Journal of Anatomy

The human bony labyrinth has attracted increasing interest because of its taxonomic, evolutionary, and functional significance. Although sexual dimorphism has been reported in several aspects of the temporal bone, the extent to which sex, age, size, and allometry contribute to labyrinth shape variation remains poorly understood. Here, we investigated patterns of sexual shape variation in the human bony labyrinth using three-dimensional geometric morphometrics in a sample of 98 archaeological individuals from South America with known genomic sex. Centroid size and allometric effects were assessed in a subset of 90 individuals with comparable metric scaling. In addition to analysing the complete labyrinth, the cochlea and semicircular canals were examined separately to evaluate region-specific patterns of sexual shape variation. Principal Component Analysis showed extensive overlap between females and males, and overall labyrinth shape did not differ significantly between sexes. Males exhibited significantly larger labyrinths than females, and centroid size explained a small but significant proportion of overall shape variation. Regional analyses showed no evidence of significant sexual shape differences in the cochlea or in any individual semicircular canal when analysed separately. In contrast, the combined semicircular canal system exhibited subtle but significant sexual shape variation independent of centroid size, whereas morphological disparity did not differ between sexes. The geometric comparison of the female and male consensus configurations further showed that sexual shape variation was regionally heterogeneous. Whereas the cochlea exhibited a pattern of localized changes with low directional coherence, the semicircular canals displayed more coordinated regional shape changes. The male consensus also exhibited slightly higher canal circularity across all three semicircular canals, particularly the posterior canal, while differences in canal-plane orientation remained minimal. These findings demonstrate that sexual shape variation in the human bony labyrinth is subtle and anatomically partitioned among its components. Although significant sex differences in centroid size were detected across most anatomical regions, overall labyrinth shape and cochlear morphology were primarily influenced by allometry, whereas significant sex-related shape differences were detected only when the semicircular canals were considered as an integrated anatomical system. These findings demonstrate that sexual dimorphism in the human bony labyrinth is subtle but regionally heterogeneous, with the cochlea and semicircular canals exhibiting distinct patterns of shape variation, suggesting that these structures are influenced by different developmental, functional, and evolutionary processes.

Background: In humans, haploinsufficiency of TWIST1 leads to Saethre-Chotzen Syndrome, characterized by limb abnormalities and craniofacial defects. In mouse, Twist1 promotes limb bud outgrowth via maintenance of the apical ectodermal ridge (AER), in addition to its craniofacial roles. In zebrafish, two twist1 paralogs, twist1a and twist1b, are known to influence cranial neural crest and cranial suture development but have not yet been implicated in limb formation. Results: We find that twist1a and twist1b act redundantly during zebrafish pectoral fin development. While twist1b mutants have normal fins, twist1a mutants have small fins, and twist1a;twist1b double mutants lack fins. These defects appear to originate with impaired establishment of the pectoral fin field, followed by failure of AER formation, likely due to reduced fgf10a expression in the fin mesenchyme. Anterior-posterior patterning of the fin bud is relatively normal in twist1a mutants and twist1a;twist1b double mutants, albeit with an anterior extension of shha expression in some embryos. Conclusions: Together, our results show that twist1a and twist1b play crucial and overlapping roles in zebrafish pectoral fin development, echoing roles played by Twist1 in the mouse limb bud and highlighting an early impact of twist1 genes on the initial formation of the zebrafish forelimb field.

