Journal of Anatomy最新文献

Down syndrome (DS) is caused by an extra copy of human chromosome 21 (HSA21) and is associated with significant craniofacial anomalies among other systemic traits. While animal models have been pivotal in advancing DS research, most of the mouse models replicate only a portion of the human genetic condition. The recently developed transchromosomic rodent models of DS, TcMAC21 mice, and TcHSA21rat carry nearly complete copies of HSA21q and all of HSA21, respectively. While both TcMAC21 and TcHSA21rat express DS-like craniofacial malformations, no comprehensive interspecies comparisons have been conducted between the two. Here, we quantitatively compare the craniofacial skeleton of TcMAC21, TcHSA21rat, and their respective unaffected littermates using high-resolution micro-computed tomography images, landmark-based geometric morphometrics, and advanced multivariate statistics to assess overall craniofacial shape and integration patterns between the neurocranial and facial components. Both models reflect the craniofacial morphology of DS, exhibiting increased neurocranial globularity (supero-inferiorly) and overall facial retraction (anteroposteriorly). However, the rat model expresses a more prominent brachycephalic phenotype compared with its murine counterpart. The integration between the cranial components was found to be evolutionarily conserved across species; however, the trisomic animals maintained their distinct DS-specific configuration compared with their euploid littermates. Our findings establish a methodological framework for cross-species comparisons in DS animal models and provide important insights into characteristic manifestations of trisomy 21 and evolutionarily conserved aspects of the mammalian craniofacial skeleton.

The auditory cortex is central to auditory perception, but its detailed structural organization in sheep (Ovis aries) has not been thoroughly investigated. In this study, we sought to address this gap by providing an in-depth anatomical description of the cytoarchitecture and myeloarchitecture of the sheep auditory cortex, using cresyl violet staining and the neurochemical markers myelin basic protein and parvalbumin. Cresyl violet tissue samples from four sheep were used to characterize cortical layers and cellular composition, revealing a six-layered organization with variations in cell density and distribution. Myelin basic protein staining highlighted myelinated regions, while parvalbumin staining identified the distribution of a subpopulation of GABAergic interneurons, indicating the potential location of the primary auditory cortex. Overall, the organization of the ovine auditory cortex aligns with findings in other mammals, suggesting a conserved neural architecture across species and supporting the idea of evolutionary conservation in auditory processing mechanisms.

The temporomandibular joint (TMJ) plays a key role in facilitating complex mammalian jaw movements required for daily life. It is formed between the condylar process of the mandible (or dentary bone) of the lower jaw, the glenoid (or mandibular) fossa of the squamosal/temporal bone in the upper jaw and an interposed fibrocartilage disc. Structural defects in any component of the TMJ can disrupt the entire joint, contributing to TMJ disorders. Embryonic defects in the condyle in mice have been shown to have an impact on the shape and development of the glenoid fossa, highlighting the importance of coordinated development of the two sides of the joint. Although recent research has focused on the condylar process, much less is known about the development and homeostasis of the glenoid fossa, and defects in the glenoid fossa are also evident in disease. Here, we have analysed the formation and molecular identity of the glenoid fossa using the mouse as a model. Our findings revealed distinct patterns of development of the fossa in the anterior, middle and posterior regions. Interestingly, the cartilage marker Sox9 was transiently expressed in the lateral branch of the glenoid fossa during early TMJ development, and the loss of Sox9 in Wnt1-cre;Sox9fl/fl mice resulted in the absence of this part of the fossa. Postnatal maturation of the murine glenoid fossa was marked by the initiation of a fibrocartilage layer, the formation of which coincided with the onset of independent feeding, suggesting a role for mechanical force in glenoid fossa fibrocartilage induction. In contrast to the condyle, the fossa fibrocartilage expressed low levels of FSP1, a marker of the stem/progenitor population of the condyle. Depletion of FSP1-positive cells by conditional diphtheria toxin activity in FSP1-Cre;DTA mice has previously been shown to cause a severe TMJ osteoarthritis phenotype and enlargement of the condylar head postnatally. Interestingly, here, we show that in reaction to changes in condylar shape, these mutants develop an increase in glenoid fossa angulation over time, associated with increased remodelling activity, particularly in the lateral branch of the fossa. These findings highlight that the fibrocartilage of the glenoid fossa and condyle are not equivalent and that changes in the condyle can have a knock-on secondary effect on the 3D structure of the fossa. This coordinated response would allow for alignment of the TMJ, maintaining function throughout life, even in the case of disease.

Cover image: see A. Griffing et al., ’Diversity and development of the hemibacula of croaking geckos (Sphaerodactylidae: Aristelliger)‘, this issue.

Psittaciformes have a broad distribution across the southern hemisphere, and this wide ecological range is coupled with high levels of morphological diversity, particularly in the skull and beak structure, which has been previously linked to diet and body size. This paper studies how the beak and cranial shape vary in relation to predominant diet across a broad taxonomic range of parrots, using 2D geometric morphometric techniques and regression analyses. The data suggest that whilst there are some levels of significance between diet and beak shape, body mass was a much stronger co-variate. This indicated that skull morphology is more likely explained by parrot body mass and that whilst diet may partially explain beak shape in parrots when compared to other avian groups, it is not determining beak shape within the clade. Further study into other factors related to beak morphology, such as bite force, may prove key in explaining the evolutionary forces shaping the skull in parrots and other birds.

