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Seebacher F, Little AG. Thyroid hormone links environmental signals to DNA methylation. Philos Trans R Soc Lond B Biol Sci 2024; 379:20220506. [PMID: 38310936 PMCID: PMC10838643 DOI: 10.1098/rstb.2022.0506] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2023] [Accepted: 08/14/2023] [Indexed: 02/06/2024] Open
Abstract
Environmental conditions experienced within and across generations can impact individual phenotypes via so-called 'epigenetic' processes. Here we suggest that endocrine signalling acts as a 'sensor' linking environmental inputs to epigenetic modifications. We focus on thyroid hormone signalling and DNA methylation, but other mechanisms are likely to act in a similar manner. DNA methylation is one of the most important epigenetic mechanisms, which alters gene expression patterns by methylating cytosine bases via DNA methyltransferase enzymes. Thyroid hormone is mechanistically linked to DNA methylation, at least partly by regulating the activity of DNA methyltransferase 3a, which is the principal enzyme that mediates epigenetic responses to environmental change. Thyroid signalling is sensitive to natural and anthropogenic environmental impacts (e.g. light, temperature, endocrine-disrupting pollution), and here we propose that thyroid hormone acts as an environmental sensor to mediate epigenetic modifications. The nexus between thyroid hormone signalling and DNA methylation can integrate multiple environmental signals to modify phenotypes, and coordinate phenotypic plasticity at different time scales, such as within and across generations. These dynamics can have wide-ranging effects on health and fitness of animals, because they influence the time course of phenotypic adjustments and potentially the range of environmental stimuli that can elicit epigenetic responses. This article is part of the theme issue 'Endocrine responses to environmental variation: conceptual approaches and recent developments'.
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Affiliation(s)
- Frank Seebacher
- School of Life and Environmental Sciences A08, University of Sydney, New South Wales 2006, Australia
| | - Alexander G. Little
- Department of Biology, Life Sciences Building, McMaster University, Ontario, Canada L8S 4K1
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2
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Grossklaus R, Liesenkötter KP, Doubek K, Völzke H, Gaertner R. Iodine Deficiency, Maternal Hypothyroxinemia and Endocrine Disrupters Affecting Fetal Brain Development: A Scoping Review. Nutrients 2023; 15:nu15102249. [PMID: 37242131 DOI: 10.3390/nu15102249] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2023] [Revised: 05/04/2023] [Accepted: 05/05/2023] [Indexed: 05/28/2023] Open
Abstract
This scoping review critically discusses the publications of the last 30 years on the impact of mild to moderate iodine deficiency and the additional impact of endocrine disrupters during pregnancy on embryonal/fetal brain development. An asymptomatic mild to moderate iodine deficiency and/or isolated maternal hypothyroxinemia might affect the development of the embryonal/fetal brain. There is sufficient evidence underlining the importance of an adequate iodine supply for all women of childbearing age in order to prevent negative mental and social consequences for their children. An additional threat to the thyroid hormone system is the ubiquitous exposure to endocrine disrupters, which might exacerbate the effects of iodine deficiency in pregnant women on the neurocognitive development of their offspring. Ensuring adequate iodine intake is therefore essential not only for healthy fetal and neonatal development in general, but it might also extenuate the effects of endocrine disruptors. Individual iodine supplementation of women of childbearing age living in areas with mild to moderate iodine deficiency is mandatory as long as worldwide universal salt iodization does not guarantee an adequate iodine supply. There is an urgent need for detailed strategies to identify and reduce exposure to endocrine disrupters according to the "precautional principle".
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Affiliation(s)
- Rolf Grossklaus
- Department of Food Safety, Federal Institute for Risk Assessment, D-10589 Berlin, Germany
| | | | - Klaus Doubek
- Professional Association of Gynecologists, D-80337 Munich, Germany
| | - Henry Völzke
- Study of Health in Pomerania/Clinical-Epidemiological Research, Institute for Community Medicine, University Medicine Greifswald, D-17475 Greifswald, Germany
| | - Roland Gaertner
- Medical Clinic IV, University of Munich, D-80336 Munich, Germany
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3
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Lafontaine N, Wilson SG, Walsh JP. DNA Methylation in Autoimmune Thyroid Disease. J Clin Endocrinol Metab 2023; 108:604-613. [PMID: 36420742 DOI: 10.1210/clinem/dgac664] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/15/2022] [Revised: 11/02/2022] [Accepted: 11/14/2022] [Indexed: 11/25/2022]
Abstract
Graves disease and Hashimoto disease form part of the spectrum of autoimmune thyroid disease (AITD), to which genetic and environmental factors are recognized contributors. Epigenetics provides a potential link between environmental influences, gene expression, and thyroid autoimmunity. DNA methylation (DNAm) is the best studied epigenetic process, and global hypomethylation of leukocyte DNA is reported in several autoimmune disorders. This review summarizes the current understanding of DNAm in AITD. Targeted DNAm studies of blood samples from AITD patients have reported differential DNAm in the promoter regions of several genes implicated in AITD, including TNF, IFNG, IL2RA, IL6, ICAM1, and PTPN22. In many cases, however, the findings await replication and are unsupported by functional studies to support causal roles in AITD pathogenesis. Furthermore, thyroid hormones affect DNAm, and in many studies confounding by reverse causation has not been considered. Recent studies have shown that DNAm patterns in candidate genes including ITGA6, PRKAA2, and DAPK1 differ between AITD patients from regions with different iodine status, providing a potential mechanism for associations between iodine and AITD. Research focus in the field is moving from candidate gene studies to an epigenome-wide approach. Genome-wide methylation studies of AITD patients have demonstrated multiple differentially methylated positions, including some in immunoregulatory genes such as NOTCH1, HLA-DRB1, TNF, and ICAM1. Large, epigenome-wide studies are required to elucidate the pathophysiological role of DNAm in AITD, with the potential to provide novel diagnostic and prognostic biomarkers as well as therapeutic targets.
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Affiliation(s)
- Nicole Lafontaine
- Department of Endocrinology & Diabetes, Sir Charles Gairdner Hospital, Nedlands, Western Australia 6009, Australia
- Medical School, University of Western Australia, Crawley, Western Australia 6009, Australia
| | - Scott G Wilson
- Department of Endocrinology & Diabetes, Sir Charles Gairdner Hospital, Nedlands, Western Australia 6009, Australia
- School of Biomedical Sciences, University of Western Australia, Crawley, Western Australia 6009, Australia
| | - John P Walsh
- Department of Endocrinology & Diabetes, Sir Charles Gairdner Hospital, Nedlands, Western Australia 6009, Australia
- Medical School, University of Western Australia, Crawley, Western Australia 6009, Australia
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Hernandez A, Martinez ME, Chaves C, Anselmo J. Epigenetic developmental programming and intergenerational effects of thyroid hormones. VITAMINS AND HORMONES 2023; 122:23-49. [PMID: 36863795 PMCID: PMC10938172 DOI: 10.1016/bs.vh.2023.01.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/11/2023]
Abstract
Mounting evidence is showing that altered signaling through the nuclear hormone receptor superfamily can cause abnormal, long-term epigenetic changes which translate into pathological modifications and susceptibility to disease. These effects seem to be more prominent if the exposure occurs early in life, when transcriptomic profiles are rapidly changing. At this time, the coordination of the complex coordinated processes of cell proliferation and differentiation that characterize mammalian development. Such exposures may also alter the epigenetic information of the germ line, potentially leading to developmental changes and abnormal outcomes in subsequent generations. Thyroid hormone (TH) signaling is mediated by specific nuclear receptors, which have the ability to markedly change chromatin structure and gene transcription, and can also regulate other determinants of epigenetic marks. TH exhibits pleiotropic effects in mammals, and during development, its action is regulated in a highly dynamic manner to suit the rapidly evolving needs of multiple tissues. Their molecular mechanisms of action, timely developmental regulation and broad biological effects place THs in a central position to play a role in the developmental epigenetic programming of adult pathophysiology and, through effects on the germ line, in inter- and trans-generational epigenetic phenomena. These areas of epigenetic research are in their infancy, and studies regarding THs are limited. In the context of their characteristics as epigenetic modifiers and their finely tuned developmental action, here we review some of the observations underscoring the role that altered TH action may play in the developmental programming of adult traits and in the phenotypes of subsequent generations via germ line transmission of altered epigenetic information. Considering the relatively high prevalence of thyroid disease and the ability of some environmental chemicals to disrupt TH action, the epigenetic effects of abnormal levels of TH action may be important contributors to the non-genetic etiology of human disease.
