A comparison of nest-site characteristics for two sympatric Estrildid finches (Uraeginthus spp.) in Tanzania.

It is well known that birds have great diversity in nesting strategies, but we still have limited knowledge of the variation among species that share the habitat. Here, I will report and compare the nesting strategies between the two sympatric songbirds. Blue-capped (Uraeginthus cyanocephalus) and red-cheeked cordon-bleus (Uraeginthus bengalus) are socially monogamous, biparental songbirds (family Estrildidae) that sympatrically inhabit arid landscapes with trees and bushes in East Africa. Both species build domed nests with grasses that are often located near wasp nests. They also sometimes take over old weaver (family Ploceidae) nests. While these nesting strategies are already described as common behavioral traits in both species in the literature, interspecies variation in these nesting strategies in areas of sympatry is not reported. My initial field observation during their breeding season suggested that whether these nesting strategies were adopted or not varied somewhat between the sympatric cordon-bleus. Thus, I carried out a more formal investigation to test these differences. I found that red-cheeked cordon-bleus built their nests near wasp nests more frequently than blue-capped cordon-bleus, while I did not find any other significant differences between the nesting sites of the two species, such as the use of weaver nests, the types of nesting plants, or nest heights. These results suggest that the sympatric cordon-bleus share several nest-site characteristics, but that red-cheeked cordon-bleus have an affinity for nesting near wasp nests. Further studies will be required to elucidate the costs and benefits of these nesting strategies or the role that adjacency to wasp nests might play in the sympatry of the two species.

Activation of the NRF2 pathway in Keap1-knockdown mice attenuates progression of age-related hearing loss.

Age-related hearing loss (AHL) is a progressive sensorineural hearing loss in elderly people. Although no prevention or treatments have been established for AHL, recent studies have demonstrated that oxidative stress is closely related to pathogenesis of AHL, suggesting that suppression of oxidative stress leads to inhibition of AHL progression. NRF2 is a master transcription factor that regulates various antioxidant proteins and cytoprotection factors. To examine whether NRF2 pathway activation prevents AHL, we used Keap1-knockdown (Keap1FA/FA) mice, in which KEAP1, a negative regulator of NRF2, is decreased, resulting in the elevation of NRF2 activity. We compared 12-month-old Keap1FA/FA mice with age-matched wild-type (WT) mice in the same breeding colony. In the Keap1FA/FA mice, the expression levels of multiple NRF2 target genes were verified to be significantly higher than the expression levels of these genes in the WT mice. Histological analysis showed that cochlear degeneration at the apical and middle turns was ameliorated in the Keap1FA/FA mice. Auditory brainstem response (ABR) thresholds in the Keap1FA/FA mice were significantly lower than those in the WT mice, in particular at low-mid frequencies. Immunohistochemical detection of oxidative stress markers suggested that oxidative stress accumulation was attenuated in the Keap1FA/FA cochlea. Thus, we concluded that NRF2 pathway activation protects the cochlea from oxidative damage during aging, in particular at the apical and middle turns. KEAP1-inhibiting drugs and phytochemicals are expected to be effective in the prevention of AHL.

Enhancer remodeling promotes tumor-initiating activity in NRF2-activated non-small cell lung cancers.

Transcriptional dysregulation, which can be caused by genetic and epigenetic alterations, is a fundamental feature of many cancers. A key cytoprotective transcriptional activator, NRF2, is often aberrantly activated in non-small cell lung cancers (NSCLCs) and supports both aggressive tumorigenesis and therapeutic resistance. Herein, we find that persistently activated NRF2 in NSCLCs generates enhancers at gene loci that are not normally regulated by transiently activated NRF2 under physiological conditions. Elevated accumulation of CEBPB in NRF2-activated NSCLCs is found to be one of the prerequisites for establishment of the unique NRF2-dependent enhancers, among which the NOTCH3 enhancer is shown to be critical for promotion of tumor-initiating activity. Enhancer remodeling mediated by NRF2-CEBPB cooperativity promotes tumor-initiating activity and drives malignancy of NRF2-activated NSCLCs via establishment of the NRF2-NOTCH3 regulatory axis.

