SETDB1/NSD-dependent H3K9me3/H3K36me3 dual heterochromatin maintains gene expression profiles by bookmarking poised enhancers.

Gene silencing by heterochromatin plays a crucial role in cell identity. Here, we characterize the localization, the biogenesis, and the function of an atypical heterochromatin, which is simultaneously enriched in the typical H3K9me3 mark and in H3K36me3, a histone mark usually associated with gene expression. We identified thousands of dual regions in mouse embryonic stem (ES) cells that rely on the histone methyltransferases SET domain bifurcated 1 (SETDB1) and nuclear set domain (NSD)-containing proteins to generate H3K9me3 and H3K36me3, respectively. Upon SETDB1 removal, dual domains lose both marks, gain signatures of active enhancers, and come into contact with upregulated genes, suggesting that it might be an important pathway by which genes are controlled by heterochromatin. In differentiated tissues, a subset of these dual domains is destabilized and becomes enriched in active enhancer marks, providing a mechanistic insight into the involvement of heterochromatin in the maintenance of cell identity.

Insects and incest: Sib-mating tolerance in natural populations of a parasitoid wasp.

Sib-mating avoidance is a pervasive behaviour that is expected to evolve in species subject to inbreeding depression. Although laboratory studies provide elegant demonstrations, small-scaled bioassays minimize the costs of mate finding and choice, and thus may produce spurious findings. We therefore combined laboratory experiments with field observations to examine the existence of inbreeding avoidance using the parasitoid wasp Venturia canescens. In the laboratory, our approach consisted of mate-choice experiments to assess kin discrimination in population cages with competitive interactions. A higher mating probability after sib rejections suggested that females could discriminate their sibs; however, in contrast to previous findings, sib-mating avoidance was not observed. To compare our laboratory results to field data, we captured 241 individuals from two populations. Females laid eggs in the lab, and 226 daughters were obtained. All individuals were genotyped at 18 microsatellite loci, which allowed inference of the genotype of each female's mate and subsequently the relatedness within each mating pair. We found that the observed rate of sib-mating did not differ from the probability that sibs encountered one another at random in the field, which is consistent with an absence of sib-mating avoidance. In addition, we detected a weak but significant male-biased dispersal, which could reduce encounters between sibs. We also found weak fitness costs associated with sib-mating. As such, the sex-biased dispersal that we found is probably sufficient to mitigate these costs. These results imply that kin discrimination has probably evolved for purposes other than mate choice, such as superparasitism avoidance.

Drastic neofunctionalization associated with evolution of the timezyme AANAT 500 Mya.

Melatonin (N-acetyl-5-methoxytrypamine) is the vertebrate hormone of the night: circulating levels at night are markedly higher than day levels. This increase is driven by precisely regulated increases in acetylation of serotonin in the pineal gland by arylalkylamine N-acetyltransferase (AANAT), the penultimate enzyme in the synthesis of melatonin. This unique essential role of AANAT in vertebrate timekeeping is recognized by the moniker the timezyme. AANAT is also found in the retina, where melatonin is thought to play a paracrine role. Here, we focused on the evolution of AANAT in early vertebrates. AANATs from Agnathans (lamprey) and Chondrichthyes (catshark and elephant shark) were cloned, and it was found that pineal glands and retinas from these groups express a form of AANAT that is compositionally, biochemically, and kinetically similar to AANATs found in bony vertebrates (VT-AANAT). Examination of the available genomes indicates that VT-AANAT is absent from other forms of life, including the Cephalochordate amphioxus. Phylogenetic analysis and evolutionary rate estimation indicate that VT-AANAT evolved from the nonvertebrate form of AANAT after the Cephalochordate-Vertebrate split over one-half billion years ago. The emergence of VT-AANAT apparently involved a dramatic acceleration of evolution that accompanied neofunctionalization after a duplication of the nonvertebrate AANAT gene. This scenario is consistent with the hypotheses that the advent of VT-AANAT contributed to the evolution of the pineal gland and lateral eyes from a common ancestral photodetector and that it was not a posthoc recruitment.

Fruiting Strategies of Perennial Plants: A Resource Budget Model to Couple Mast Seeding to Pollination Efficiency and Resource Allocation Strategies.