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Affiliation(s)
- Arturo Hernandez
- Center for Molecular Medicine, MaineHealth Institute for Research, MaineHealth, Scarborough, ME, United States; Graduate School for Biomedical Sciences and Engineering, University of Maine, Orono, ME, United States; Department of Medicine, Tufts University School of Medicine, Boston, MA, United States.
| | - M Elena Martinez
- Center for Molecular Medicine, MaineHealth Institute for Research, MaineHealth, Scarborough, ME, United States
| | - Carolina Chaves
- Serviço de Endocrinologia e Nutrição, Hospital Divino Espírito Santo, Ponta Delgada, Açores, Portugal
| | - Joao Anselmo
- Serviço de Endocrinologia e Nutrição, Hospital Divino Espírito Santo, Ponta Delgada, Açores, Portugal
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Reverdatto S, Prasad A, Belrose JL, Zhang X, Sammons MA, Gibbs KM, Szaro BG. Developmental and Injury-induced Changes in DNA Methylation in Regenerative versus Non-regenerative Regions of the Vertebrate Central Nervous System. BMC Genomics 2022; 23:2. [PMID: 34979916 PMCID: PMC8725369 DOI: 10.1186/s12864-021-08247-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2021] [Accepted: 12/09/2021] [Indexed: 02/08/2023] Open
Abstract
BACKGROUND Because some of its CNS neurons (e.g., retinal ganglion cells after optic nerve crush (ONC)) regenerate axons throughout life, whereas others (e.g., hindbrain neurons after spinal cord injury (SCI)) lose this capacity as tadpoles metamorphose into frogs, the South African claw-toed frog, Xenopus laevis, offers unique opportunities for exploring differences between regenerative and non-regenerative responses to CNS injury within the same organism. An earlier, three-way RNA-seq study (frog ONC eye, tadpole SCI hindbrain, frog SCI hindbrain) identified genes that regulate chromatin accessibility among those that were differentially expressed in regenerative vs non-regenerative CNS [11]. The current study used whole genome bisulfite sequencing (WGBS) of DNA collected from these same animals at the peak period of axon regeneration to study the extent to which DNA methylation could potentially underlie differences in chromatin accessibility between regenerative and non-regenerative CNS. RESULTS Consistent with the hypothesis that DNA of regenerative CNS is more accessible than that of non-regenerative CNS, DNA from both the regenerative tadpole hindbrain and frog eye was less methylated than that of the non-regenerative frog hindbrain. Also, consistent with observations of CNS injury in mammals, DNA methylation in non-regenerative frog hindbrain decreased after SCI. However, contrary to expectations that the level of DNA methylation would decrease even further with axotomy in regenerative CNS, DNA methylation in these regions instead increased with injury. Injury-induced differences in CpG methylation in regenerative CNS became especially enriched in gene promoter regions, whereas non-CpG methylation differences were more evenly distributed across promoter regions, intergenic, and intragenic regions. In non-regenerative CNS, tissue-related (i.e., regenerative vs. non-regenerative CNS) and injury-induced decreases in promoter region CpG methylation were significantly correlated with increased RNA expression, but the injury-induced, increased CpG methylation seen in regenerative CNS across promoter regions was not, suggesting it was associated with increased rather than decreased chromatin accessibility. This hypothesis received support from observations that in regenerative CNS, many genes exhibiting increased, injury-induced, promoter-associated CpG-methylation also exhibited increased RNA expression and association with histone markers for active promoters and enhancers. DNA immunoprecipitation for 5hmC in optic nerve regeneration found that the promoter-associated increases seen in CpG methylation were distinct from those exhibiting changes in 5hmC. CONCLUSIONS Although seemingly paradoxical, the increased injury-associated DNA methylation seen in regenerative CNS has many parallels in stem cells and cancer. Thus, these axotomy-induced changes in DNA methylation in regenerative CNS provide evidence for a novel epigenetic state favoring successful over unsuccessful CNS axon regeneration. The datasets described in this study should help lay the foundations for future studies of the molecular and cellular mechanisms involved. The insights gained should, in turn, help point the way to novel therapeutic approaches for treating CNS injury in mammals.
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Affiliation(s)
- Sergei Reverdatto
- Department of Biological Sciences, University at Albany, State University of New York, Albany, NY, 12222, USA
- Center for Neuroscience Research, University at Albany, State University of New York, Albany, NY, 12222, USA
- RNA Institute, University at Albany, State University of New York, Albany, NY, 12222, USA
| | - Aparna Prasad
- Department of Biological Sciences, University at Albany, State University of New York, Albany, NY, 12222, USA
- Center for Neuroscience Research, University at Albany, State University of New York, Albany, NY, 12222, USA
- RNA Institute, University at Albany, State University of New York, Albany, NY, 12222, USA
| | - Jamie L Belrose
- Department of Biological Sciences, University at Albany, State University of New York, Albany, NY, 12222, USA
- Center for Neuroscience Research, University at Albany, State University of New York, Albany, NY, 12222, USA
| | - Xiang Zhang
- Department of Environmental and Public Health Sciences, University of Cincinnati College of Medicine, Cincinnati, OH, 45267, USA
| | - Morgan A Sammons
- Department of Biological Sciences, University at Albany, State University of New York, Albany, NY, 12222, USA
- RNA Institute, University at Albany, State University of New York, Albany, NY, 12222, USA
| | - Kurt M Gibbs
- Department of Biology & Chemistry, Morehead State University, Morehead, KY, 40351, USA
| | - Ben G Szaro
- Department of Biological Sciences, University at Albany, State University of New York, Albany, NY, 12222, USA.
- Center for Neuroscience Research, University at Albany, State University of New York, Albany, NY, 12222, USA.
- RNA Institute, University at Albany, State University of New York, Albany, NY, 12222, USA.
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Espina JEC, Bagamasbad PD. Synergistic gene regulation by thyroid hormone and glucocorticoid in the hippocampus. VITAMINS AND HORMONES 2021; 118:35-81. [PMID: 35180933 DOI: 10.1016/bs.vh.2021.11.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
The hippocampus is considered the center for learning and memory in the brain, and its development and function is greatly affected by the thyroid and stress axes. Thyroid hormone (TH) and glucocorticoids (GC) are known to have a synergistic effect on developmental programs across several vertebrate species, and their effects on hippocampal structure and function are well-documented. However, there are few studies that focus on the processes and genes that are cooperatively regulated by the two hormone axes. Cross-regulation of the thyroid and stress axes in the hippocampus occurs on multiple levels such that TH can regulate the expression of the GC receptor (GR) while GC can modulate tissue sensitivity to TH by controlling the expression of TH receptor (TR) and enzymes involved in TH biosynthesis. Thyroid hormone and GC are also known to synergistically regulate the transcription of genes associated with neuronal function and development. Synergistic gene regulation by TH and GC may occur through the direct, cooperative action of TR and GR on common target genes, or by indirect mechanisms involving gene regulatory cascades activated by TR and GR. In this chapter, we describe the known physiological effects and underlying molecular mechanisms of TH and GC synergistic gene regulation in the hippocampus.
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Affiliation(s)
- Jose Ezekiel C Espina
- National Institute of Molecular Biology and Biotechnology, University of the Philippines Diliman, Quezon City, Philippines
| | - Pia D Bagamasbad
- National Institute of Molecular Biology and Biotechnology, University of the Philippines Diliman, Quezon City, Philippines.
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Transcriptome and Methylome Analysis Reveal Complex Cross-Talks between Thyroid Hormone and Glucocorticoid Signaling at Xenopus Metamorphosis. Cells 2021; 10:cells10092375. [PMID: 34572025 PMCID: PMC8468809 DOI: 10.3390/cells10092375] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2021] [Revised: 08/31/2021] [Accepted: 09/03/2021] [Indexed: 12/29/2022] Open
Abstract
Background: Most work in endocrinology focus on the action of a single hormone, and very little on the cross-talks between two hormones. Here we characterize the nature of interactions between thyroid hormone and glucocorticoid signaling during Xenopus tropicalis metamorphosis. Methods: We used functional genomics to derive genome wide profiles of methylated DNA and measured changes of gene expression after hormonal treatments of a highly responsive tissue, tailfin. Clustering classified the data into four types of biological responses, and biological networks were modeled by system biology. Results: We found that gene expression is mostly regulated by either T3 or CORT, or their additive effect when they both regulate the same genes. A small but non-negligible fraction of genes (12%) displayed non-trivial regulations indicative of complex interactions between the signaling pathways. Strikingly, DNA methylation changes display the opposite and are dominated by cross-talks. Conclusion: Cross-talks between thyroid hormones and glucocorticoids are more complex than initially envisioned and are not limited to the simple addition of their individual effects, a statement that can be summarized with the pseudo-equation: TH ∙ GC > TH + GC. DNA methylation changes are highly dynamic and buffered from genome expression.
