Abstract CADM1 and CADM2 are cell‐adhesion molecules with likely roles in cell migration, axon guidance and synapse formation. Both are considered potential susceptibility genes for various neurodevelopmental disorders. However, their expression patterns in early human brain development have not been explored. Here we employed transcriptomics, RNAScope in situ hybridisation (ISH) and immunofluorescence (IF) to determine the time course and location of expression in the human cerebral cortex and thalamus between 7.5–17 postconceptional weeks (PCW). In the cerebral cortex, tissue RNAseq revealed both to be highly expressed throughout this period. CADM1 exhibited very high expression which declined slightly with age. CADM2 exhibited high expression which increased over time. Single‐cell RNA‐seq and ISH revealed that both genes were co‐expressed in most cells; however, IF revealed different patterns of cellular localisation. At 8 PCW, expression for both CADMs was similar throughout the cortex and predominantly located in the cytoplasm/cell surface in the cortical plate (CP) but with stronger expression of CADM1 in the subventricular zone. However, from 10 PCW onwards, the strongest immunoreactivity for CADM1 was in the cell nucleus with weak cytoplasmic localisation, whereas CADM2 was expressed on the cell surface and increasingly in axons with age. By 17 PCW, CADM2 exhibited strong immunoreactivity in the thalamocortical and callosal corticocortical axons but was weakly expressed in corticofugal pathways. In the thalamus, CADM2 expression in posterior and lateral projection neurons contributing to thalamocortical pathways was confirmed. CADM1 and CADM2 show differential expression in the thalamus and associated nuclei, suggesting a role in their segregation; CADM1 favouring anterior and medial thalamic nuclei and the ventromedial subthalamus, CADM2 the lateral habenula, lateral and posterior thalamus and dorsolateral subthalamus. CADM1 and CADM2 may play important and varied roles in early fetal human forebrain development, guiding cell migration and aggregation, and axon guidance and fasciculation.
Very little is known about the early brain evolution of Metatheria, and no brain endocast of this group has been described from prior to the Cretaceous-Paleogene (K-Pg) boundary. This has led to great uncertainty regarding the ancestral condition of the therian brain. Here, we aim to fill some of this gap by describing the first brain endocast of a Cretaceous metatherian, Lotheridium mengi from the Late Cretaceous of Henan, China. Lotheridium has an encephalization quotient comparable to the Cretaceous multituberculate Chulsanbaatar and eutherian Asioryctes and reaches the lower range of crown mammals. Together with patterns observed in other Mesozoic mammals, this suggests that increased encephalization evolved independently in several major mammalian lineages. The endocast is characterized by relatively small olfactory bulbs, well-developed petrosal lobules, and a prominent hypophyseal cast, differentiating it from earlier mammals. With the addition of a dorsally exposed midbrain, Lotheridium closely resembles the condition observed in Cretaceous eutherians. We propose that reduced olfactory bulb proportions and increased endocranial volume in Cretaceous eutherians and metatherians reflect a major shift in mammalian brain evolution, from primarily olfactory bulb expansion in the Jurassic to predominantly neocortical, brainstem, and cerebellar expansion in the Late Cretaceous. The endocranial morphology of Lotheridium further indicates that several neuroanatomical features characteristic of Paleogene and extant marsupials, including relatively enlarged olfactory bulbs and a smaller brain size compared to eutherians, are unlikely to represent the plesiomorphic condition for Metatheria. Ultimately, Lotheridium provides crucial new information regarding the ancestral condition of marsupial brains.
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.
