Metamorphic gene regulation programs in Xenopus tropicalis tadpole brain.

Amphibian metamorphosis is controlled by thyroid hormone (TH), which binds TH receptors (TRs) to regulate gene expression programs that underlie morphogenesis. Gene expression screens using tissues from premetamorphic tadpoles treated with TH identified some TH target genes, but few studies have analyzed genome-wide changes in gene regulation during spontaneous metamorphosis. We analyzed RNA sequencing data at four developmental stages from the beginning to the end of spontaneous metamorphosis, conducted on the neuroendocrine centers of Xenopus tropicalis tadpole brain.

An Intact Krüppel-like factor 9 Gene Is Required for Acute Liver Period 1 mRNA Response to Restraint Stress.

The clock protein period 1 (PER1) is a central component of the core transcription-translation feedback loop governing cell-autonomous circadian rhythms in animals. Transcription of Per1 is directly regulated by the glucocorticoid (GC) receptor (GR), and Per1 mRNA is induced by stressors or injection of GC. Circulating GCs may synchronize peripheral clocks with the central pacemaker located in the suprachiasmatic nucleus of the brain.

Stress hormone-mediated antipredator morphology improves escape performance in amphibian tadpoles.

Complete functional descriptions of the induction sequences of phenotypically plastic traits (perception to physiological regulation to response to outcome) should help us to clarify how plastic responses develop and operate. Ranid tadpoles express several plastic antipredator traits mediated by the stress hormone corticosterone, but how they influence outcomes remains uncertain. We investigated how predator-induced changes in the tail morphology of wood frog (Rana sylvatica) tadpoles influenced their escape performance over a sequence of time points when attacked by larval dragonflies (Anax junius).

Stress hormones mediate developmental plasticity in vertebrates with complex life cycles.

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.

Krüppel-Like Factors 9 and 13 Block Axon Growth by Transcriptional Repression of Key Components of the cAMP Signaling Pathway.

Krüppel-like factors (KLFs) are zinc finger transcription factors implicated in diverse biological processes, including differentiation of neural cells. The ability of mammalian neurons to elongate axons decreases during postnatal development in parallel with a decrease in cAMP, and increase in expression of several genes. The paralogous KLFs 9 and 13 inhibit neurite outgrowth, and we hypothesized that their actions are mediated through repression of cAMP signaling.

Thyroid Hormone Induces DNA Demethylation in Xenopus Tadpole Brain.

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).

Molecular Mechanisms for Krüppel-Like Factor 13 Actions in Hippocampal Neurons.

Krüppel-like factors (KLFs) play key roles in nervous system development and function. Several KLFs are known to promote, and then maintain neural cell differentiation. Our previous work focused on the actions of KLF9 in mouse hippocampal neurons.

The Paralogous Krüppel-like Factors 9 and 13 Regulate the Mammalian Cellular Circadian Clock Output Gene .

An intricate transcription-translation feedback loop (TTFL) governs cellular circadian rhythms in mammals. Here, we report that the zinc finger transcription factor Krüppel-like factor 9 (KLF9) is regulated by this TTFL, it associates in chromatin at the core circadian clock and clock-output genes, and it acts to modulate transcription of the clock-output gene . Our earlier genome-wide analysis of the mouse hippocampus-derived cell line HT22 showed that KLF9 associates in chromatin with , , , , , , , and .

DNA methylation dynamics underlie metamorphic gene regulation programs in Xenopus tadpole brain.

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.

Coordinated transcriptional regulation by thyroid hormone and glucocorticoid interaction in adult mouse hippocampus-derived neuronal cells.

The hippocampus is a well-known target of thyroid hormone (TH; e.g., 3,5,3'-triiodothyronine-T3) and glucocorticoid (GC; e.

Thyroid Hormone Receptor Alpha Is Required for Thyroid Hormone-Dependent Neural Cell Proliferation During Tadpole Metamorphosis.

Thyroid hormone (T) plays several key roles in development of the nervous system in vertebrates, controlling diverse processes such as neurogenesis, cell migration, apoptosis, differentiation, and maturation. In anuran amphibians, the hormone exerts its actions on the tadpole brain during metamorphosis, a developmental period dependent on T. Thyroid hormone regulates gene transcription by binding to two nuclear receptors, TRα and TRβ.

Evolutionary Conservation of Thyroid Hormone Receptor and Deiodinase Expression Dynamics in a Direct-Developing Frog, .

Direct development is a reproductive mode in amphibians that has evolved independently from the ancestral biphasic life history in at least a dozen anuran lineages. Most direct-developing frogs, including the Puerto Rican coquí, , lack a free-living aquatic larva and instead hatch from terrestrial eggs as miniature adults. Their embryonic development includes the transient formation of many larval-specific features and the formation of adult-specific features that typically form postembryonically-during metamorphosis-in indirect-developing frogs.

Bulk Electroporation-Mediated Gene Transfer into Tadpole Brain.

In vivo gene transfer is a powerful tool for investigating protein function and gene regulation in living organisms. Delivery of plasmid DNA to the brain of tadpoles by bulk electroporation-mediated (EM) gene transfer can be used to study the effects of ectopic gene expression on development, physiology, and behavior. It can also be used to mark cells for lineage tracing, investigate the in vivo function of gene regulatory elements when linked to a reporter gene, and introduce mutations into the genome of transfected cells, among other applications.