Tessellated calcified cartilage (TCC) is a hallmark of the chondrichthyan skeleton, yet its development early in ontogeny across the four major groups (batoids, galeomorphs, squalomorphs, and holocephalans) remains poorly understood. Specialised traits of TCC, such as multi-layered TCC and internal mineralised trabeculae, typically develop in response to feeding mechanics. In this study, we evaluated TCC morphology in the jaws of 12 representative taxa to observe its structure at an early ontogenetic stage to determine whether these specialised features had yet developed. Batoids consistently exhibited well-developed, homogeneous, polygonal tesserae early in ontogeny regardless of jaw morphology or feeding habit. In contrast, galeomorphs displayed high morphological heterogeneity. Notably, we document the first report of an extensive internal trabecular network in a non-batoid elasmobranch, observed in Ginglymostoma cirratum, which may serve to resist the mechanical pressures of specialised suction feeding. Furthermore, we identified voussoir tesserae in galeomorphs for the first time, extending their documented presence across all elasmobranch groups, where they display an inverted aspect ratio (wider than tall) compared to mature forms. The durophagous Mustelus mustelus exhibited surprisingly poor TCC development despite being a durophagous feeder, pointing to a pronounced ontogenetic lag. In Squatina oculata, TCC was characterised by large and thick tesserae and extensive fused tesseral regions which may relate to its explosive ambush predation mode, whereas the holocephalan Chimaera exhibited a poorly mineralized, mesh-like structure without resolvable discrete tesserae or trabeculae-matching findings from previous studies. Across all specimens, multi-layered TCC was absent, confirming that multi-layering develops later in ontogeny. These results demonstrate that generalised models of TCC development based on one group or a few taxa fail to capture the broader diversity of TCC morphology. It also opens up many exciting avenues for further study, and forms the basis for comparisons with fossil chondrichthyans, to investigate the evolution of TCC.

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.

Ecdysozoans is one of the most abundant and diverse groups of metazoans and grow through moulting the rigid exoskeleton that provided protection. But the moulting process is often dangerous, resulting in malformations or death. Injuries have been well documented in the calcitic exoskeleton of trilobites, some of which have been attributed to moulting complications when long spines are deformed. Injuries in trilobites are often found in the trunk rather than the cephalon, and abnormal genal spines are rarely documented. Here we examine injuries in eleven specimens of Olenoides serratus from the Burgess Shale (Cambrian, Wuluian) and demonstrate an increased frequency of genal spine malformations compared to other trilobites. The unusual pattern of malformations may be attributed to moulting injuries of the long and delicate genal spines in O. serratus. To moult, trilobites curved ventrally to press the anterior margin of their cephalon into the substrate and open the facial sutures. This process exerted force on the librigenae. To exit the exuvia, the genal spines were forced to bend as the old librigenae dipped ventrally along the anterior edge, resulting in the injured genal spines in O. serratus. A similar process of moulting resulting in injuries may be seen in other early Euarthropods.

Skeletal dysplasias can occur in animals, including humans, and are attributed to both environmental and genetic causes. As our understanding of the distinguishing phenotypes of different skeletal dysplasias improves, alongside elucidation of the mechanisms and genetic networks that contribute to skeletal development, identifying and controlling genetic mutations in livestock populations has become increasingly possible, including approaches beyond selective breeding alone. Within Scotland an 'achondroplasia' syndrome that was first described in the South Country Cheviot breed of sheep (OMIA 000004-9940), has continued to occur periodically within the same geographical locations, despite culling of affected lambs over many decades. Affected lambs exhibit rounded heads, short legs, a loss of hooves, abnormal stance and short twisted tails. As the condition has been observed in flocks and as progeny from specific ram and ewe matings, and cases have been co-twinned to normal siblings, this suggests a syndrome caused by a recessive genetic condition rather than environmental factors. Through homozygosity mapping and whole genome sequence analyses, we identified a 10 bp deletion in the open reading frame of the PRICKLE1 gene that encodes prickle planar cell polarity protein 1 and is essential for normal vertebrate embryonic development. We identified additional phenotypes present in affected lambs, including a loss of phalanges, neural tube defects, vertebral and articular chondrocyte defects, hair orientation differences and polycystic kidneys, consistent with a loss of PRICKLE1 function based on comparisons to mouse mutant lines. These findings enabled the development of a simple DNA test for the identified PRICKLE1 mutation that was made commercially available to facilitate the elimination of this genetic disease from sheep flocks.