Tap dancers in the wild: field observations of multimodal courtship displays in socially monogamous songbirds.

Multimodal signaling systems are shaped not only by a signaler's physical abilities but also by external factors such as the position of signal receivers and the properties of the medium through which the signals are transmitted. To fully understand the evolution and function of multimodal communication, it is essential to investigate the behavior in the wild. Here, I present evidence that socially monogamous songbirds perform complex courtship displays that can produce multimodal and multicomponent signals in wild conditions. Cordon-bleus (Uraeginthus spp.) are socially monogamous songbirds from East Africa. Both sexes of cordon-bleus perform multimodal courtship displays by holding a piece of nest material, bobbing up and down, and singing. My previous laboratory study using high-speed video cameras revealed that courtship bobbing includes multiple rapid steps similar to human tap-dancing, which presumably contributes to producing non-vocal sounds and/or vibrations in addition to visual signals. As a result of field observation and behavioral analysis, I found that wild cordon-bleus perform tap-dance like displays just as captive cordon-bleus. I also observed that wild cordon-bleus produced non-vocal sounds and shook branches during courtship, which can contribute to multimodal signal production (i.e., visual, acoustic, and vibrational signals). My findings imply that the courtship displays of cordon-bleus are an ideal candidate for investigating the role and function of multimodal communication in animals, and demonstrate the importance of further quantitative studies in both laboratory and field.

Lactate dehydrogenase C is required for the protein expression of a sperm-specific isoform of lactate dehydrogenase A.

Metabolites are sensitive indicators of moment-to-moment cellular status and activity. Expecting that tissue-specific metabolic signatures unveil a unique function of the tissue, we examined metabolomes of mouse liver and testis and found that an unusual metabolite, 2-hydroxyglutarate (2-HG), was abundantly accumulated in the testis. 2-HG can exist as D- or L-enantiomer, and both enantiomers interfere with the activities of 2-oxoglutarate (2-OG)-dependent dioxygenases, such as the Jumonji family of histone demethylases. Whereas D-2-HG is produced by oncogenic mutants of isocitrate dehydrogenases (IDH) and known as an oncometabolite, L-2-HG was the major enantiomer detected in the testis, suggesting that a distinct mechanism underlies the testicular production of this metabolite. We clarified that lactate dehydrogenase C (LDHC), a testis-specific lactate dehydrogenase, is responsible for L-2-HG accumulation by generating and analysing Ldhc-deficient mice. Although the inhibitory effects of 2-HG on 2-OG-dependent dioxygenases were barely observed in the testis, the LDHA protein level was remarkably decreased in Ldhc-deficient sperm, indicating that LDHC is required for LDHA expression in the sperm. This unique functional interaction between LDH family members supports lactate dehydrogenase activity in the sperm. The severely impaired motility of Ldhc-deficient sperm suggests a substantial contribution of glycolysis to energy production for sperm motility.

Couples showing off: Audience promotes both male and female multimodal courtship display in a songbird.

Social environments can shape animal communication. Although mutual courtship displays are generally thought to function in private communication between a male and a female, we provide experimental evidence that they work in a broader social context than previously thought. We examined the audience effect on mutual courtship in blue-capped cordon-bleus, a socially monogamous songbird. This species is characterized by conspicuous courtship shared between sexes: Both sexes sing songs and sometimes add a unique dance display that looks like human tap dancing. We found that in both sexes, multimodal courtship displays (song accompanied by dance) were promoted in the presence of an audience, especially if it was the opposite sex. In contrast, unimodal displays (song without dance) were suppressed by audiences. Because birds directed the courtship dancing toward their partners (but not the audience), multimodal courtship displays are likely meant to advertise their current mating status to other cordon-bleus.

