Search

Orofacial morphology in mammals plays a critical role in essential life functions such as feeding and communication, which are influenced by the shapes of these anatomical structures. Bats are known to exhibit highly diversified orofacial morphotypes within their clade, reflecting their varied diets and echolocation behaviors. The presence of bony discontinuities between the premaxilla and maxilla or among the premaxillae is a notable feature of bat orofacial morphology, observed in certain lineages. It is suggested that these unique orofacial morphotypes, not generally found in other mammals, have evolved in relation to dietary adaptations rather than merely for echolocation mode. Until now, the developmental background of the bony discontinuities in the bat orofacial complex has been insufficiently investigated. Here, we present a comparative study of the chondrocranium and epithelial organs in the orofacial complex of three bat species: Cynopterus sphinx, Rhinolophus malayanus, and Vespertilio sinensis. Our observations indicate that the preceding morphogenesis of orofacial cartilage and epithelial structures is remarkably different among these three species. In C. sphinx and V. sinensis, the region forming from the regression of the palatine process of the premaxilla was filled with orofacial cartilage and epithelial structures. We also found that the clefted morphology observed in R. malayanus and V. sinensis was formed via contrastingly divergent developmental processes. Midline clefts among Yangochiroptera have been previously categorized to represent a uniform morphotype, but our study highlights that attributing midline clefts into a singular category should be revisited, advocating for a nuanced categorization of cleft morphology based on their morphogenetic patterns. Further research on the bat orofacial complex may enhance our understanding of bat evolutionary diversification and offer insights into the developmental mechanisms of human cleft palate., (© 2024 Anatomical Society.)

Background: Mutations in genes encoding spliceosome components result in craniofacial structural defects in humans, referred to as spliceosomopathies. The SF3b complex is a crucial unit of the spliceosome, but model organisms generated through genetic modification of the complex do not perfectly mimic the phenotype of spliceosomopathies. Since the phenotypes are suggested to be determined by the extent of spliceosome dysfunction, an alternative experimental system that can seamlessly control SF3b function is needed., Methods: To establish another experimental system for model organisms elucidating relationship between spliceosome function and human diseases, we administered Pladienolide-B (PB), a SF3b complex inhibitor, to mouse and zebrafish embryos and assessed resulting phenotypes., Results: PB-treated mouse embryos exhibited neural tube defect and exencephaly, accompanied by apoptosis and reduced cell proliferation in the neural tube, but normal structure in the midface and jaw. PB administration to heterozygous knockout mice of Sf3b4, a gene coding for a SF3b component, influenced the formation of cranial neural crest cells (CNCCs). Despite challenges in continuous PB administration and a high death rate in mice, PB was stably administered to zebrafish embryos, resulting in prolonged survival. Brain, cranial nerve, retina, midface, and jaw development were affected, mimicking spliceosomopathy phenotypes. Additionally, alterations in cell proliferation, cell death, and migration of CNCCs were detected., Conclusions: We demonstrated that zebrafish treated with PB exhibited phenotypes similar to those observed in human spliceosomopathies. This experimental system may serve as a valuable research tool for understanding spliceosome function and human diseases., (© 2024 The Author(s). Birth Defects Research published by Wiley Periodicals LLC.)

Craniofacial morphology is extremely diversified within bat phylogeny, however growth and development of the palate in bats remains unstudied. The formation of both midline and bilateral orofacial clefts in laryngeally echolocating bats, morphologically similar to the syndromic and non-syndromic cleft palate in humans, are not well understood. Developmental series of prenatal samples (n = 128) and adults (n = 10) of eight bat species (two pteropodids, four rhinolophoids, and two yangochiropterans), and two non-bat mammals (Mus musculus and Erinaceus amurensis), were CT-scanned and cranial bones forming the upper jaw complex were three-dimensionally visualised to assess whether differences in palate development can be observed across bat phylogeny. Volumetric data of bones composing the upper jaw complex were measured to quantify palate growth. The premaxilla is relatively reduced in bats compared to other mammals and its shape is heterogeneous depending on the presence and type of orofacial cleft across bat phylogeny. The palatine process of premaxillary bones is lacking in pteropodids and yangochiropterans, whereas the premaxilla is a mobile structure which is only in contact caudally with the maxilla by a fibrous membrane or suture in rhinolophoids. In all bats, maxillary bones progressively extend caudally and palatine bones, in some cases split into three branches, extend caudally so that they are completely fused to another one medially prior to the birth. Ossification of the vomer and fusion of the maxillary and palatine bones occur earlier in rhinolophoids than in pteropodids and yangochiropterans. The vomer ossifies bilaterally from two different ossification centres in yangochiropterans, which is uncommon in other bats and non-bat mammals. Analysis of ontogenetic allometric trajectories of the upper jaw complex revealed faster development of maxillary, vomer, and palatine bones in yangochiropterans compared to other bats, especially rhinolophoids. Ancestral state reconstruction revealed that yangochiropterans have a higher magnitude of change in ossification rate compared to other bats and E. amurensis a lower magnitude compared to M. musculus and bats. This study provides new evidence of heterochronic shifts in craniofacial development and growth across bat phylogeny that can improve understanding of the developmental differences characterising nasal and oral emission strategies., (© 2024 The Author(s). Journal of Anatomy published by John Wiley & Sons Ltd on behalf of Anatomical Society.)

Background: The hyolaryngeal apparatus generates biosonar pulses in the laryngeally echolocating bats. The cartilage and muscles comprising the hyolarynx of laryngeally echolocating bats are morphologically modified compared to those of non-bat mammals, as represented by the hypertrophied intrinsic laryngeal muscle. Despite its crucial contribution to laryngeal echolocation, how the development of the hyolarynx in bats differs from that of other mammals is poorly documented. The genus Rhinolophus is one of the most sophisticated laryngeal echolocators, with the highest pulse frequency in bats. The present study provides the first detailed description of the three-dimensional anatomy and development of the skeleton, cartilage, muscle, and innervation patterns of the hyolaryngeal apparatus in two species of rhinolophid bats using micro-computed tomography images and serial tissue sections and compares them with those of laboratory mice. Furthermore, we measured the peak frequency of the echolocation pulse in active juvenile and adult individuals to correspond to echolocation pulses with hyolaryngeal morphology at each postnatal stage., Results: We found that the sagittal crests of the cricoid cartilage separated the dorsal cricoarytenoid muscle in horseshoe bats, indicating that this unique morphology may be required to reinforce the repeated closure movement of the glottis during biosonar pulse emission. We also found that the cricothyroid muscle is ventrally hypertrophied throughout ontogeny, and that the cranial laryngeal nerve has a novel branch supplying the hypertrophied region of this muscle. Our bioacoustic analyses revealed that the peak frequency shows negative allometry against skull growth, and that the volumetric growth of all laryngeal cartilages is correlated with the pulse peak frequency., Conclusions: The unique patterns of muscle and innervation revealed in this study appear to have been obtained concomitantly with the acquisition of tracheal chambers in rhinolophids and hipposiderids, improving sound intensity during laryngeal echolocation. In addition, significant protrusion of the sagittal crest of the cricoid cartilage and the separated dorsal cricoarytenoid muscle may contribute to the sophisticated biosonar in this laryngeally echolocating lineage. Furthermore, our bioacoustic data suggested that the mineralization of these cartilages underpins the ontogeny of echolocation pulse generation. The results of the present study provide crucial insights into how the anatomy and development of the hyolaryngeal apparatus shape the acoustic diversity in bats., (© 2024. The Author(s).)