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Little AG. Thyroid hormone regulation of thermal acclimation in ectotherms: Physiological mechanisms and ecoevolutionary implications. Mol Cell Endocrinol 2021; 530:111285. [PMID: 33891994 DOI: 10.1016/j.mce.2021.111285] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/10/2020] [Revised: 02/07/2021] [Accepted: 04/12/2021] [Indexed: 02/07/2023]
Abstract
The pathways that regulate adaptive thermal plasticity in ectothermic vertebrates have received little attention relative to those in birds and mammals. However, there is increasing evidence that thyroid hormone represents a critical regulator of thermal plasticity in both ectothermic and endothermic vertebrates. In this review, I summarize the evidence for thyroid hormone-mediated thermal compensation responses in ectothermic vertebrates, with specific focus on effects on the whole animal, skeletal muscle, and cardiac muscle. Interestingly, these effects can differ wildly between focal tissues and species. I move on to discuss what the role of thyroid hormone in ectotherm thermal plasticity can reveal about stressor interactions and central vs. peripheral levels of thyroid hormone regulation. Lastly, I focus on the conserved nature of thyroid hormone signaling in animal thermal responses, with specific reference to the ectotherm → endotherm spectrum. I use this framework to highlight research avenues that will further resolve the evolutionary trajectory of thyroid hormone actions across animals. I hope to emphasize what thyroid hormone-mediated cold acclimation in a 3 cm fish can contribute to ongoing debates surrounding the impacts of stressor interactions, the potential costs of plasticity, the evolution of endothermy, and the impacts of global change.
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Affiliation(s)
- A G Little
- Department of Biology, Queen's University, Kingston, Ontario, K7L 3N6, Canada.
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Schiera G, Di Liegro CM, Di Liegro I. Involvement of Thyroid Hormones in Brain Development and Cancer. Cancers (Basel) 2021; 13:2693. [PMID: 34070729 PMCID: PMC8197921 DOI: 10.3390/cancers13112693] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2021] [Revised: 05/26/2021] [Accepted: 05/27/2021] [Indexed: 12/21/2022] Open
Abstract
The development and maturation of the mammalian brain are regulated by thyroid hormones (THs). Both hypothyroidism and hyperthyroidism cause serious anomalies in the organization and function of the nervous system. Most importantly, brain development is sensitive to TH supply well before the onset of the fetal thyroid function, and thus depends on the trans-placental transfer of maternal THs during pregnancy. Although the mechanism of action of THs mainly involves direct regulation of gene expression (genomic effects), mediated by nuclear receptors (THRs), it is now clear that THs can elicit cell responses also by binding to plasma membrane sites (non-genomic effects). Genomic and non-genomic effects of THs cooperate in modeling chromatin organization and function, thus controlling proliferation, maturation, and metabolism of the nervous system. However, the complex interplay of THs with their targets has also been suggested to impact cancer proliferation as well as metastatic processes. Herein, after discussing the general mechanisms of action of THs and their physiological effects on the nervous system, we will summarize a collection of data showing that thyroid hormone levels might influence cancer proliferation and invasion.
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Affiliation(s)
- Gabriella Schiera
- Department of Biological, Chemical and Pharmaceutical Sciences and Technologies (Dipartimento di Scienze e Tecnologie Biologiche, Chimiche e Farmaceutiche) (STEBICEF), University of Palermo, 90128 Palermo, Italy; (G.S.); (C.M.D.L.)
| | - Carlo Maria Di Liegro
- Department of Biological, Chemical and Pharmaceutical Sciences and Technologies (Dipartimento di Scienze e Tecnologie Biologiche, Chimiche e Farmaceutiche) (STEBICEF), University of Palermo, 90128 Palermo, Italy; (G.S.); (C.M.D.L.)
| | - Italia Di Liegro
- Department of Biomedicine, Neurosciences and Advanced Diagnostics (Dipartimento di Biomedicina, Neuroscienze e Diagnostica avanzata) (Bi.N.D.), University of Palermo, 90127 Palermo, Italy
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Denver RJ. Stress hormones mediate developmental plasticity in vertebrates with complex life cycles. Neurobiol Stress 2021; 14:100301. [PMID: 33614863 PMCID: PMC7879041 DOI: 10.1016/j.ynstr.2021.100301] [Citation(s) in RCA: 27] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2020] [Revised: 01/04/2021] [Accepted: 01/25/2021] [Indexed: 12/24/2022] Open
Abstract
The environment experienced by developing organisms can shape the timing and character of developmental processes, generating different phenotypes from the same genotype, each with different probabilities of survival and performance as adults. Chordates have two basic modes of development, indirect and direct. Species with indirect development, which includes most fishes and amphibians, have a complex life cycle with a free-swimming larva that is typically a growth stage, followed by a metamorphosis into the adult form. Species with direct development, which is an evolutionarily derived developmental mode, develop directly from embryo to the juvenile without an intervening larval stage. Among the best studied species with complex life cycles are the amphibians, especially the anurans (frogs and toads). Amphibian tadpoles are exposed to diverse biotic and abiotic factors in their developmental habitat. They have extensive capacity for developmental plasticity, which can lead to the expression of different, adaptive morphologies as tadpoles (polyphenism), variation in the timing of and size at metamorphosis, and carry-over effects on the phenotype of the juvenile/adult. The neuroendocrine stress axis plays a pivotal role in mediating environmental effects on amphibian development. Before initiating metamorphosis, if tadpoles are exposed to predators they upregulate production of the stress hormone corticosterone (CORT), which acts directly on the tail to cause it to grow, thereby increasing escape performance. When tadpoles reach a minimum body size to initiate metamorphosis they can vary the timing of transformation in relation to growth opportunity or mortality risk in the larval habitat. They do this by modulating the production of thyroid hormone (TH), the primary inducer of metamorphosis, and CORT, which synergizes with TH to promote tissue transformation. Hypophysiotropic neurons that release the stress neurohormone corticotropin-releasing factor (CRF) are activated in response to environmental stress (e.g., pond drying, food restriction, etc.), and CRF accelerates metamorphosis by directly inducing secretion of pituitary thyrotropin and corticotropin, thereby increasing secretion of TH and CORT. Although activation of the neuroendocrine stress axis promotes immediate survival in a deteriorating larval habitat, costs may be incurred such as reduced tadpole growth and size at metamorphosis. Small size at transformation can impair performance of the adult, reducing probability of survival in the terrestrial habitat, or fecundity. Furthermore, elevations in CORT in the tadpole caused by environmental stressors cause long term, stable changes in neuroendocrine function, behavior and physiology of the adult, which can affect fitness. Comparative studies show that the roles of stress hormones in developmental plasticity are conserved across vertebrate taxa including humans.
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Affiliation(s)
- Robert J. Denver
- Department of Molecular, Cellular and Developmental Biology, and Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, 48109-1085, USA
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11
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Raj S, Kyono Y, Sifuentes CJ, Arellanes-Licea EDC, Subramani A, Denver RJ. Thyroid Hormone Induces DNA Demethylation in Xenopus Tadpole Brain. Endocrinology 2020; 161:bqaa155. [PMID: 32865566 PMCID: PMC7947600 DOI: 10.1210/endocr/bqaa155] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/01/2020] [Accepted: 08/25/2020] [Indexed: 12/29/2022]
Abstract
Thyroid hormone (T3) plays pivotal roles in vertebrate development, acting via nuclear T3 receptors (TRs) that regulate gene transcription by promoting post-translational modifications to histones. Methylation of cytosine residues in deoxyribonucleic acid (DNA) also modulates gene transcription, and our recent finding of predominant DNA demethylation in the brain of Xenopus tadpoles at metamorphosis, a T3-dependent developmental process, caused us to hypothesize that T3 induces these changes in vivo. Treatment of premetamorphic tadpoles with T3 for 24 or 48 hours increased immunoreactivity in several brain regions for the DNA demethylation intermediates 5-hydroxymethylcytosine (5-hmC) and 5-carboxylcytosine, and the methylcytosine dioxygenase ten-eleven translocation 3 (TET3). Thyroid hormone treatment induced locus-specific DNA demethylation in proximity to known T3 response elements within the DNA methyltransferase 3a and Krüppel-like factor 9 genes, analyzed by 5-hmC immunoprecipitation and methylation sensitive restriction enzyme digest. Chromatin-immunoprecipitation (ChIP) assay showed that T3 induced TET3 recruitment to these loci. Furthermore, the messenger ribonucleic acid for several genes encoding DNA demethylation enzymes were induced by T3 in a time-dependent manner in tadpole brain. A TR ChIP-sequencing experiment identified putative TR binding sites at several of these genes, and we provide multiple lines of evidence to support that tet2 contains a bona fide T3 response element. Our findings show that T3 can promote DNA demethylation in developing tadpole brain, in part by promoting TET3 recruitment to discrete genomic regions, and by inducing genes that encode DNA demethylation enzymes.