Masting, a breeding strategy common in perennial plants, is defined by seed production that is highly variable over years and synchronized at the population level. Resource budget models (RBMs) proposed that masting relies on two processes: (i) the depletion of plant reserves following high fruiting levels, which leads to marked temporal fluctuations in fruiting; and (ii) outcross pollination that synchronizes seed crops among neighboring trees. We revisited the RBM approach to examine the extent to which masting could be impacted by the degree of pollination efficiency, by taking into account various logistic relationships between pollination success and pollen availability. To link masting to other reproductive traits, we split the reserve depletion coefficient into three biological parameters related to resource allocation strategies for flowering and fruiting. While outcross pollination is considered to be the key mechanism that synchronizes fruiting in RBMs, our model counterintuitively showed that intense masting should arise under low-efficiency pollination. When pollination is very efficient, medium-level masting may occur, provided that the costs of female flowering (relative to pollen production) and of fruiting (maximum fruit set and fruit size) are both very high. Our work highlights the powerful framework of RBMs, which include explicit biological parameters, to link fruiting dynamics to various reproductive traits and to provide new insights into the reproductive strategies of perennial plants.

Faithful or not: direct and indirect effects of climate on extra-pair paternities in a population of Alpine marmots.

Despite being identified an area that is poorly understood regarding the effects of climate change, behavioural responses to climatic variability are seldom explored. Climatic variability is likely to cause large inter-annual variation in the frequency of extra-pair litters produced, a widespread alternative mating tactic to help prevent, correct or minimize the negative consequences of sub-optimal mate choice. In this study, we investigated how climatic variability affects the inter-annual variation in the proportion of extra-pair litters in a wild population of Alpine marmots. During 22 years of monitoring, the annual proportion of extra-pair litters directly increased with the onset of earlier springs and indirectly with increased snow in winters. Snowier winters resulted in a higher proportion of families with sexually mature male subordinates and thus, created a social context within which extra-pair paternity was favoured. Earlier spring snowmelt could create this pattern by relaxing energetic, movement and time constraints. Further, deeper snow in winter could also contribute by increasing litter size and juvenile survival. Optimal mate choice is particularly relevant to generate adaptive genetic diversity. Understanding the influence of environmental conditions and the capacity of the individuals to cope with them is crucial within the context of rapid climate change.

Subfunctionalization of arylalkylamine N-acetyltransferases in the sea bass Dicentrarchus labrax: two-ones for one two.

Melatonin is an important component of the vertebrates circadian system, synthetized from serotonin by the successive action of the arylalkylamine N-acetyltransferase (Aanat: serotonin→N-acetylserotonin) and acetylserotonin-O-methyltransferase (Asmt: N-acetylserotonin→melatonin). Aanat is responsible for the daily rhythm in melatonin production. Teleost fish are unique because they express two Aanat genes, aanat1 and aanat2, mainly expressed in the retina and pineal gland, respectively. In silico analysis indicated that the teleost-specific whole-genome duplication generated Aanat1 duplicates (aanat1a and aanat1b); some fish express both of them, while others express either one of the isoforms. Here, we bring the first information on the structure, function, and distribution of Aanat1a and Aanat1b in a teleost, the sea bass Dicentrarchus labrax. Aanat1a and Aanat1b displayed a wide and distinct distribution in the nervous system and peripheral tissues, while Aanat2 appeared as a pineal enzyme. Co-expression of Aanats with asmt was found in the pineal gland and the three retinal nuclear layers. Enzyme kinetics indicated subtle differences in the affinity and catalytic efficiency of Aanat1a and Aanat1b for indolethylamines and phenylethylamines, respectively. Our data are consistent with the idea that Aanat2 is a pineal enzyme involved in melatonin production, while Aanat1 enzymes have a broader range of functions including melatonin synthesis in the retina, and catabolism of serotonin and dopamine in the retina and other tissues. The data are discussed in light of the recently uncovered roles of N-acetylserotonin and N-acetyldopamine as antioxidants, neuroprotectants, and modulators of cell proliferation and enzyme activities.

Somatotropic axis genes are expressed before pituitary onset during zebrafish and sea bass development.

