Biology subjects

Kojima, D.

Publications and source records attributed to Kojima, D..

3 recordsLinked to original sources

bioRxiv2026

Light-dependent conversion of body color change pattern during zebrafish development

Zebrafish (Danio rerio) shows body color change in response to light: when light comes, it whitens body color. Our previous study has shown that larval zebrafish as early as 5 days post-fertilization (dpf) have this capacity fully developed whereas 2-dpf larvae exhibit light-induced darkening in sharp contrast (Shiraki et al. 2010). Here, we discovered that the conversion in body color change pattern between 2 dpf and 5 dpf is light-dependent: larvae reared in darkness exhibited light-induced darkening of body color, reminiscent of 2-dpf larvae. We also found that a 14-h light exposure on 3 or 4 dpf is sufficient to trigger this conversion, and that the conversion by light on 4 dpf still occurred after ablation of most exorh-expressing pineal photoreceptor cells. The dark-reared larvae had significantly lower transcription levels of pmch and pmchl, which encode melanin-concentrating hormone precursors, than the LD-reared larvae. However, the levels in larvae that had undergone the conversion (3-L and 4-L) were not significantly different from those in dark-reared larvae, indicating that the reduced pmch/pmchl expression alone does not account for the conversion. In conclusion, light exposure in rearing is indispensable for the maturation of body color change ability in larval zebrafish through a regulatory mechanism independent of exorh-expressing pineal photoreceptors.

developmental biology↗

bioRxiv2024

Descending locus coeruleus noradrenergic signaling to spinal astrocyte subset is required for stress-induced pain facilitation

It is known that stress powerfully alters pain, but its underlying mechanisms remain elusive. Here, we identified a circuit, locus coeruleus descending noradrenergic neurons projecting to the spinal dorsal horn (LC[->]SDH-NA neurons), that is activated by acute exposure to restraint stress and is required for stress-induced mechanical pain hypersensitivity in mice. Interestingly, the primary target of spinal NA released from descending LC[->]SDH-NAergic terminals causing the stress-induced pain hypersensitivity was 1A-adrenaline receptors (1ARs) in Hes5-positive (Hes5+) astrocytes located in the SDH, an astrocyte subset that has an ability to induce pain sensitization. Furthermore, activation of Hes5+ astrocytes reduced activity of SDH-inhibitory neurons (SDH-INs) that have an inhibitory role in pain processing. This astrocytic reduction of IN activity was canceled by an A1-adenosine receptor (A1R)-knockdown in SDH-INs, and the A1R-knockdown suppressed pain hypersensitivity caused by acute restraint stress. Therefore, our findings suggest that LC[->]SDH-NA neuronal signaling to Hes5+ SDH astrocytes and subsequent astrocytic reduction of SDH-IN activity are essential for mechanical pain facilitation caused by stress.

neuroscience↗

bioRxiv2021

Foxq2 determines blue cone identity in zebrafish

Most vertebrate lineages retain a tetrachromatic visual system, which is supported by a functional combination of spectrally distinct multiple cone photoreceptors, UV, blue, green, and red cones. The blue cone identity is ensured by selective expression of blue (sws2) opsin, and the mechanism is poorly understood because SWS2 gene has been lost in mammalian species such as mouse, whose visual system has been extensively studied. Here we pursued loss-of-function studies on transcription factors expressed predominantly in zebrafish cone photoreceptors and identified Foxq2 as a core factor driving sws2 gene expression. foxq2 is expressed only in the blue cone, and loss of foxq2 selectively abolishes sws2 expression. Comparative genomic analysis revealed that a wide range of vertebrate species retain both FOXQ2 and SWS2 genes. We propose that FOXQ2-dependent SWS2 expression is a prevalent regulatory mechanism that was acquired at the early stage of vertebrate evolution

neuroscience↗