Biology subjects

Koga, A.

Publications and source records attributed to Koga, A..

4 recordsLinked to original sources

bioRxiv2026

Enhanced multisensory integration in the olfactory bulb of the Mexican cavefish

Astyanax mexicanus consists of eyed, river-dwelling "surface" fish, and multiple, independently evolved cave populations, which have converged on troglobitic traits such as eye loss and reduced metabolism. However, considerably less is known about constructive adaptations, which include a larger olfactory epithelium in cavefish. It is unknown how this relates to the olfactory bulb (OB), which is the first stage of olfactory sensory processing in the brain. The goal of the present study is to begin to define the structure and functional organization of the OB in A. mexicanus, and to begin to understand how it was transformed via cave adaptation. We addressed these questions using whole-mount immunohistochemistry and in vivo Ca2+ imaging from the OB of developmentally matched surface and Pachon cavefish. The cavefish OB was significantly larger than surface fish by 14 days post fertilization (dpf), which was accompanied by a broad and proportional increase in synaptic input to most glomerular regions. Increases in the size of the OB were accompanied by increases in the number of neurons expressing tyrosine hydroxylase and calretinin, the latter of which occurred primarily in the medial OB and could not be explained as a compensatory response to a larger OB. In vivo Ca2+ imaging from the dorsal OB of surface and cavefish in response to a panel of chemical stimuli revealed odor-evoked responses that were spatially organized and highly conserved across the two populations. Surprisingly, the medial OB was consistently activated by any change in water flow in both populations, although the number of water-responsive neurons was significantly greater in cavefish when measurements were performed using either in vivo imaging or the neuronal activity marker phospho-ERK. Water-responding neurons were similarly present in the olfactory epithelium in both populations, along with neurons expressing the mechanosensitive ion channel Piezo2, with significantly more Piezo2-expressing neurons present in cavefish. Therefore, cavefish exhibit enhanced multisensory integration of olfactory and mechanosensory input in the earliest stage of olfactory sensory processing in the brain.

neuroscience↗

bioRxiv2026

The hAT transposon-like sequence homologous to Japanese medaka Tol2 was found in the European lamprey genome.

Tol2 is one of the few DNA-based transposable elements that reside in vertebrate genomes and retain transposition activity. It was first identified in the medaka fish (Oryzias latipes) and subsequently in another species of the genus Oryzias, which belongs to the order Beloniformes. Transposable elements similar in sequence to Tol2 also occur in several species of the order Cypriniformes, including the common carp. The low sequence variation of these elements relative to that of a nuclear gene provided evidence for past horizontal transfer events among host organisms. We collectively refer to Tol2 and these related elements as the Tol2 family. Here, we identified a novel transposable element in two European lamprey species (Lampetra fluviatilis and L. planeri), which we named Tel2. Lampreys belong to the jawless vertebrate lineage (infraphylum Agnatha), whereas all previously known host species of the Tol2 family are jawed vertebrates (infraphylum Gnathostomata). The nucleotide sequence similarity between Tol2 and Tel2 was higher than that observed for the nuclear gene, indicating at least one horizontal transfer event between the two infraphyla. Thus, the Tol2 family now includes Tel2 as a new member. These results indicate that Tol2 family elements have undergone multiple horizontal transfer events across a wide range of host organisms, including both jawless and jawed vertebrates. Because some members of this family still retain transposition activity, they provide an excellent and unique model for studying the role of horizontal transfer in the long-term persistence of DNA-based transposable elements.

genetics↗

bioRxiv2023

Correlating stress reduction and eye movement patterns in a world famous Kyoto Japanese garden

Visual stimuli have been repeatedly shown to elicit significant non-visual responses. In a continuing effort to explore the unique effects of viewing a Japanese garden on the physiological and psychological metrics of stress, we gained access to the world famous Murin-an garden in Kyoto, Japan. This well-maintained observation garden was designed to be viewed while seated at a single vantage point to maximize the impact of the visual scene. As a control, we used a public garden on the campus of Kyoto University that was designed in a similar style. Sixteen college age students were asked to view both gardens while we monitored their pulse rates and tracked their eye movements. We used the POMS questionnaire to determine the effect of the garden viewing on the mood of the participants. We found that the Murin-an garden was more effective in decreasing pulse rate and improving mood than the University garden. The eye tracking data showed that during their Murin-an viewing the participants gaze ranged far more broadly across the visual field both the X-Y plane and in depth, and the speed with which the eyes moved from point-to-point was greater. Taken together, our data suggest that no one element in the garden was dominant in eliciting the changes in heart rate and mood. Rather, it was the breadth and rapidity of the shifts in gaze that drove the effects, a conclusion with implications for other interventions aimed stress reduction. SignificanceViews of nature and natural phenomena have a well-recognized calming effect on humans that has recognized therapeutic value in both medical and psychological settings. Our work explores the source of this effect by having participants view Murin-an, a world-famous Japanese style garden. Using both psychological and physiological measures, we confirm and extend earlier findings showing that a well constructed garden can effectively lower heart rate and improve mood within minutes. We also find, by analogy with eye movement desensitization and reprograming (EMDR), that it is participants rapidly shifting gaze rather than a single specific visual object is the most likely source of the calming effect.

neuroscience↗

bioRxiv2020

Novel multicellular prokaryote discovered next to an underground stream

The emergence of multicellularity is a key event in the evolution of life and is an attractive challenge among researchers, including those investigating the artificial design of cellular behavior1. Multicellular organisms are widely distributed on Earth, and retracing the specific conditions conducive for the initial transition from unicellularity to multicellularity is difficult. However, by examining organisms that inhabit unique (e.g., isolated) environmental niches, we may be able to get a glimpse into primitive multicellularity in the context of a given environment. Here we report the discovery of a new bacterium that displayed multicellular-like characteristics and behavior. The bacterium, which was isolated adjacent to an underground stream in a limestone cave, is to be named Jeongeupia sacculi sp. nov. HS-3. On a solid surface, HS-3 self-organizes its filamentous cells to form an appearance similar to the nematic phase of a liquid crystal2. Mature colonies produce and accommodate clusters of coccobacillus progeny, and release them upon contact with water. HS-3 demonstrated novel, spatiotemporally regulated multicellularity that can resolve the so-called competition-dispersal trade-off problem3. This study illustrates a hypothetical missing link on the emergence of multicellularity.

evolutionary biology↗