Sexual dimorphism is a well-studied phenomenon in which males and females of a species exhibit different phenotypic characteristics. However, the degree of sexual dimorphism within a species may vary among populations and may be influenced by geographic factors such as seasonality, prey availability, and population density. In this study, we examined the effects of sexual dimorphism and geographic region on the craniomandibular morphology of bobcats (Lynx rufus) in Washington State. Using digital calipers, we measured 13 craniomandibular traits from 35 males and 42 females. We found that the degree of skull dimorphism does not differ between the eastern and western side of the Cascade Mountains. However, we found significant effects of sex and geographic region on craniomandibular morphology. Across the geographic regions, males were significantly larger than females in most craniomandibular traits, excluding postorbital constriction breadth (POC). After correcting for expected size differences, only condylobasal length (CBL) was disproportionately longer in males, indicating subtle shape dimorphism within this trait, that is largely unexplained by allometry. Mechanical advantage (MA) of the temporalis and masseter muscles did not differ between the sexes at the canine or the molar bite points. Comparisons between populations east and west of the Cascade Range revealed that while sex remains the primary indicator of overall size, there is a small regional effect on size as western bobcats are slightly larger than eastern bobcats. These regional differences highlight how environmental pressures including local prey availability and severe winter conditions may influence functional skull design. Future ecological and behavioral studies are needed to further clarify how these localized environmental drivers shape phenotypic variation across populations.

Study design Retrospective cohort study. Objectives To correlate Hounsfield unit (HU) values, using elliptical regions of interest (ROI), that can be easily defined in routine clinical practice with magnetic resonance imaging (MRI) T2-hyperintense area fraction, as a surrogate for paraspinal muscle fat infiltration and to establish specific HU screening thresholds that may be applied with standard picture archiving and communication system (PACS). Methods We included 136 patients (71 men; 61.0 {+/-} 15.4 years) who underwent preoperative computed tomography (CT) and MRI within an 8-week period. Elliptical ROI HU values were measured at L2/3 and L4/5 for erector spinae, multifidus, and psoas major. MRI T2-hyperintense area fraction (Otsu thresholding) served as the fat infiltration reference. Linear mixed-effects (LME) models were used to assess the HU-T2 association and level-specific receiver operating characteristic (ROC) analyses (lower HU value side; n=136 per muscle-level) to identify thresholds for [≥]30% and [≥]50% infiltration criteria. Results Intraclass coefficients = 0.709 (HU) and 0.857 (T2 fraction); Goutallier weighted kappa = 0.579. In the overall LME, {beta} was -0.880 HU per 1% T2-fraction increase (95% confidence interval -0.935 to -0.825; marginal R2 =0.502); the association was steeper in multifidus ({beta} = -1.020) than in erector spinae ({beta} = -0.753). Psoas major (R = -0.226) was excluded from ROC analyses. Difference between L2/3 and L4/5 HU cutoffs was ~20 HU. The [≥]50% criterion revealed higher discrimination. Conclusions Elliptical ROI-based HU measurements may reliably screen paraspinal muscle fat infiltration in erector spinae and multifidus using standard PACS. Specific thresholds may allow practical preoperative evaluation without additional costs or radiation.

Background: Acute osteoporotic vertebral fractures (OVFs) may be difficult to detect on conventional radiographs, particularly before substantial vertebral collapse occurs. Comparing supine and sitting lateral radiographs may reveal load-dependent vertebral mobility. This preliminary study evaluated the diagnostic accuracy of supine to sitting dynamic radiography for detecting MRI confirmed acute OVFs. Methods: This retrospective, single center diagnostic accuracy study included consecutive patients who underwent paired supine and sitting lateral radiography and MRI of the same spinal region between April 2024 and July 2026. Dynamic radiographs were interpreted by a board certified orthopedic and spine surgeon who was blinded to the MRI findings. MRI was independently interpreted by a second board certified orthopedic surgeon and served as the reference standard. The primary outcome was patient-level sensitivity and specificity. Vertebra level diagnostic accuracy was evaluated secondarily, with patient cluster bootstrap confidence intervals used to account for within patient correlation. Results: Sixty three patients (mean age, 80.6 years; 51 women [81.0%]) and 490 evaluable vertebrae were analyzed. MRI identified acute OVFs in 34 patients and 36 vertebrae. At the patient level, dynamic radiography yielded 31 true positive, no false-positive, three false negative, and 29 true negative results. Sensitivity was 91.2% (95% confidence interval [CI], 76.3%-98.1%), specificity was 100.0% (95% CI, 88.1%-100.0%), positive predictive value was 100.0%, negative predictive value was 90.6%, and overall accuracy was 95.2%. At the vertebral level, sensitivity was 91.7% (33/36; patient cluster bootstrap 95% CI, 81.3%-100.0%) and specificity was 100.0% (454/454). The three missed fractures involved T9, L2, and L3. No false-positive vertebrae were observed. Conclusions: Supine to sitting dynamic radiography demonstrated high patient level sensitivity and no observed false positive findings for MRI confirmed acute OVFs. It may provide a practical complementary diagnostic option when MRI is not immediately available. However, a negative dynamic radiographic examination does not exclude an acute fracture, and the apparent perfect specificity requires validation in larger, prospective multi-reader studies.

