducin (Gt). The ratio of rhodopsin (Rho) to Pd is 15. 5 +/- 3.5 to 1. The rate of Pd phosphorylation in rod outer segment preparations was dependent on [cAMP]. K1/2 for cAMP was 0.56 +/- 0. 09 microM, and the maximal rate of phosphorylation was approximately 500 pmol PO4 incorporated/min/nmol Rho. In the presence of Gtbetagamma this rate was decreased approximately 50-fold. From these data, one can estimate a t1/2 of approximately 3 min for the rephosphorylation of Pd in rods during the recovery period after a light response. This relatively slow rephosphorylation of the Pd.Gtbetagamma complex may provide a period of molecular memory in which sensitivity to further light stimuli is reduced as a result of sequestration of Gtbetagamma by Pd.

Regulation of phosducin phosphorylation in retinal rods by Ca2+/calmodulin-dependent adenylyl cyclase

The phosphoprotein phosducin (Pd) regulates many guanine nucleotide binding protein (G protein)-linked signaling pathways. In visual signal transduction, unphosphorylated Pd blocks the interaction of light-activated rhodopsin with its G protein (Gt) by binding to the beta gamma subunits of Gt and preventing their association with the Gt alpha subunit. When Pd is phosphorylated by cAMP-dependent protein kinase, it no longer inhibits Gt subunit interactions. Thus, factors that determine the phosphorylation state of Pd in rod outer segments are important in controlling the number of Gts available for activation by rhodopsin. The cyclic nucleotide dependencies of the rate of Pd phosphorylation by endogenous cAMP-dependent protein kinase suggest that cAMP, and not cGMP, controls Pd phosphorylation. The synthesis of cAMP by adenylyl cyclase in rod outer segment preparations was found to be dependent on Ca2+ and calmodulin. The Ca2+ dependence was within the physiological range of Ca2+ concentrations in rods (K1/2 = 230 +/- 9 nM) and was highly cooperative (n app = 3.6 +/- 0.5). Through its effect on adenylyl cyclase and cAMP-dependent protein kinase, physiologically high Ca2+ (1100 nM) was found to increase the rate of Pd phosphorylation 3-fold compared to the rate of phosphorylation at physiologically low Ca2+ (8 nM). No evidence for Pd phosphorylation by other (Ca2+)-dependent kinases was found. These results suggest that Ca2+ can regulate the light response at the level of Gt activation through its effect on the phosphorylation state of Pd.

The phosphorylation state of phosducin determines its ability to block transducin subunit interactions and inhibit transducin binding to activated rhodopsin

Heterotrimeric GTP-binding proteins (G-proteins) serve many different signal transduction pathways. Phosducin, a 28-kDa phosphoprotein, is expressed in a variety of mammalian cell types and blocks activation of several classes of G-proteins. Phosphorylation of phosducin by cyclic AMP-dependent protein kinase prevents phosducin-mediated inhibition of G-protein GTPase activity (Bauer, P. H., Müller, S., Puzicha, M., Pippig, S., Obermaier, B., Helmreich, E. J. M., and Lohse, M. J. (1992) Nature 358, 73-76). In retinal rods, phosducin inhibits transducin (Gt) activation by binding its beta gamma subunits. While rod phosducin is phosphorylated in the dark and dephosphorylated after illumination (Lee, R.-H., Brown, B. M., and Lolley, R. N. (1984) Biochemistry 23, 1972-1977), the significance of these reactions is still unclear. The data presented here permit a more precise characterization of phosducin function and the consequences of its phosphorylation. Dephosphophosducin blocked binding of the Gt alpha 1 subunit to activated rhodopsin in the presence of stoichiometric amounts of Gt beta gamma, whereas phosphophosducin did not. Surprisingly, the binding affinity of phosphophosducin for Gt beta gamma was not significantly reduced compared with the binding affinity of dephosphophosducin. However, the association of phosducin with Gt beta gamma in a size exclusion column matrix was dependent on the phosphorylation state of phosducin. Moreover, the ability of phosducin to compete with Gt alpha for binding to Gt beta gamma was also dependent on the phosphorylation state of phosducin. No interaction was found between phosducin and Gt alpha. These data indicate that phosducin decreases rod responsiveness by binding to the beta gamma subunits of Gt and preventing their interaction with Gt alpha, thereby inhibiting Gt alpha activation by the activated receptor. Moreover, phosphorylation of phosducin blocks its ability to compete with Gt alpha for binding to Gt beta gamma.

