Strain-specific changes in nucleus accumbens transcriptome and motivation for palatable food reward in mice exposed to maternal separation.

Introduction: In humans, adversity in childhood exerts enduring effects on brain and increases the vulnerability to psychiatric diseases. It also leads to a higher risk of eating disorders and obesity. Maternal separation (MS) in mice has been used as a proxy of stress during infancy. We hypothesized that MS in mice affects motivation to obtain palatable food in adulthood and changes gene expression in reward system. Methods: Male and female pups from C57Bl/6J and C3H/HeN mice strains were subjected to a daily MS protocol from postnatal day (PND) 2 to PND14. At adulthood, their motivation for palatable food reward was assessed in operant cages. Results: Compared to control mice, male and female C3H/HeN mice exposed to MS increased their instrumental response for palatable food, especially when the effort required to obtain the reward was high. Importantly, this effect is shown in animals fed ad libitum. Transcriptional analysis revealed 375 genes differentially expressed in the nucleus accumbens of male MS C3H/HeN mice compared to the control group, some of these being associated with the regulation of the reward system (e.g., Gnas, Pnoc). Interestingly, C57Bl/6J mice exposed to MS did not show alterations in their motivation to obtain a palatable reward, nor significant changes in gene expression in the nucleus accumbens. Conclusion: MS produces long-lasting changes in motivation for palatable food in C3H/HeN mice, but has no impact in C57Bl/6J mice. These behavioral alterations are accompanied by drastic changes in gene expression in the nucleus accumbens, a key structure in the regulation of motivational processes.

Epigenetic origin of adaptive phenotypic variants in the human blood fluke Schistosoma mansoni.

BACKGROUND: Adaptive evolution is not possible without the generation of phenotypic variants. The origin of these variations has been a central topic in evolutionary biology. Up to now, it was commonly accepted that standing genetic variation is the only cause of phenotypic variants. However, epigenetic information is emerging as a complementary source of heritable phenotypic variation that contributes to evolution. The relative importance of genetics and epigenetics in generating heritable phenotypic variation is nevertheless a matter of debate. RESULTS: We used a host-parasite system to address this question. The human blood fluke Schistosoma mansoni can adapt rapidly to new intermediate snail hosts. The interaction between parasite and mollusk is characterized by a compatibility polymorphism illustrating the evolutionary dynamics in this system. The principal molecular marker for compatibility (infection success) is the expression pattern of a group of polymorphic mucins (SmPoMuc) in the parasite. We show here that chromatin structure changes as the SmPoMuc promoters are the cause for SmPoMuc transcription polymorphism leading to phenotypic novelty and increase in infection success, i.e., fitness. CONCLUSION: We establish that epigenetic changes can be the major if not only cause of adaptive phenotypic variants in Schistosoma mansoni, suggesting that epimutations can provide material for adaptive evolution in the absence of genetic variation in other systems. In addition, our results indicate that epidrugs can be used to control parasite development but also parasite evolution.

[Epigenetics in transgenerational responses to environmental impacts: from facts and gaps]. / Épigénétique et réponses transgénérationnelles aux impacts de l'environnement--Des faits aux lacunes.

The existence of non-genetic and non-cultural mechanisms that transfer information on the memory of parental exposures to various environments, determining the reactivity of the following generations to their environments during their life, are of growing interest. Yet fundamental questions remain about the nature, the roles and relative importance of epigenetic marks and processes, non-coding RNAs, or other mechanisms, and their persistence over generations. A model incorporating the various transmission systems, their cross-talks and windows of susceptibility to the environment as a function of sex/gender of parent and offspring, has yet to be built.

[Epigenetics and Nutrition: maternal nutrition impacts on placental development and health of offspring]. / Epigénétique et Nutrition : impacts de l'alimentation maternelle sur le développement placentaire et la santé de la descendance.