The somatotropic axis, or growth hormone-insulin-like growth factor-1 (GH-IGF-1) axis, of fish is involved in numerous physiological process including regulation of ionic and osmotic balance, lipid, carbohydrate and protein metabolism, growth, reproduction, immune function and behavior. It is thought that GH plays a role in fish development but conflicting results have been obtained concerning the ontogeny of the somatotropic axis. Here we investigated the developmental expression of GH, GH-receptor (GHR) and IGF-1 genes and of a GH-like protein from fertilization until early stages of larval development in two Teleosts species, Danio rerio and Dicentrarchus labrax, by PCR, in situ hybridization and Western blotting. GH, GHR and IGF-1 mRNA were present in unfertilized eggs and at all stages of embryonic development, all three displaying a similar distribution in the two species. First located in the whole embryo (until 12 hpf in zebrafish and 76 hpf in sea bass), the mRNAs appeared then distributed in the head and tail, from where they disappeared progressively to concentrate in the forming pituitary gland. Proteins immunoreactive with a specific sea bass anti-GH antibody were also detected at all stages in this species. Differences in intensity and number of bands suggest that protein processing varies from early to later stages of development. The data show that all actors of the somatotropic axis are present from fertilization in these two species, suggesting they plays a role in early development, perhaps in an autocrine/paracrine mode as all three elements displayed a similar distribution at each stage investigated.

Evolution of AANAT: expansion of the gene family in the cephalochordate amphioxus.

BACKGROUND: The arylalkylamine N-acetyltransferase (AANAT) family is divided into structurally distinct vertebrate and non-vertebrate groups. Expression of vertebrate AANATs is limited primarily to the pineal gland and retina, where it plays a role in controlling the circadian rhythm in melatonin synthesis. Based on the role melatonin plays in biological timing, AANAT has been given the moniker "the Timezyme". Non-vertebrate AANATs, which occur in fungi and protists, are thought to play a role in detoxification and are not known to be associated with a specific tissue. RESULTS: We have found that the amphioxus genome contains seven AANATs, all having non-vertebrate type features. This and the absence of AANATs from the genomes of Hemichordates and Urochordates support the view that a major transition in the evolution of the AANATs may have occurred at the onset of vertebrate evolution. Analysis of the expression pattern of the two most structurally divergent AANATs in Branchiostoma lanceolatum (bl) revealed that they are expressed early in development and also in the adult at low levels throughout the body, possibly associated with the neural tube. Expression is clearly not exclusively associated with the proposed analogs of the pineal gland and retina. blAANAT activity is influenced by environmental lighting, but light/dark differences do not persist under constant light or constant dark conditions, indicating they are not circadian in nature. bfAANAT alpha and bfAANAT delta' have unusually alkaline (> 9.0) optimal pH, more than two pH units higher than that of vertebrate AANATs. CONCLUSIONS: The substrate selectivity profiles of bfAANAT alpha and delta' are relatively broad, including alkylamines, arylalkylamines and diamines, in contrast to vertebrate forms, which selectively acetylate serotonin and other arylalkylamines. Based on these features, it appears that amphioxus AANATs could play several roles, including detoxification and biogenic amine inactivation. The presence of seven AANATs in amphioxus genome supports the view that arylalkylamine and polyamine acetylation is important to the biology of this organism and that these genes evolved in response to specific pressures related to requirements for amine acetylation.

Kin recognition: Neurogenomic response to mate choice and sib mating avoidance in a parasitic wasp.

Sib mating increases homozygosity, which therefore increases the risk of inbreeding depression. Selective pressures have favoured the evolution of kin recognition and avoidance of sib mating in numerous species, including the parasitoid wasp Venturia canescens. We studied the female neurogenomic response associated with sib mating avoidance after females were exposed to courtship displays by i) unrelated males or ii) related males or iii) no courtship (controls). First, by comparing the transcriptional responses of females exposed to courtship displays to those exposed to controls, we saw a rapid and extensive transcriptional shift consistent with social environment. Second, by comparing the transcriptional responses of females exposed to courtship by related to those exposed to unrelated males, we characterized distinct and repeatable transcriptomic patterns that correlated with the relatedness of the courting male. Network analysis revealed 3 modules of specific 'sib-responsive' genes that were distinct from other 'courtship-responsive' modules. Therefore, specific neurogenomic states with characteristic brain transcriptomes associated with different behavioural responses affect sib mating avoidance behaviour.

SETDB1-dependent heterochromatin stimulates alternative lengthening of telomeres.

