Postnatal development of bitter taste avoidance behavior in mice is associated with ACTIN-dependent localization of bitter taste receptors to the microvilli of taste cells

Bitter taste avoidance behavior (BAB) plays a fundamental role in the avoidance of toxic substances with a bitter taste. However, the molecular basis underlying the development of BAB is unknown. To study critical developmental events by which taste buds turn into functional organs with BAB, we investigated the early phase development of BAB in postnatal mice in response to bitter-tasting compounds, such as quinine and thiamine. Postnatal mice started to exhibit BAB for thiamine and quinine at postnatal day 5 (PD5) and PD7, respectively. Histological analyses of taste buds revealed the formation of microvilli in the taste pores starting at PD5 and the localization of type 2 taste receptor 119 (TAS2R119) at the microvilli at PD6. Treatment of the tongue epithelium with cytochalasin D (CytD), which disturbs ACTIN polymerization in the microvilli, resulted in the loss of TAS2R119 localization at the microvilli and the loss of BAB for quinine and thiamine. The release of ATP from the circumvallate papillae tissue due to taste stimuli was also declined following CytD treatment. These results suggest that the localization of TAS2R119 at the microvilli of taste pores is critical for the initiation of BAB.     

The bitter truth about morality: virtue, not vice, makes a bland beverage taste nice

To demonstrate that sensory and emotional states play an important role in moral processing, previous research has induced physical disgust in various sensory modalities (visual, tactile, gustatory, and olfactory modalities, among others) and measured its effects on moral judgment. To further assess the strength of the connection between embodied states and morality, we investigated whether the directionality of the effect could be reversed by exposing participants to different types of moral events prior to rating the same neutral tasting beverage. As expected, reading about moral transgressions, moral virtues, or control events resulted in inducing gustatory disgust, delight, or neutral taste experiences, respectively. Results are discussed in terms of the relation between embodied cognition and processing abstract conceptual representations.     

Incorporation of 3H-lysine into a rapidly labelling neuronal protein fraction in visual cortex is suppressed in dark reared rats

In normal rat cortex, incorporation of ³H-lysine into protein is higher in neurons than neuropil at periods up to 2 hrs, but is higher in neuropil than neurons at later times. This observation implies the presence of a rapidly labelling neuronal protein fraction which is subsequently absent from the neurons, possibly due to transport into other cell compartments. When rats are reared in the dark, incorporation into neuronal proteins is suppressed in the visual cortex but not in the motor cortex; this suppression appears to include the rapidly-labelling fraction.     

Increasing temperature, not mean temperature, is a cue for avian timing of reproduction

Timing of reproduction in temperate-zone birds is strongly correlated with spring temperature, with an earlier onset of breeding in warmer years. Females adjust their timing of egg laying between years to be synchronized with local food sources and thereby optimize reproductive output. However, climate change currently disrupts the link between predictive environmental cues and spring phenology. To investigate direct effects of temperature on the decision to lay and its genetic basis, we used pairs of great tits (Parus major) with known ancestry and exposed them to simulated spring scenarios in climate-controlled aviaries. In each of three years, we exposed birds to different patterns of changing temperature. We varied the timing of a temperature change, the daily temperature amplitude, and the onset and speed of a seasonal temperature rise. We show that females fine-tune their laying in response to a seasonal increase in temperature, whereas mean temperature and daily temperature variation alone do not affect laying dates. Luteinizing hormone concentrations and gonadal growth in early spring were not influenced by temperature or temperature rise, possibly posing a constraint to an advancement of breeding. Similarities between sisters in their laying dates indicate genetic variation in cue sensitivity. These results refine our understanding of how changes in spring climate might affect the mismatch in avian timing and thereby population viability.     

Respiratory response to passive limb movement is suppressed by a cognitive task.

Feedback from muscles stimulates ventilation at the onset of passive movement. We hypothesized that central neural activity via a cognitive task source would interact with afferent feedback, and we tested this hypothesis by examining the fast changes in ventilation at the transition from rest to passive leg movement, under two conditions: 1) no task and 2) solving a computer-based puzzle. Resting breathing was greater in condition 2 than in condition 1, evidenced by an increase in mean +/- SE breathing frequency (18.2 +/- 1.1 vs. 15.0 +/- 1.2 breaths/min, P = 0.004) and ventilation (10.93 +/- 1.16 vs. 9.11 +/- 1.17 l/min, P < 0.001). In condition 1, the onset of passive movement produced a fast increase in mean +/- SE breathing frequency (change of 2.9 +/- 0.4 breaths/min, P < 0.001), tidal volume (change of 233 +/- 95 ml, P < 0.001), and ventilation (change of 6.00 +/- 1.76 l/min, P < 0.001). However, in condition 2, the onset of passive movement only produced a fast increase in mean +/- SE breathing frequency (change of 1.3 +/- 0.4 breaths/min, P = 0.045), significantly smaller than in condition 1 (P = 0.007). These findings provide evidence for an interaction between central neural cognitive activity and the afferent feedback mechanism, and we conclude that the performance of a cognitive task suppresses the respiratory response to passive movement.     