Abstract Background: Most animal models of HCM are mouse-based, but the thin interventricular septum in mice makes it difficult to clearly distinguish pathological hypertrophy, which introduces substantial errors and constrains basic HCM research. Cats develop HCM spontaneously, and the common MYBPC3-A31P variant in cats is homologous to human mutations in both genetics and pathology, with a larger body size that makes them suitable as large-animal models. This study examines how heterozygosity or homozygosity for the p.A31P mutation (c.91G>C) in the MYBPC3 gene affects the phenotype and severity of HCM in affected cats, with the aim of establishing an ideal large-animal model for clinical risk stratification and precision diagnosis and treatment of human HCM. Methods: Forty-nine Maine Coon cats were enrolled and stratified into homozygous mutant (HOM, n=8), heterozygous mutant (HET, n=26), and wild-type (WT, n=15) groups. All cats underwent echocardiography, blood pressure measurement, physiological assessment, hematological and biochemical analyses, and cross-species sequence conservation analysis. Results: No significant differences in baseline characteristics including age and body weight were observed among groups (P>0.05). HOM cats exhibited significantly higher left ventricular outflow tract pressure gradients and greater basal septal thickness compared to WT cats (P<0.05), with HET cats showing intermediate values. Analysis of hematological and serum biochemical parameters revealed no evidence of systemic inflammation or hepatic injury. Sequence conservation analysis confirmed that the A31 residue is highly conserved across mammalian species. Conclusions: This study provides a phenotypic characterization of Maine Coon cats carrying the MYBPC3-A31P mutation, revealing marked gene-dose effects on cardiac structure and function, with homozygous individuals exhibiting more severe phenotypic features. This model serves as a large-animal translational platform that not only clarifies genotype-phenotype correlations but also supports risk stratification and precision therapeutic strategies in human HCM. Its spontaneous nature and genetic homology to human disease make it particularly valuable for bridging preclinical findings to clinical application.

Objective: Kabuki syndrome type 2 (KS2) is a rare X-linked disorder caused by pathogenic variants in KDM6A and is frequently associated with hearing impairment. Because auditory phenotypes include sensorineural, conductive, and mixed hearing loss, we examined whether Kdm6a deficiency directly impairs cochlear morphology or auditory function in mice. Methods: We generated Nestin-Cre; Kdm6a conditional mutants and a germline-derived global Kdm6a deletion model using Sox2-Cre-mediated germline recombination. Auditory function and cochlear morphology were assessed by auditory brainstem responses (ABRs), distortion product otoacoustic emissions (DPOAEs), and histological analyses. Results: Whole-body hemizygous or homozygous Kdm6a deletion resulted in embryonic lethality. Analyses therefore focused on Nestin-Cre; Kdm6aflox/Y males and females carrying a germline-derived heterozygous Kdm6a deletion. In Nestin-Cre mutants, ABR thresholds, wave I amplitudes and latencies, and DPOAE measures at 8, 16, and 32 kHz were comparable with littermate controls at 4 and 8 weeks. In heterozygous deletion females, ABR thresholds, wave I amplitudes and latencies at 4-64 kHz and DPOAE measures at 8, 16, and 32 kHz were comparable with male and female wild-type controls. No overt cochlear pathology was observed in either model. Conclusion: Kdm6a deficiency in the viable mouse models examined did not produce overt cochlear pathology or baseline auditory dysfunction. These findings suggest that partial Kdm6a loss alone is insufficient to produce a robust primary cochlear phenotype in young mice and highlight the potential contributions of non-cochlear, developmental, central, and later-onset mechanisms to hearing impairment in KS2. Clinically, these findings support careful evaluation for potentially treatable middle-ear disease.

