Infection by the parasitic helminth Trichinella spiralis activates a Tas2r-mediated signaling pathway in intestinal tuft cells.

The parasitic helminth Trichinella spiralis, which poses a serious health risk to animals and humans, can be found worldwide. Recent findings indicate that a rare type of gut epithelial cell, tuft cells, can detect the helminth, triggering type 2 immune responses. However, the underlying molecular mechanisms remain to be fully understood. Here we show that both excretory-secretory products (E-S) and extract of T. spiralis can stimulate the release of the cytokine interleukin 25 (IL-25) from the mouse small intestinal villi and evoke calcium responses from tuft cells in the intestinal organoids, which can be blocked by a bitter-taste receptor inhibitor, allyl isothiocyanate. Heterologously expressed mouse Tas2r bitter-taste receptors, the expression of which is augmented during tuft-cell hyperplasia, can respond to the E-S and extract as well as to the bitter compound salicin whereas salicin in turn can induce IL-25 release from tuft cells. Furthermore, abolishment of the G-protein γ13 subunit, application of the inhibitors for G-protein αo/i, Gßγ subunits, and phospholipase Cß2 dramatically reduces the IL-25 release. Finally, tuft cells are found to utilize the inositol triphosphate receptor type 2 (Ip3r2) to regulate cytosolic calcium and thus Trpm5 activity, while potentiation of Trpm5 by a sweet-tasting compound, stevioside, enhances tuft cell IL-25 release and hyperplasia in vivo. Taken together, T. spiralis infection activates a signaling pathway in intestinal tuft cells similar to that of taste-bud cells, but with some key differences, to initiate type 2 immunity.

Mammalian Taste Bud Cells Utilize Extragemmal 5-Hydroxy-L-Tryptophan to Biosynthesize the Neurotransmitter Serotonin.

Serotonin or 5-hydroxytryptamine (5-HT) is an important neurotransmitter that is found in mammalian taste buds and can regulate the output of intragemmal signaling networks onto afferent nerve fibers. However, it is unclear how 5-HT is produced, synthesized locally inside taste buds or absorbed from outside sources. In this study, we attempt to address this question by delineating the process of possible 5-HT biosynthesis within taste buds. First, we verified that the rate-limiting enzyme tryptophan hydroxylase (TPH2) responsible for converting L-tryptophan into the intermediate 5-hydroxy-L-tryptophan (5-HTP) is expressed in a subset of type II taste bud cells (TBCs) whereas the enzyme aromatic L-aromatic amino acid decarboxylase (AADC) capable of converting 5-HTP into 5-HT is found in type III TBCs. And abolishment of TPH2 did not affect the production of intragemmal 5-HT or alter TBCs; the mutant mice did not show any changes in behavioral responses to all five primary taste qualities: sweet, umami, bitter, salty, and sour. Then we identified that 5-HTP as well as AADC are abundant in type III TBCs; and application of an AADC inhibitor significantly blocked the production of 5-HT in taste buds. In contrast, administration of an inhibitor on serotonin-reuptake transporters had minimal impact on the 5-HT amount in taste buds, indicating that exogenous 5-HT is not a major source for the intragemmal transmitter. Taken together, our data indicate that intragemmal serotonin is not biosynthesized de novo from tryptophan; instead, it is produced by AADC-mediated conversion of 5-HTP absorbed from the plasma and/or nerve fibers into 5-HT. Thus, our results suggest that the overall bodily 5-HTP level in the plasma and nervous system can regulate taste buds' physiological function, and provide an important molecular mechanism connecting these peripheral taste organs with the circulatory and nervous systems.

G protein γ subunit Gγ13 is essential for olfactory function and aggressive behavior in mice.

Most olfactory receptors in vertebrates are G protein-coupled receptors, whose activation by odorants initiates intracellular signaling cascades through heterotrimeric G proteins consisting of α, ß, and γ subunits. Abolishment of the α subunits such as Gαolf in the main olfactory epithelium and Gαi2 and Gαo in the vomeronasal organ resulted in anosmia and/or impaired behavioral responses. In this study, we report that a G protein γ subunit, Gγ13, is expressed in a spatiotemporal manner similar to those of Gαolf and Gαi2 in the olfactory system and vomeronasal organ, respectively. In addition, Gγ13 was found in the glomeruli of the main olfactory bulb but was largely absent in the glomeruli of the accessory olfactory bulb. Using the Cre-loxP system, the Gγ13's gene Gng13 was nullified in the mature olfactory sensory neurons and apical vomeronasal sensory neurons where the Cre recombinase was expressed under the promoter of the Omp gene for the olfactory marker protein. Immunohistochemistry indicated much reduced expression of Gγ13 in the apical vomeronasal epithelium of the mutant mice. Behavioral experiments showed that the frequency and duration of aggressive encounters in the male mutant mice were significantly lower than in WT male mice. Taken together, these data suggest that the Gγ13 subunit is a critical signaling component in both the main olfactory epithelium and apical vomeronasal epithelium, and it plays an essential role in odor-triggered social behaviors including male-male aggression.

In vivo bioelectronic nose using transgenic mice for specific odor detection.