Glucocorticoid receptor signaling represses the antioxidant response by inhibiting histone acetylation mediated by the transcriptional activator NRF2.

NRF2 (nuclear factor erythroid 2-related factor 2) is a key transcriptional activator that mediates the inducible expression of antioxidant genes. NRF2 is normally ubiquitinated by KEAP1 (Kelch-like ECH-associated protein 1) and subsequently degraded by proteasomes. Inactivation of KEAP1 by oxidative stress or electrophilic chemicals allows NRF2 to activate transcription through binding to antioxidant response elements (AREs) and recruiting histone acetyltransferase CBP (CREB-binding protein). Whereas KEAP1-dependent regulation is a major determinant of NRF2 activity, NRF2-mediated transcriptional activation varies from context to context, suggesting that other intracellular signaling cascades may impact NRF2 function. To identify a signaling pathway that modifies NRF2 activity, we immunoprecipitated endogenous NRF2 and its interacting proteins from mouse liver and identified glucocorticoid receptor (GR) as a novel NRF2-binding partner. We found that glucocorticoids, dexamethasone and betamethasone, antagonize diethyl maleate-induced activation of NRF2 target genes in a GR-dependent manner. Dexamethasone treatment enhanced GR recruitment to AREs without affecting chromatin binding of NRF2, resulting in the inhibition of CBP recruitment and histone acetylation at AREs. This repressive effect was canceled by the addition of histone deacetylase inhibitors. Thus, GR signaling decreases NRF2 transcriptional activation through reducing the NRF2-dependent histone acetylation. Consistent with these observations, GR signaling blocked NRF2-mediated cytoprotection from oxidative stress. This study suggests that an impaired antioxidant response by NRF2 and a resulting decrease in cellular antioxidant capacity account for the side effects of glucocorticoids, providing a novel viewpoint for the pathogenesis of hypercorticosteroidism.

Digestion of chrysanthemum stunt viroid by leaf extracts of Capsicum chinense indicates strong RNA-digesting activity.

KEY MESSAGE: CSVd could not infect Nicotiana benthamiana when the plants were pretreated with crude leaf extract of Capsicum chinense 'Sy-2'. C. chinense leaves were revealed to contain strong RNA-digesting activity. Several studies have identified active antiviral and antiviroid agents in plants. Capsicum plants are known to contain antiviral agents, but the mechanism of their activity has not been determined. We aimed to elucidate the mechanism of Capsicum extract's antiviroid activity. Chrysanthemum stunt viroid (CSVd) was inoculated into Nicotiana benthamiana plants before or after treating the plants with a leaf extract of Capsicum chinense 'Sy-2'. CSVd infection was determined using quantitative reverse transcription-polymerase chain reaction (qRT-PCR) 3 weeks after inoculation. When Capsicum extract was sprayed or painted onto N. benthamiana before inoculation, it was effective in preventing infection by CSVd. To evaluate CSVd digestion activity in leaf extracts, CSVd was mixed with leaf extracts of Mirabilis, Phytolacca, Pelargonium and Capsicum. CSVd-digesting activities were examined by quantifying undigested CSVd using qRT-PCR, and RNA gel blotting permitted visualization of the digested CSVd. Only Capsicum leaf extract digested CSVd, and in the Capsicum treatment, small digested CSVd products were detected by RNA gel blot analysis. When the digesting experiment was performed for various cultivars and species of Capsicum, only cultivars of C. chinense showed strong CSVd-digesting activity. Our observations indicated that Capsicum extract contains strong RNA-digesting activity, leading to the conclusion that this activity is the main mechanism for protection from infection by CSVd through spraying or painting before inoculation. To our knowledge, this is the first report of a strong RNA-digesting activity by a plant extract.

The Mediator Subunit MED16 Transduces NRF2-Activating Signals into Antioxidant Gene Expression.

