Function and Evolution of Nuclear Receptors in Environmental-Dependent Postembryonic Development

Estrogen-related receptors regulate innate and adaptive muscle mitochondrial energetics through cooperative and distinct actions

Mitochondrial energy metabolism is vital for muscle function and is tightly controlled at the transcriptional level, both in the basal state and during adaptive muscle remodeling. The importance of the transcription factors estrogen-related receptors (ERRs) in controlling innate mitochondrial energetics has been recently demonstrated. However, whether different ERR isoforms display distinct functions in glycolytic versus oxidative myofibers is largely unknown. Moreover, their roles in regulating exercise-induced adaptive mitochondrial biogenesis remain unclear. Using muscle-specific single and combinatorial knockout mouse models, we have identified both cooperative and distinct roles of the ERR isoforms ERRα and ERRγ in regulating mitochondrial energy metabolism in different muscles. We demonstrate the essential roles of both these ERRs in mediating adaptive mitochondrial biogenesis in response to exercise training. We further show that PGC1α-induced mitochondrial biogenesis is completely abolished in primary myotubes with ERRα deletion but not ERRγ, highlighting distinct roles of these two isoforms in adaptive mitochondrial remodeling. Mechanistically, we find that both ERRs directly bind to the majority of mitochondrial energetic genes and control their expression, largely through collaborative binding to the same genomic loci. Collectively, our findings reveal critical and direct regulatory roles of ERRα and ERRγ in governing both innate and adaptive mitochondrial energetics in skeletal muscle.

Exploring transcriptomic mechanisms underlying pulmonary adaptation to diverse environments in Indian rams

BACKGROUND

The Changthangi sheep thrive at high altitudes in the cold desert regions of Ladakh, India while Muzaffarnagri sheep are well-suited to the low altitude plains of northern India. This study investigates the molecular mechanisms of pulmonary adaptation to diverse environments by analyzing gene expression profiles of lung tissues through RNA sequencing.

METHODS AND RESULTS

Four biological replicates of lung tissue from each breed were utilized to generate the transcriptomic data. Differences in gene expression analysis revealed discrete expression profiles in lungs of each breed. In Changthangi sheep, genes related to immune responses, particularly cytokine signaling, were significantly enriched. Pathway analysis highlighted the activation of NF-kB signaling, a key mediator of inflammation and immune response. Additionally, the gene network analysis indicated a strong association between cytokine signaling, hypoxia-inducible factor (HIF) and NF-kB activation, suggesting a coordinated response to hypoxic stress in lungs of Changthangi sheep. In Muzaffarnagri sheep, the gene expression profiles were enriched for pathways related to energy metabolism, homeostasis and lung physiology. Key pathways identified include collagen formation and carbohydrate metabolism, both of which are crucial for maintaining lung function and structural integrity. Gene network analysis further reinforced this by revealing a strong connection between genes associated with lung structure and function.

CONCLUSIONS

Our findings shed light on the valuable insights into gene expression mechanisms that enable these sheep breeds to adapt to their respective environments and contribute to a better understanding of high altitude adaptation in livestock.

Lack of membrane sex steroid receptors for mediating rapid endocrine responses in molluscan nervous systems

