Technical Section / Phenotype Research Center / Cell Architecture Laboratory

Zooid arrangement and colony growth in Porpita porpita

Kohei Oguchi, Akiteru Maeno, Keita Yoshida, Gaku Yamamoto, Hisanori Kohtsuka and Casey W. Dunn

Frontiers in Zoology (2025) 22, 11 1-12 DOI:10.1186/s12983-025-00565-3

The blue button Porpita porpita shows a highly integrated colony composed of functionally specialized zooids. Surface-floating organisms like P. porpita are called pleuston and form unique ecosystems in the ocean’s surface layers. However, due to their sensitivity to wind and currents, predicting their appearance is difficult, and their life history remains poorly understood. P. porpita is especially fragile and hard to maintain in captivity, making its colony development largely unknown. In this study, we analyzed specimens of various sizes collected from Sagami Bay, Japan, using histological sections and micro-CT. We found that each colony always had one central gastrozooid, and the number and size of gonozooids and dactylozooids increased with colony growth. Budding zones and the colony’s regenerative capacity suggest how such a superorganism is developed.

This work was supported by a NIG-JOINT (25A2020,70A2021) from National Institute of Genetics, Grant-in-Aid for Research Activity Start-up (No. 22K20662) from the Ministry of Education, Culture, Sports, Science, and Technology of Japan and a grant from the Research Institute of Marine Invertebrates.

Figure: (A) Colony of Porpita porpita. (B) Cross-sectional image of the colony obtained by micro-CT. (C) Schematic diagram of the internal structure of the P. porpita colony as revealed in this study. Growth zones of dactylozooids are located along the colony margin, particularly at the base of the mantle, while those of gonozooids are widely distributed within the epithelium of the coenosarc.

Maeshima Group / Genome Dynamics Laboratory

Euchromatin and heterochromatin: implications for DNA accessibility and transcription

Katsuhiko Minami#, Adilgazy Semeigazin#, Kako Nakazato, and Kazuhiro Maeshima*
# co-first authors; * corresponding author

Journal of Molecular Biology (2025) DOI:10.1016/j.jmb.2025.169270

In higher eukaryotic cells, such as those in humans, genomic DNA wraps around core histone proteins to form nucleosomes. These nucleosomes further fold into condensed chromatin domains that exhibit a range of folding patterns—from transcriptionally active euchromatin to inactive heterochromatin. Over the past 15 years, research, including that conducted by the authors, has revealed that these chromatin domains display liquid-like behaviors. Katsuhiko Minami (Postdoctoral Fellow, former SOKENDAI student, and JSPS Research Fellow DC2), Adilgazy Semeigazin (SOKENDAI student and MEXT Scholar), Kako Nakazato (SOKENDAI student), and Professor Kazuhiro Maeshima of the Genome Dynamics Laboratory have discussed in this paper the physical properties and dynamic behaviors of chromatin in living cells. They have further examined how these physical characteristics are linked to the regulation of gene transcription and DNA replication from the perspective of “DNA accessibility.”

Their recent findings, based on single-nucleosome imaging (paper link or NIG press release), revealed that within condensed chromatin domains, euchromatin behaves more like a liquid, while heterochromatin behaves more like a gel. These physical properties directly impact how large proteins can penetrate into the chromatin environment (accessibility), and they are considered to play critical roles in regulating genome functions such as transcription, DNA replication, and repair (see figure). The authors also discussed that euchromatin and heterochromatin have comparable accessibility on a long time scale, based on findings from DNA adenine methyltransferase (Dam) experiments. This paper is published in the Journal of Molecular Biology special issue, “Imaging of the Central Dogma.”

This work was supported by the Japan Society for the Promotion of Science (JSPS) and MEXT KAKENHI grants (JP23K17398, JP24H00061, JP23KJ0998), the Platform for Advanced Genome Science (PAGS; JP22H04925), JST SPRING (JPMJSP2104), JSPS Research Fellowship (23KJ0998), and the Takeda Science Foundation.

