Forced Moves or Good Tricks in Design Space? Landmarks in the Evolution of Neural Mechanisms for Action Selection

This review considers some important landmarks in animal evolution, asking to what extent specialized action-selection mechanisms play a role in the functional architecture of different nervous system plans, and looking for “forced moves” or “good tricks” (see Dennett, D., 1995, Darwin’s Dangerous Idea, Penguin Books, London) that could possibly transfer to the design of robot control systems. A key conclusion is that while cnidarians (e.g. jellyfish) appear to have discovered some good tricks for the design of behavior-based control systems—largely lacking specialized selection mechanisms—the emergence of bilaterians may have forced the evolution of a central ganglion, or “archaic brain”, whose main function is to resolve conflicts between peripheral systems. Whilst vertebrates have many interesting selection substrates it is likely that here too the evolution of centralized structures such as the medial reticular formation and the basal ganglia may have been a forced move because of the need to limit connection costs as brains increased in size

Evolutionary Expansions and Neofunctionalization of Ionotropic Glutamate Receptors in Cnidaria

Reef ecosystems are composed of a variety of organisms, transient species of fish and invertebrates, microscopic bacteria and viruses, and structural organisms that build the living foundation, coral. Sessile cnidarians, corals and anemones, interpret dynamic environments of organisms and abiotic factors through a molecular interface. Recognition of foreign molecules occurs through innate immunity via receptors identifying conserved molecular patterns. Similarly, chemosensory receptors monitor the environment through specific ligands. Chemosensory receptors include ionotropic glutamate receptors (iGluRs), transmembrane ion channels involved in chemical sensing and neural signal transduction. Recently, an iGluR homolog was implicated in cnidarian immunological resistance to recurrent infections of bacterial pathogens. I postulate that iGluRs in cnidarians may act as danger-sensing and/or pathogen recognition receptors adjacent to immune defense and nervous system signaling. In Chapter One, I explain the exploration of diversity and divergence within cnidarian iGluRs, complimented with predicted functions in the context of correlated response to biological and environmental signals, setting the groundwork for functional characterization. In Chapter Two, I characterized the divergence of cnidarian iGluRs in comparison to other metazoans through maximum likelihood phylogenetic analyses, which revealed greater evolutionary expansion of cnidarian iGluR lineages, including a Cnidaria-specific class. Gene expression differentiation implies select iGluRs respond transcriptionally to bacterial challenge, supporting the hypothesis that cnidarian iGluRs respond to pathogen signals. In Chapter Three, I investigated a putative endogenous rhythm to iGluR expression, as chemosensory receptors may have the capacity to anticipate daily environmental fluctuations. While a circadian rhythm does not appear to be a primary contributor to biological rhythms in iGluR gene expression, symbiosis and diurnal fluctuations are implicated factors. In Chapter Four, I chromogenically localized Exaiptasia pallidaiGluR expression to the epidermis and concentrated within sensory tentacles, alongside cnidocytes. Expression of iGluRs in proximity of sensory cells is consistent with the putative function of iGluRs in cnidarian neural signaling. In the final chapter, I synthesized my research in its entirety; highlighting that cnidarian iGluRs expansions indicate cnidarian-specific neofunctionalization towards functions of chemosensory cnidarian-environmental signaling. New hypotheses and future research are presented to continue the study of iGluRs as chemosensory receptors within the cnidarian nervous system

Cell lineage specification during postembryonic brain development in drosophila : "expression and function of the cephalic gap gene empty spiracles"

The cephalic gap gene empty spiracles (ems) encodes a homeodomain transcription factor that is essential for the regional specification of the early embryonic brain in Drosophila. This thesis presents the analysis of ems expression and function during larval and pupal development of the brain. In the late larval brain eight neuroblast lineages express ems. In seven lineages ems is only transiently expressed and expression disappears in the early pupa. In contrast, all adult-specific neurons of the medial-most lineage (EM lineage) continuously express ems throughout larval and pupal development as well as in the adult brain. In a first study (Chapter II) we have investigated the function of ems in the EM lineage. The cell bodies of the EM lineage are located ventral to the antennal lobes from where they extend fine neurite arborizations into the suboesophageal ganglion and a prominent projection into the superior medial protocerebrum. Clonal mutant analysis of the adult-specific cells in the EM lineage has revealed three distinct functions of ems during larval development. First, the number of cells was reduced by half. This could be rescued by blocking apoptosis in ems mutant clones suggesting a function of ems in cell survival. Second, all mutant clones extended undirected misprojections into the surrounding neuropile. Third, the projection into the superior protocerebrum was missing in half of the clones. A closer examination of the projection patterns of ems mutant single-cell clones demonstrated that ems is required cell-autonomously in postmitotic neurons for the correct extension of the protocerebral projection. In our second study (Chapter III) we have examined the role of ems in development of the olfactory projection neurons (PNs). Two of the transiently expressing ems-positive lineages in the larval brain correspond to the adult-specific anterodorsal and lateral PN lineages (adPN and lPN, respectively). Clonal mutant analysis of the GH146-positive PNs revealed different roles of ems in the two lineages. In the adPN lineage transient ems expression is required for precise dendritic targeting. In the lPN lineage ems function is necessary for the formation of the correct number of progeny during larval development. Furthermore, timely down-regulation of ems expression is necessary for the proper connectivity of PNs. The finding that ems and its mammalian homologs Emx1/Emx2 are both expressed in second order olfactory PNs suggests conserved genetic mechanisms for the specific relay of olfactory information to higher brain centres