Alternative lengthening of telomeres, or ALT, is a recombination-based process that maintains telomeres to render some cancer cells immortal. The prevailing view is that ALT is inhibited by heterochromatin because heterochromatin prevents recombination. To test this model, we used telomere-specific quantitative proteomics on cells with heterochromatin deficiencies. In contrast to expectations, we found that ALT does not result from a lack of heterochromatin; rather, ALT is a consequence of heterochromatin formation at telomeres, which is seeded by the histone methyltransferase SETDB1. Heterochromatin stimulates transcriptional elongation at telomeres together with the recruitment of recombination factors, while disrupting heterochromatin had the opposite effect. Consistently, loss of SETDB1, disrupts telomeric heterochromatin and abrogates ALT. Thus, inhibiting telomeric heterochromatin formation in ALT cells might offer a new therapeutic approach to cancer treatment.

Melatonin effects on the hypothalamo-pituitary axis in fish.

Melatonin, a hormonal output signal of vertebrate circadian clocks, contributes to synchronizing behaviors and neuroendocrine regulations with the daily and annual variations of the photoperiod. Conservation and diversity characterize the melatonin system: conservation because its pattern of production and synchronizing properties are a constant among vertebrates; and diversity because regulation of both its synthesis and modes of action have been profoundly modified during vertebrate evolution. Studies of the targets and modes of action of melatonin in fish, and their parallels in mammals, are of interest to our understanding of time-related neuroendocrine regulation and its evolution from fish to mammals, as well as for aquacultural purposes.

Cloning and retinal expression of melatonin receptors in the European sea bass, Dicentrarchus labrax.

Melatonin contributes to synchronizing behaviors and physiological functions to daily and seasonal rhythm in fish. However, no coherent vision emerges because the effects vary with the species, sex, age, moment of the year or sexual cycle. And, scarce information is available concerning the melatonin receptors, which is crucial to our understanding of the role melatonin plays. We report here the full length cloning of three different melatonin receptor subtypes in the sea bass Dicentrarchus labrax, belonging, respectively, to the MT1, MT2 and Mel1c subtypes. MT1, the most abundantly expressed, was detected in the central nervous system, retina, and gills. MT2 was detected in the pituitary gland, blood cells and, to a lesser extend, in the optic tectum, diencephalon, liver and retina. Mel1c was mainly expressed in the skin; traces were found in the retina. The cellular sites of MT1 and MT2 expressions were investigated by in situ hybridization in the retina of pigmented and albino fish. The strongest signals were obtained with the MT1 riboprobes. Expression was seen in cells also known to express the enzymes of the melatonin biosynthesis, i.e., in the photoreceptor, inner nuclear and ganglion cell layers. MT1 receptor mRNAs were also abundant in the retinal pigment epithelium. The results are consistent with the idea that melatonin is an autocrine (neural retina) and paracrine (retinal pigment epithelium) regulator of retinal function. The molecular tools provided here will be of valuable interest to further investigate the targets and role of melatonin in nervous and peripheral tissues of fish.

Cognitive adaptation in asexual and sexual wasps living in contrasted environments.

Differences in learning and memory dynamics between populations are suspected to result from differences in ecological constraints such as resource distribution. The two reproductive modes (strains) of the parasitoid wasp Venturia canescens share the same geographical areas but live in contrasting habitats: arrhenotokous wasps live in the wild (generally orchards), whereas thelytokous ones live mostly in stored-products buildings (e.g. granaries). This species thus represents a relevant biological model for understanding the relationship between the ecological constraints faced by a species and its memory and learning ability. We showed that after having laid eggs in presence of both a synthetic odour and natural olfactory cues of their host, arrhenotokous wasps exhibited a change in their behavioural response towards the synthetic odour that was at least as pronounced as in thelytokous ones even though they were faster in their decision-making process. This is consistent with better learning skills in arrhenotokous wasps. The corresponding memory trace persisted in both strains for at least 51 h. We compare and discuss the learning and memory ablities of both strains as a function of their costs and benefits in their preferential habitats.

Melatonin receptors in the brain of the European sea bass: An in situ hybridization and autoradiographic study.