Despite the lack of endogenous synthesis and relevant nuclear receptors, several papers have been published over the decades claiming that the physiology of mollusks is affected by natural and synthetic sex steroids. With scant evidence for the existence of functional steroid nuclear receptors in mollusks, some scientists have speculated that the effects of steroids might be mediated via membrane receptors (i.e. via non-genomic/non-classical actions) - a mechanism that has been well-characterized in vertebrates. However, no study has yet investigated the ligand-binding ability of such receptor candidates in mollusks. The aim of the present study was to further trace the evolution of the endocrine system by investigating the presence of functional membrane sex steroid receptors in a mollusk, the great pond snail (Lymnaea stagnalis). We detected sequences homologous to the known vertebrate membrane sex steroid receptors in the Lymnaea transcriptome and genome data: G protein-coupled estrogen receptor-1 (GPER1); membrane progestin receptors (mPRs); G protein-coupled receptor family C group 6 member A (GPRC6A); and Zrt- and Irt-like protein 9 (ZIP9). Sequence analyses, including conserved domain analysis, phylogenetics, and transmembrane domain prediction, indicated that the mPR and ZIP9 candidates appeared to be homologs, while the GPER1 and GPRC6A candidates seemed to be non-orthologous receptors. All candidates transiently transfected into HEK293MSR cells were found to be localized at the plasma membrane, confirming that they function as membrane receptors. However, the signaling assays revealed that none of the candidates interacted with the main vertebrate steroid ligands. Our findings strongly suggest that functional membrane sex steroid receptors which would be homologous to the vertebrate ones are not present in Lymnaea. Although further experiments are required on other molluscan model species as well, we propose that both classical and non-classical sex steroid signaling for endocrine responses are specific to chordates, confirming that molluscan and vertebrate endocrine systems are fundamentally different.

Recent advances in dietary androgen receptor inhibitors

As a nuclear transcription factor, the androgen receptor (AR) plays a crucial role not only in normal male sexual differentiation and growth of the prostate, but also in benign prostatic hyperplasia, prostatitis, and prostate cancer. Multiple population-based epidemiological studies demonstrated that prostate cancer risk was inversely associated with increased dietary intakes of green tea, soy products, tomato, and so forth. Therefore, this review aimed to summarize the structure and function of AR, and further illustrate the structural basis for antagonistic mechanisms of the currently clinically available antiandrogens. Due to the limitations of these antiandrogens, a series of natural AR inhibitors have been identified from edible plants such as fruits and vegetables, as well as folk medicines, health foods, and nutritional supplements. Hence, this review mainly focused on recent experimental, epidemiological, and clinical studies about natural AR inhibitors, particularly the association between dietary intake of natural antiandrogens and reduced risk of prostatic diseases. Since natural products offer multiple advantages over synthetic antiandrogens, this review may provide a comprehensive and updated overview of dietary-derived AR inhibitors, as well as their potential for the nutritional intervention against prostatic disorders.

Functional analysis of nuclear receptor genes in molting and metamorphosis of the cigarette beetle, Lasioderma serricorne

Nuclear receptors (NRs) are ligand-regulated transcription factors that are important for the normal growth and development of insects. However, systematic function analysis of NRs in the molting process of Lasioderma serricorne has not been reported. In this study, we identified and characterized 16 NR genes from L. serricorne. Spatiotemporal expression analysis revealed that six NRs were mainly expressed in 3-d-old 4th-instar larvae; five NRs were primarily expressed in 5-d-old adults and four NRs were predominately expressed in prepupae. All the NRs were highly expressed in epidermis, fat body and foregut. RNA interference (RNAi) experiments revealed that knockdown of 15 NRs disrupted the larva-pupa-adult transitions and caused 64.44-100 % mortality. Hematoxylin-eosin staining showed that depletion of 12 NRs prevented the formation of new cuticle and disrupted apolysis of old cuticle. Silencing of LsHR96, LsSVP and LsE78 led to newly formed cuticle that was thinner than the controls. The 20E titer and chitin content significantly decreased by 17.67-95.12 % after 15 NR dsRNA injection and the gene expression levels of 20E synthesis genes and chitin metabolism genes were significantly reduced. These results demonstrated that 15 NR genes are essential for normal molting and metamorphosis of L. serricorne by regulating 20E synthesis and chitin metabolism.

