Oxford University Press (OUP) Acta Medica Okayama 0278-0372 46 3 2026 Estimating the distributional expansion of the invasive crayfish Procambarus clarkii (Girard, 1852) (Decapoda: Astacidea: Cambaridae) in South Korea using environmental DNA analysis ruag033 EN Seong-Nam Ham Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Kaito Moriuchi Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Mayuko Hamada Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Kazuyoshi Nakata Graduate School of Environmental, Life, Natural Science and Technology, Okayama University The red swamp crayfish Procambarus clarkii (Girard, 1852) is a globally invasive species that poses serious threats to native biodiversity and ecosystem functioning. In South Korea, established populations of P. clarkii have been documented from the Jiseokcheon River in the Yeongsangang River basin since 2018; however, information on its current nationwide distribution remains limited. We conducted environmental DNA (eDNA) surveys at 19 sites across 11 river systems in South Korea, including sites with no prior distributional records, to evaluate the current distribution and potential range expansion of P. clarkii. Water samples collected during July-August 2024 were analyzed using quantitative real-time PCR (qPCR) with two species-specific primer-probe sets targeting the mitochondrial COI gene. Procambarus clarkii eDNA was detected at three sites in the Yeongsangang River basin, whereas no eDNA was detected in the other surveyed river systems. Notably, P. clarkii eDNA was not detected at a site in the Mangyeonggang River system despite previous reports of individuals and eDNA data sampled there, indicating a possible local population decline or very low abundance. By contrast, detections within the Yeongsangang River basin, together with elevated eDNA concentrations at some sites, are consistent with localized upstream expansion and increased local abundance. The concordant results from the two primer-probe sets, together with Sterivex-based on-site filtration, support the reliability of the applied eDNA framework. These findings identify the Yeongsangang River basin as the current primary focus of the P. clarkii invasion in South Korea, with evidence consistent with localized upstream expansion and increasing abundance, and provide baseline data for early detection and long-term monitoring, as well as for developing management strategies. No potential conflict of interest relevant to this article was reported.

Elsevier BV Acta Medica Okayama 0012-1606 520 2025 Tunicate-specific protein Epi-1 is essential for conferring hydrophilicity to the larval tunic in the ascidian Ciona 41 52 EN Kazu Kuroiwa Shimoda Marine Research Center, University of Tsukuba Kaoru Mita-Yoshida Shimoda Marine Research Center, University of Tsukuba Mayuko Hamada Ushimado Marine Institute, Okayama University Akiko Hozumi Shimoda Marine Research Center, University of Tsukuba Atsuo S. Nishino Department of Biology, Faculty of Agriculture and Life Science, Hirosaki University Yasunori Sasakura Shimoda Marine Research Center, University of Tsukuba Animals must avoid adhesion to objects in the environment to maintain their mobility and independence. The marine invertebrate chordate ascidians are characterized by an acellular matrix tunic enveloping their entire body for protection and swimming. The tunic of ascidian larvae consists of a surface cuticle layer and inner matrix layer. Hydrophilic substances coat the cuticle; this modification is thought to be for preventing adhesion. However, the molecule responsible for regulating this modification has not been clarified. We here found that the tunicate-specific protein Epi-1 is responsible for preventing adhesiveness of the tunic in the ascidian Ciona intestinalis Type A. Ciona mutants with homozygous knockouts of Epi-1 exhibited adhesion to plastic plates and to other individuals. The cuticle of the Epi-1 mutants was fragile, and it lost the glycosaminoglycans supplied by test cells, the accessory cells that normally attach to the tunic surface. Although it has an apparent signal peptide for membrane trafficking, we showed that the Epi-1 protein is localized to the cytosol of the epidermal cells. Our study suggests that the emergence of the tunicate-specific protein Epi-1 made the tunic less adhesive, providing a selective advantage for the last common tunicate ancestor. No potential conflict of interest relevant to this article was reported.