To eat or not to eat: ontogeny of hypothalamic feeding controls and a role for leptin in modulating life-history transition in amphibian tadpoles.

Many animal life histories entail changing feeding ecology, but the molecular bases for these transitions are poorly understood. The amphibian tadpole is typically a growth and dispersal life-history stage. Tadpoles are primarily herbivorous, and they capitalize on growth opportunities to reach a minimum body size to initiate metamorphosis.

Genetic accommodation via modified endocrine signalling explains phenotypic divergence among spadefoot toad species.

Phenotypic differences among species may evolve through genetic accommodation, but mechanisms accounting for this process are poorly understood. Here we compare hormonal variation underlying differences in the timing of metamorphosis among three spadefoot toads with different larval periods and responsiveness to pond drying. We find that, in response to pond drying, Pelobates cultripes and Spea multiplicata accelerate metamorphosis, increase standard metabolic rate (SMR), and elevate whole-body content of thyroid hormone (the primary morphogen controlling metamorphosis) and corticosterone (a stress hormone acting synergistically with thyroid hormone to accelerate metamorphosis).

Leptin Induces Mitosis and Activates the Canonical Wnt/β-Catenin Signaling Pathway in Neurogenic Regions of Tadpole Brain.

In addition to its well-known role as an adipostat in adult mammals, leptin has diverse physiological and developmental actions in vertebrates. Leptin has been shown to promote development of hypothalamic circuits and to induce mitosis in different brain areas of mammals. We investigated the ontogeny of leptin mRNA, leptin actions on cell proliferation in the brain, and gene expression in the preoptic area/hypothalamus of tadpoles of .

The Krüppel-like factor 9 cistrome in mouse hippocampal neurons reveals predominant transcriptional repression via proximal promoter binding.

Background: Krüppel-like factor 9 (Klf9) is a zinc finger transcription factor that functions in neural cell differentiation, but little is known about its genomic targets or mechanism of action in neurons.

Results: We used the mouse hippocampus-derived neuronal cell line HT22 to identify genes regulated by Klf9, and we validated our findings in mouse hippocampus. We engineered HT22 cells to express a Klf9 transgene under control of the tetracycline repressor, and used RNA sequencing to identify genes modulated by Klf9.

Developmental and Thyroid Hormone Regulation of the DNA Methyltransferase 3a Gene in Xenopus Tadpoles.

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.

Liganded Thyroid Hormone Receptors Transactivate the DNA Methyltransferase 3a Gene in Mouse Neuronal Cells.

Thyroid hormone (T3) is essential for proper neurological development. The hormone, bound to its receptors, regulates gene transcription in part by modulating posttranslational modifications of histones. Methylation of DNA, which is established by the de novo DNA methyltransferase (DNMT)3a and DNMT3b, and maintained by DNMT1 is another epigenetic modification influencing gene transcription.

A Mechanism to Enhance Cellular Responsivity to Hormone Action: Krüppel-Like Factor 9 Promotes Thyroid Hormone Receptor-β Autoinduction During Postembryonic Brain Development.

Thyroid hormone (TH) receptor (TR)-β (trb) is induced by TH (autoinduced) in Xenopus tadpoles during metamorphosis. We previously showed that Krüppel-like factor 9 (Klf9) is rapidly induced by TH in the tadpole brain, associates in chromatin with the trb upstream region in a developmental stage and TH-dependent manner, and forced expression of Klf9 in the Xenopus laevis cell line XTC-2 accelerates and enhances trb autoinduction. Here we investigated whether Klf9 can promote trb autoinduction in tadpole brain in vivo.

Deciphering the regulatory logic of an ancient, ultraconserved nuclear receptor enhancer module.

Cooperative, synergistic gene regulation by nuclear hormone receptors can increase sensitivity and amplify cellular responses to hormones. We investigated thyroid hormone (TH) and glucocorticoid (GC) synergy on the Krüppel-like factor 9 (Klf9) gene, which codes for a zinc finger transcription factor involved in development and homeostasis of diverse tissues. We identified regions of the Xenopus and mouse Klf9 genes 5-6 kb upstream of the transcription start sites that supported synergistic transactivation by TH plus GC.

Ancient origins and evolutionary conservation of intracellular and neural signaling pathways engaged by the leptin receptor.

In mammals, leptin acts on leptin receptor (LepR) -expressing neurons in the brain to suppress food intake and stimulate whole-body metabolism. A similar action of leptin on food intake has been reported in the frog Xenopus laevis and in several bony fishes. However, the intracellular signaling and neural pathways by which leptin regulates energy balance have not been investigated outside of mammals.

Krüppel-like factors are effectors of nuclear receptor signaling.

Binding of steroid and thyroid hormones to their cognate nuclear receptors (NRs) impacts virtually every aspect of postembryonic development, physiology and behavior, and inappropriate signaling by NRs may contribute to disease. While NRs regulate genes by direct binding to hormone response elements in the genome, their actions may depend on the activity of other transcription factors (TFs) that may or may not bind DNA. The Krüppel-like family of transcription factors (KLF) is an evolutionarily conserved class of DNA-binding proteins that influence many aspects of development and physiology.