Presence, variation, and potential ecological impact of microplastics in the largest shallow lake of Central Europe

The presence of microplastics (MPs) in the global ecosystem has generated a rapidly growing concern worldwide. Although their presence in the marine environment has been well-studied, much less data are available on their abundance in freshwaters. MPs alone and in combination with different chemicals has been shown to cause acute and chronic effects on algae and aquatic invertebrate and vertebrate species at different biological levels. However, the combined ecotoxicological effects of MPs with different chemicals on aquatic organisms are still understudied in many species and the reported data are often controversial. In the present study, we investigated, for the first time, the presence of MPs in Lake Balaton, which is the largest shallow lake of Central Europe and an important summer holiday destination. Moreover, we exposed neonates of the well-established ecotoxicological model organism Daphnia magna to different MPs (polystyrene [3 μm] or polyethylene [≤ 100 μm]) alone and in combination with three progestogen compounds (progesterone, drospirenone, levonorgestrel) at an environmentally relevant concentration (10 ng L^-1) for 21 days. The presence of 7 polymer types of MPs in the size range of 50-100 μm was detected in Lake Balaton. Similarly to the global trends, polypropylene and polyethylene MPs were the most common types of polymer. The calculated polymer-independent average particle number was 5.5 particles m^-3 (size range: 50 μm - 100 μm) which represents the values detected in other European lakes. Our ecotoxicological experiments confirmed that MPs and progestogens can affect D. magna at the behavioral (body size and reproduction) and biochemical (detoxification-related enzyme activity) levels. The joint effects were negligible. The presence of MPs may lead to reduced fitness in the aquatic biota in freshwaters such as Lake Balaton, however, the potential threat of MPs as vectors for progestogens may be limited.

Thyroid hormone as a temporal switch in mouse development

Thyroid hormones are known to trigger metamorphosis in an amphibian. This review discusses the hypothesis according to which they act in a similar manner to synchronize the post-natal development of mice, using brain, brown adipose tissue, and heart as examples.

Microbiota mediated plasticity promotes thermal adaptation in the sea anemone Nematostella vectensis

At the current rate of climate change, it is unlikely that multicellular organisms will be able to adapt to changing environmental conditions through genetic recombination and natural selection alone. Thus, it is critical to understand alternative mechanisms that allow organisms to cope with rapid environmental changes. Here, we use the sea anemone Nematostella vectensis, which has evolved the capability of surviving in a wide range of temperatures and salinities, as a model to investigate the microbiota as a source of rapid adaptation. We long-term acclimate polyps of Nematostella to low, medium, and high temperatures, to test the impact of microbiota-mediated plasticity on animal acclimation. Using the same animal clonal line, propagated from a single polyp, allows us to eliminate the effects of the host genotype. The higher thermal tolerance of animals acclimated to high temperature can be transferred to non-acclimated animals through microbiota transplantation. The offspring fitness is highest from F0 females acclimated to high temperature and specific members of the acclimated microbiota are transmitted to the next generation. These results indicate that microbiota plasticity can contribute to animal thermal acclimation and its transmission to the next generation may represent a rapid mechanism for thermal adaptation.

This study shows that sea anemones acclimated to high temperatures exhibit increased resistance to thermal stress and that this improved fitness can be transferred by microbiome transplantation. These results indicate that plasticity mediated by the microbiota might be an important factor facilitating thermal adaptations in animals.

Hormone-controlled changes in the differentiation state of post-mitotic neurons

While we think of neurons as having a fixed identity, many show spectacular plasticity.^1-10 Metamorphosis drives massive changes in the fly brain;^11,12 neurons that persist into adulthood often change in response to the steroid hormone ecdysone.^13,14 Besides driving remodeling,^11-14 ecdysone signaling can also alter the differentiation status of neurons.^7,15 The three sequentially born subtypes of mushroom body (MB) Kenyon cells (γ, followed by α'/β', and finally α/β)¹⁶ serve as a model of temporal fating.^17-21 γ neurons are also used as a model of remodeling during metamorphosis. As γ neurons are the only functional Kenyon cells in the larval brain, they serve the function of all three adult subtypes. Correspondingly, larval γ neurons have a similar morphology to α'/β' and α/β neurons-their axons project dorsally and medially. During metamorphosis, γ neurons remodel to form a single medial projection. Both temporal fate changes and defects in remodeling therefore alter γ-neuron morphology in similar ways. Mamo, a broad-complex, tramtrack, and bric-à-brac/poxvirus and zinc finger (BTB/POZ) transcription factor critical for temporal specification of α'/β' neurons,^18,19 was recently described as essential for γ remodeling.²² In a previous study, we noticed a change in the number of adult Kenyon cells expressing γ-specific markers when mamo was manipulated.¹⁸ These data implied a role for Mamo in γ-neuron fate specification, yet mamo is not expressed in γ neurons until pupariation,^18,22 well past γ specification. This indicates that mamo has a later role in ensuring that γ neurons express the correct Kenyon cell subtype-specific genes in the adult brain.