The environment, defined broadly by all that is external to the individual, conditions the phenotype during development, particularly the susceptibility to develop non-communicable diseases. This notion, called Developmental Origins of Health and Disease (DOHaD), is based on numerous epidemiological studies as well as animal models. Thus, parental nutrition and obesity can predispose the offspring to develop metabolic and cardiovascular diseases in adulthood. The known underlying mechanisms include an altered development of tissues that adapt to maternal metabolic condition, and a placental dysfunction, which in turn impacts fetal growth and development. Epigenetic mechanisms modulate gene expression without affecting the DNA sequence itself. The main epigenetic marks are DNA methylation and histone post-translational modifications. These marks are erased and set-up during gametogenesis and development in order to ensure cellular identity. Therefore, they can lead to a memorisation of early environment and induce long-term alteration of cell and tissue functions, which will condition the susceptibility to non-communicable diseases. The placenta is a programming agent of adult disease. The environment, such as smoking or psychosocial stress, is able to modify epigenetic processes in placenta, such as small RNA expression and DNA methylation. We showed that placenta is sensitive to maternal obesity and maternal nutrition, in terms of histology, transcription and epigenetic marks. A clear sexual dimorphism is remarkable in the placental response to maternal environment. In adulthood, the phenotype is also different between males and females. Epigenetic mechanisms could underlie this differential response of males and females to the same environment. The DOHaD can no longer be ignored in Biology of Reproduction. The prevention of non-communicable diseases must take this new paradigm into account. Research will allow a better comprehension of the mechanisms of this early conditioning and the marked sexual dimorphism it is associated to.

Elucidating the molecular bases of epigenetic inheritance in non-model invertebrates: the case of the root-knot nematode Meloidogyne incognita.

Root-knot nematodes of the genus Meloidogyne are biotrophic plant parasites that exhibit different life cycles and reproduction modes, ranging from classical amphimixis to obligatory mitotic parthenogenesis (apomixis), depending on the species. Meloidogyne incognita, an apomictic species, exhibits a worldwide distribution and a wide host range affecting more than 3000 plant species. Furthermore, evidences suggest that apomixis does not prevent M. incognita from adapting to its environment in contrast to what is expected from mitotic parthenogenesis that should theoretically produce clonal progenies. This raises questions about mechanisms of genome plasticity leading to genetic variation and adaptive evolution in apomictic animals. We reasoned that epigenetic mechanisms might in part be responsible for the generation of phenotypic variants that provide potential for rapid adaptation. We established therefore a pipeline to investigate the principal carriers of epigenetic information, DNA methylation and post-translational histone modifications. Even if M. incognita possesses the epigenetic machinery i.e., chromatin modifying enzymes, 5-methyl-cytosine and 5-hydroxy-methyl-cytosine content is absent or very weak. In contrast, we demonstrated that the canonical histone modifications are present and chromatin shows typical nucleosome structure. This work is the first characterization of carriers of epigenetic information in M. incognita and constitutes a preamble to further investigate if M. incognita development and its adaptation to plant hosts are under epigenetic control. Our pipeline should allow performing similar types of studies in any non-model organism.

Schistosoma mansoni mucin gene (SmPoMuc) expression: epigenetic control to shape adaptation to a new host.

The digenetic trematode Schistosoma mansoni is a human parasite that uses the mollusc Biomphalaria glabrata as intermediate host. Specific S. mansoni strains can infect efficiently only certain B. glabrata strains (compatible strain) while others are incompatible. Strain-specific differences in transcription of a conserved family of polymorphic mucins (SmPoMucs) in S. mansoni are the principle determinants for this compatibility. In the present study, we investigated the bases of the control of SmPoMuc expression that evolved to evade B. glabrata diversified antigen recognition molecules. We compared the DNA sequences and chromatin structure of SmPoMuc promoters of two S. mansoni strains that are either compatible (C) or incompatible (IC) with a reference snail host. We reveal that although sequence differences are observed between active promoter regions of SmPoMuc genes, the sequences of the promoters are not diverse and are conserved between IC and C strains, suggesting that genetics alone cannot explain the evolution of compatibility polymorphism. In contrast, promoters carry epigenetic marks that are significantly different between the C and IC strains. Moreover, we show that modifications of the structure of the chromatin of the parasite modify transcription of SmPoMuc in the IC strain compared to the C strain and correlate with the presence of additional combinations of SmPoMuc transcripts only observed in the IC phenotype. Our results indicate that transcription polymorphism of a gene family that is responsible for an important adaptive trait of the parasite is epigenetically encoded. These strain-specific epigenetic marks are heritable, but can change while the underlying genetic information remains stable. This suggests that epigenetic changes may be important for the early steps in the adaptation of pathogens to new hosts, and might be an initial step in adaptive evolution in general.