Hydrozoa is a group of relatively simple animals with a well-developed nervous system. The nervous system in all hydrozoan medusae is highly conserved and includes outer and inner nerve rings at the bell margin, a neural network in the manubrium, and radial neural pathways that connect them. However, one element of the nervous system shows substantial variability among species: the subumbrella neural network. We examined the structure of the nervous and muscular systems in the subumbrella of 14 species of hydrozoan medusae. The main conclusion of this study is that the distribution of neural networks in the subumbrella strongly correlates with the distribution of smooth radial muscles. This correlation suggests that smooth radial muscles are the primary target of the subumbrella nervous system. Most species in the order Anthoathecata show a trend toward secondary loss of the neural networks and radial smooth muscle fibers in the subumbrella region, concentrating neural elements and smooth muscles only in the radial pathways along the radial canals. By contrast, all studied species in the order Leptothecata have neural networks in the subumbrella area, as well as radial smooth muscle fibers spread throughout the entire subumbrella region. The correlation between radial smooth muscles and the nervous system is also observed in the radial pathways along the radial canals. All species with thick bundles of smooth radial muscles along the radial canals have clearly defined, dense neural pathways running along or even embedded within the smooth muscle bundles.

The feline auditory cortex is understood to consist of 13 distinct subregions with unique anatomical and functional properties. Differential patterns of SMI-32 immunoreactivity are commonly used to identify the borders between these subregions; however, the detailed description of areal differences that is commonly cited did not include descriptions of the patterns observed along the posterior ectosylvian gyrus. Thus, the current manuscript aims to provide a more complete data set that can used to delineate the dorsal, intermediate, and ventral divisions of the posterior ectosylvian gyrus (auditory cortical regions dPE, iPE, and vPE, respectively) based on SMI-32 reactivity using the same methods and measures. Taken together, the current data and those published previously allow for a standardized approach to identifying all 13 auditory cortical subregions in this essential model of auditory cortical structure and function.

Heart regeneration varies among vertebrates, with zebrafish serving as a reference species for efficient cardiac restoration. How this capacity diversified across teleosts is an emerging question, particularly following the recent identification of non-regenerative cardiac repair in medaka and cavefish. Here, we investigate heart restorative capacity following cryoinjury in two livebearers, platyfish and swordtails (Xiphophorus species), belonging to the Poeciliidae family. We demonstrate that their hearts lack the vascularized compact myocardium, a ventricular layer implicated in the restorative response in zebrafish. Following cryoinjury, both poeciliids failed to rapidly deposit fibrotic tissue that normally reinforces the damaged ventricle. This deficiency correlates with pronounced wound protrusion. Although the remaining myocardium displayed an initial proliferative response, subsequently deposited collagenous scar tissue permanently sealed the ventricular wall, precluding complete regeneration. Transcriptomic analysis identified several divergently regulated pathways between cryoinjured hearts of zebrafish and platyfish, most notably in immune response regulation. These differences were validated by delayed leukocyte infiltration and sustained inflammation in platyfish, contrasting with the rapid and self-resolving inflammatory response in zebrafish. Our findings demonstrate that Xiphophorus species have evolved hearts with compromised regenerative capacity, characterized by initial wound protrusion and permanent scarring. These results establish that lineage-specific evolutionary traits can profoundly shape regenerative competence across teleosts, with broad implications for understanding the mechanistic basis of cardiac repair. Highlights{middle dot} Viviparous poeciliids lack vascularized compact myocardium. {middle dot} Inflammation and fibrosis are delayed in the cryoinjured platyfish ventricle. {middle dot} Ventricular cryoinjury in Xiphophorus leads to transient bulging-type deformation. {middle dot} Failure to form a myocardial bridge results in permanent scarring.

