Membrane-bound D-mannose isomerase of acetic acid bacteria: finding, characterization, and application.

D-Mannose isomerase (EC 5.3.1.7) catalyzing reversible conversion between D-mannose and D-fructose was found in acetic acid bacteria. Cell fractionation confirmed the enzyme to be a typical membrane-bound enzyme, while all sugar isomerases so far reported are cytoplasmic. The optimal enzyme activity was found at pH 5.5, which was clear contrast to the cytoplasmic enzymes having alkaline optimal pH. The enzyme was heat stable and the optimal reaction temperature was observed at around 40 to 60˚C. Purified enzyme after solubilization from membrane fraction showed the total molecular mass of 196 kDa composing of identical four subunits of 48 kDa. Washed cells or immobilized cells were well functional at nearly 80% of conversion ratio from D-mannose to D-fructose and reversely 20-25% of D-fructose to D-mannose. Catalytic properties of the enzyme were discussed with respect to the biotechnological applications to high fructose syrup production from konjac taro.

Pup odor and ultrasonic vocalizations synergistically stimulate maternal attention in mice.

Pup ultrasonic vocalizations (USVs), which are emitted by hypothermic pups, and pup odor are thought to be triggers of maternal behavior in mice. We investigated whether pup odor stimulated maternal responses to pup USVs in mother C57BL/6 mice. Two-choice tests were conducted by introducing mothers into a test cage in which a tube was attached on each long wall, and the duration spent in each tube was compared. Pup USVs were reproduced by an ultrasonic speaker at the tube end. In some cases, cotton with pup odor was also presented at the end of the tube. Compared to no stimuli, mothers did not specifically approach the sole presentation of either reproduced pup USVs or pup odor. However, compared to the sole presentation of pup odor, the simultaneous presentation of pup USVs and odor induced a specific approach response. These results suggested that pup USVs and odor synergistically stimulated maternal behavior. In addition, it was confirmed that mothers approached hypothermic pups emitting pup USVs for longer than anesthetized silent pups. To investigate the underlying neural mechanisms, we observed neural responses to various stimuli with the immunohistochemistry of c-fos expression. In the bed nucleus of the stria terminalis, the medial preoptic area, the central nucleus of the amygdala, and the basolateral amygdala, the numbers of c-fos-positive cells were significantly increased following the simultaneous presentation of pup USVs and odor compared to the presentation of each alone, suggesting that these nuclei were involved in multimodal processing related to maternal behavior.

The effects of social experience and gonadal hormones on retrieving behavior of mice and their responses to pup ultrasonic vocalizations.

Pup ultrasonic vocalizations (USVs) are emitted from maternally separated pups and are thought to be a trigger for eliciting maternal behavior in mice. We investigated the effects of social experience and gonadectomy on the retrieving behavior of mice and their responses to pup USVs produced by a nanocrystalline silicon thermo-acoustic emitter. In each experiment, virgin, gonadectomized, sham-operated, sexually experienced, and parenting mice of both sexes were used, and the effects of these manipulations were compared in each sex. The retrieving behavior of both sexes increased with social experience or gonadectomy. In particular, mothers showed the highest retrieving activity among female groups, while castrated male mice showed the highest retrieving activity among male groups. All groups of female mice responded to pup USVs, with the responsiveness of sexually experienced female mice being the most enhanced. Unlike the females, virgin male mice did not respond to pup USVs, although socially experienced or castrated males showed this response; fathers exhibited the highest responsiveness. These results suggest that not only parenting experience, but also mating experience, may enhance retrieving activity and response to pup USVs in mice of both sexes. Nevertheless, the degree to which parenting experience contributed to the enhancement of both activities differed between the sexes. Furthermore, gonadectomy enhanced both activities in both sexes, although its effect was more prominent in males. Overall, our findings suggest that alteration in responsiveness of mice to pup USVs might be one of the changes in parental behavior caused by social experiences or gonadal hormones.

Maternal approaches to pup ultrasonic vocalizations produced by a nanocrystalline silicon thermo-acoustic emitter.

When infant rodents are isolated from their mother and littermates, they cool rapidly and emit ultrasonic vocalizations (USVs). The effect of pup USVs on the mother has been investigated using models of pup USVs from ultrasonic speakers. We used a nanocrystalline silicon thermo-acoustic emitter (nc-Si emitter) to investigate mothers' responses to digitally reproduced pup USVs in mice. The nc-Si emitter could reproduce ultrasonic sounds more accurately than conventional emitters. We compared the sound properties of pup USVs and reproduced USVs. We then investigated maternal responses to hypothermic pups, which emit USVs, and anesthetized pups, which are silent, as well as maternal responses to pup USVs reproduced by the nc-Si emitter and a silent mode. The nc-Si emitter can reproduce pup USVs very accurately in terms of duration, frequency, and sound pressure level. Mothers approached reproduced digitally recorded pup USVs from the nc-Si emitter and their behavior was similar to their behavior toward hypothermic pups. In contrast, mothers did not approach other synthesized ultrasounds, such as double-duration USVs, double-silence domain ultrasounds nor double-ultrasonic domain ultrasounds, indicating that they approach the specific profiles of pup USVs. These results indicate that the nc-Si emitter can be useful to elucidate the role of ultrasonic acoustic communication in rodents.