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Affiliation(s)
- Samhitha Raj
- Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, Michigan
| | - Yasuhiro Kyono
- Neuroscience Graduate Program, University of Michigan, Ann Arbor, Michigan
| | - Christopher J Sifuentes
- Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, Michigan
| | | | - Arasakumar Subramani
- Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, Michigan
| | - Robert J Denver
- Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, Michigan
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12
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Lauby SC, McGowan PO. Early life variations in temperature exposure affect the epigenetic regulation of the paraventricular nucleus in female rat pups. Proc Biol Sci 2020; 287:20201991. [PMID: 33109014 PMCID: PMC7661289 DOI: 10.1098/rspb.2020.1991] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2020] [Accepted: 10/06/2020] [Indexed: 11/12/2022] Open
Abstract
Early life maternal care received has a profound effect on later-life behaviour in adult offspring, and previous studies have suggested epigenetic mechanisms are involved. Changes in thyroid hormone receptor signalling may be related to differences in maternal care received and DNA methylation modifications. We investigated the effects of variations in temperature exposure (a proxy of maternal contact) and licking-like tactile stimulation on these processes in week-old female rat pups. We assessed thyroid hormone receptor signalling by measuring circulating triiodothyronine and transcript abundance of thyroid hormone receptors and the thyroid hormone-responsive genes DNA methyltransferase 3a and oxytocin in the paraventricular nucleus of the hypothalamus. DNA methylation of the oxytocin promoter was assessed in relation to changes in thyroid hormone receptor binding. Repeated room temperature exposure was associated with a decrease in thyroid hormone receptor signalling measures relative to nest temperature exposure, while acute room temperature exposure was associated with an increase. Repeated room temperature exposure also increased thyroid hormone receptor binding and DNA methylation at the oxytocin promoter. These findings suggest that repeated room temperature exposure may affect DNA methylation levels as a consequence of alterations in thyroid hormone receptor signalling.
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Affiliation(s)
- Samantha C. Lauby
- Department of Biological Sciences, University of Toronto, Scarborough Campus, SW548, 1265 Military Trail, Scarborough, Toronto, Ontario, Canada M1C 1A4
- Department of Cell and Systems Biology, University of Toronto, Toronto, Ontario, Canada
| | - Patrick O. McGowan
- Department of Biological Sciences, University of Toronto, Scarborough Campus, SW548, 1265 Military Trail, Scarborough, Toronto, Ontario, Canada M1C 1A4
- Department of Cell and Systems Biology, University of Toronto, Toronto, Ontario, Canada
- Department of Psychology, University of Toronto, Toronto, Ontario, Canada
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
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Paus R, Ramot Y, Kirsner RS, Tomic-Canic M. Topical L-thyroxine: The Cinderella among hormones waiting to dance on the floor of dermatological therapy? Exp Dermatol 2020; 29:910-923. [PMID: 32682336 PMCID: PMC7722149 DOI: 10.1111/exd.14156] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2020] [Revised: 06/28/2020] [Accepted: 07/13/2020] [Indexed: 12/15/2022]
Abstract
Topical hormone therapy with natural or synthetic ligands of nuclear hormone receptors such as glucocorticoids, vitamin D analogues and retinoids has a long and highly successful tradition in dermatology. Yet the dermatological potential of thyroid hormone receptor (TR) agonists has been widely ignored, despite abundant clinical, cell and molecular biology, mouse in vivo, and human skin and hair follicle organ culture data documenting a role of TR-mediated signalling in skin physiology and pathology. Here, we review this evidence, with emphasis on wound healing and hair growth, and specifically highlight the therapeutic potential of repurposing topical L-thyroxine (T4) for selected applications in future dermatological therapy. We underscore the known systemic safety and efficacy profile of T4 in clinical medicine, and the well-documented impact of thyroid hormones on, for example, human epidermal and hair follicle physiology, hair follicle epithelial stem cells and pigmentation, keratin expression, mitochondrial energy metabolism and wound healing. On this background, we argue that short-term topical T4 treatment deserves careful further preclinical and clinical exploration for repurposing as a low-cost, effective and widely available dermatotherapeutic, namely in the management of skin ulcers and telogen effluvium, and that its predictable adverse effects are well-manageable.
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Affiliation(s)
- Ralf Paus
- Dr. Phillip Frost Department of Dermatology & Cutaneous Surgery, University of Miami Miller School of Medicine, Miami, FL, USA
- Centre for Dermatology Research, University of Manchester & NIHR Manchester Biomedical Research Centre, Manchester, UK
- Monasterium Laboratory, Münster, Germany
| | - Yuval Ramot
- Department of Dermatology, Hadassah Medical Center, The Faculty of Medicine, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Robert S. Kirsner
- Dr. Phillip Frost Department of Dermatology & Cutaneous Surgery, University of Miami Miller School of Medicine, Miami, FL, USA
| | - Marjana Tomic-Canic
- Dr. Phillip Frost Department of Dermatology & Cutaneous Surgery, University of Miami Miller School of Medicine, Miami, FL, USA
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14
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Kyono Y, Raj S, Sifuentes CJ, Buisine N, Sachs L, Denver RJ. DNA methylation dynamics underlie metamorphic gene regulation programs in Xenopus tadpole brain. Dev Biol 2020; 462:180-196. [PMID: 32240642 PMCID: PMC7251973 DOI: 10.1016/j.ydbio.2020.03.013] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2019] [Revised: 02/28/2020] [Accepted: 03/23/2020] [Indexed: 01/07/2023]
Abstract
Methylation of cytosine residues in DNA influences chromatin structure and gene transcription, and its regulation is crucial for brain development. There is mounting evidence that DNA methylation can be modulated by hormone signaling. We analyzed genome-wide changes in DNA methylation and their relationship to gene regulation in the brain of Xenopus tadpoles during metamorphosis, a thyroid hormone-dependent developmental process. We studied the region of the tadpole brain containing neurosecretory neurons that control pituitary hormone secretion, a region that is highly responsive to thyroid hormone action. Using Methylated DNA Capture sequencing (MethylCap-seq) we discovered a diverse landscape of DNA methylation across the tadpole neural cell genome, and pairwise stage comparisons identified several thousand differentially methylated regions (DMRs). During the pre-to pro-metamorphic period, the number of DMRs was lowest (1,163), with demethylation predominating. From pre-metamorphosis to metamorphic climax DMRs nearly doubled (2,204), with methylation predominating. The largest changes in DNA methylation were seen from metamorphic climax to the completion of metamorphosis (2960 DMRs), with 80% of the DMRs representing demethylation. Using RNA sequencing, we found negative correlations between differentially expressed genes and DMRs localized to gene bodies and regions upstream of transcription start sites. DNA demethylation at metamorphosis revealed by MethylCap-seq was corroborated by increased immunoreactivity for the DNA demethylation intermediates 5-hydroxymethylcytosine and 5-carboxymethylcytosine, and the methylcytosine dioxygenase ten eleven translocation 3 that catalyzes DNA demethylation. Our findings show that the genome of tadpole neural cells undergoes significant changes in DNA methylation during metamorphosis, and these changes likely influence chromatin architecture, and gene regulation programs occurring during this developmental period.
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Affiliation(s)
- Yasuhiro Kyono
- Neuroscience Graduate Program, The University of Michigan, Ann Arbor, MI, 48109, USA
| | - Samhitha Raj
- Department of Molecular, Cellular and Developmental Biology, The University of Michigan, Ann Arbor, MI, 48109, USA
| | - Christopher J Sifuentes
- Department of Molecular, Cellular and Developmental Biology, The University of Michigan, Ann Arbor, MI, 48109, USA
| | - Nicolas Buisine
- UMR-7221, Centre National de la recherche scientifique (CNRS), Muséum National d'Histoire Naturelle, 75005, Paris, France
| | - Laurent Sachs
- UMR-7221, Centre National de la recherche scientifique (CNRS), Muséum National d'Histoire Naturelle, 75005, Paris, France
| | - Robert J Denver
- Department of Molecular, Cellular and Developmental Biology, The University of Michigan, Ann Arbor, MI, 48109, USA.
