Journal of Anatomy最新文献

Hippopotamoidea is a superfamily of cetartiodactyls that are nowadays limited to two extant species: Hippopotamus amphibius, the common hippopotamus, and Choeropsis liberiensis, the Liberian hippopotamus. These two mammals are endemic to Africa and inhabit ecosystems closely linked to water. They are the only extant members of a specialized ecological guild called the large semi-aquatic herbivores. The majority of the diversity of this superfamily was composed by the paraphyletic anthracotheres, a geographically, temporally, and ecologically more diverse group from which hippopotamids likely originated. Historically, the phylogenetical relationships of these taxa were debated, especially since the establishment of the clade Cetancodonta which comprises cetaceans and hippopotamids. Research in this area has sought to address these issues using cranial, intracranial morphology, and dental anatomy. Their postcranial anatomy has until now been mostly unexploited data, sometimes due to poor preservation. At Toros-Menalla (TM), a Late Miocene fossiliferous area in Chad, the last African anthracothere Libycosaurus bahri has been found coexisting with the large hippopotamid Hexaprotodon garyam. Their coexistence in humid environments suggests some form of niche-partitioning. The locomotor apparatus is a significant means by which animals interact with their environment. It is a valuable resource for clarifying the phylogenetic issues previously cited, as well as for discussing functional and ecological considerations mentioned in previous literature. This study proposes an anatomical comparison between these two coexisting hippopotamoids and their closest extant ecomorph, the common hippopotamus. We have established a framework for the identification and differentiation of the postcranial skeleton of hippopotamoids by observing characters on a sample of approximately 650 specimens. We also highlight the importance of including the postcranial skeleton in future phylogenetical analyses. Additionally, we discuss the postcranial anatomy of those taxa in the context of the African Miocene environments, allowing new functional and ecological interpretations for the interaction between hippopotamoids and changes in their wet environments, which remain a major driver in the evolutionary history of these large artiodactyls.

Mineralization sequences of cranial elements (often referred to as ossification sequences) are used for a variety of purposes. Believed to be consistent within species (even though they exhibit some variation) and conserved within lineages, they have been assembled using a variety of developmental timetables-absolute time using developmental days; relative time using either increase in size of embryonic dimensions or developmental staging. The relationship between these developmental timetables is unclear in terms of how mineralization sequences are expressed, although they are generally treated as being able to achieve equivalent levels of resolution. Regardless of the developmental timetable employed, mineralization sequences are replete with ties representing simultaneous mineralization of several elements, even though ties are suspected to be rare. Herein we examine the resolution attainable of cranial mineralization events in the leopard gecko by subjecting the same set of embryos, raised under controlled conditions, to sequence analysis using all three of the above-mentioned timetables, with the working hypotheses being that all three would yield the same level of resolution and that we could improve upon the level of resolution attained for gekkotans so far. We found that developmental stage timetabling yielded far less variability in the determination of mineralization sequence as well as considerably better resolution than those for developmental days or embryonic dimensions. We were able to obtain much greater resolution for the leopard gecko than that so far attained for gekkotans for all three developmental timetables, but especially so when ordering the specimens by developmental stage. Furthermore, we found that subdividing embryonic stages into substages (established using additional morphological features) and assessing intensity of staining of mineralizing elements hold promise for achieving improved levels of resolution. Even so, we were only about 55% successful in resolving the cranial mineralization sequence into a series of unique events, indicating that many such events are so closely spaced in developmental time that apparent simultaneity of element mineralization will be challenging to resolve further.

Bioengineered tissues offer vital platforms capable of fundamental research, screening interventions and reducing the use of animals in scientific research. However, their predictive accuracy is dependent upon how closely their structure and function resemble their native counterpart. In this study, we present a novel in vitro engineered construct representative of the human nasal mucosa, consisting of both stromal and epithelial compartments. Communication between the stroma and the overlying epithelium is an essential factor involved in tissue development and homeostasis yet is often lacking in the majority of published tissue constructs. Described is the construction of a pseudostratified epithelium consisting of an organised heterogeneous cell population consistent with the respiratory region of the nasal mucosa that forms on a stromal foundation populated with tissue-specific fibroblasts and endogenous extracellular matrix. In addition, for the first time, we provide an extensive ultrastructural analysis of a bioengineered nasal tissue using both scanning and transmission electron microscopic techniques. This in-depth characterisation revealed microanatomical hallmarks consistent with the native tissue, including motile cilia, mucin secretions, intercellular junctions, dynamic basement membrane, microvilli and glycocalyx. Given each of these features play pivotal physiological roles in the specialised functions of the respiratory epithelium, their presence in vitro lends itself to tissue equivalents with enhanced physiological relevance and greater predictive accuracy. In summary, we present a highly characterised in vitro nasal mucosal construct that accurately reflects native microanatomy. Such technology will be of value to a wide range of applications, most notably, undertaking basic research and in vitro pharmaceutical screening, of which nasal mucosal models have become increasingly applicable due to the popularity of intranasal drug and vaccine delivery methods.