eLife Sciences Publications, Ltd Acta Medica Okayama 2050-084X 13 2025 Stimulatory and inhibitory G-protein signaling relays drive cAMP accumulation for timely metamorphosis in the chordate Ciona RP99825 EN Akiko Hozumi Shimoda Marine Research Center, University of Tsukuba Nozomu M Totsuka Department of Biosciences and Informatics, Faculty of Science and Technology, Keio University Arata Onodera Shimoda Marine Research Center, University of Tsukuba Yanbin Wang Shimoda Marine Research Center, University of Tsukuba Mayuko Hamada Ushimado Marine Institute, Okayama University Akira Shiraishi Bioorganic Research Institute, Suntory Foundation for Life Sciences Honoo Satake Bioorganic Research Institute, Suntory Foundation for Life Sciences Takeo Horie Laboratory for Single-cell Neurobiology, Graduate School of Frontier Biosciences, Osaka University Kohji Hotta Department of Biosciences and Informatics, Faculty of Science and Technology, Keio University Yasunori Sasakura Shimoda Marine Research Center, University of Tsukuba Larvae of the ascidian Ciona initiate metamorphosis tens of minutes after adhesion to a substratum via their adhesive organ. The gap between adhesion and metamorphosis initiation is suggested to ensure the rigidity of adhesion, allowing Ciona to maintain settlement after losing locomotive activity through metamorphosis. The mechanism producing the gap is unknown. Here, by combining gene functional analyses, pharmacological analyses, and live imaging, we propose that the gap represents the time required for sufficient cyclic adenosine monophosphate (cAMP) accumulation to trigger metamorphosis. Not only the Gs pathway but also the Gi and Gq pathways are involved in the initiation of metamorphosis in the downstream signaling cascade of the neurotransmitter GABA, the known initiator of Ciona metamorphosis. The mutual crosstalk of stimulatory and inhibitory G-proteins functions as the accelerator and brake for cAMP production, ensuring the faithful initiation of metamorphosis at an appropriate time and in the right situation. No potential conflict of interest relevant to this article was reported.

eLife Sciences Publications, Ltd Acta Medica Okayama 2050-084X 14 2026 Dorsoventral-mediated Shh induction is required for axolotl limb regeneration RP106917 EN Sakiya Yamamoto Okayama University, Graduate School of Environmental, Life, Natural Science and Technology Saya Furukawa Okayama University, Graduate School of Environmental, Life, Natural Science and Technology Ayaka Ohashi Okayama University, Graduate School of Environmental, Life, Natural Science and Technology Mayuko Hamada Okayama University, Graduate School of Environmental, Life, Natural Science and Technology Akira Satoh Okayama University, Graduate School of Environmental, Life, Natural Science and Technology Axolotls (Ambystoma mexicanum) exhibit a remarkable ability to regenerate limbs. Classical experiments have suggested that contact between cells derived from distinct orientations—dorsal, ventral, anterior, and posterior—within the regenerating blastema is necessary for accurate limb pattern formation. However, the molecular basis for this requirement has remained largely unknown. Here, we demonstrate that both dorsal and ventral tissues are required for limb formation via induction of Shh expression, which plays a crucial role in limb patterning. Using the accessory limb model, we induced position-specific blastemas lacking cells derived from a single orientation (anterior, posterior, dorsal, or ventral). Limb patterning occurred only in blastemas containing both dorsal- and ventral-derived cells. We further observed that Shh expression requires dorsoventral contact within a blastema, highlighting the necessity of dorsoventral contact for inducing Shh expression. Additionally, we identified WNT10B and FGF2 as dorsal- and ventral-mediated signals, respectively, that create the inductive environment for Shh expression. Our findings clarify the role of dorsal and ventral cells in inducing Shh, a mechanism that has rarely been studied in the context of limb regeneration and pattern formation. This model provides new insights into how cells with different positional identities drive the regeneration process. No potential conflict of interest relevant to this article was reported.