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15
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Martinez ME, Duarte CW, Stohn JP, Karaczyn A, Wu Z, DeMambro VE, Hernandez A. Thyroid hormone influences brain gene expression programs and behaviors in later generations by altering germ line epigenetic information. Mol Psychiatry 2020; 25:939-950. [PMID: 30356120 PMCID: PMC6482106 DOI: 10.1038/s41380-018-0281-4] [Citation(s) in RCA: 36] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/30/2018] [Revised: 08/16/2018] [Accepted: 09/26/2018] [Indexed: 11/09/2022]
Abstract
Genetic factors do not fully account for the relatively high heritability of neurodevelopmental conditions, suggesting that non-genetic heritable factors contribute to their etiology. To evaluate the potential contribution of aberrant thyroid hormone status to the epigenetic inheritance of neurological phenotypes, we examined genetically normal F2 generation descendants of mice that were developmentally overexposed to thyroid hormone due to a Dio3 mutation. Hypothalamic gene expression profiling in postnatal day 15 F2 descendants on the paternal lineage of ancestral male and female T3-overexposed mice revealed, respectively, 1089 and 1549 differentially expressed genes. A large number of them, 675 genes, were common to both sets, suggesting comparable epigenetic effects of thyroid hormone on both the male and female ancestral germ lines. Oligodendrocyte- and neuron-specific genes were strongly overrepresented among genes showing, respectively, increased and decreased expression. Altered gene expression extended to other brain regions and was associated in adulthood with decreased anxiety-like behavior, increased marble burying and reduced physical activity. The sperm of T3-overexposed male ancestors revealed significant hypomethylation of CpG islands associated with the promoters of genes involved in the early development of the central nervous system. Some of them were candidates for neurodevelopmental disorders in humans including Nrg3, Nrxn1, Gabrb3, Gabra5, Apba2, Grik3, Reln, Nsd1, Pcdh8, En1, and Elavl2. Thus, developmental levels of thyroid hormone influence the epigenetic information of the germ line, disproportionately affecting genes with critical roles in early brain development, and leading in future generations to disease-relevant alterations in postnatal brain gene expression and adult behavior.
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Affiliation(s)
- M. Elena Martinez
- Center for Molecular Medicine, Maine Medical Center Research Institute, Maine Medical Center, Scarborough, ME, 04074, USA
| | - Christine W. Duarte
- Center for Outcomes Research and Evaluation, Maine Medical Center Research Institute, Maine Medical Center, Scarborough, ME, 04074, USA,Graduate School for Biomedical Science and Engineering, University of Maine, Orono, ME, 04469, USA
| | - J. Patrizia Stohn
- Center for Molecular Medicine, Maine Medical Center Research Institute, Maine Medical Center, Scarborough, ME, 04074, USA
| | - Aldona Karaczyn
- Center for Molecular Medicine, Maine Medical Center Research Institute, Maine Medical Center, Scarborough, ME, 04074, USA
| | - Zhaofei Wu
- Center for Molecular Medicine, Maine Medical Center Research Institute, Maine Medical Center, Scarborough, ME, 04074, USA
| | - Victoria E DeMambro
- Center for Molecular Medicine, Maine Medical Center Research Institute, Maine Medical Center, Scarborough, ME, 04074, USA
| | - Arturo Hernandez
- Center for Molecular Medicine, Maine Medical Center Research Institute, Maine Medical Center, Scarborough, ME, 04074, USA. .,Graduate School for Biomedical Science and Engineering, University of Maine, Orono, ME, 04469, USA. .,Department of Medicine, Tufts University School of Medicine, Boston, MA, USA.
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16
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Krude H, Biebermann H, Schuelke M, Müller TD, Tschöp M. Allan-Herndon-Dudley-Syndrome: Considerations about the Brain Phenotype with Implications for Treatment Strategies. Exp Clin Endocrinol Diabetes 2020; 128:414-422. [PMID: 32242326 DOI: 10.1055/a-1108-1456] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Despite its first description more than 75 years ago, effective treatment for "Allan-Herndon-Dudley-Syndrome (AHDS)", an X-linked thyroid hormone transporter defect, is unavailable. Mutations in the SLC16A2 gene have been discovered to be causative for AHDS in 2004, but a comprehensive understanding of the function of the encoded protein, monocarboxylate transporter 8 (MCT8), is incomplete. Patients with AHDS suffer from neurodevelopmental delay, as well as extrapyramidal (dystonia, chorea, athetosis), pyramidal (spasticity), and cerebellar symptoms (ataxia). This suggests an affection of the pyramidal tracts, basal ganglia, and cerebellum, most likely already during fetal brain development. The function of other brain areas relevant for mood, behavior, and vigilance seems to be intact. An optimal treatment strategy should thus aim to deliver T3 to these relevant structures at the correct time points during development. A potential therapeutic strategy meeting these needs might be the delivery of T3 via a "Trojan horse mechanism" by which T3 is delivered into target cells by a thyroid hormone transporter independent T3 internalization.
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Affiliation(s)
- Heiko Krude
- Institute of Experimental Pediatric Endocrinology, Charité - Universitätsmedizin, Berlin, Germany
| | - Heike Biebermann
- Institute of Experimental Pediatric Endocrinology, Charité - Universitätsmedizin, Berlin, Germany
| | - Markus Schuelke
- Department of Neuropediatrics, Charité - Universitätsmedizin, Berlin, Germany
| | - Timo D Müller
- Institute for Diabetes and Obesity, Helmholtz Diabetes Center at Helmholtz Centre Munich, Germany.,German Center for Diabetes Research (DZD), Neuherberg, Germany.,Department of Pharmacology and Experimental Therapy, Institute of Experimental and Clinical Pharmacology and Toxicology, Eberhard Karls University Hospitals and Clinics, Tübingen, Germany
| | - Matthias Tschöp
- Division of Metabolic Diseases, Technische Universität München, Munich, Germany.,German Center for Diabetes Research (DZD), Neuherberg, Germany.,Helmholtz Zentrum München, Germany
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Demeneix BA. Evidence for Prenatal Exposure to Thyroid Disruptors and Adverse Effects on Brain Development. Eur Thyroid J 2019; 8:283-292. [PMID: 31934553 PMCID: PMC6944944 DOI: 10.1159/000504668] [Citation(s) in RCA: 40] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/06/2019] [Accepted: 11/11/2019] [Indexed: 12/15/2022] Open
Abstract
Thyroid hormone regulates vital processes in early brain development such as neuronal stem cell proliferation, migration, and myelination. The fetal thyroid is not fully functional until mid-pregnancy (18-20 weeks), so placental transfer of maternal thyroid hormones during early pregnancy is crucial, as is the maternal iodine status. The volume of chemical production has increased 300-fold since the 1970s. Thus, chemical exposure is ubiquitous; every child born today has dozens of man-made xenobiotic compounds in its blood. Increasing evidence from both epidemiological and animal or in vitro studies demonstrates that many of these chemicals have the potential to interfere with thyroid hormone availability and action at different physiological levels. These chemicals are found in numerous consumer products and include certain plastics, pesticides, perfluorinated compounds, and flame retardants. The last decades have seen exponential increases in neurodevelopmental disease including autism spectrum disorder and attention deficit/hyperactivity disorder. We hypothesize that prenatal exposure to mixtures of thyroid hormone-disrupting chemicals, with iodine deficiency potentially exacerbating the situation, has a strong probability of contributing to this increased incidence of neurodevelopmental disease, but could also entail a surreptitious, but socio-economically consequential, loss of IQ. Thyroid hormone receptor actions can modulate gene transcription, most often through epigenetic mechanisms. Thus, interference with epigenetic regulations is increasingly thought to link neurodevelopmental disease and IQ loss to thyroid hormone disruption.