5-methyl-cytosine and 5-hydroxy-methyl-cytosine in the genome of Biomphalaria glabrata, a snail intermediate host of Schistosoma mansoni.

BACKGROUND: Biomphalaria glabrata is the mollusc intermediate host for Schistosoma mansoni, a digenean flatworm parasite that causes human intestinal schistosomiasis. An estimated 200 million people in 74 countries suffer from schistosomiasis, in terms of morbidity this is the most severe tropical disease after malaria. Epigenetic information informs on the status of gene activity that is heritable, for which changes are reversible and that is not based on the DNA sequence. Epigenetic mechanisms generate variability that provides a source for potentially heritable phenotypic variation and therefore could be involved in the adaptation to environmental constraint. Phenotypic variations are particularly important in host-parasite interactions in which both selective pressure and rate of evolution are high. In this context, epigenetic changes are expected to be major drivers of phenotypic plasticity and co-adaptation between host and parasite. Consequently, with characterization of the genomes of invertebrates that are parasite vectors or intermediate hosts, it is also essential to understand how the epigenetic machinery functions to better decipher the interplay between host and parasite. METHODS: The CpGo/e ratios were used as a proxy to investigate the occurrence of CpG methylation in B. glabrata coding regions. The presence of DNA methylation in B. glabrata was also confirmed by several experimental approaches: restriction enzymatic digestion with isoschizomers, bisulfite conversion based techniques and LC-MS/MS analysis. RESULTS: In this work, we report that DNA methylation, which is one of the carriers of epigenetic information, occurs in B. glabrata; approximately 2% of cytosine nucleotides are methylated. We describe the methylation machinery of B. glabrata. Methylation occurs predominantly at CpG sites, present at high ratios in coding regions of genes associated with housekeeping functions. We also demonstrate by bisulfite treatment that methylation occurs in multiple copies of Nimbus, a transposable element. CONCLUSIONS: This study details DNA methylation for the first time, one of the carriers of epigenetic information in B. glabrata. The general characteristics of DNA methylation that we observed in the B. glabrata genome conform to what epigenetic studies have reported from other invertebrate species.

The association of a La module with the PABP-interacting motif PAM2 is a recurrent evolutionary process that led to the neofunctionalization of La-related proteins.

La-related proteins (LARPs) are largely uncharacterized factors, well conserved throughout evolution. Recent reports on the function of human LARP4 and LARP6 suggest that these proteins fulfill key functions in mRNA metabolism and/or translation. We report here a detailed evolutionary history of the LARP4 and 6 families in eukaryotes. Genes coding for LARP4 and 6 were duplicated in the common ancestor of the vertebrate lineage, but one LARP6 gene was subsequently lost in the common ancestor of the eutherian lineage. The LARP6 gene was also independently duplicated several times in the vascular plant lineage. We observed that vertebrate LARP4 and plant LARP6 duplication events were correlated with the acquisition of a PABP-interacting motif 2 (PAM2) and with a significant reorganization of their RNA-binding modules. Using isothermal titration calorimetry (ITC) and immunoprecipitation methods, we show that the two plant PAM2-containing LARP6s (LARP6b and c) can, indeed, interact with the major plant poly(A)-binding protein (PAB2), while the third plant LARP6 (LARP6a) is unable to do so. We also analyzed the RNA-binding properties and the subcellular localizations of the two types of plant LARP6 proteins and found that they display nonredundant characteristics. As a whole, our results support a model in which the acquisition by LARP4 and LARP6 of a PAM2 allowed their targeting to mRNA 3' UTRs and led to their neofunctionalization.