Biology subjects

Kohtsuka, H.

Publications and source records attributed to Kohtsuka, H..

3 recordsLinked to original sources

bioRxiv2026

Axial Patterning Beyond the Individual: Colony-level Organization in a Siphonophore Colony

Colonial animals composed of clonally produced units can achieve a high degree of functional integration, challenging the distinction between an individual and a higher-order organism. Siphonophores (Cnidaria: Hydrozoa) exemplify this condition, forming highly organized colonies in which genetically identical zooids are specialized for functions such as locomotion, feeding, and reproduction, and are precisely arranged along a shared stem. All zooids arise from two spatially separated budding zones, the nectosomal and siphosomal growth zones, suggesting that positional information along the stem patterns colony organization at the level of the colony rather than individual zooids. However, the molecular basis of this colony-level axial patterning remains poorly understood. Here, we analyze gene expression along the stem of the siphonophore Agalma okenii using RNA sequencing and in situ hybridization chain reaction (HCR). We show that conserved developmental regulators, including Hox and Wnt pathway genes, exhibit region-specific expression corresponding to distinct budding zones and zooid distributions. These results indicate that canonical axial patterning systems are deployed at the level of the colony axis. Our findings demonstrate that developmental gene networks classically associated with anterior-posterior patterning can operate at a higher level of biological organization, providing a mechanistic framework for the evolution of integrated, superorganism-like body plans in colonial animals.

developmental biology↗

bioRxiv2026

Establishing genetically controlled, closed 1 colonies of an ascidian

Recent technological advances have made many "non-model" organisms accessible for experimental studies. However, reference inbred strains were not necessarily available, especially in marine invertebrates, and genetic background of organisms used for experiments are often non-uniform. This situation potentially affects experimental reproducibility. Although ascidians, Ciona intestinalis (type A, or C. robusta), are a widely used marine animal for many areas of experimental biology including developmental studies, no reference strains have been obtained despite extensive efforts. As an alternative way to improve reproducibility, we have established and maintained ascidian colonies through intra-population breeding every year from 2016 to 2020, and monitored genomic variants of these colonies. This method does not reduce genetic variations but instead manages and monitors genetic variations in the colonies, providing an easy and cost-effective way of increasing experimental reproducibility. Furthermore, we recently upgraded these genetically isolated, closed colonies that were re-established every year, and have maintained them for more than three years only through intra-population breeding and occasional back-cross using cryopreserved sperm. Genetic variants that we revealed using 3.7 tera-bases of sequence data will help to design future experiments in this species. Our data also show that two wild-populations, which were used to establish the colonies, have maintained distinct genetic backgrounds, although their habitats are directly linked to the Pacific Ocean and only 170 km apart. More importantly, genetic information regarding these colonies will undoubtedly improve experimental reproducibility and traceability, and our method will provide a realistic solution for performing reproducible experiments using non-model organisms.

developmental biology↗

bioRxiv2025

Histological transition during ovotestis formation in a female-to-male sex-change fish, the harlequin sandsmelt (Parapercis pulchella)

Many teleost fishes are capable of sex change, and some species possess intersex gonads known as ovotestes, which contain both ovarian and testicular tissues. Uncovering the developmental processes in ovotestis formation is critical for elucidating the mechanisms of intersexuality in vertebrates. However, such developmental processes have been described in only a limited number of species. In this study, we examined the histological structure of juvenile gonads in the harlequin sandsmelt (Parapercis pulchella), a female-to-male sex-change fish in which mature females possess ovotestes. Juveniles measuring up to 32.2 mm in total length exhibited gonads containing cyst-formed developing oogonia and a small number of oocytes. In contrast, larger juveniles possessed more developed ovaries but showed no detectable spermatogenic germ cells. These results suggest that gonads initially differentiate as ovaries and subsequently develop into ovotestes through the emergence of male germ cells. Together with previous studies, our results also indicate that a similar developmental sequence may be shared among sex-change fishes.

zoology↗