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Affiliation(s)
- Barbara A. Demeneix
- CNRS/UMR7221, Muséum National d'Histoire Naturelle/Université Paris-Sorbonne, Paris, France
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18
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Noyes PD, Friedman KP, Browne P, Haselman JT, Gilbert ME, Hornung MW, Barone S, Crofton KM, Laws SC, Stoker TE, Simmons SO, Tietge JE, Degitz SJ. Evaluating Chemicals for Thyroid Disruption: Opportunities and Challenges with in Vitro Testing and Adverse Outcome Pathway Approaches. ENVIRONMENTAL HEALTH PERSPECTIVES 2019; 127:95001. [PMID: 31487205 PMCID: PMC6791490 DOI: 10.1289/ehp5297] [Citation(s) in RCA: 103] [Impact Index Per Article: 20.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2019] [Revised: 07/01/2019] [Accepted: 08/13/2019] [Indexed: 05/19/2023]
Abstract
BACKGROUND Extensive clinical and experimental research documents the potential for chemical disruption of thyroid hormone (TH) signaling through multiple molecular targets. Perturbation of TH signaling can lead to abnormal brain development, cognitive impairments, and other adverse outcomes in humans and wildlife. To increase chemical safety screening efficiency and reduce vertebrate animal testing, in vitro assays that identify chemical interactions with molecular targets of the thyroid system have been developed and implemented. OBJECTIVES We present an adverse outcome pathway (AOP) network to link data derived from in vitro assays that measure chemical interactions with thyroid molecular targets to downstream events and adverse outcomes traditionally derived from in vivo testing. We examine the role of new in vitro technologies, in the context of the AOP network, in facilitating consideration of several important regulatory and biological challenges in characterizing chemicals that exert effects through a thyroid mechanism. DISCUSSION There is a substantial body of knowledge describing chemical effects on molecular and physiological regulation of TH signaling and associated adverse outcomes. Until recently, few alternative nonanimal assays were available to interrogate chemical effects on TH signaling. With the development of these new tools, screening large libraries of chemicals for interactions with molecular targets of the thyroid is now possible. Measuring early chemical interactions with targets in the thyroid pathway provides a means of linking adverse outcomes, which may be influenced by many biological processes, to a thyroid mechanism. However, the use of in vitro assays beyond chemical screening is complicated by continuing limits in our knowledge of TH signaling in important life stages and tissues, such as during fetal brain development. Nonetheless, the thyroid AOP network provides an ideal tool for defining causal linkages of a chemical exerting thyroid-dependent effects and identifying research needs to quantify these effects in support of regulatory decision making. https://doi.org/10.1289/EHP5297.
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Affiliation(s)
- Pamela D Noyes
- National Center for Environmental Assessment, Office of Research and Development (ORD), U.S. Environmental Protection Agency (EPA), Washington, DC, USA
| | - Katie Paul Friedman
- National Center for Computational Toxicology, ORD, U.S. EPA, Research Triangle Park, North Carolina, USA
| | - Patience Browne
- Environment Health and Safety Division, Environment Directorate, Organisation for Economic Co-operation and Development (OECD), Paris, France
| | - Jonathan T Haselman
- Mid-Continent Ecology Division, National Health and Environmental Effects Research Laboratory (NHEERL), ORD, U.S. EPA, Duluth, Minnesota, USA
| | - Mary E Gilbert
- Toxicity Assessment Division, NHEERL, ORD, U.S. EPA, Research Triangle Park, North Carolina, USA
| | - Michael W Hornung
- Mid-Continent Ecology Division, National Health and Environmental Effects Research Laboratory (NHEERL), ORD, U.S. EPA, Duluth, Minnesota, USA
| | - Stan Barone
- Office of Pollution Prevention and Toxics, Office of Chemical Safety and Pollution Prevention, U.S. EPA, Washington, DC, USA
| | - Kevin M Crofton
- National Center for Computational Toxicology, ORD, U.S. EPA, Research Triangle Park, North Carolina, USA
| | - Susan C Laws
- Toxicity Assessment Division, NHEERL, ORD, U.S. EPA, Research Triangle Park, North Carolina, USA
| | - Tammy E Stoker
- Toxicity Assessment Division, NHEERL, ORD, U.S. EPA, Research Triangle Park, North Carolina, USA
| | - Steven O Simmons
- National Center for Computational Toxicology, ORD, U.S. EPA, Research Triangle Park, North Carolina, USA
| | - Joseph E Tietge
- Mid-Continent Ecology Division, National Health and Environmental Effects Research Laboratory (NHEERL), ORD, U.S. EPA, Duluth, Minnesota, USA
| | - Sigmund J Degitz
- Mid-Continent Ecology Division, National Health and Environmental Effects Research Laboratory (NHEERL), ORD, U.S. EPA, Duluth, Minnesota, USA
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19
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Cognition-Enhancing Vagus Nerve Stimulation Alters the Epigenetic Landscape. J Neurosci 2019; 39:3454-3469. [PMID: 30804093 DOI: 10.1523/jneurosci.2407-18.2019] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2018] [Revised: 02/15/2019] [Accepted: 02/16/2019] [Indexed: 01/27/2023] Open
Abstract
Vagus nerve stimulation (VNS) has been shown to enhance learning and memory, yet the mechanisms behind these enhancements are unknown. Here, we present evidence that epigenetic modulation underlies VNS-induced improvements in cognition. We show that VNS enhances novelty preference (NP); alters the hippocampal, cortical, and blood epigenetic transcriptomes; and epigenetically modulates neuronal plasticity and stress-response signaling genes in male Sprague Dawley rats. Brain-behavior analysis revealed structure-specific relationships between NP test performance (NPTP) and epigenetic alterations. In the hippocampus, NPTP correlated with decreased histone deacetylase 11 (HDAC11), a transcriptional repressor enriched in CA1 cells important for memory consolidation. In the cortex, the immediate early gene (IEG) ARC was increased in VNS rats and correlated with transcription of plasticity genes and epigenetic regulators, including HDAC3. For rats engaged in NPTP, ARC correlated with performance. Interestingly, blood ARC transcripts decreased in VNS rats performing NPTP, but increased in VNS-only rats. Because DNA double-strand breaks (DSBs) facilitate transcription of IEGs, we investigated phosphorylated H2A.X (γH2A.X), a histone modification known to colocalize with DSBs. In agreement with reduced cortical stress-response transcription factor NF-κB1, chromatin immunoprecipitation revealed reduced γH2A.X in the ARC promoter. Surprisingly, VNS did not significantly reduce transcription of cortical or hippocampal proinflammatory cytokines. However, TNFRSF11B (osteoprotegerin) correlated with NPTP as well as plasticity, stress-response signaling, and epigenetic regulation transcripts in both hippocampus and cortex. Together, our findings provide the first evidence that VNS induces widespread changes in the cognitive epigenetic landscape and specifically affects epigenetic modulators associated with NPTP, stress-response signaling, memory consolidation, and cortical neural remodeling.SIGNIFICANCE STATEMENT Recent studies have implicated vagus nerve stimulation (VNS) in enhanced learning and memory. However, whereas epigenetic modifications are known to play an important role in memory, the particular mechanisms involved in VNS-enhanced cognition are unknown. In this study, we examined brain and behavior changes in VNS and sham rats performing a multiday novelty preference (NP) task. We found that VNS activated specific histone modifications and DNA methylation changes at important stress-response signaling and plasticity genes. Both cortical and hippocampal plasticity changes were predictive of NP test performance. Our results reveal important epigenetic alterations associated with VNS cognitive improvements, as well as new potential pharmacological targets for enhancing cortical and hippocampal plasticity.
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Forini F, Nicolini G, Pitto L, Iervasi G. Novel Insight Into the Epigenetic and Post-transcriptional Control of Cardiac Gene Expression by Thyroid Hormone. Front Endocrinol (Lausanne) 2019; 10:601. [PMID: 31555215 PMCID: PMC6727178 DOI: 10.3389/fendo.2019.00601] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/18/2019] [Accepted: 08/16/2019] [Indexed: 12/17/2022] Open
Abstract
Thyroid hormone (TH) signaling is critically involved in the regulation of cardiovascular physiology. Even mild reductions of myocardial TH levels, as occur in hypothyroidism or low T3 state conditions, are thought to play a role in the progression of cardiac disorders. Due to recent advances in molecular mechanisms underlying TH action, it is now accepted that TH-dependent modulation of gene expression is achieved at multiple transcriptional and post-transcriptional levels and involves the cooperation of many processes. Among them, the epigenetic remodeling of chromatin structure and the interplay with non-coding RNA have emerged as novel TH-dependent pathways that add further degrees of complexity and broaden the network of genes controlled by TH signaling. Increasing experimental and clinical findings indicate that aberrant function of these regulatory mechanisms promotes the evolution of cardiac disorders such as post-ischemic injury, pathological hypertrophy, and heart failure, which may be reversed by the correction of the underlying TH dyshomeostasis. To encourage the clinical implementation of a TH replacement strategy in cardiac disease, here we discuss the crucial effect of epigenetic modifications and control of non-coding RNA in TH-dependent regulation of biological processes relevant for cardiac disease evolution.
