Biology subjects

Deguchi, R.

Publications and source records attributed to Deguchi, R..

5 recordsLinked to original sources

bioRxiv2025

A light-modulated clock mechanism in a hydrozoan jellyfish that synchronises evening gamete release.

For marine species that reproduce by external fertilisation, spawning is precisely coordinated within a local cohort to maximise the chances of producing offspring. Gamete release is often synchronised with respect to the daily light changes at sunrise and sunset. In the hydrozoan jellyfish Clytia hemisphaerica, morning spawning occurs when oocyte maturation and gamete release are induced by maturation-inducing hormone (MIH) neuropeptides released from opsin-expressing cells in the gonad directly upon light stimulus. Here, we characterise the distinct spawning cycle of a previously undescribed species Clytia sp. IZ-D identified on the Pacific coast of Japan, which releases gametes in the evening. Clytia sp. IZ-D jellyfish spawn 14 hours after light stimuli under a 24-hour light-dark cycle and exhibit autonomous and synchronised spawning cycles with a 20-hour interval under constant light. We found that the female spawning cycle reflects the growth and acquisition of maturation competence by oocytes, such that each day a new batch of growing oocytes becomes responsive to MIH at a time that correlates with the timing of actual spawning. We propose that the synchronised evening spawning in this species is controlled by an unusual circadian timing mechanism based on the progressive development of gamete competence to MIH and modulation of the opsin-controlled MIH signalling pathway. This mechanism may provide resilience to light cycle instability due to local climate variation and ensure reproductive isolation from other Clytia species by alternating the gamete release timing.

developmental biology↗

bioRxiv2025

Positive selection of a starch synthesis gene and phenotypic differentiation of starch accumulation in symbiotic and free-living coral symbiont dinoflagellate species

Symbiosis is a basis for species diversification through interactions between organisms. In tropical and subtropical oceans, dinoflagellate symbionts belonging to the family Symbiodiniaceae, including the genus Symbiodinium, support the flourishment of cnidarian hosts, including corals, and thereby the ecology of oligotrophic oceans through their photosynthate carbon transfers. Although the genus Symbiodinium includes both free-living and symbiotic species, the detailed genetic background of their lifestyle differences remains unclear. In this study, we identified candidate genes involved in the evolutionary acquisition or maintenance of symbiosis in Symbiodinium spp. by detecting genes that have undergone positive selection during symbiotic and free-living lifestyle diversification. Using multiple Symbiodinium genomes to detect positive selection, 35 genes were identified, including a gene encoding soluble starch synthase SSY1 and genes related to metabolite secretion, which may be preferred for symbiotic lifestyles. In particular, our in silico analyses revealed that the SSY1 gene family has undergone extensive gene duplications in an ancestral dinoflagellate, and that the mutations detected as positive selection have occurred in the intrinsically disordered region of one of the homologs. Consistent with molecular evolution, the phenotypes of intracellular starch synthesis/accumulation were distinct between the symbiotic and free-living species of Symbiodinium when cultured under different pH and nitrogen conditions. These results provide molecular and phenotypic insights into symbiotic Symbiodinium-coral relationships. Significance statementClarifying how coral symbiont algae of the family Symbiodiniaceae are functionally diversified is crucial for understanding the molecular mechanisms of symbiotic relationships and interactions in animal-algal symbioses. However, gene-level molecular evolution that contributes to symbiotic relationships remains unclear. Our genome-wide single-gene analyses of the genus Symbiodinium, comprising both symbiotic and free-living species, successfully detected several dozen protein-coding genes that underwent symbiont-specific positive selection after divergence from the free-living species in the genus. Furthermore, our cultivation experiments demonstrated differences in photosynthate-related phenotypes between the symbiotic and free-living species. Our findings provide a key to illuminating the molecular evolution involved in phenotypic changes that potentially contribute to symbiotic lifestyles in Symbiodinium.

evolutionary biology↗

bioRxiv2022

Environmental pH signals the release of monosaccharides from cell wall in coral symbiotic alga

Reef-building corals thrive in oligotrophic environments due to their possession of endosymbiotic algae. Confined to the low pH interior of the symbiosome within the cell, the algal symbiont provides the coral host with photosynthetically fixed carbon. However, it remains unknown how carbon is released from the algal symbiont for uptake by the host. Here we show, using cultured symbiotic dinoflagellate, Breviolum sp., that decreases in pH directly accelerates the release of monosaccharides, i.e., glucose and galactose, into the ambient environment. Under low pH conditions, the cell surface structures were deformed and genes related to cellulase were significantly upregulated in Breviolum. Importantly, the release of monosaccharides was suppressed by the cellulase inhibitor, glucopyranoside, linking the release of carbon to degradation of the agal cell wall. Our results suggest that the low pH signals the cellulase-mediated release of monosaccharides from the algal cell wall as an environmental response in coral reef ecosystems.

evolutionary biology↗

bioRxiv2017

Jellyfish Oocyte Maturation Inducing Hormone And Neuroendocrine Regulation Of Reproduction

Oocyte meiotic maturation is a critical process for sexually reproducing animals, and its core cytoplasmic regulators are highly conserved between species. In contrast, the few known Maturation Inducing Hormones (MIHs) that act on oocytes to initiate this process have highly variable molecular natures. Using the hydrozoan jellyfish species Clytia and Cladonema, which undergo oocyte maturation in response to dark-light and light-dark transitions respectively, we deduced from gonad transcriptome data amidated tetrapeptide sequences and found that synthetic peptides could induce maturation of isolated oocytes at nanomolar concentrations. Antibody preabsorption experiments conclusively demonstrated that these W/RPRPamide-related neuropeptides account for endogenous MIH activity produced by isolated gonads. We further showed that the MIH peptides are synthesised by neural-type cells in the gonad, are released following dark-light / light-dark transitions, and probably act on the oocyte surface. They are produced by male as well as female jellyfish and can trigger both sperm and egg release, suggesting a role in spawning coordination. We propose an evolutionary link between hydrozoan MIH and the neuropeptide hormones that regulate reproduction upstream of MIH in bilaterian species.

developmental biology↗

bioRxiv2017

CRISPR/Cas9 Mutation Of A Gonad-Expressed Opsin Prevents Jellyfish Light-Induced Spawning

Across the animal kingdom, environmental light cues are widely involved in regulating gamete release, but the molecular and cellular bases of the photoresponsive mechanisms are poorly understood. In hydrozoan jellyfish, spawning is triggered by dark-light or light-dark transitions acting on the gonad, and is mediated by oocyte maturation-inducing neuropeptide hormones (MIHs) released from the ectoderm. We determined in Clytia hemisphaerica that blue-cyan light triggers spawning in isolated gonads. A candidate opsin (Opsin9) was found co-expressed with MIH within specialised ectodermal cells. Opsin9 knockout jellyfish generated by CRISPR/Cas9 failed to undergo oocyte maturation and spawning, a phenotype reversible by synthetic MIH. Gamete maturation and release in Clytia is thus regulated by gonadal photosensory-neurosecretory cells that secrete MIH in response to light via Opsin9. Similar cells in ancestral eumetazoans may have allowed tissue-level photo-regulation of diverse behaviours, a feature elaborated in cnidarians in parallel with expansion of the opsin gene family.

evolutionary biology↗