Quantifying skeletal mineralization phenotypes in larval fish is complicated by the natural curvature of the notochord and by sample-to-sample variability in orientation, staining and imaging. Consequently, many studies rely on summary measures such as vertebral counts or total stain intensity. Here we present SCAMP (Spinal Calcification & Mineralization Profiler), an open-source, GUI-based Python tool that computationally straightens the curved notochord of Alizarin Red S-stained fish larvae and generates standardized mineralization profiles along the spinal axis. This approach reduces positional and shape variability, allowing direct, quantitative comparison of calcification patterns within and between experimental cohorts, without requiring programming expertise. We validate SCAMP using a zebrafish model of Pseudoxanthoma elasticum (abcc6aelu15/elu15), recovering genotype-specific differences in the intensity, extent and spatial distribution of ectopic calcification. Using SCAMP, we further show that inorganic pyrophosphate (PPi) supplementation of the medium suppresses ectopic notochord calcification, alters the anterior-posterior distribution of mineralized regions in homozygous mutants, and promotes mineralization at physiological vertebral sites. We also show that methylene blue, a routine antifungal additive in fish medium, reduces baseline calcification, with the most pronounced effects observed in heterozygous controls. SCAMP is freely available and has the potential to be adapted to other fish species used in skeletal and mineralization research.

The spiraling tooth of the narwhal (Monodon monoceros) has long intrigued scientists, but the growth rates of its "tusk" are poorly constrained due to the difficulty to age narwhal. To learn more about the population dynamics and life history of this exploited species, previous studies have used sectioned teeth to age narwhals and calibrate other ageing methods based on aspartic acid racemization, radiocarbon or trace element analysis. However, few such studies have been conducted due to the method's difficulty and the need to sacrifice the tooth. In this study, computed tomography (CT) was used on five teeth as a non-destructive means of estimating the age of narwhals, revealing different growth rates between erupted and embedded teeth during adolescence. Moreover, in combination with our reanalysis of all relevant literature, CT data clarify the annual growth rates of narwhal tusks, which peak before the age of 10 (~100 mm yr-1). This approach will be useful for investigating private and museum collections, and might also better constrain the use of trace element proxies in narwhal teeth and support sustainable harvest management.

INTRODUCTION: Osteogenesis imperfecta (OI) is a genetic disorder primarily due to mutations in collagen type I-encoding genes, resulting in fragile bones, frequent fractures, pain, and mobility issues. Disease severity and phenotype vary widely, even with the same mutation, suggesting the importance of other factors within the bone microenvironment that influence disease severity. To study the role of such factors, we analyzed bone samples from OI patients and healthy controls using single-cell RNA sequencing to reveal if RNA expression profiles may uncover mechanisms behind OI phenotype. METHODS: Bone samples from surgeries of OI patients and healthy individuals isolated and RNA single-cell sequencing was performed, followed by quality control and bioinformatics analysis. Two healthy and three OI patients were included: two with type-I OI, characterized by a mutation in COL1A1 (collagen type I), and another with type-VIII OI, associated with LEPRE1 mutations, which disrupt the 3-hydroxylation of type I collagen. RESULTS: Clustering and differential expression analysis showed distinct subpopulations in mesenchymal and immune cells. In all OI samples, mesenchymal stromal cell (MSC) proportions were reduced compared to healthy controls. OI type-I patients showed decreased osteoblast numbers alongside an increase in osteoclast precursor cells. Whereas in OI type-VIII, all bone turnover-related cells (osteoblast, osteoclast precursor, and osteoclast) were elevated. Notably, BMP5 and RUNX1 were downregulated in MSCs from both OI types. DISCUSSION: This study demonstrates that the bone marrow microenvironment in OI is significantly altered beyond the known collagen defects. Single-cell RNA sequencing revealed reduced MSC numbers and downregulated osteogenic gene expression. Furthermore, alterations are patient-specific: OI type-I is characterized by reduced osteoblast counts, whereas OI type-VIII exhibits increased osteoblasts and osteoclasts. These findings highlight the critical role of impaired osteogenic differentiation and an abnormal bone remodeling environment in the pathology of OI.

