Motor Neural Circuit Laboratory • Hirata Group

RNA helicases regulate RNA metabolism, but their substrate specificity and in vivo function remain largely unknown. We isolated spontaneous mutant zebrafish that exhibit an abnormal dorsal bend at the beginning of tactile-evoked escape swimming. Similar behavioral defects were observed in zebrafish embryos treated with strychnine, which blocks glycine receptors (GlyRs), suggesting that the abnormal motor response in mutants may be attributable to a deficit in glycinergic synaptic transmission. We identified a missense mutation in the gene encoding RNA helicase Dhx37. In Dhx37 mutants, GlyR alpha subunit mRNA levels were decreased due to a splicing defect. Overexpression of GlyR alpha subunits in Dhx37-deficient embryos restored normal behavior. Conversely, antisense knockdown of multiple GlyR alpha subunits in wild-type embryos was required to recapitulate the Dhx37 mutant phenotype. These results indicate that Dhx37 is specifically required for the biogenesis of a subset of GlyR alpha subunit mRNAs, thereby regulating glycinergic synaptic transmission and associated motor behaviors.

Mouse Genomics Resource Laboratory (MGRL) • Koide Group

Humans have developed many domestic animals for various purposes. Tameness is a behavioral characteristic that is changed during domestication process of wild ancestors. However, it is still need to be clarified how tameness change the behavior of animals. In this point of view, we took particular note of a book written by an American zoologist, Edward O. Price. He defined tameness as “a measure of the extent to which an individual is reluctant to avoid or motivated to approach humans.” In order to address this point, we developed three behavioral tests to measure the level of two different classes of tameness in mice. We characterized tame behavior using 17 inbred mouse strains: ten wild strains, one Japanese fancy-mouse strain, and six laboratory strains. As a results, most of the domesticated strains showed significantly greater reluctance to avoid humans than wild strains, whereas there was no significant difference in the level of motivation to approach humans between these two groups. These results suggest that domesticated strains were predominantly selected for reluctance to avoid humans over the course of their domestication history.

Dr. Tatsuhiko Goto worked on this project as a project researcher in Transdisciplinary Research Integration Center.

Figure 1. Dr. Kazuo Moriwaki, an emeritus professor, introduced wild mice from many countries and developed wild-derived inbred strains (wild strains). Given that these strains have not been subjected to deliberate attempts at domestication during inbreeding, these mice still show the characteristic behavior of wildness, such as quick movements, aggression, and higher responsiveness to handling by humans.
Figure 2. Tame tests developed for measuring levels of tameness in mice
Figure 3. Most of the domesticated strains showed significantly higher level of reluctance to avoid human than wild-derived mice, whereas there was no significant difference in the level of motivated to approach human.

Microbial Genetics Laboratory • Niki Group

Many fungi respond to light and regulate fungal development and behavior. A blue light-activated complex has been identified in Neurospora crassa as the product of the wc-1 and wc-2 genes. Orthologs of WC-1 and WC-2 have hitherto been found only in filamentous fungi and not in yeast, with the exception of the basidiomycete pathogenic yeast Cryptococcus. Here, we report that the fission yeast Schizosaccharomyces japonicus responds to blue light depending on Wcs1 and Wcs2, orthologs of components of the WC complex. Surprisingly, those of ascomycete S. japonicus are more closely related to those of the basidiomycete. S. japonicus reversibly changes from yeast to hyphae in response to environmental stresses. After incubation at 30°C, a colony of yeast was formed, and then hyphal cells extended from the periphery of the colony. When light cycles were applied, distinct dark- and bright-colored hyphal cell stripes were formed because the growing hyphal cells had synchronously activated cytokinesis. In addition, temperature cycles of 30°C for 12 h and 35°C for 12 h or of 25°C for 12 h and 30°C for 12 h during incubation in the dark induced a response in the hyphal cells similar to that of light. The stripe formation of the temperature cycles was independent of the wcs genes. Both light and temperature, which are daily external cues, have the same effect on growing hyphal cells. A dual sensing mechanism of external cues allows organisms to adapt to daily changes of environmental alteration.

After incubation at 30°C, a colony of yeast was formed (a), and then hyphal cells extended from the periphery of the colony (b). When light cycles were applied, distinct dark- and bright-colored hyphal cell stripes were formed because the growing hyphal cells had synchronously activated cytokinesis (c).