Melatonin is synthesized in the pineal organ and retina of vertebrates and exhibits a clear nocturnal rhythm of secretion. This hormone influences a number of important physiological processes acting through specific transmembrane G-protein-coupled receptors. Recently, we have cloned three different melatonin receptors in sea bass belonging to the MT1, MT2, and Mel1c subtypes. In this paper, we have analyzed the central expression of the MT1 gene by in situ hybridization and compared its distribution with the localization of 2-[(125)I]-iodomelatonin binding sites. In situ hybridization and autoradiographic studies provided consistent results. Melatonin receptors were mainly expressed in visually related areas of the sea bass brain, such as the pretectal area, glomerular complex, optic tectum, torus longitudinalis, and thalamus. A conspicuous expression was also detected in neuroendocrine regions including the ventral telencephalon, preoptic area, and hypothalamus. Furthermore, melatonin receptors were evident in the ganglionic cell layer of the cerebellum. The presence of iodomelatonin binding and/or MT1 mRNA-expressing cells was also observed in the hindbrain, in particular in the oculomotor and trigeminal nuclei and in the reticular formation. Our results suggest an important role of MT1 in the mediation of melatonin actions in visual/light integration, mechanoreception, somatosensation, eye-body motor coordination, and integrative and neuroendocrine functions. Remarkable differences in the number and distribution of brain nuclei expressing MT1 mRNAs in sea bass and trout, the only fish species analyzed to date, represent another piece of evidence for differences in the organization of the visual and circadian systems observed between salmoniform and perciform teleosts.

Structural and functional evolution of the pineal melatonin system in vertebrates.

In most species daily rhythms are synchronized by the photoperiodic cycle. They are generated by the circadian system, which is made of a pacemaker, an entrainment pathway to this clock, and one or more output signals. In vertebrates, melatonin produced by the pineal organ is one of these outputs. The production of this time-keeping hormone is high at night and low during the day. Despite the fact that this is a well-preserved pattern, the pathways through which the photoperiodic information controls the rhythm have been profoundly modified from early vertebrates to mammals. The photoperiodic control is direct in fish and frogs and indirect in mammals. In the former, full circadian systems are found in photoreceptor cells of the pineal organ, retina, and possibly brain, thus forming a network where melatonin could be a hormonal synchronizer. In the latter, the three elements of a circadian system are scattered: the photoreceptive units are in the eyes, the clocks are in the suprachiasmatic nuclei of the hypothalamus, and the melatonin-producing units are in the pineal cells. Intermediate situations are observed in sauropsids. Differences are also seen at the level of the arylalkylamine N-acetyltransferase (AANAT), the enzyme responsible for the daily variations in melatonin production. In contrast to tetrapods, teleost fish AANATs are duplicated and display tissue-specific expression; also, pineal AANAT is special--it responds to temperature in a species-specific manner, which reflects the fish ecophysiological preferences. This review summarizes anatomical, structural, and molecular aspects of the evolution of the melatonin-producing system in vertebrates.

[Photoperiodic control of melatonin synthesis in fish pineal and retina]. / Contrôle photopériodique de la synthèse de mélatonine par la rétine et l'épiphyse de poisson.

Melatonin is the time-keeping molecule of vertebrates. The daily and annual variations of its rhythmic production allow synchronizing physiological functions and behaviours to the variations of the environment. In fish, melatonin is produced by the photoreceptor cells of the retina and pineal organ. It is also synthesized by other retinal cell types of the inner nuclear and ganglion cell layers. In most of the species investigated, the melatonin rhythm displays a high-at-night profile, resulting from the circadian control of the arylalkylamine N-acetyltranferase (AANAT) activity; AANAT is the penultimate enzyme in the melatonin biosynthesis pathway. Some fish species escape the high-at-night rule in the retina, and the rhythm displays a high-at-day profile, intermediate situations being sometimes observed. This review summarizes our current knowledge on the molecular and cellular mechanisms of the rhythmic control of production of an important circadian clock messenger, underlying their plasticity.

[Melatonin and neuroendocrine regulations in fish]. / Mélatonine et régulations neuroendocrines chez le poisson.

Melatonin is the time-keeping molecule of the organism. The production by the pineal organ is responsible for the diurnal and annual rhythms of plasma melatonin content. This contributes to synchronizing behavioural, biochemical and physiological processes to the environmental variations in photoperiod and temperature. Conservation and diversity characterize the melatonin system in vertebrates: conservation because its nocturnal pattern of production as well as its synchronizing properties are a constant; diversity because the modalities of its biosynthesis and modes of action have been profoundly modified in the course of evolution. This review summarizes our current knowledge on the targets and modes of action of melatonin in fish and comparisons are made with mammals.