Comparative Approaches in Vertebrate Cartilage Histogenesis and Regulation: Insights from Lampreys and Hagfishes

Jawed vertebrates (gnathostomes) have been the dominant lineage of deuterostomes for nearly three hundred fifty million years. Only a few lineages of jawless vertebrates remain in comparison. Composed of lampreys and hagfishes (cyclostomes), these jawless survivors are important systems for understanding the evolution of vertebrates. One focus of cyclostome research has been head skeleton development, as its evolution has been a driver of vertebrate morphological diversification. Recent work has identified hyaline-like cartilage in the oral cirri of the invertebrate chordate amphioxus, making cyclostomes critical for understanding the stepwise acquisition of vertebrate chondroid tissues. Our knowledge of cyclostome skeletogenesis, however, has lagged behind gnathostomes due to the difficulty of manipulating lamprey and hagfish embryos. In this review, we discuss and compare the regulation and histogenesis of cyclostome and gnathostome skeletal tissues. We also survey differences in skeletal morphology that we see amongst cyclostomes, as few elements can be confidently homologized between them. A recurring theme is the heterogeneity of skeletal morphology amongst living vertebrates, despite conserved genetic regulation. Based on these comparisons, we suggest a model through which these mesenchymal connective tissues acquired distinct histologies and that histological flexibility in cartilage existed in the last common ancestor of modern vertebrates.

Lamprey Lecticans Link New Vertebrate Genes to the Origin and Elaboration of Vertebrate Tissues

ABSTRACTThe evolution of vertebrates from an invertebrate chordate ancestor involved the evolution of new organs, tissues, and cell types. It was also marked by the origin and duplication of new gene families. If, and how, these morphological and genetic innovations are related is an unresolved question in vertebrate evolution. Hyaluronan is an extracellular matrix (ECM) polysaccharide important for water homeostasis and tissue structure. Vertebrates possess a novel family of hyaluronan binding proteins called Lecticans, and studies in jawed vertebrates (gnathostomes) have shown they function in many of the cells and tissues that are unique to vertebrates. This raises the possibility that the origin and/or expansion of this gene family helped drive the evolution of these vertebrate novelties. In order to better understand the evolution of the lectican gene family, and its role in the evolution of vertebrate morphological novelties, we investigated the phylogeny, genomic arrangement, and expression patterns of all lecticans in the sea lamprey (Petromyzon marinus), a jawless vertebrate. Though both P. marinus and gnathostomes have four lecticans, our phylogenetic and syntenic analyses suggest lamprey lecticans are the result of one or more cyclostome-specific duplications. Despite the independent expansion of the lamprey and gnathostome lectican families, we find highly conserved expression of lecticans in vertebrate-specific and mesenchyme-derived tissues. We also find that, unlike gnathostomes, lamprey expresses its lectican paralogs in distinct subpopulations of head skeleton precursors, potentially reflecting an ancestral diversity of skeletal tissue types. Together, these observations suggest that the ancestral pre-duplication lectican had a complex expression pattern, functioned to support mesenchymal histology, and likely played a role in the evolution of vertebrate-specific cell and tissue types.

Insights into vertebrate head development: from cranial neural crest to the modelling of neurocristopathies

Although the vertebrate head has evolved to a wide collection of adaptive shapes, the fundamental signalling pathways and cellular events that outline the head skeleton have proven to be highly conserved. This conservation suggests that major morphological differences are due to changes in differentiation and morphogenetic programs downstream of a well-maintained developmental prepattern. Here we provide a brief examination of the mechanisms and pathways responsible for vertebrate head development, as well as an overview of the animal models suitable for studying face development. Besides, we describe the criteria for neurocristopathies classification, highlighting the contribution of zebrafish to the modelling of Treacher Collins/Franceschetti Syndrome, an emblematic neurocristopathy. The contributions from our laboratory reveal that proper zebrafish head development depends on the fine-tuning of developmental-gene expression mediated by nucleic acid binding proteins able to regulate the DNA conformation and / or neuroepithelium redox state.

Anatomy of the dromedary head skeleton revisited

Introduction: Dromedary Camel is known for its specific adaptation to the hostile environment of desert areas. Hence, it is a very interesting model to consider for biological and veterinary sciences. A good knowledge of camel head osteology is relevant to overcome the lack of accurate data useful for comparative anatomy, radiology and clinical practice. Methods: The present work studied the osteology of the camel skull at different age and investigates blood vessels and nerves passing through its foramina. Results: The obtained data show similarities with domestic mammals but also several peculiarities. These include particularly; the existence of an extensive temporal fossa; a prominent external sagittal crest in the adults which is replaced by a large parietal planum in the youngest; the supra-orbital foramina give access only to the frontal vein and thus cannot be used for the nerve block and anesthesia of the upper eyelids; supplementary foramens including, a retroarticular, a lateral sphenopalatine, an accessory maxillary and a lacrimal fontanel were described for the first time. Unlike that reported in the literature, the lacerate foramen is covered by a fibro-cartilaginous layer; whereas the carotid foramen is located caudally to the jugular foramen. The hyoid lingual process is lacking while the epihyoideum is well developed. The mandibular symphysis is well extended reaching 13.2 ± 0.8cm. Also, the literature controversy concerning the lower jaw dental formula was discussed and elucidated: I3-C1-PM2-M3. Conclusion: This study provides a deep anatomy description of the camel skull. The presented results are important for comparative anatomy and clinical investigations.

Development sites and early stages of eleven species of Clusiidae (Diptera) occurring in Europe

Two hundred and ninety-six rearing records of 11 clusiid species (Diptera, Clusiidae) were obtained from 8 tree species in England, Finland, France, Norway, Russiaand Scotland, mainly during the period 1994 to 2004. Larvae and puparia were found between annual layers of whitewood (sapwood and heartwood) of wet, decay-softened, dead wood. Levels of host tree specificity were low, most species were reared from 2–4 host trees, maximum 6. The clusiid larva is distinguished by: a small, translucent head skeleton with an obliquely-shaped apex to the artium; a pseudocephalon fixed in an inverted position except for an external, flattened section bearing the antennomaxillary organs; a spherical prothorax with a truncate rim embedded with sensilla and, a wedge-shaped anal segment bearing a pair of conspicuous, sclerotised, red-brown hooks on the inner margins of which are the posterior spiracular plates. Many of these features support a distinctive feeding mechanism, spot-sucking of biofilm coating wet, decaying whitewood. Early stage characters support the results of recent supraspecific taxonomic and systematic investigations, such as the synonymy of Paraclusia Czerny under Clusia Haliday and the recognition of species groups in Clusiodes Coquillett. Based on early stages, supraspecific clusiid taxa are easily recognised but at species level, differences are relatively fine-grained and minor. A key is provided to identify puparia of species reared in this study.