Central projections of the lateral line nerves in the shovelnose sturgeon

Primary projections of the anterior (ALLN) and posterior (PLLN) lateral line nerves were traced in the shovelnose sturgeon by means of horseradish peroxidase (HRP) histochemistry and silver degeneration. The trunk of the ALLN divides into dorsal and ventral roots as it enters the medulla. Fibers of the dorsal root form ascending and descending branches that terminate within the ipsilateral dorsal octavolateralis nucleus and the dorsal granular component of the lateral eminentia granularis. Fibers of the ventral root of the ALLN, as well as fibers of the PLLN, enter the medulla ventral to the dorsal root of the ALLN where some of the fibers terminate among the dendrites of the magnocellular octaval nucleus. The bulk of the fibers form ascending and descending branches that terminate within the ipsilateral medial octavolateralis nucleus. A portion of the ascending fibers continue more rostrally land terminate in the ipsilateral eminentia granularis and bilaterally in the cerebellar corpus. Some fibers of the descending rami of both the ALLN and PLLN extend beyond the caudal limit of the medial octavolateralis nucleus to terminate in the caudal octavolateralis nucleus. The HRP cases also revealed retrogradely filled large neurons whose axons course peripherally in the lateral line nerve and are likely efferent to the lateral line organs.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/50022/1/902250114_ftp.pd

Evolutionary Changes in the Complexity of the Tectum of Nontetrapods: A Cladistic Approach

Background: The tectum is a structure localized in the roof of the midbrain in vertebrates, and is taken to be highly conserved in evolution. The present article assessed three hypotheses concerning the evolution of lamination and citoarchitecture of the tectum of nontetrapod animals: 1) There is a significant degree of phylogenetic inertia in both traits studied (number of cellular layers and number of cell classes in tectum); 2) Both traits are positively correlated accross evolution after correction for phylogeny; and 3) Different developmental pathways should generate different patterns of lamination and cytoarchitecture. Methodology/Principal Findings: The hypotheses were tested using analytical-computational tools for phylogenetic hypothesis testing. Both traits presented a considerably large phylogenetic signal and were positively associated. However, no difference was found between two clades classified as per the general developmental pathways of their brains. Conclusions/Significance: The evidence amassed points to more variation in the tectum than would be expected by phylogeny in three species from the taxa analysed; this variation is not better explained by differences in the main course of development, as would be predicted by the developmental clade hypothesis. Those findings shed new light on th

Insights from Amphioxus into the Evolution of Vertebrate Cartilage

Central to the story of vertebrate evolution is the origin of the vertebrate head, a problem difficult to approach using paleontology and comparative morphology due to a lack of unambiguous intermediate forms. Embryologically, much of the vertebrate head is derived from two ectodermal tissues, the neural crest and cranial placodes. Recent work in protochordates suggests the first chordates possessed migratory neural tube cells with some features of neural crest cells. However, it is unclear how and when these cells acquired the ability to form cellular cartilage, a cell type unique to vertebrates. It has been variously proposed that the neural crest acquired chondrogenic ability by recruiting proto-chondrogenic gene programs deployed in the neural tube, pharynx, and notochord. To test these hypotheses we examined the expression of 11 amphioxus orthologs of genes involved in neural crest chondrogenesis. Consistent with cellular cartilage as a vertebrate novelty, we find that no single amphioxus tissue co-expresses all or most of these genes. However, most are variously co-expressed in mesodermal derivatives. Our results suggest that neural crest-derived cartilage evolved by serial cooption of genes which functioned primitively in mesoderm

Molecular and cellular mechanisms underlying the evolution of form and function in the amniote jaw.

The amniote jaw complex is a remarkable amalgamation of derivatives from distinct embryonic cell lineages. During development, the cells in these lineages experience concerted movements, migrations, and signaling interactions that take them from their initial origins to their final destinations and imbue their derivatives with aspects of form including their axial orientation, anatomical identity, size, and shape. Perturbations along the way can produce defects and disease, but also generate the variation necessary for jaw evolution and adaptation. We focus on molecular and cellular mechanisms that regulate form in the amniote jaw complex, and that enable structural and functional integration. Special emphasis is placed on the role of cranial neural crest mesenchyme (NCM) during the species-specific patterning of bone, cartilage, tendon, muscle, and other jaw tissues. We also address the effects of biomechanical forces during jaw development and discuss ways in which certain molecular and cellular responses add adaptive and evolutionary plasticity to jaw morphology. Overall, we highlight how variation in molecular and cellular programs can promote the phenomenal diversity and functional morphology achieved during amniote jaw evolution or lead to the range of jaw defects and disease that affect the human condition

Elongated Polyproline Motifs Facilitate Enamel Evolution through Matrix Subunit Compaction

How does proline-repeat motif length in the proteins of teeth and bones relate to the evolution of vertebrates? Counterintuitively, longer repeat stretches are associated with smaller aggregated subunits within a supramolecular matrix, resulting in enhanced crystal length in mammalian versus amphibian tooth enamel

US hegemony and the origins of Japanese nuclear power : the politics of consent

This paper deploys the Gramscian concepts of hegemony and consent in order to explore the process whereby nuclear power was brought to Japan. The core argument is that nuclear power was brought to Japan as a consequence of US hegemony. Rather than a simple manifestation of one state exerting material ‘power over' another, bringing nuclear power to Japan involved a series of compromises worked out within and between state and civil society in both Japan and the USA. Ideologies of nationalism, imperialism and modernity underpinned the process, coalescing in post-war debates about the future trajectory of Japanese society, Japan's Cold War alliance with the USA and the role of nuclear power in both. Consent to nuclear power was secured through the generation of a psychological state in the public mind combining the fear of nuclear attack and the hope of unlimited consumption in a nuclear-fuelled post-modern world