The Royal Society Acta Medica Okayama 1744-957X 21 7 2025 Animal–chlorophyte photosymbioses: evolutionary origins and ecological diversity EN Isabel Jiah-Yih Liao Biodiversity Research Center, Academia Sinica Tosuke Sakagami Biodiversity Research Center, Academia Sinica Thomas D. Lewin Biodiversity Research Center, Academia Sinica Xavier Bailly Laboratoire des Modèles Marins Multicellulaires, Station Biologique de Roscoff Mayuko Hamada Ushimado Marine Institute, Okayama University Yi-Jyun Luo Biodiversity Research Center, Academia Sinica Photosynthetic symbiosis occurs across diverse animal lineages, including Porifera, Cnidaria, Xenacoelomorpha and Mollusca. These associations between animal hosts and photosynthetic algae often involve the exchange of essential macronutrients, supporting adaptation to a wide range of aquatic environments. A small yet taxonomically widespread subset of animals host photosymbionts from the core chlorophytes, a phylogenetically expansive clade of green algae. These rare instances of ‘plant-like’ animals have arisen independently across distantly related lineages, resulting in striking ecological and physiological diversity. Although such associations provide valuable insights into the evolution of symbiosis and adaptation to novel ecological niches, animal–chlorophyte photosymbioses remain relatively understudied. Here, we present an overview of photosymbioses between animals and chlorophytes, highlighting their independent evolutionary origins, ecological diversity and emerging genomic resources. Focusing on Porifera, Cnidaria and Xenacoelomorpha, we review shared and lineage-specific adaptations underlying these associations. We also contrast them with dinoflagellate-based systems to demonstrate their distinct ecological and cellular features. Our work sets the stage for elucidating the molecular mechanisms underlying these associations, enhancing our understanding of how interspecies interactions drive adaptation to unique ecological niches through animal–chlorophyte symbiosis. No potential conflict of interest relevant to this article was reported.

Zoological Society of Japan Acta Medica Okayama 0289-0003 40 1 2023 Fbxl4 Regulates the Photic Entrainment of Circadian Locomotor Rhythms in the Cricket Gryllus bimaculatus 53 63 EN Kazuki Takeuchi Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan Mirai Matsuka Graduate School of Natural Science and Technology, Okayama University Tsugumichi Shinohara Graduate School of Natural Science and Technology, Okayama University Mayuko Hamada Ushimado Marine Institute (UMI), Graduate School of Natural Science and Technology, Okayama University Yasuaki Tomiyama Graduate School of Natural Science and Technology, Okayama University Kenji Tomioka Graduate School of Natural Science and Technology, Okayama University Photic entrainment is an essential property of the circadian clock that sets the appropriate timing of daily behavioral and physiological events. However, the molecular mechanisms underlying the entrainment remain largely unknown. In the cricket Gryllus bimaculatus, the immediate early gene c-fosB plays an important role in photic entrainment, followed by a mechanism involving cryptochromes (crys). However, the association between c-fosB expression and crys remains unclear. In the present study, using RNA-sequencing analysis, we found that five Fbxl family genes (Fbxl4, Fbxl5, Fbxl16, Fbxl-like1, and Fbxl-like2) encoding F-box and leucine-rich repeat proteins are likely involved in the mechanism following light-dependent c-fosB induction. RNA interference (RNAi) of c-fosA/B significantly downregulated Fbxls expression, whereas RNAi of the Fbxl genes exerted no effect on c-fosB expression. The Fbxl genes showed rhythmic expression under light-dark cycles (LDs) with higher expression levels in early day (Fbxl16), whole day (Fbxl-like1), or day-to-early night (Fbxl4, Fbxl5, and Fbxl-like2), whereas their expression was reduced in the dark. We then examined the effect of their RNAi on the photic entrainment of the locomotor rhythm and found that RNAi of Fbxl4 either disrupted or significantly delayed the re-entrainment of the locomotor rhythm to shifted LDs. These results suggest that light-induced c-fosB expression stimulates Fbxl4 expression to reset the circadian clock. No potential conflict of interest relevant to this article was reported.

