Biology subjects

Kusano, S.

Publications and source records attributed to Kusano, S..

4 recordsLinked to original sources

bioRxiv2026

A Wnt-responsive fibrocartilage progenitor system coordinates postnatal mandibular condylar cartilage growth

Postnatal growth of the mandibular condyle requires coordinated expansion of fibrocartilage and production of chondrocytes, yet the cellular populations that organize this process remain incompletely defined. Here we identify a Wnt-responsive fibrocartilage progenitor population that contributes to postnatal mandibular condylar cartilage growth. Using a direct Wnt activity reporter (R26-WntVis), inducible genetic lineage tracing (Axin2CreERT2), and single-cell transcriptomics, we define a Wnt-enriched progenitor-like cluster localized predominantly within the fibrocartilage zone. Lineage tracing demonstrates that Axin2-lineage cells expand laterally within fibrocartilage and generate vertically aligned chondrocytes in the chondrocartilage compartment, indicating bidirectional growth contribution in vivo. Conditional ablation of {beta}-catenin in Axin2-lineage cells results in depletion of the fibrocartilage compartment and premature activation of chondrogenic differentiation programs, whereas constitutive {beta}-catenin activation disrupts compartmental organization without enhancing proliferation. Mechanistically, we identify Foxm1 as a Wnt-associated proliferative mediator enriched in fibrocartilage, and genetic reduction of Foxm1 cooperates with {beta}-catenin deficiency to impair condylar growth. In parallel, {beta}-catenin loss derepresses TGF-{beta}-Smad signaling and enhances chondrogenic differentiation, indicating that canonical Wnt activity coordinates proliferative maintenance while restraining lineage commitment within the same cellular compartment. Together, these findings identify a Wnt-responsive fibrocartilage progenitor system that regulates postnatal mandibular condylar cartilage growth by coupling Foxm1-associated proliferative maintenance with suppression of TGF-{beta}-dependent chondrogenic differentiation during temporomandibular joint development. Graphical abstractWnt-responsive fibrocartilage progenitors coordinate postnatal mandibular condylar cartilage growth through Foxm1-dependent proliferative maintenance and suppression of TGF-{beta}-driven chondrogenic differentiation.

developmental biology↗

bioRxiv2026

Two-step polar plastid migration via F-actin and microtubules ensures unequal inheritance during asymmetric division of Arabidopsis zygote

The zygote is the origin of development, and in most angiosperms, it divides asymmetrically to establish the apical-basal axis. In Arabidopsis thaliana, various organelles in the zygote undergo polar migration along actin filaments (F-actin), resulting in unequal inheritance, but the behavior of plastids, essential precursors of chloroplasts, has remained unclear. Here, using quantitative live-cell imaging, we reveal that plastids undergo two-step polar migration: they first move apically together with the nucleus along F-actin, and when nuclear migration slows, they switch to microtubule (MT)-dependent migration to move further apically. This results in unequal plastid inheritance by the apical cell. Although these plastids are amyloplasts containing starch granules, starch is dispensable for migration, unlike the gravity response. Instead, a fertilization-activated MAP kinase pathway is required for polar plastid migration. Our results demonstrate that the zygote possesses a spatiotemporal regulatory mechanism that ensures unequal plastid inheritance at the onset of plant ontogeny.

plant biology↗

bioRxiv2025

TMEM2 maintains hyaluronan turnover and cartilage homeostasis during early osteoarthritis progression

Osteoarthritis (OA) is a degenerative joint disease characterized by progressive disruption of the cartilage extracellular matrix (ECM), yet the molecular mechanisms governing ECM turnover during disease initiation remain incompletely defined. Hyaluronan (HA) is a major structural component of articular cartilage, and its regulated turnover is essential for maintaining tissue integrity. Transmembrane protein 2 (TMEM2) is a cell-surface hyaluronidase capable of degrading high-molecular weight HA under physiological conditions, but its role in joint tissues has remained unclear. Here, we examine the spatiotemporal expression and functional contribution of TMEM2 in articular cartilage using single-cell transcriptomic analysis, histological approaches, and a chondrocyte-specific conditional knockout mouse model. Under physiological conditions, Tmem2 was predominantly expressed in non-calcified articular chondrocytes. Following joint destabilization, Tmem2 expression was transiently increased during early osteoarthritis, coinciding with reduced cartilage HA content, consistent with altered HA turnover. Importantly, genetic ablation of Tmem2 in chondrocytes markedly exacerbated osteoarthritis progression, resulting in accelerated cartilage delamination, increased chondrocyte apoptosis, reduced proliferative activity, and enhanced hypertrophic differentiation. These changes occurred without detectable abnormalities in the synovium, subchondral bone, or osteophyte formation, indicating a cartilage-intrinsic phenotype. Collectively, these findings identify TMEM2 as an important regulator of hyaluronan homeostasis within the cartilage ECM and provide in vivo genetic evidence that TMEM2- dependent HA turnover contributes to the maintenance of articular cartilage integrity during osteoarthritis progression.

molecular biology↗

bioRxiv2024

Cluster effect through the oligomerisation of bioactive disaccharide AMOR on pollen tube capacitation in Torenia fournieri

ABSTRACRTArabinogalactan proteins (AGPs) are plant-specific glycoproteins involved in cellular mechanics and signal transduction. There has been major progress in understanding the structure, synthesis, and molecular functions of their carbohydrate chains; however, the mechanisms by which they function as signalling molecules remain unclear. Here, methyl-glucuronosyl arabinogalactan (AMOR; Me-GlcA-{beta}(1,6)-Gal), a disaccharide structure at the end of AGP carbohydrate chains, was oligomerised via chemical synthesis. The biological activity of AMOR oligomers was enhanced via clustering of the carbohydrate chains. Furthermore, AMOR oligomers yielded a pollen tube morphology (i.e., callose plug formation) similar to that when cultured with native AMOR, suggesting it may be functionally similar to native AMOR.

biochemistry↗