Biology subjects

Tojima, S.

Publications and source records attributed to Tojima, S..

4 recordsLinked to original sources

bioRxiv2026

Three-dimensional imaging reveals distinct muscle-vessel-nerve relationships during dorsal and ventral muscle splitting in the chicken forelimb

During vertebrate limb development, muscles, blood vessels, and nerves undergo coordinated morphogenesis. Limb muscles form through progressive splitting of the dorsal and ventral muscle masses, but the three-dimensional relationships between muscle splitting and surrounding tissues remain incompletely understood. Although blood vessels have been implicated in muscle splitting, whether this association is shared among different muscle masses is unclear. Here, we established a three-dimensional imaging approach for chicken embryonic forelimbs by combining fluorescent vascular labeling, whole-mount immunostaining, tissue clearing, and confocal microscopy. We compared three hydrophilic clearing methods, ScaleS, CUBIC, and SeeDB2, for compatibility with fluorescent ink, LCA-lectin, and PKH26 vascular labeling. SeeDB2 preserved all three vascular signals. We then developed a modified SeeDB2 protocol incorporating blood decolorization and used it to examine muscle, vessel, and nerve relationships from E5.0 to E6.0. In the ventral muscle mass, multiple vascular extensions were observed around the splitting region at E5.5. In contrast, no prominent vascular extension was detected around the splitting region of the dorsal muscle mass despite ongoing splitting at the same stage. Nerve projections also showed distinct spatial patterns between the dorsal and ventral muscle masses. These findings indicate that vascular extension is not a universal feature of limb muscle splitting and suggest that individual splitting events occur within distinct local tissue environments. Our three-dimensional approach provides new morphological insight into the coordinated development of muscle, vasculature, and peripheral nerves in the embryonic limb.

developmental biology↗

bioRxiv2026

Morphological characteristics of the forelimb flexor digitorum muscles and their distinctive innervation pattern in koalas (Phascolarctos cinereus): implications for function and morphogenesis

Koalas (Phascolarctos cinereus) are marsupials highly specialized for arboreal life and are considered a representative example of convergent evolution with primates, which are also adapted to arboreal habitats. The forelimb digital flexors play a crucial role in arboreal locomotion by flexing the digits and enabling the claws or fingers to engage with tree trunks and branches. Although the morphology and function of the digital flexors have been extensively examined in primates, anatomical information on koala digital flexors has not been sufficiently updated in modern anatomical studies. In this study, we examined the digital flexor muscles and their innervation in four forelimbs from three koalas to clarify both shared and distinctive structural features among arboreal mammals. The flexor digitorum profundus (FDP) was markedly developed, formed a U-shaped muscle belly, and received dual innervation from the median and ulnar nerves. In contrast, the flexor digitorum superficialis (FDS) was small, arose from the superficial surface of the FDP, was partially enclosed by the FDP muscle belly, and gave rise to extremely slender tendons inserting into digits II-V. The branch supplying the FDS arose from the main trunk of the median nerve near the carpal region, ascended proximally in a recurrent course, and terminated within the FDS. This unusual course may be consistent with a morphogenetic process underlying FDS formation. These findings indicate that the koala digital flexors are characterized by a markedly developed FDP, a relatively reduced FDS, and a distinctive innervation pattern of the FDS. Thus, even among mammals adapted to arboreal life, koalas and primates appear to have achieved arboreal adaptation through different morphological specializations within the forearm digital flexor system.

zoology↗

bioRxiv2026

Disruption of Histone H4C genes impairs skeletal development and cortical neurogenesis, modeling rare neurodevelopmental syndromes

Histone proteins, which reside in the nuclei of eukaryotic cells, are involved in diverse cellular processes. The core histone H4 serves as a structural component of the nucleosome. Patients carrying mutations in H4Clustered histone (H4C) genes exhibit a broad spectrum of developmental abnormalities, including short stature, microcephaly, intellectual disability, growth retardation, and digital anomalies. However, the impact of H4 mutations on mammalian embryogenesis remains largely unclear. Here, we demonstrate that histone H4C genes play crucial roles in skeletal development and cortical neurogenesis. We found that mRNAs of the histone H4C gene family are specifically expressed in proliferating progenitor cells in the developing mouse neocortex and in human induced pluripotent stem cell-derived cortical organoids. CRISPR-mediated disruption of H4C3 in mice caused severe defects in skeletal formation and neocortical neurogenesis. Furthermore, overexpression of a mutant form of H4C3 resulted in altered expression of genes associated with cellular migration and motility. Together, these findings suggest that histone H4 plays a critical role in regulating the balance between proliferation and differentiation during mammalian embryonic development, thereby explaining the broad spectrum of patient phenotypes.

developmental biology↗

bioRxiv2021

Gross anatomy of the gluteal and posterior thigh muscles in koalas based on their innervations

There are not many descriptions of the muscle morphology of marsupials, despite the fact that they should show diversity according to the adaptation and dispersal to a variety of environments. Most of the previous studies regarding the gross anatomy of marsupials were conducted in the 1800 - 1900s, and many issues still remain that need to be reexamined. For instance, the muscle identification had been performed based only on their attachments and thus, muscle descriptions are often inconsistent among the studies. These classic studies often do not include figures or photographs, so the discrepancies in the descriptions of the muscles could only be verified by performing the muscle identification again with a more reliable method. This problem can be solved by performing muscle identification by innervation. This method, which focuses on the ontogenic origin of the muscle as opposed to the attachment site, is prone to individual and interspecies variation and is a common technique in recent anatomical research. This technique is more reliable than previous methods and is suitable for comparison with other taxa (i.e., eutherians). In this study, we first conducted muscle identification based on innervation in the gluteal and posterior thighs of koalas in order to reorganize the anatomical knowledge of marsupials. This is because the gluteus and posterior thighs of koalas are the areas where previous studies have been particularly inconsistent. We dissected five individual koalas and clarified discrepancies in previous studies, as well as investigated the unique muscle morphology and their function in koalas. Specifically, the koalas gluteal muscle group is suitable for abduction, while the posterior thigh muscles are particularly suitable for flexion. In the future, we will update the anatomical findings of marsupials in the same way to clarify the adaptive dissipation process of marsupials, as well as to contribute to the understanding of the evolutionary morphology of mammals.

zoology↗