• Free access link (until 8/7)

Figure: Physical properties and accessibility of euchromatin and heterochromatin
Euchromatic (actively transcribed) nucleosomes fluctuate like a liquid, while heterochromatin (transcription is repressed) behaves like a gel. Such local nucleosome fluctuations facilitate protein access to chromatin domains on a short time scale. Euchromatin and heterochromatin have comparable accessibility on a long time scale.

Kawakami Group / Laboratory of Molecular and Developmental Biology 

Production of multi-subunit proteins in CHO cells by transposase-mediated integration of subunit-splitting vectors.

Keina Yamaguchi, Risa Ogawa, Masayoshi Tsukahara and Koichi Kawakami

Scientific reports (2025) 15, 18512 DOI:10.1038/s41598-025-03301-3

Chinese Hamster Ovary (CHO) cells are widely used for therapeutic protein production. We previously developed a method using the Tol2 transposon system to efficiently establish protein-producing cell lines via multiple genomic integrations of the gene of interest. In this study, we introduced two separate vectors—one carrying the light chain　(LC) gene and the other the heavy chain (HC) gene—into CHO cells, rather than a single vector with both genes. As a result, we obtained cell lines that stably produced monoclonal antibodies for up to 12 weeks and showed high productivity in fed-batch culture. Each cell line exhibited variable copy numbers of integrated LC and HC vectors, depending on the antibody type. High-producing lines had optimal ratios of LC and HC gene copies. Notably, optimization was achieved even when the drug resistance gene was present only in the HC vector. These findings highlight the potential of the Tol2 system for efficient production of monoclonal antibodies and other multi-subunit proteins.

Figure: Overview of the method.
Separate transposon vectors carrying the heavy chain (HC) and light chain (LC) genes are co-transfected into CHO cells. The drug resistance gene (cycloheximide resistance) is present only in the LC vector. In the transfected cells, the HC and LC vectors are integrated into the host genome in varying copy numbers. Cell lines carrying optimal copy numbers of both HC and LC vectors can be selected as cell lines that efficiently produce monoclonal antibodies.

Miyagishima Group / Symbiosis and Cell Evolution Laboratory

Costs of photosynthesis and cellular remodeling in trophic transitions of the unicellular red alga Galdieria partita

Shota Yamashita, Shunsuke Hirooka, Takayuki Fujiwara, Baifeng Zhou, Fumi Yagisawa, Kei Tamashiro, Hiroki Murakami, Koichiro Awai, and Shin-ya Miyagishima

Communications Biology (2025) 8, 891 DOI:10.1038/s42003-025-08284-5

As in plastid differentiation in land plants, some unicellular algae reversibly remodel photosynthetic plastids into a colorless heterotrophic state (bleaching) in the presence of organic carbon sources. To understand these mechanisms and their significance, we performed comparative omics analyses on the photoautotrophic and heterotrophic states and their transitions in the genetically tractable red alga Galdieria partita. Photoautotrophic cells require 1.5, 1.3 and 1.7 times more nitrogen, protein, and fatty acids than heterotrophic cells. In the photoautotrophic cells, plastid- and nucleus-encoded proteins for photosynthesis are highly synthesized, while in the heterotrophic state, cytoplasmic and mitochondrial proteins are more abundant, enabling 1.6 times faster growth. Changes in non-plastid metabolic enzymes are limited, with some upregulated in the photoautotrophic state to support fatty acid and glycolipid synthesis in the plastid for thylakoid membranes. In contrast, solute transporters show broader changes. Bleaching occurs upon adding certain sugars or sugar alcohols, regardless of light, not by active digestion of photosynthetic machinery, but by dilution due to suppressed synthesis at the transcriptional level and faster cell growth. Thus, when assimilable organic carbon is available, the cells repress the synthesis of proteins, lipids, and pigments for photosynthesis, reallocating resources to promote faster growth.

This study was supported by JSPS KAKENHI (22K15166, 24KJ0224, 24H00579), and JST-MIRAI Program (JPMJMI22E1).

Figure: Liquid culture (left) and micrographs of cells (right) of Galdieria partita grown under light or dark conditions with or without exogenous glucose. Modified from Fig. 1A and B of the paper.