Studies on a widely-recognized snail model species (Lymnaea stagnalis) provide further evidence that vertebrate steroids do not have a hormonal role in the reproduction of mollusks

Experiments were carried out to determine whether, as with other mollusks that have been studied, the snail, Lymnaea stagnalis, can absorb, esterify and store vertebrate steroids that are present in the water. We also carried out experiments to determine whether neural tissues of the snail could be immunohistochemically stained with an antibody to human aromatase (a key enzyme that catalyzes the conversion of testosterone [T] to 17β-estradiol [E₂]); and, if so, to determine the significance of such staining. Previous studies on other mollusks have reported such staining and have proposed this as decisive evidence that mollusks have the same steroid synthesis pathway as vertebrates. We found that snails absorb, esterify and retain esterified T, E₂, progesterone and ethinyl-estradiol (albeit with an absorption rate about four times slower, on a weight basis, than the mussel, Mytilus edulis). We also found that not only anti-human aromatase, but also anti-human nuclear progesterone receptor (nPR) and anti-human gonadotropin-releasing hormone antibodies immunohistochemically stained snail neural cells. However, further experiments, involving gel electrophoretic separation, followed by immunostaining, of proteins extracted from the neural tissue, found at least two positively-stained bands for each antibody, none of which had masses matching the human proteins to which the antibodies had been raised. The anti-aromatase antibody even stained the 140 kDA ladder protein used as a molecular weight marker on the gels. Mass spectrometric analysis of the bands did not find any peptide sequences that corresponded to the human proteins. Our findings confirm that the presence of vertebrate-like sex steroids in molluscan tissues is not necessarily evidence of endogenous origin. The results also show that immunohistochemical studies using antibodies against human proteins are grossly non-specific and likely to have little or no value in studying steroid synthesis or activity in mollusks. Our conclusions are consistent with the fact that genes for aromatase and nPR have not been found in the genome of the snail or of any other mollusk. Our overarching conclusion, from this and our previous studies, is that the endocrinology of mollusks is not the same as that of humans or any other vertebrates and that continuing to carry out physiological and ecotoxicological studies on mollusks on the basis of this false assumption, is an unconscionable waste of resources.

Evolution of non-genomic nuclear receptor function

Nuclear receptors (NRs) are responsible for the regulation of diverse developmental and physiological systems in metazoans. NR actions can be the result of genomic and non-genomic mechanisms depending on whether they act inside or outside of the nucleus respectively. While the actions of both mechanisms have been shown to be crucial to NR functions, non-genomic actions are considered less frequently than genomic actions. Furthermore, hypotheses on the origin and evolution of non-genomic NR signaling pathways are rarely discussed in the literature. Here we summarize non-genomic NR signaling mechanisms in the context of NR protein family evolution and animal phyla. We find that NRs across groups and phyla act via calcium flux as well as protein phosphorylation cascades (MAPK/PI3K/PKC). We hypothesize and discuss a possible synapomorphy of NRs in the NR1 and NR3 families, including the thyroid hormone receptor, vitamin D receptor, ecdysone receptor, retinoic acid receptor, steroid receptors, and others. In conclusion, we propose that the advent of non-genomic NR signaling may have been a driving force behind the expansion of NR diversity in Cnidarians, Placozoans, and Bilaterians.