The olfactory system is a natural biosensor since its peripheral olfactory sensory neurons (OSNs) respond to the external stimuli and transmit the signals to the olfactory bulb (OB) where they are integrated and processed. The axonal connections from the OSNs expressing about 1000 different types of odorant receptors are precisely organized and sorted out onto 1800 glomeruli in the OB, from which the olfactory information is delivered to and perceived by the central nervous system. This process is carried out with particularly high sensitivity, specificity and rapidity, which can be used for explosive detection. Biomimetic olfactory biosensors use various biological components from the olfactory system as sensing elements, possessing great commercial prospects. In this study, we utilized the genetically labeled murine M72 olfactory sensory neurons with the green fluorescent protein (GFP) as sensing components and obtained long-term in vivo electrophysiological recordings from the M72 OSNs by implanting the microelectrode arrays (MEAs) into the behaving mouse's OB. The electrophysiological responses showed high reliability, reproducibility and specificity for odor detection, and particularly, the high sensitivity for the detection of odorants that contain benzene rings. Furthermore, our results indicated that it can detect trinitrotoluene (TNT) in liquid at a concentration as low as 10-5M and can distinguish TNT from other chemicals with a similar structure. Thus our study demonstrated that the in vivo biomimetic olfactory system could provide novel approaches to enhancing the specificity and increasing working lifespan of olfactory biosensors capable of detecting explosives.

A study on removing nitrogen from paddy field rainfall runoff by an ecological ditch-zeolite barrier system.

Ecological ditches and zeolite have been widely applied in the removal of farmland nonpoint source pollution separately; little research has been done on the effects of combining the two methods. Specifically, few studies have focused on the in situ regeneration of zeolite. A 2-year field experiment using an ecological ditch-zeolite barrier system was conducted in a paddy field of summer rice-winter wheat rotation in the Taihu Lake area. The system consisted of two zeolite barriers positioned at one third and two thirds of the length of the ditch. This study focused on the effect of the system on in situ nitrogen removal during the rice-growing season. Simultaneous laboratory kinetics experiments with natural zeolite and a series of adsorbed zeolites taken from the ditch at different time were also conducted. The concentration removal efficiencies of total nitrogen are averaged 24.66% in 2014 and 30.39% in 2015. Meanwhile, the cumulative adsorption quantity of ammonia nitrogen by the two barriers accounted for 49.27% of the ammonia nitrogen removed in 2014 and 54.35% of that in 2015. The amount of nitrogen adsorbed by plants was larger than that adsorbed by zeolite. The breakthrough curves of the zeolite and the characteristics of the zeolite surface structures from different periods all demonstrated that the zeolite can be regenerated in situ in the case of unsaturated zeolite within the ecological ditch. It can be concluded that an ecological ditch-zeolite barrier system is a realistic option for removing nitrogen from agricultural rainfall runoff in the Taihu Lake area.

First flush characteristics of rainfall runoff from a paddy field in the Taihu Lake watershed, China.

Nonpoint storm runoff remains a major threat to surface water quality in China. As a paddy matures, numerous fertilizers are needed, especially in the rainy seasons; the concentration of nitrogen and phosphorus in rainfall runoff from farmland is much higher than at other times, and this poses a great threat to water bodies and is the main reason for water eutrophication, especially in high concentration drainages. To date, most studies regarding the characteristics of pollutants in rainfall runoff have mainly been concentrated on urban runoff and watershed runoff; therefore, it is particularly important to investigate the characteristics of nitrogen and phosphorus loss in rainfall runoff from paddy fields. To study the characteristics of nitrogen and phosphorus loss and whether the first flush effect exists, continuous monitoring of the rainfall runoff process of six rainfall events was conducted in 2013, of which four rainfall events during storm, high, middle, and low intensity rainfalls were analyzed, and runoff and quality parameters, such as suspended solids (SS), total nitrogen (TN), ammonium nitrogen (NH4+-N), nitrate nitrogen (NO3--N), total phosphorus (TP), and phosphate (PO43--P), were analyzed to determine the relationship between runoff and water quality. The paddy field is located north of Wuxi Lake Basin along the Hejia River upstream in Zhoutie town, Yixing city. An analysis of the load distribution during rainfall runoff was conducted. Event mean concentration (EMC) was used to evaluate the pollution situation of the paddy field's rainfall runoff. A curve of the dimensionless normalized cumulative load (L) vs. normalized cumulative flow (F) (L-F curve), the probability of the mass first flush (MFFn), and the pollutants carried by the initial 25% of runoff (FF25) were used to analyze the first flush effect of the paddy field runoff, and different contaminants show different results: the concentration of nitrogen and phosphorus fluctuate and follow a similar trend as runoff changes, NO3--N concentration is lower in the early part of runoff and higher in the later, and TP mainly occurs in the particle state in storm runoff and mainly in the dissolved state when the rainfall intensity is smaller. Nitrogen and phosphorus losses from paddy fields are closely related to the average rainfall intensity and the max rainfall intensity, and the runoff loss of nitrogen and phosphorus is more severe when the rainfall intensity is large. Based on an analysis of multiple methodologies, TN and NH4+-N show a certain degree of a first flush effect, whereas the first flush effect of TP is not obvious. The first flush effect of SS is obvious in larger intensity rainfall and shows a slight secondary flush effect in smaller rainfall events.

Using natural Chinese zeolite to remove ammonium from rainfall runoff following urea fertilization of a paddy rice field.

The potential of natural Chinese zeolite to remove ammonium from rainfall runoff following urea applications to a paddy rice field is assessed in this study. Laboratory batch kinetic and isotherm experiments were carried out first to investigate the ammonium adsorption capacity of the natural zeolite. Field experiments using zeolite adsorption barriers installed at drain outlets in a paddy rice field were also carried out during natural rainfall events to evaluate the barrier's dynamic removal capacity of ammonium. The results demonstrate that the adsorption kinetics are accurately described by the Elovich model, with a coefficient of determination (R (2)) ranging from 0.9705 to 0.9709, whereas the adsorption isotherm results indicate that the Langmuir-Freundlich model provides the best fit (R (2) = 0.992) for the equilibrium data. The field experiments show that both the flow rate and the barrier volume are important controls on ammonium removal from rainfall runoff. A low flow rate leads to a higher ammonium removal efficiency at the beginning of the tests, while a high flow rate leads to a higher quantity of ammonium adsorbed over the entire runoff process.