Two-toed sloths are larger than three-toed forms and potentially have the capacity for greater strength and power associated with their high frequency of suspensory behaviors. However, fiber architecture and whole muscle functional capacities remain completely unknown for either species of Choloepus. Part two of this study provides novel quantifications of muscle architectural properties in the forelimb of Hoffmann's two-toed sloth (C. hoffmanni). A suite of geometric measurements, including muscle mass, belly length, fascicle length, and pennation angle, were used to calculate physiological cross-sectional area (PCSA) and estimate isometric force, joint torque, and instantaneous power. In general, the musculature becomes progressively more pennate from the extrinsic to the distal intrinsic regions of the forelimb, and all flexors are larger than their counterpart extensors. Except for a few pairs of small joint stabilizer muscles, the majority of bellies in each region of the forelimb have greater ability for shortening but limited ability for sized-scaled force production. Nonetheless, several large, strong shoulder (e.g., m. latissimus dorsi) and elbow (e.g., m. brachioradialis) flexors are capable of applying large joint torques over an extended range of contractile excursion by having elongated moment arms. Modification to limb muscle gearing is further exemplified by pairs of synergistic muscles with opposing fast joint rotational velocity versus mechanical advantage arrangements in each functional group. Lastly, the digital flexors have variable architectural properties, but their collectively large PCSA and estimated maximum force production capability (~2.2× bodyweight force) indicates exceptional grip strength. The muscle functional properties determined herein match well with the observed myological traits in Choloepus and provide further evidence of their abilities for frequent and prolonged suspension that are divergent from three-toed sloths.

The medial pterygoid plate plays a critical role in mammalian craniofacial function during suckling and swallowing. The plate supports the tensor veli palatini (TVP) muscle, which stiffens the soft palate to create a posterior seal. Despite its functional importance, the developmental origins and structural integration of the medial pterygoid plate and associated pterygoid hamulus remain incompletely understood. In this study, we investigated the ontogeny and lineage of the medial pterygoid plate using wildtype and conditional knockout mice with immunofluorescence and lineage tracing. Analysis from embryonic day (E)14.5 to E17.5 confirmed that the medial pterygoid plate formed as a bipartite structure, which later fused to the basisphenoid. The dorsal region of the medial pterygoid plate ossified via Runx2-dependent intramembranous bone formation, while the ventral region formed as a secondary cartilage, undergoing Sox9-dependent chondrogenesis, followed by endochondral ossification. The pterygoid hamulus was evident at E14.5 as a condensation of Sox9-positive mesenchyme at the end of the medial pterygoid plate. Confirming the different modes of development, the ventral and dorsal parts of the medial pterygoid plate showed distinct timing and pattern of collagen remodelling, as shown by B-CHP. Lineage tracing with Wnt1Cre;tdTom and Mesp1Cre;tdTom mice demonstrated that the entire pterygoid process formed from neural crest-derived mesenchyme. In keeping with this, conditional loss of Runx2 in the neural crest lineage disrupted ossification of the dorsal part of the medial pterygoid plate, whereas conditional loss of Sox9 abolished chondrogenesis of the ventral part of the medial pterygoid plate and the pterygoid hamulus. Notably, TVP muscle fibres were able to maintain their orientation around the residual cartilage in conditional Wnt1creRunx2flfl mutants, while the TVP in conditional Wnt1creSox9flfl mutants formed a ball of cells that failed to extend towards the palatal region. The ventral portion of the medial pterygoid plate and hamulus is therefore required to guide early muscle pathfinding. These findings establish the medial pterygoid plate as a compound craniofacial element with distinct ossification modes and an important role interacting and directing neighbouring tissues.

Many tetrapods possess two distinct olfactory organs: the olfactory epithelium (OE) and the vomeronasal organ (VNO). Fish have only the OE, but lungfish-the closest living relative of tetrapods among fish- possess a lamellar OE and a primitive VNO called a recess epithelium (RecE). Vomeronasal receptor type 2 (V2R) genes in lungfish can be classified into three categories: those expressed only in the lamellar OE, those expressed only in the RecE, and those expressed in both the lamellar OE and the RecE. In this study, we compared V2R expression patterns in Protopterus annectens of different body sizes to examine how expression changes with growth. V2Rs expressed exclusively in the lamellar OE in small individuals remained restricted to the lamellar OE in large individuals, and V2Rs expressed exclusively in the RecE in small individuals also remained RecE-specific in large individuals. In contrast, among the V2Rs expressed in both the lamellar OE and the RecE in small individuals, some maintained expression in both tissues, while others became restricted to the RecE in large individuals. Medium-sized individuals showed intermediate expression patterns between small and large specimens. These results suggest that a subset of V2Rs initially expressed in both the lamellar OE and the RecE lose expression in the lamellar OE as the individual matures, becoming restricted to the RecE, and that functional separation between the lamellar OE and the RecE is still incomplete in juveniles and becomes more distinct during growth. These findings might represent the developmental process of the bimodal olfactory system in vertebrates. In the common ancestors of lungfish and tetrapods, there might be no functional separation between the OE and VNO. However, it can be speculated that olfactory functions have partially separated between the OE (lamellar OE) and VNO (RecE) in extant lungfish, while they have completely separated between the OE and VNO in extant tetrapods which acquired more developed VNO.