Background: Viable pediatric human growth plate (GP) tissue is rarely available for translational research, limiting direct investigation of human longitudinal bone growth and pediatric growth disorders. In this proof-of-concept study, we aimed to determine whether it is feasible to establish a clinically integrated ex vivo human GP model using tissue obtained during routine percutaneous epiphysiodesis (PE) procedures in adolescents treated for extreme tall stature or leg length difference due to trauma. Methods: GP tissue and cells were collected during PE and processed using protocols adapted from established methods of human osteoarthritic cartilage processing within the RAAK study. Feasibility was assessed by evaluating tissue collection, cell isolation, contamination rate, monolayer expansion, and generation of three-dimensional cartilage pellets. Proliferation of GP-derived chondrocytes was compared with osteoarthritis-derived articular chondrocytes, and histological assessment was performed to evaluate cartilage-like matrix formation. Results: Across consecutive surgical procedures, viable GP tissue could be obtained reproducibly, with only few samples failing to yield cells and no relevant contamination issues. Isolated GP chondrocytes expanded successfully in two-dimensional culture and showed a strong early proliferative response compared with RAAK-derived chondrocytes. In addition, GP-derived cells formed three-dimensional organoids and histology confirmed cartilage-like matrix deposition supporting their capacity to generate neo-cartilage tissue in vitro. Conclusion: This study demonstrates feasibility to obtain, culture, and functionally assess viable human GP tissue from routine PE surgery. As such, the Leiden ex vivo human GP model provides a unique platform to study local mechanisms of endochondral bone growth, link genetic determinants of height to functional GP biology, and support future therapeutic research in pediatric growth disorders.

The nautilus (Nautilus sp.) is an early-branching cephalopods. It retains several conchiferan synapomorphies, including an external planispiral biomineralized shell. The shells complex structure allows it to withstand hydrostatic pressure, control buoyancy, and protect against external hazards. In this study, we comprehensively examined shell microstructures across different shell components and regions representing various ontogenetic stages in two adult museum shell specimens. We found that the nautilus shell is composed of five microstructural types (spherulitic, prismatic, nacreous, semi-prismatic, and irregularly oriented prismatic structures) organized into layered architectures within individual shell components and coordinated across the shell as an integrated system. Our observations highlight transitions between distinct microstructures within and across shell components and local variation within individual components such as the dorsal and ventral shell walls, suggesting that these patterns may contribute to shell strength and overall mechanical performance. Variation in caecum morphology suggests that this structure may be developmentally plastic and subject to relatively relaxed structural constraints. These findings show that the Nautilus shell is an integrated biomineral system in which diverse microstructures are organized across shell components to meet functional demands and provide the mechanical strength needed for survival.

Hox genes play central roles in specifying positional identities along the vertebrate anterior-posterior axis. In mice, genetic analyses have demonstrated that Hox genes distributed among the four Hox clusters contribute to vertebral patterning, with extensive functional redundancy among paralogous genes. Our previous genetic analysis in zebrafish identified important roles for HoxB- and HoxC-related genes in specifying anterior vertebral identities, whereas the contributions of HoxA- and HoxD-related genes remained unresolved. Here, we examined adult zebrafish carrying extensive combinations of hoxaa, hoxab, and hoxda cluster deletions and generated five-gene homozygous mutants carrying frameshift mutations in hoxa3a, hoxa4a, hoxa5a, hoxd3a, and hoxd4a. X-ray micro-CT analysis revealed no obvious alterations in anterior vertebral morphology in either the compound cluster mutants or the five-gene mutants. These results indicate that HoxA/D genes make only a limited detectable contribution to anterior vertebral patterning in zebrafish. Together with our previous findings, they suggest that vertebral patterning functions are distributed unevenly among zebrafish Hox clusters, with a predominant contribution from HoxB/C-related genes.