The candidate sour taste receptor, PKD2L1, is expressed by type III taste cells in the mouse

The transient receptor potential channel, PKD2L1, is reported to be a candidate receptor for sour taste based on molecular biological and functional studies. Here, we investigated the expression pattern of PKD2L1-immunoreactivity (IR) in taste buds of the mouse. PKD2L1-IR is present in a few elongate cells in each taste bud as reported previously. The PKD2L1-expressing cells are different from those expressing PLCbeta2, a marker of Type II cells. Likewise PKD2L1-immunoreactive taste cells do not express ecto-ATPase which marks Type I cells. The PKD2L1-positive cells are immunoreactive for neural cell adhesion molecule, serotonin, PGP-9.5 (ubiquitin carboxy-terminal transferase), and chromogranin A, all of which are present in Type III taste cells. At the ultrastructural level, PKD2L1-immunoreactive cells form synapses onto afferent nerve fibers, another feature of Type III taste cells. These results are consistent with the idea that different taste cells in each taste bud perform distinct functions. We suggest that Type III cells are necessary for transduction and/or transmission of information about "sour", but have little or no role in transmission of taste information of other taste qualities.     

Osteogenic differentiation of the mesenchymal progenitor cells, Kusa is suppressed by Notch signaling

Notch receptor plays a crucial role in proliferation and differentiation of many cell types. To elucidate the function of Notch signaling in osteogenesis, we transfected the constitutively active Notch1 (Notch intracellular domain, NICD) into two different osteoblastic mesenchymal cell lines, KusaA and KusaO, and examined the changes of their osteogenic potentials. In NICD stable transformants (KusaA(NICD) and KusaO(NICD)), osteogenic properties including alkaline phosphatase activity, expression of osteocalcin and type I collagen, and in vitro calcification were suppressed. Transient transfection of NICD attenuated the promoter activities of Cbfa1 and Ose2 element. KusaA was capable of forming trabecular bone-like tissues when injected into mouse abdomen, but this in vivo bone forming activity was significantly suppressed in KusaA(NICD). Osteoclasts were induced in the KusaA-derived bone-like tissues, but lacked in the KusaA(NICD)-derived tissues. These results suggest that Notch signaling suppresses the osteoblastic differentiation of mesenchymal progenitor cells.     

HmCRIP,a cysteine-rich intestinal protein,is expressed by an identified regenerating nerve cell

A Hirudo medicinalis cDNA isolated from regenerating CNS tissue at 24 h post-axotomy was identified as a leech homologue of the mammalian cysteine-rich intestinal proteins (CRIPs) and named HmCRIP. HmCRIP is up-regulated within 6 h of axotomy, peaking at 24 h. This is the first demonstration of a CRIP homologue in regenerating CNS and in a serotonergic neurone. In rodents CRIP is an important factor in the regulation of the inflammatory immune response through control of Th1/Th2 differentiation. The role of HmCRIP in the regeneration competent environment of the annelid central nervous system is discussed.     

Evaluation of the bitterness of green tea catechins by a cell-based assay with the human bitter taste receptor hTAS2R39

Catechins have a broad range of physiological functions and act as the main taste ingredient of green tea. Although catechins show a strong bitterness, the bitter taste receptor for catechins has not been fully understood. The objective of this study was to identify the receptor for the major green tea catechins such as (−)-epicatechin (EC), (−)-epicatechin gallate (ECg), (−)-epigallocatechin (EGC), and (−)-epigallocatechin gallate (EGCg). By the cell-based assay using cultured cells expressing human bitter taste receptor, a clear response of hTAS2R39-expressing cells was observed to 300 μM of either ECg or EGCg, which elicit a strong bitterness in humans. The response of hTAS2R39-expressing cells to ECg was the strongest among the tested catechins, followed by EGCg. Because the cellular response to EC and EGC is much weaker than those of ECg and EGCg, galloyl groups was strongly supposed to be involved in the bitter intensity. This finding is similar to the observations of taste intensity obtained from a human sensory study. Our results suggest the participation of hTAS2R39 in the detection of catechins in humans, indicating the possibility that bitterness of tea catechins can be evaluated by using cells expressing hTAS2R39.     