American Association for the Advancement of Science (AAAS) Acta Medica Okayama 2375-2548 8 9 2022 Vasopressin-oxytocin–type signaling is ancient and has a conserved water homeostasis role in euryhaline marine planarians eabk0331 EN Aoshi Kobayashi Ushimado Marine Institute (UMI), Graduate School of Natural Science and Technology, Okayama University Mayuko Hamada Ushimado Marine Institute (UMI), Graduate School of Natural Science and Technology, Okayama University Masa-aki Yoshida Oki Marine Biological Station, Shimane University Yasuhisa Kobayashi Ushimado Marine Institute (UMI), Graduate School of Natural Science and Technology, Okayama University Naoaki Tsutsui Ushimado Marine Institute (UMI), Graduate School of Natural Science and Technology, Okayama University Toshio Sekiguchi Noto Marine Laboratory, Institute of Nature and Environmental Technology, Division of Marine Environmental Studies, Kanazawa University Yuta Matsukawa Ushimado Marine Institute (UMI), Graduate School of Natural Science and Technology, Okayama University Sho Maejima Ushimado Marine Institute (UMI), Graduate School of Natural Science and Technology, Okayama University Joseph J. Gingell Vertex Pharmaceuticals (Europe) Ltd. Shoko Sekiguchi Ushimado Marine Institute (UMI), Graduate School of Natural Science and Technology, Okayama University Ayumu Hamamoto Ushimado Marine Institute (UMI), Graduate School of Natural Science and Technology, Okayama University Debbie L. Hay School of Biological Sciences and Maurice Wilkins Centre for Molecular Biodiscovery, University of Auckland John F. Morris Department of Physiology, Anatomy, and Genetic, Le Gros Clark Building, University of Oxford Tatsuya Sakamoto Ushimado Marine Institute (UMI), Graduate School of Natural Science and Technology, Okayama University Hirotaka Sakamoto Ushimado Marine Institute (UMI), Graduate School of Natural Science and Technology, Okayama University, Ushimado Vasopressin/oxytocin (VP/OT)–related peptides are essential for mammalian antidiuresis, sociosexual behavior, and reproduction. However, the evolutionary origin of this peptide system is still uncertain. Here, we identify orthologous genes to those for VP/OT in Platyhelminthes, intertidal planarians that have a simple bilaterian body structure but lack a coelom and body-fluid circulatory system. We report a comprehensive characterization of the neuropeptide derived from this VP/OT-type gene, identifying its functional receptor, and name it the “platytocin” system. Our experiments with these euryhaline planarians, living where environmental salinities fluctuate due to evaporation and rainfall, suggest that platytocin functions as an “antidiuretic hormone” and also organizes diverse actions including reproduction and chemosensory-associated behavior. We propose that bilaterians acquired physiological adaptations to amphibious lives by such regulation of the body fluids. This neuropeptide-secreting system clearly became indispensable for life even without the development of a vascular circulatory system or relevant synapses. No potential conflict of interest relevant to this article was reported.

Zoological Society of Japan Acta Medica Okayama 0289-0003 39 1 2022 Observing Phylum-Level Metazoan Diversity by Environmental DNA Analysis at the Ushimado Area in the Seto Inland Sea 157 165 EN Takeshi Kawashima National Institute of Genetics Masa-aki Yoshida Marine Biological Science Section, Education and Research Center Biological Resources, Faculty of Life and Environmental Science, Shimane University Hideyuki Miyazawa National Institute of Genetics Hiroaki Nakano Shimoda Marine Research Center, University of Tsukuba Natumi Nakano Department of Biology, Nara Medical University Tatsuya Sakamoto Ushimado Marine Institute, Okayama University Mayuko Hamada Ushimado Marine Institute, Okayama University The dynamics of microscopic marine plankton in coastal areas is a fundamental theme in marine biodiversity research, but studies have been limited because the only available methodology was collection of plankton using plankton-nets and microscopic observation. In recent years, environmental DNA (eDNA) analysis has exhibited potential for conducting comprehensive surveys of marine plankton diversity in water at fixed points and depths in the ocean. However, few studies have examined how eDNA analysis reflects the actual distribution and dynamics of organisms in the field, and further investigation is needed to determine whether it can detect distinct differences in plankton density in the field. To address this, we analyzed eDNA in seawater samples collected at 1 km intervals at three depths over a linear distance of approximately 3.0 km in the Seto Inland Sea. The survey area included a location with a high density of Acoela (Praesagittifera naikaiensis). However, the eDNA signal for this was little to none, and its presence would not have been noticed if we did not have this information beforehand. Meanwhile, eDNA analysis enabled us to confirm the presence of a species of Placozoa that was previously undiscovered in the area. In summary, our results suggest that the number of sequence reads generated from eDNA samples in our project was not sufficient to predict the density of a particular species. However, eDNA can be useful for detecting organisms that have been overlooked using other methods. No potential conflict of interest relevant to this article was reported.