The ductus arteriosus (DA) is a critical fetal vascular structure that shunts blood from the pulmonary artery to the aorta, bypassing the non-functional fetal lungs. Postnatally, it undergoes active remodeling and closure, forming the ligamentum arteriosum. Abnormal persistence (patent DA, PDA) can lead to significant health issues. Chicken embryos, with their rapid development and accessibility, serve as a valuable model for studying DA morphogenesis. This study explores how 3D transparent technologies have advanced our understanding of DA development in chicken embryos, emphasizing pre- and post-hatching morphological changes. We use glycerol transparency technology to show the DA development processes with 3D stereo effect and the H.E technology to show variation of the horizontal sections of DA. Chicken models provide insights into PDA pathophysiology, aiding drug testing (e.g., caffeine exposure). 3D imaging could validate therapeutic efficacy in vivo, bridging preclinical and clinical research.

Chemosensory cell clusters are taste bud-like sensory structures located in the pharyngo-laryngeal mucosa. These clusters are densely distributed at the entrance of lower airways to detect chemical stimuli and trigger respiratory reflexes; however, their postnatal development remains poorly understood. In this study, we examined postnatal changes in the morphology and distribution of chemosensory clusters in rat laryngeal whole-mount preparations using immunofluorescence for alpha-gustducin (GNAT3, a marker of type II taste cells) and synaptotagmin-1 (Syt1, a marker of type III taste cells). Chemosensory cell clusters were detected along the margin of the epiglottis on postnatal day 2 (PD2). Their numbers rapidly increased by PD7 (26 ± 4.5) and plateaued by postnatal week 3 (PW3, 84.0 ± 4.9), whereas the number of constituent cells continued to increase until PW8. Clusters at early stages (PD2-PD7) contained 2-3 spindle GNAT3-immunoreactive cells and round Syt1-immunoreactive cells. As the cluster matured, both cell types elongated longitudinally, extended the apical tip of their cytoplasmic processes to the epithelial surface, and GNAT3-immunoreactive cells developed branched cytoplasmic processes. P2X3-immunoreactive afferent nerve endings contacted GNAT3- and Syt1-immunoreactive cells throughout development. The results indicate the constant presence of chemosensory cell clusters in the laryngeal entrance and the establishment of neuronal connections as early as PD2. These clusters may be sentinel chemoreceptors at the entrance of the larynx. Because stabilization of chemosensory cell cluster numbers coincides with the weaning period, the postnatal development of these clusters may be associated with feeding behaviors in rats.

Woodpeckers exhibit a unique pecking behaviour that subjects their skulls to extreme mechanical stresses, requiring specialised morphology. Several adaptations enabling them to withstand these impacts have been identified, yet the interaction between osteological features that mitigate biomechanical stress, craniofacial architecture, and macroevolutionary patterns remain underexplored. Here, we examine the quadrato-mandibular joint and analyse cranial shape in woodpeckers compared with other insectivorous non-picid birds using geometric morphometrics and phylogenetic comparative methods. We document previously undescribed reinforcing articular contacts within the cranioquadrate-mandibular system, including an expanded articular surface on the condylus medialis of the quadrate forming a trochlea lateralis that contacts the caudal facet of the mandibular crista intercotylaris, as well as multiple stabilising interfaces between the quadrate and the neurocranium involving the suprameatic, zygomatic, and basicranial regions. These features are present across Picidae but vary markedly in their degree of development, being weakly expressed in Picumninae (Picumnus cirratus) and most pronounced in Picinae, particularly in taxa specialised for forceful pecking such as Campephilus. Shape analyses reveal among woodpeckers a decoupling from the craniofacial evolutionary allometry seen in other birds, replaced by a significant influence of relative brain size on skull shape, and uncover distinctive cranial configurations with important biomechanical implications (e.g., reduced maxillary base, altered temporal fossa position and quadrate orientation). This skull-brain association, together with woodpeckers' unique anatomy, likely enhances mandibular stability and quadrate articulation, providing additional support and increasing resistance to impact forces during pecking. The selection of this alternative morphological transformation trend in woodpeckers optimised a demanding ecological performance while allowing morphological diversity without compromising biomechanical stability. Our findings provide new insights into the biomechanical strategies underlying woodpeckers' pecking and highlight the role of skull macroevolution in their ecological specialisation.