Proximal femoral medullary canal morphology is a key determinant of cementless stem fit, primary stability, and load transfer in total hip arthroplasty (THA), yet population-level three-dimensional characterization remains limited. This study was designed to quantify variability in canal geometry and to capture dominant anatomical modes of variation with statistical shape modeling (SSM). Computed tomography data from 763 candidates for primary THA (389 female, 374 male; 20-92 years) were analyzed. Endosteal contours of the proximal canal were processed to build a point-correspondent SSM by principal component analysis (PCA). Five geometric features were evaluated per specimen: equivalent radius (normalized), roundness, major-axis angle (torsion), flare index, and curvature. Substantial inter-individual variability was observed across all features, with differences by sex and age. The first three principal components accounted for 68.4% of total variance, and each showed interpretable associations with at least one geometric feature. Model behavior was examined by synthetic sampling within ±2 SD (specificity) and by 10-fold cross-validation (generalization), indicating faithful reconstruction of real shapes and stable performance on held-out data. These findings provide a compact description of proximal canal shape variation and its key geometric drivers. The resulting population map is expected to support implant selection and sizing in preoperative planning, inform shape-based classification, and guide design envelopes for standard and personalized stems, with potential efficiencies in manufacturing and material use.

Bone remodeling is the fundamental process of internal turnover through which bone tissue is renewed, repaired, and maintained. Achieved by the spatially and temporally coordinated actions of the basic cellular unit (BMU), this process is intimately linked to age-related increases in cortical porosity, which could be attributed to the imbalance or uncoupling between resorption and formation. Classically, the space carved out by the BMU is depicted to have a cutting cone tunneling through the bone matrix, and a tapering closing cone being filled in with new bone. The morphology of these spaces can reflect the dynamics of the BMU, where excess resorption leads to an enlarged cutting cone, decreased formation results in a shortened closing cone and larger Haversian canal diameter, and the uncoupling or delayed coupling creates a prolonged transition zone between resorption and formation. Using a micro-CT imaging modality that allows for three-dimensional visualization of remodeling events, we hypothesized that with aging, remodeling spaces would exhibit evidence of imbalance and/or uncoupling and this pattern would be more pronounced in women due to the effect of menopause. Micro-CT scans of anterior femoral midshaft specimens from 58 human donors (22 females, 36 males; age range: 20-82 years) were analyzed, yielding a total of 184 remodeling spaces with classically described morphology (a cutting cone followed by a closing cone and then a canal with stable diameter). Lengths and radii representative of the 3D size and shape of the remodeling spaces were measured and analyzed. Results showed that remodeling space morphology exhibits great inter and intraindividual variation, while no differences in the distribution of any measurements were found between sexes. Counter to our hypothesis, remodeling space dimensions decrease with increasing age, and no linear relationship between transition zone length and age was found. Rather, transition zone length was longer in older females but also in younger males, potentially indicating different underlying mechanisms causing prolonged transition zones, with the caveat that this pattern is only significant after removal of outliers. This study was the first to demonstrate the value of 3D analysis at the level of individual remodeling spaces in human cortical bone. Sex and age differences in morphology (or the lack thereof) indicate the intricate interplay of local and systemic controls from different mechanical, hormonal and cell senescence factors on remodeling dynamics, and the potential existence of seemingly normal remodeling events superimposed against the backdrop of overall progressive age-related bone loss. Importantly, our focus on classical remodeling space morphology excludes irregular patterns arising from interconnecting or coalescing pores and trabecularization of the cortex, which is a main limitation to be considered.

The Late Permian Weigeltisauridae are the world's first gliding reptiles, but much remains unknown regarding the anatomy of their patagium (or wing), which, in turn, confounds our understanding of their gliding mechanism and paleobiology. Here, we examine the morphology and osteo-histology of the patagial skeleton of weigeltisaurids using an array of imaging techniques and several thin sections through the wing skeleton of a specimen of Weigeltisaurus from the Late Permian of Germany. We demonstrate that patagials and gastralia share a one-to-one articulation, permitted by the uniquely specialized anatomy of the lateral gastralia. We also show, based on skeletal anatomy, histology, and inferred musculoskeletal relationships, that patagials are likely neomorphic ossifications and are thus not strictly homologous to the gastralia. We provide the first reconstruction of the musculoskeletal anatomy of the weigeltisaurid wing, suggesting that the base of the patagials was likely embedded in the M. obliquus externus group. Similar to the condition in the extant flying lizard Draco, these muscles may have contributed to the unfolding of the patagium, which was likely supported by hooking the manual claws onto the leading edge of the patagium. This would have provided weigeltisaurids with a means to maintain the patagium expanded and under tension while gliding, as well as some measure of control of the dihedral angle of the wing, thereby offering a means to control stability and maneuverability in flight. Wing folding may have been permitted by muscular and tendinous connections between the elements of the patagial skeleton, generating elastic tension toward a folded state, as in Draco. Lastly, the cross sections of the patagials show a bimodal cortical distribution with much thicker cortices along their cross-sectional long axis than short axis. This made the patagials rigid, which likely helped prevent patagial collapse during gliding. This work represents a critical step toward understanding the wing structure and gliding mechanism in weigeltisaurids, paving the way for future morphofunctional or biomechanical studies on the locomotion of the world's first flying vertebrates.