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21
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Stepien BK, Huttner WB. Transport, Metabolism, and Function of Thyroid Hormones in the Developing Mammalian Brain. Front Endocrinol (Lausanne) 2019; 10:209. [PMID: 31001205 PMCID: PMC6456649 DOI: 10.3389/fendo.2019.00209] [Citation(s) in RCA: 42] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/22/2019] [Accepted: 03/14/2019] [Indexed: 12/22/2022] Open
Abstract
Ever since the discovery of thyroid hormone deficiency as the primary cause of cretinism in the second half of the 19th century, the crucial role of thyroid hormone (TH) signaling in embryonic brain development has been established. However, the biological understanding of TH function in brain formation is far from complete, despite advances in treating thyroid function deficiency disorders. The pleiotropic nature of TH action makes it difficult to identify and study discrete roles of TH in various aspect of embryogenesis, including neurogenesis and brain maturation. These challenges notwithstanding, enormous progress has been achieved in understanding TH production and its regulation, their conversions and routes of entry into the developing mammalian brain. The endocrine environment has to adjust when an embryo ceases to rely solely on maternal source of hormones as its own thyroid gland develops and starts to produce endogenous TH. A number of mechanisms are in place to secure the proper delivery and action of TH with placenta, blood-brain interface, and choroid plexus as barriers of entry that need to selectively transport and modify these hormones thus controlling their active levels. Additionally, target cells also possess mechanisms to import, modify and bind TH to further fine-tune their action. A complex picture of a tightly regulated network of transport proteins, modifying enzymes, and receptors has emerged from the past studies. TH have been implicated in multiple processes related to brain formation in mammals-neuronal progenitor proliferation, neuronal migration, functional maturation, and survival-with their exact roles changing over developmental time. Given the plethora of effects thyroid hormones exert on various cell types at different developmental periods, the precise spatiotemporal regulation of their action is of crucial importance. In this review we summarize the current knowledge about TH delivery, conversions, and function in the developing mammalian brain. We also discuss their potential role in vertebrate brain evolution and offer future directions for research aimed at elucidating TH signaling in nervous system development.
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22
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Singh BK, Sinha RA, Yen PM. Novel Transcriptional Mechanisms for Regulating Metabolism by Thyroid Hormone. Int J Mol Sci 2018; 19:E3284. [PMID: 30360449 PMCID: PMC6214012 DOI: 10.3390/ijms19103284] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2018] [Revised: 10/11/2018] [Accepted: 10/18/2018] [Indexed: 12/14/2022] Open
Abstract
The thyroid hormone plays a key role in energy and nutrient metabolisms in many tissues and regulates the transcription of key genes in metabolic pathways. It has long been believed that thyroid hormones (THs) exerted their effects primarily by binding to nuclear TH receptors (THRs) that are associated with conserved thyroid hormone response elements (TREs) located on the promoters of target genes. However, recent transcriptome and ChIP-Seq studies have challenged this conventional view as discordance was observed between TH-responsive genes and THR binding to DNA. While THR association with other transcription factors bound to DNA, TH activation of THRs to mediate effects that do not involve DNA-binding, or TH binding to proteins other than THRs have been invoked as potential mechanisms to explain this discrepancy, it appears that additional novel mechanisms may enable TH to regulate the mRNA expression. These include activation of transcription factors by SIRT1 via metabolic actions by TH, the post-translational modification of THR, the THR co-regulation of transcription with other nuclear receptors and transcription factors, and the microRNA (miR) control of RNA transcript expression to encode proteins involved in the cellular metabolism. Together, these novel mechanisms enlarge and diversify the panoply of metabolic genes that can be regulated by TH.
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Affiliation(s)
- Brijesh Kumar Singh
- Laboratory of Hormonal Regulation, Cardiovascular and Metabolic Disorders Program, Duke-NUS Medical School, Singapore 169857, Singapore.
| | - Rohit Anthony Sinha
- Department of Endocrinology, Sanjay Gandhi Post Graduate Institute of Medical Sciences, Raebareli Road, Lucknow 226014, Uttar Pradesh, India.
| | - Paul Michael Yen
- Laboratory of Hormonal Regulation, Cardiovascular and Metabolic Disorders Program, Duke-NUS Medical School, Singapore 169857, Singapore.
- Division of Endocrinology, Metabolism, and Nutrition, Department of Medicine, Duke Molecular Physiology Institute, Duke University School of Medicine, Durham, NC 27710, USA.
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24
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Mughal BB, Fini JB, Demeneix BA. Thyroid-disrupting chemicals and brain development: an update. Endocr Connect 2018; 7:R160-R186. [PMID: 29572405 PMCID: PMC5890081 DOI: 10.1530/ec-18-0029] [Citation(s) in RCA: 89] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/04/2018] [Accepted: 03/14/2018] [Indexed: 12/12/2022]
Abstract
This review covers recent findings on the main categories of thyroid hormone-disrupting chemicals and their effects on brain development. We draw mostly on epidemiological and experimental data published in the last decade. For each chemical class considered, we deal with not only the thyroid hormone-disrupting effects but also briefly mention the main mechanisms by which the same chemicals could modify estrogen and/or androgen signalling, thereby exacerbating adverse effects on endocrine-dependent developmental programmes. Further, we emphasize recent data showing how maternal thyroid hormone signalling during early pregnancy affects not only offspring IQ, but also neurodevelopmental disease risk. These recent findings add to established knowledge on the crucial importance of iodine and thyroid hormone for optimal brain development. We propose that prenatal exposure to mixtures of thyroid hormone-disrupting chemicals provides a plausible biological mechanism contributing to current increases in the incidence of neurodevelopmental disease and IQ loss.
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Affiliation(s)
- Bilal B Mughal
- CNRS/UMR7221Muséum National d'Histoire Naturelle, Sorbonne Universités, Paris, France
| | - Jean-Baptiste Fini
- CNRS/UMR7221Muséum National d'Histoire Naturelle, Sorbonne Universités, Paris, France
| | - Barbara A Demeneix
- CNRS/UMR7221Muséum National d'Histoire Naturelle, Sorbonne Universités, Paris, France
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25
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Calzà L, Baldassarro VA, Fernandez M, Giuliani A, Lorenzini L, Giardino L. Thyroid Hormone and the White Matter of the Central Nervous System: From Development to Repair. VITAMINS AND HORMONES 2018; 106:253-281. [DOI: 10.1016/bs.vh.2017.04.003] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
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26
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Singh BK, Sinha RA, Ohba K, Yen PM. Role of thyroid hormone in hepatic gene regulation, chromatin remodeling, and autophagy. Mol Cell Endocrinol 2017; 458:160-168. [PMID: 28216439 DOI: 10.1016/j.mce.2017.02.018] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/30/2016] [Revised: 02/09/2017] [Accepted: 02/10/2017] [Indexed: 01/21/2023]
Abstract
Thyroid hormone (TH) actions on development and metabolism have been studied ever since the discovery of thyroxine almost a century ago. Initial studies focused on the physiological and biochemical actions of TH. Later, the cloning of the thyroid hormone receptor (THR) isoforms and the development of techniques enabled the study of TH regulation of complex cellular processes (such as gene transcription). Recently we found that TH activates secondary transcription factors such as FOXO1, to amplify gene transcription; and also is a potent inducer of autophagy that was critical for fatty acid β-oxidation in the liver. This review summarizes the recent advancements in our understanding of TH regulation of gene expression of metabolic genes (via co-regulators/transcription factors and epigenetic control) and autophagy in the liver. Our deeper understanding of TH action recently has led to the development of tissue- and THR isoform-specific TH mimetics that may be useful for the treatment of metabolic disorders.
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Affiliation(s)
- Brijesh Kumar Singh
- Laboratory of Hormonal Regulation, Cardiovascular and Metabolic Disorders Program, Duke-NUS Medical School, 169857, Singapore
| | - Rohit Anthony Sinha
- Laboratory of Hormonal Regulation, Cardiovascular and Metabolic Disorders Program, Duke-NUS Medical School, 169857, Singapore
| | - Kenji Ohba
- Laboratory of Hormonal Regulation, Cardiovascular and Metabolic Disorders Program, Duke-NUS Medical School, 169857, Singapore; Department of Internal Medicine, Enshu Hospital, Hamamatsu, Shizuoka 430-0929, Japan
| | - Paul Michael Yen
- Laboratory of Hormonal Regulation, Cardiovascular and Metabolic Disorders Program, Duke-NUS Medical School, 169857, Singapore.
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Flamant F, Cheng SY, Hollenberg AN, Moeller LC, Samarut J, Wondisford FE, Yen PM, Refetoff S. Thyroid Hormone Signaling Pathways: Time for a More Precise Nomenclature. Endocrinology 2017; 158:2052-2057. [PMID: 28472304 PMCID: PMC6283428 DOI: 10.1210/en.2017-00250] [Citation(s) in RCA: 108] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/13/2017] [Accepted: 04/24/2017] [Indexed: 12/31/2022]
Abstract
Current literature makes a distinction between two pathways for thyroid hormone signaling: genomic and nongenomic. However, this classification is a source of confusion. We propose a clarification in the nomenclature that may help to avoid unproductive controversies and favor progress in this field of research. Four types of thyroid hormone signaling are defined, and the experimental criteria for classification are discussed.