Ram mating performance in Border Leicesters and related breed types. 3. Relationships of ram serving capacity, testis diameter, liveweight, breed and age with flock fertility

Relationships of ram serving capacity (a measure of serving frequency in pen tests), testis diameter, liveweight, breed and age with flock fertility were studied in 40 rams joined individually for 7 days at high ewe:ram ratios. Rams were either Border Leicester, BLI (a high prolificacy line derived from the Border Leicester and Merino and since released as the Glen Vale breed) or BLI x Border Leicester, and aged either 1.5 or 2.5 years. Joinings were over 2 periods, 2-9 April or 16-23 April. Breed, age, period and interaction effects were also examined. On average (± s.e.), the number of ewes with mating marks in 7 days increased by 2.03 ± 0.52 ( P < 0.001) per serve per hour of serving capacity and by 0.40 ± 0.18 ( P < 0.05) per kg liveweight. Relationships with pregnancy rate in marked ewes differed between classes of rams. Larger testes were of most benefit when rams were of high serving capacity ( P < 0.0 1 ) or low liveweight (P<0.01). Only serving capacity was related to number of ewes pregnant, the number increasing by an average (± s.e.) of 1.73 ± 0.57 ewes per serve per hour (P<0.01). This suggests that a ram's capacity for more frequent service was more important to fertility than was extra testicular tissue. BLI x Border Leicester, BLI, and 2.5-year-old Border Leicester rams impregnated 30-40% more ewes than did 1.5-year-old Border Leicester rams. We estimate that the 1.5-year-old Border Leicester rams could be satisfactorily joined to about 46 ewes and the other rams to about 60 ewes.

Fetal mortality from day 30 of pregnancy in Merino ewes offered different levels of nutrition

The effect of nutritional restriction during mid pregnancy on fetal mortality was examined in 3 experiments in which multiparous 3-6 year old Merino ewes were fed at maintenance (M) or 0.3M from about day 30 to 90 of pregnancy, followed by M or 2M for the remainder of gestation. Fetal wellbeing was determined by ultrasound examination at periodic intervals throughout pregnancy. Among 134 single borne fetuses, mortality was detected in only 3, between days 70-92 of pregnancy. There were no losses in 58 ewes bearing twins and fed at M. By comparison, 9 of 93 ewes bearing twins and fed at 0.3M lost 1 or both fetuses between days 30 and 95, and a further 3 of 66 remaining ewes had fetal losses between days 95 and 140. It was concluded that such losses in ewes bearing twins during periods of nutritional restriction may need to be considered when using scanning to predict the number of lambs born. Also it highlights the need to confirm the viability of each fetus during ultrasound examinations of multiple fetuses.

Holoprosencephaly in Border Leicester lambs

Holoprosencephaly in Border Leicester lambs is described. This defect is characterised by lack of the longitudinal cerebral fissure, fusion of the cerebral hemispheres and a single lateral ventricle. Facial defects are also associated with this condition. Results of a breeding experiment suggest that it is inherited in an autosomal recessive manner. Results from a survey indicate that the condition is widespread in Border Leicester sheep.

Production responses in selenium supplemented sheep in northern New South Wales. 1. Infertility in ewes and associated production

Responses in fertility after selenium supplementation of breeding ewes in northern New South Wales were examined. The treatment (5 mg selenium) was given orally as sodium selenite three weeks before joining, and responses were measured in terms of the proportion of ewes lambing. A total of 14 experiments was conducted on eight commercial properties over three years. In some flocks the effect of selenium supplementation on wool production and liveweight was also assessed. All sites were in areas of likely selenium deficiency. Selenium supplementation significantly increased the proportion of ewes lambing in 5 sf the 14 flocks studied but responses were quite variable between properties and years. The effect of supplementation on greasy wool production was small, but significant in two of the seven flocks measured. The treatment did not affect liveweight.