The KEAP1-NRF2 system plays a central role in cytoprotection. NRF2 is stabilized in response to electrophiles and activates transcription of antioxidant genes. Although robust induction of NRF2 target genes confers resistance to oxidative insults, how NRF2 triggers transcriptional activation after binding to DNA has not been elucidated. To decipher the molecular mechanisms underlying NRF2-dependent transcriptional activation, we purified the NRF2 nuclear protein complex and identified the Mediator subunits as NRF2 cofactors. Among them, MED16 directly associated with NRF2. Disruption of Med16 significantly attenuated the electrophile-induced expression of NRF2 target genes but did not affect hypoxia-induced gene expression, suggesting a specific requirement for MED16 in NRF2-dependent transcription. Importantly, we found that 75% of NRF2-activated genes exhibited blunted inductions by electrophiles in Med16-deficient cells compared to wild-type cells, which strongly argues that MED16 is a major contributor supporting NRF2-dependent transcriptional activation. NRF2-dependent phosphorylation of the RNA polymerase II C-terminal domain was absent in Med16-deficient cells, suggesting that MED16 serves as a conduit to transmit NRF2-activating signals to RNA polymerase II. MED16 indeed turned out to be essential for cytoprotection against oxidative insults. Thus, the KEAP1-NRF2-MED16 axis has emerged as a new regulatory pathway mediating the antioxidant response through the robust activation of NRF2 target genes.

Tap dancing birds: the multimodal mutual courtship display of males and females in a socially monogamous songbird.

According to classical sexual selection theory, complex multimodal courtship displays have evolved in males through female choice. While it is well-known that socially monogamous songbird males sing to attract females, we report here the first example of a multimodal dance display that is not a uniquely male trait in these birds. In the blue-capped cordon-bleu (Uraeginthus cyanocephalus), a socially monogamous songbird, both sexes perform courtship displays that are characterised by singing and simultaneous visual displays. By recording these displays with a high-speed video camera, we discovered that in addition to bobbing, their visual courtship display includes quite rapid step-dancing, which is assumed to produce vibrations and/or presumably non-vocal sounds. Dance performances did not differ between sexes but varied among individuals. Both male and female cordon-bleus intensified their dance performances when their mate was on the same perch. The multimodal (acoustic, visual, tactile) and multicomponent (vocal and non-vocal sounds) courtship display observed was a combination of several motor behaviours (singing, bobbing, stepping). The fact that both sexes of this socially monogamous songbird perform such a complex courtship display is a novel finding and suggests that the evolution of multimodal courtship display as an intersexual communication should be considered.

Alcohol dehydrogenase 3 contributes to the protection of liver from nonalcoholic steatohepatitis.

Nutritional steatohepatitis is closely associated with dysregulation of lipid metabolism and oxidative stress control. ADH3 is a highly conserved bifunctional enzyme involved in formaldehyde detoxification and termination of nitric oxide signaling. Formaldehyde and nitric oxide are nonenzymatically conjugated with glutathione, which is regenerated after ADH3 metabolizes the conjugates. To clarify roles of ADH3 in nutritional liver diseases, we placed Adh3-null mice on a methionine- and choline-deficient (MCD) diet. The Adh3-null mice developed steatohepatitis more rapidly than wild-type mice, indicating that ADH3 protects liver from nutritional steatohepatitis. NRF2, which is a key regulator of cytoprotective genes against oxidative stress, was activated in the Adh3-null mice with liver damage. In the absence of NRF2, the Adh3 disruption caused severe steatohepatitis by the MCD diet feeding accompanied by significant decrease in glutathione, suggesting cooperative function between ADH3 and NRF2 in the maintenance of cellular glutathione level for cytoprotection. Conversely, with enhanced NRF2 activity, the Adh3 disruption did not cause steatohepatitis but induced steatosis, suggesting that perturbation of lipid metabolism in ADH3-deficiency is not compensated by NRF2. Thus, ADH3 protects liver from steatosis by supporting normal lipid metabolism and prevents progression of steatosis into steatohepatitis by maintaining the cellular glutathione level.