Abstract The mouse masseter muscle comprises distinct superficial and deep layers, but the tendinous tissue located between these layers remains poorly characterized. In this study, we investigated the anatomical, molecular, and ultrastructural characteristics of this tissue. Serial anatomical and histological analyses demonstrated that the intramuscular tendon (IMT), located between the superficial and deep masseter layers, was anatomically distinct from the superficial aponeurosis–external tendon complex. These structures also exhibited different skeletal attachments: the aponeurosis–external tendon complex attached to the maxilla, whereas the IMT attached to the mandible. Spatial transcriptomic analysis revealed different gene‐expression patterns between the aponeurosis and IMT, with several extracellular matrix‐related transcripts, including Col16a1 , Col13a1 , Col5a2 , Tnn , Postn , and Col22a1 , showing relatively higher expression in the IMT. Within the IMT, several transcripts showed preferential distribution toward the bone‐side region, where immunofluorescence analysis demonstrated significantly higher POSTN immunoreactivity than in the middle‐ and lateral‐side regions. BGLAP exhibited a similar but statistically nonsignificant pattern, whereas COL22 was predominantly localized along the myotendinous junction. Transmission electron microscopy revealed distinct cellular characteristics between the middle‐ and lateral‐side regions. In the lateral‐side region, spindle‐shaped cells were observed, some of which were oriented toward the tendon interior. In contrast, the middle‐side region contained cells with elongated cytoplasmic processes extending toward neighboring cells, forming apparent intercellular contacts. IMT‐like tendinous structures were also observed in the jaw muscles of spiny dogfish, Cynops pyrrhogaster , and Xenopus laevis . Together, these findings demonstrate that the mouse masseter IMT is anatomically distinct from the superficial aponeurosis and exhibits regional molecular and ultrastructural heterogeneity. This characterization of the normal IMT may provide an anatomical and molecular reference for future investigations into masticatory muscle‐tendon‐aponeurosis hyperplasia (MMTAH).
Abstract Diabetic foot ulcers (DFU) are debilitating chronic wounds which affect up to a third of diabetic patients. Due to the underlying diabetic pathophysiology, normal wound healing is perturbed. In particular, there is insufficient re‐vascularisation of the wound bed, ultimately leading to the development of chronic wounds. Current treatment protocols are insufficient to stimulate re‐vascularisation and wound closure, ultimately leading to ~20% of patients with a DFU requiring lower limb amputation. Extracellular matrix (ECM)‐derived biomaterials have demonstrated great promise to promote tissue vascularisation and wound repair. In the present study, the overarching goal was to develop a decellularised ECM from human induced pluripotent stem cell (hiPSC)‐derived vascular cells, and incorporate it into a hyaluronic acid‐based hydrogel for wound healing. Vascular differentiation of hiPSCs yielded a heterogenous population containing both CD31 expressing endothelial cells (iEC), and CD31‐negative stromal cells (iSC). ECM deposition by iSCs was stimulated by treatment with ascorbic acid and macromolecular crowder carrageenan. Post‐decellularisation, the ECM composition was analysed by immunofluorescent and histological staining, indicating the presence of ECM components such as fibronectin, fibrillar collagens, perlecan and glycosaminoglycans, all having implications in angiogenic processes. Decellularised ECM accelerated the capacity of iECs to form tube‐like structures when added to cell culture media in 2D. Decoration of hyaluronic acid (HyA)‐based hydrogels with this decellularised ECM enhanced metabolic activity and attachment of both HUVECs and human dermal fibroblasts seeded on these hydrogels. Taken together, this ECM‐decorated HyA‐based hydrogel has the potential to enhance angiogenesis and revascularisation in chronic wound applications such as DFU.