Production responses in selenium supplemented sheep in northern New South Wales. 2. Liveweight gain, wool production and reproductive performance in young Merino ewes given selenium and copper supplements

Young Merino ewes on five commercial properties in northern New South Wales were supplemented with selenium and their production was compared with untreated flock mates. They were studied from weaning till first lambing at about two years of age. Treatments of 5 mg selenium were given orally every six weeks for approximately 12 months. Copper treatments were also included to test for a possible concurrent deficiency or interaction with selenium. There were significant responses to selenium in liveweight in four of the five flocks and in wool production in two of the flocks at both shearings. Reproductive performance at first mating was also significantly better in two flocks. There were no beneficial effects of copper treatment nor were there any significant interactions with selenium treatment in any aspect of production measured.

Selenium concentration in the blood of ruminants grazing in Northern New South Wales. 1. Analysis of samples collected in the National Brucellosis Eradication Scheme

Bovine blood samples collected for the Brucellosis Eradication Scheme were analysed for selenium as a means of surveying the selenium status of grazing cattle in 10 Pastures Protection Board areas of northern New South Wales. Sources of error were also examined. The average standard deviation of repeat samplings from the same farm was �0.019�g selenium ml-1 and the seasonal variation in blood selenium concentration appeared to be relatively small. Relationships were calculated for predicting the selenium concentration in bovine plasma and liver, and in ovine whole blood, plasma and liver, from the selenium concentration of bovine blood; they were used to extend the survey results to grazing sheep. Samples were collected from 794 farms, and there were significant differences between Pastures Protection Board areas. Cattle in the Glen Innes and Armidale areas had the lowest selenium status with 26 and 14% respectively of herds having blood selenium concentrations = 0.02 �g selenium ml-1.

Low release of selenium from recovered ruminal pellets

The effectiveness of selenium pellets in grazing Merino sheep was examined by comparing the selenium status of treated and untreated animals over a 13 month period. The selenium status of treated sheep, as measured by blood glutathione peroxidase levels, had reached a maximum 3 months after treatment and there was a marked decline between 5 and 13 months. All pellets were recovered from treated sheep at slaughter this confirmed that the observed decline was not due to a loss of pellets. In a separate study sheep were slaughtered 14 months after treatment and some of the recovered pellets were readministered to sheep maintained on a low selenium diet. The selenium status of the sheep receiving recovered pellets remained low. This bioassay technique indicated that there was little available selenium released from these pellets. The selenium status of sheep given previously unused pellets was declining after 18 weeks.

Effect of serving capacity of the ram syndicate on flock fertility

Serving capacity was measured in nine Merino rams during two pen-mating tests each of 2 hours duration. Two groups each of four rams were subsequently formed; a high serving capacity group (group H) of mean serving capacity 11.50 � 0.50 (SEM) in two hours, and a low serving capacity group (group L) of mean serving capacity 3.50 � 0.62. Each group was then mated to separate flocks of approximately 200 ewes each, for 6 weeks. Group H rams raddled significantly more ewes during the first 16 days of mating and inseminated a significantly greater proportion of the raddled ewes than did group L rams. Estimates of fertilization rates and embryo loss were similar for both groups. The proportion of ewes lambing as a result of the 6 weeks mating was similar in both groups (95.3% in group H and 93.5% in group L).

Haemoglobin oxidation in whole blood samples from sheep in relation to glutathione peroxidase activity

A high correlation was observed between H2O2-induced oxidation of haemoglobin and glutathione peroxidase activity in whole blood samples from sheep. A role of this enzyme in the prevention of oxidative damage to the erythrocyte and its contents has been previously demonstrated. The possibility of using haemoglobin oxidation in whole blood as an alternative assessment of glutathione peroxidase activity and hence of selenium status is proposed.