Formation of embryogenic cell clumps from carrot epidermal cells is suppressed by 5-azacytidine, a DNA methylation inhibitor

Using a direct somatic embryogenesis system in carrot, we examined the role of DNA methylation in the change of cellular differentiation state, from somatic to embryogenic. 5-Azacytidine (aza-C), an inhibitor of DNA methylation suppressed the formation of embryogenic cell clumps from epidermal carrot cells. Aza-C also downregulated the expression of DcLEC1c, a LEC1-like embryonic gene in carrot, during morphogenesis of embryos. A carrot DNA methyltransferase gene, Met1-5 was expressed transiently after the induction of somatic embryogenesis by 2,4-dichlorophenoxyacetic acid (2,4-D), before the formation of embryogenic cell clumps. These findings suggested the significance of DNA methylation in acquiring the embryogenic competence in somatic cells in carrot.     

PGK1 induction by a hydrogen peroxide treatment is suppressed by antioxidants in human colon carcinoma cells

Few protein biomarkers for oxidative stress have been reported. In this study, we attempted to identify the proteins selectively overexpressed in human colon tumor cells by treating with hydrogen peroxide as oxidative stress. A proteomic analysis followed by western blotting showed that phosphoglycerate kinase 1 (PGK1) was induced by hydrogen peroxide in a dose-dependent manner, while its expression was suppressed by a co-treatment with delphinidin, a known antioxidant. Furthermore, several antioxidants, including alpha-tocopherol, butylated hydroxytoluene (BHT), and Trolox, also inhibited the PGK1 induction caused by hydrogen peroxide. The data suggest that PGK1 might be a potential protein biomarker of intracellular oxidative status.     

FXYD6, a Na,K-ATPase regulator, is expressed in type II taste cells

Taste buds contain three types of taste cells. Each type can respond to taste stimulation, and type II and III taste cells are electrically excitable. However, there are differences between the properties of type II and III taste cells. In this study, we found that Fxyd6, an Na,K-ATPase regulator gene, is expressed in type II taste cells in the taste buds of mice. Double-labeled in situ hybridization analysis showed that Fxyd6 was coexpressed with transient receptor potential cation channel, subfamily M, member 5 (Trpm5), a critical component of the sweet, bitter, and umami taste signal transduction pathways and that it was specifically expressed in type II taste cells. We also found that taste cells frequently coexpressed Fxyd6 and Na,K-ATPase β1. These results indicate the presence of an inherent mechanism that regulated transmembrane Na(+) dynamics in type II taste cells.     

Semaphorin 5A is a bifunctional axon guidance cue regulated by heparan and chondroitin sulfate proteoglycans

The response of neuronal growth cones to axon guidance cues depends on the developmental context in which these cues are encountered. We show here that the transmembrane protein semaphorin 5A (Sema5A) is a bifunctional guidance cue exerting both attractive and inhibitory effects on developing axons of the fasciculus retroflexus, a diencephalon fiber tract associated with limbic function. The thrombospondin repeats of Sema5A physically interact with the glycosaminoglycan portion of both chondroitin sulfate proteoglycans (CSPGs) and heparan sulfate proteoglycans (HSPGs). CSPGs function as precisely localized extrinsic cues that convert Sema5A from an attractive to an inhibitory guidance cue. Therefore, glycosaminoglycan bound guidance cues provide a molecular mechanism for CSPG-mediated inhibition of axonal extension. Further, axonal HSPGs are required for Sema5A-mediated attraction, suggesting that HSPGs are components of functional Sema5A receptors. Thus, neuronal responses to Sema5A are proteoglycan dependent and interpreted according to the biological context in which this membrane bound guidance cue is presented.     

Agonist-independent internalization of metabotropic glutamate receptor 1a is arrestin- and clathrin-dependent and is suppressed by receptor inverse agonists

Three group I mGluR antagonists CPCCOEt, LY367385 and BAY36-7620, were analyzed for their effect on cell surface expression of metabotropic glutamate receptor 1a and 1b. All three antagonists inhibited glutamate-induced internalization of mGluR1a and mGluR1b. However, when added alone, either LY367385 or BAY36-7620 increased the cell surface expression of mGluR1a but not mGluR1b. Both LY367385 and BAY36-7620 displayed inverse agonist activity as judged by their ability to inhibit basal inositol phosphate accumulation in cells expressing the constitutively active mGluR1a. Interestingly, mGluR1a but not mGluR1b was constitutively internalized in HEK293 cells and both LY367385 and BAY36-7620 inhibited the constitutive internalization of this splice variant. Furthermore, coexpression of dominant negative mutant constructs of arrestin-2 [arrestin-2-(319-418)] or Eps15 [Eps15(E Delta 95-295)] increased cell surface expression of mGluR1a and blocked constitutive receptor internalization. In the presence of these dominant negative mutants, incubation of cells with LY367385 and BAY36-7620 produced no further increase in cell surface expression of mGluR1a. Taken together, these results suggest that the constitutive activity of mGluR1a triggers the internalization of the receptor through an arrestin- and clathrin-dependent pathway, and that inverse agonists increase the cell surface expression of mGluR1a by promoting an inactive form of mGluR1a, which does not undergo constitutive internalization.