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Affiliation(s)
- Frédéric Flamant
- Institut de Génomique Fonctionnelle de Lyon, INRA USC 1370, Université de Lyon, Université Lyon 1, CNRS UMR 5242, Ecole Normale Supérieure de Lyon, 69364 Lyon cedex 07, France
| | - Sheue-Yann Cheng
- Gene Regulation Section, Laboratory of Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892-6264
| | - Anthony N Hollenberg
- Division of Endocrinology, Diabetes and Metabolism, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts 02215
| | - Lars C Moeller
- Division of Laboratory Research, Department of Endocrinology and Metabolic Diseases, University of Duisburg-Essen, 45127 Essen, Germany
| | - Jacques Samarut
- Institut de Génomique Fonctionnelle de Lyon, INRA USC 1370, Université de Lyon, Université Lyon 1, CNRS UMR 5242, Ecole Normale Supérieure de Lyon, 69364 Lyon cedex 07, France
| | - Fredric E Wondisford
- Department of Medicine, Rutgers-Robert Wood Johnson Medical School, New Brunswick, New Jersey 08903
| | - Paul M Yen
- Laboratory of Hormonal Regulation, Cardiovascular and Metabolic Disorders Program, Duke-NUS Medical School, 169857, Singapore
| | - Samuel Refetoff
- Department of Medicine, University of Chicago, Chicago, Illinois 60637
- Department of Pediatrics, University of Chicago, Chicago, Illinois 60637
- Department of Genetics, University of Chicago, Chicago, Illinois 60637
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28
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Flamant F, Gauthier K, Richard S. Genetic Investigation of Thyroid Hormone Receptor Function in the Developing and Adult Brain. Curr Top Dev Biol 2017; 125:303-335. [PMID: 28527576 DOI: 10.1016/bs.ctdb.2017.01.001] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Thyroid hormones exert a broad influence on brain development and function, which has been extensively studied over the years. Mouse genetics has brought an important contribution, allowing precise analysis of the interplay between TRα1 and TRβ1 nuclear receptors in neural cells. However, the exact contribution of each receptor, the possible intervention of nongenomic signaling, and the nature of the genetic program that is controlled by the receptors remain poorly understood.
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Affiliation(s)
- Frédéric Flamant
- Institut de Génomique Fonctionnelle de Lyon, Université de Lyon, Université Lyon 1, CNRS UMR 5242, INRA USC 1370, Ecole Normale Supérieure de Lyon, Lyon cedex, France.
| | - Karine Gauthier
- Institut de Génomique Fonctionnelle de Lyon, Université de Lyon, Université Lyon 1, CNRS UMR 5242, INRA USC 1370, Ecole Normale Supérieure de Lyon, Lyon cedex, France
| | - Sabine Richard
- Institut de Génomique Fonctionnelle de Lyon, Université de Lyon, Université Lyon 1, CNRS UMR 5242, INRA USC 1370, Ecole Normale Supérieure de Lyon, Lyon cedex, France
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29
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Bernal J. Thyroid hormone regulated genes in cerebral cortex development. J Endocrinol 2017; 232:R83-R97. [PMID: 27852726 DOI: 10.1530/joe-16-0424] [Citation(s) in RCA: 88] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/31/2016] [Accepted: 11/16/2016] [Indexed: 12/19/2022]
Abstract
The physiological and developmental effects of thyroid hormones are mainly due to the control of gene expression after interaction of T3 with the nuclear receptors. To understand the role of thyroid hormones on cerebral cortex development, knowledge of the genes regulated by T3 during specific stages of development is required. In our laboratory, we previously identified genes regulated by T3 in primary cerebrocortical cells in culture. By comparing these data with transcriptomics of purified cell types from the developing cortex, the cellular targets of T3 can be identified. In addition, many of the genes regulated transcriptionally by T3 have defined roles in cortex development, from which the role of T3 can be derived. This review analyzes the specific roles of T3-regulated genes in the different stages of cortex development within the physiological frame of the developmental changes of thyroid hormones and receptor concentrations in the human cerebral cortex during fetal development. These data indicate an increase in the sensitivity to T3 during the second trimester of fetal development. The main cellular targets of T3 appear to be the Cajal-Retzius and the subplate neurons. On the other hand, T3 regulates transcriptionally genes encoding extracellular matrix proteins, involved in cell migration and the control of diverse signaling pathways.
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Affiliation(s)
- Juan Bernal
- Instituto de Investigaciones BiomédicasConsejo Superior de Investigaciones Científicas y Universidad Autónoma de Madrid, and Center for Biomedical Research on Rare Diseases, Instituto de Salud Carlos III, Madrid, Spain
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30
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Kyono Y, Sachs LM, Bilesimo P, Wen L, Denver RJ. Developmental and Thyroid Hormone Regulation of the DNA Methyltransferase 3a Gene in Xenopus Tadpoles. Endocrinology 2016; 157:4961-4972. [PMID: 27779916 PMCID: PMC5133355 DOI: 10.1210/en.2016-1465] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/05/2016] [Accepted: 10/21/2016] [Indexed: 11/19/2022]
Abstract
Thyroid hormone is essential for normal development in vertebrates. In amphibians, T3 controls metamorphosis by inducing tissue-specific gene regulation programs. A hallmark of T3 action is the modification of chromatin structure, which underlies changes in gene transcription. We found that mRNA for the de novo DNA methyltransferase (DNMT) dnmt3a, but not dnmt1, increased in the brain of Xenopus tadpoles during metamorphosis in parallel with plasma [T3]. Addition of T3 to the rearing water caused a time-dependent increase in dnmt3a mRNA in tadpole brain, tail, and hind limb. By analyzing data from a genome-wide analysis of T3 receptor (TR) binding in tadpole tail, we identified several putative T3 response elements (TREs) within the dnmt3a locus. Using in vitro DNA binding, transient transfection-reporter, and chromatin immunoprecipitation assays for TRs, we identified two functional TREs at -7.1 kb and +5.1 kb relative to the dnmt3a transcription start site. Sequence alignment showed that these TREs are conserved between two related frog species, X. laevis and X. tropicalis, but not with amniotes. Our previous findings showed that this gene is directly regulated by liganded TRs in mouse brain, and whereas the two mouse TREs are conserved among Eutherian mammals, they are not conserved in Xenopus species. Thus, although T3 regulation of dnmt3a may be an ancient pathway in vertebrates, the genomic sites responsible for hormone regulation may have diverged or arisen by convergent evolution. We hypothesize that direct T3 regulation of dnmt3a may be an important mechanism for modulating global changes in DNA methylation.
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Affiliation(s)
- Yasuhiro Kyono
- Neuroscience Graduate Program (Y.K.), The University of Michigan, Ann Arbor, Michigan 48109-1048; UMR-7221, Centre National de la Recherche Scientifique (L.M.S., P.B.), Muséum National d'Histoire Naturelle, 75005 Paris, France; and Department of Molecular, Cellular, and Developmental Biology (L.W., R.J.D.), The University of Michigan, Ann Arbor, Michigan 48109-1048
| | - Laurent M Sachs
- Neuroscience Graduate Program (Y.K.), The University of Michigan, Ann Arbor, Michigan 48109-1048; UMR-7221, Centre National de la Recherche Scientifique (L.M.S., P.B.), Muséum National d'Histoire Naturelle, 75005 Paris, France; and Department of Molecular, Cellular, and Developmental Biology (L.W., R.J.D.), The University of Michigan, Ann Arbor, Michigan 48109-1048
| | - Patrice Bilesimo
- Neuroscience Graduate Program (Y.K.), The University of Michigan, Ann Arbor, Michigan 48109-1048; UMR-7221, Centre National de la Recherche Scientifique (L.M.S., P.B.), Muséum National d'Histoire Naturelle, 75005 Paris, France; and Department of Molecular, Cellular, and Developmental Biology (L.W., R.J.D.), The University of Michigan, Ann Arbor, Michigan 48109-1048
| | - Luan Wen
- Neuroscience Graduate Program (Y.K.), The University of Michigan, Ann Arbor, Michigan 48109-1048; UMR-7221, Centre National de la Recherche Scientifique (L.M.S., P.B.), Muséum National d'Histoire Naturelle, 75005 Paris, France; and Department of Molecular, Cellular, and Developmental Biology (L.W., R.J.D.), The University of Michigan, Ann Arbor, Michigan 48109-1048
| | - Robert J Denver
- Neuroscience Graduate Program (Y.K.), The University of Michigan, Ann Arbor, Michigan 48109-1048; UMR-7221, Centre National de la Recherche Scientifique (L.M.S., P.B.), Muséum National d'Histoire Naturelle, 75005 Paris, France; and Department of Molecular, Cellular, and Developmental Biology (L.W., R.J.D.), The University of Michigan, Ann Arbor, Michigan 48109-1048
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