Abstract Among modern aquatic amniote clades that evolved pelagic locomotion, whales are a prime example, but timing and mode of evolutionary changes in their swimming are poorly understood. Here, we use 3D vertebral microanatomy derived from CT scanning to investigate swimming patterns in extinct whales. All vertebral centra from a single specimen of the extant common dolphin Delphinus delphis were used to provide a baseline for the correlation of microanatomical parameters and spinal movements in our dataset of fossil whales. We find that bone anisotropy, and to some extent bone compactness, mirrors the amount of compression and movement in vertebral regions. We use these parameters to infer regional movements and thus swimming mode for several lineages of stem cetaceans ( Natchitochia jonesi , Pachycetus wardi , Zygorhiza kochii ) and crown cetaceans ( Maiabalaena nesbittae, an undescribed Oligocene odontocete and a modern minke whale). Natchitochia jonesi could walk on land, whereas Pachycetus wardi and Zygorhiza kochii were obligately aquatic, but show more spinal flexibility than modern taxa. The early Oligocene mysticete and odontocete differ in microstructural properties and might have experienced a different trajectory towards their extant bauplans. Overall, microanatomical data confirm increasing pelagic specializations in cetacean evolution that include a stiffer torso, but our data also highlight modular patterns of compactness within vertebral regions. Our approach is promising for future use of three‐dimensional vertebral microanatomical data to understand locomotory patterns.
The flexor digitorum brevis (FDB) is a key intrinsic foot muscle that contributes not only to toe flexion but also to energy absorption and generation during bipedal locomotion in humans. Despite its functional importance, the homology among hominid species and morphological alterations during evolution in each species of the FDB remain insufficiently understood. A more detailed morphological analysis, particularly a comparative analysis of origin sites and innervation, is necessary to clarify the homology of FDB among hominids. In this comparative anatomical study, the feet of eight humans, three chimpanzees, and three orangutans were analysed. In humans, the FDB typically originates from the calcaneal tuberosity and plantar aponeurosis and is innervated by the medial plantar nerve (MPN). However, in one case, dual innervation from both the medial and lateral plantar nerves (LPNs) was observed. The accessory muscle belly from the flexor digitorum longus tendon, found in four human cases, was inserted variably into digits IV and/or V, similar to the FDB tendon, and was innervated by the MPN in all cases. In chimpanzees, the FDB originates from two sites, the calcaneus and flexor digitorum tibialis (FDT) tendon, both innervated by the MPN in all cases. In one orangutan specimen, the FDB was divided into two bellies originating from the calcaneus: one inserted into digit II and was innervated by the MPN, while the other merged with the flexor digitorum fibularis tendon to digit III and received dual innervation from both the medial and LPNs. In another orangutan case, the FDB originated from the calcaneus as a single muscle inserted into digits II-IV and was innervated by the MPN, with the accessory belly from the FDT tendon innervated by the LPN. The third orangutan case showed a single FDB into digits II-IV innervated by the MPN and dual innervation of the muscle belly originating from the FDT tendon via the medial and LPNs. These findings suggest that the dual-origin sites and innervation of the FDB, which was previously considered a variation in humans, may be a common morphological feature shared by hominids. The combination of dual-origin sites and innervation accounts for the greater diversity of the muscle compared with those with a single origin site or innervation. The characteristics in humans may be consistent with the morphological alterations of the foot, which are adaptations to habitual bipedal locomotion, such as a robust and posteroinferiorly elongated calcaneal tuberosity and a medial shift of the functional foot axis.
Abstract Fragmentary skull remains are common in zooarchaeological assemblages, yet they pose significant challenges for taxonomic identification because complete skulls are rare. This study investigated whether three resilient cranial regions: the body of the maxilla, the exoccipital region, and the bony palate, retain sufficient shape information to discriminate among caprine taxa. The sample comprised domestic sheep ( Ovis aries ), wild Marco Polo sheep ( Ovis ammonpolii ), domestic goat ( Capra hircus ), and Tatra chamois ( Rupicapra tatrica ). Three‐dimensional landmarks were digitized on surface‐scanned skulls. All three regions exhibited significant inter‐group shape differences ( p : 0.0001). The body of the maxilla provided the strongest discrimination ( R 2 = 0.520), clearly separating ovine from caprine taxa along an axis linked to the relative position of the caudodorsal facial‐orbital region versus the infraorbital and alveolar sectors. The exoccipital region showed intermediate discriminatory power, whereas the bony palate exhibited the weakest group structure and the greatest overlap. Centroid size differed significantly among groups (wild sheep being the largest), but shape differences remained significant after accounting for size. Isolated skull fragments, particularly the maxillary body, retain reliable diagnostic shape information for distinguishing caprine taxa. When analyzed using geometric morphometrics, these fragments can serve as valuable analytical units in zooarchaeological studies, even in highly fragmented assemblages.