A Post-Synaptic Scaffold at the Origin of the Animal Kingdom

The evolution of complex sub-cellular structures such as the synapse requires the assembly of multiple proteins, each conferring added functionality to the integrated structure. Tracking the early evolution of synapses has not been possible without genomic information from the earliest branching animals. As the closest extant relatives to the Eumetazoa, Porifera (sponges) represent a pivotal group for understanding the evolution of nervous systems, because sponges lack neurons with clearly recognizable synapses, in contrast to eumetazoan animals.We show that the genome of the demosponge Amphimedon queenslandica possesses a nearly complete set of post-synaptic protein homologs whose conserved interaction motifs suggest assembly into a complex structure. In the critical synaptic scaffold gene, dlg, residues that make hydrogen bonds and van der Waals interactions with the PDZ ligand are 100% conserved between sponge and human, as is the motif organization of the scaffolds. Expression in Amphimedon of multiple post-synaptic gene homologs in larval flask cells further supports the existence of an assembled structure. Among the few post-synaptic genes absent from Amphimedon, but present in Eumetazoa, are receptor genes including the entire ionotropic glutamate receptor family.Highly conserved protein interaction motifs and co-expression in sponges of multiple proteins whose homologs interact in eumetazoan synapses indicate that a complex protein scaffold was present at the origin of animals, perhaps predating nervous systems. A relatively small number of crucial innovations to this pre-existing structure may represent the founding changes that led to a post-synaptic element

Current directions and future perspectives from the third Nematostella research conference

Author Posting. © The Author(s), 2014. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution. The definitive version was published in Zoology 118 (2015): 135-140, doi:10.1016/j.zool.2014.06.005.The third Nematostella vectensis Research Conference took place in December 2013 in Eilat, Israel, as a satellite to the 8th International Conference on Coelenterate Biology. The starlet sea anemone, Nematostella vectensis, has emerged as a powerful cnidarian model, in large part due to the extensive genomic and transcriptomic resources and molecular approaches that are becoming available for Nematostella, which were the focus of several presentations. In addition, research was presented highlighting the broader utility of this species for studies of development, circadian rhythms, signal transduction, and gene–environment interactions.Research in the authors’ laboratories on Nematostella is supported by National Science Foundation grants MCB-1057354 to A.M.T. and MCB-0924749 to T.D.G. Travel support for the meeting was provided to T.D.G. by Illumina, Inc. (San Diego, CA, USA), to A.M.R. by the University of North Carolina at Charlotte, and to A.M.T. by the Israel–US Binational Science Foundation (Jerusalem, Israel)

Ion channels and the tree of life

The field of comparative neurobiology has deep roots. I will begin by giving an overview of the parts of its history that I feel are most relevant for this dissertation. Within this history lies a wealth of zoological research and penetrating theories that are underutilized by modern evolutionary biologists. The age of whole-genome sequencing provides a perfect opportunity to revisit and perhaps update this corpus to better understand the phylogenetic history of organismal behavior. The first three chapters of my dissertation will be case studies on the evolution of sodium-selective ion channels. Sodium channels are responsible for much of the electrical signaling in animal nervous systems and muscles, but their evolutionary relationships have not yet been explored with the modern tools of phylogenetics and comparative genomics. Chapter 1 will deal with the classic Nav channels which create action potentials in nerves and muscles. There I will show that this gene family pre-dates the nervous system and even animal multicellularity. Chapter two will investigate sodium leak channels, which likley create the leak conductance measured by Hodgkin and Huxley. These channels turn out to be close relatives of fungal calcium channels, a relationship which illuminates the evolution of both groups. Chapter three is on bacterial sodium channels and their use as models for other sodium channel types. The final chapter will turn away from sodium channels in particular and discuss the evolution of animal nervous systems by means of ion channel genomics. In that chapter I will show that the genomic complements of ion channels that animals with nervous systems possess evolved independently to large degree, and that the early evolution of nervous systems also involved periods of gene loss. I will end with a more general discussion of convergent evolution, a key theme of this dissertation, and its effect on comparative analyses in the age of genomics.Ecology, Evolution and Behavio

Handbook of Marine Model Organisms in Experimental Biology

"The importance of molecular approaches for comparative biology and the rapid development of new molecular tools is unprecedented. The extraordinary molecular progress belies the need for understanding the development and basic biology of whole organisms. Vigorous international efforts to train the next-generation of experimental biologists must combine both levels – next generation molecular approaches and traditional organismal biology. This book provides cutting-edge chapters regarding the growing list of marine model organisms. Access to and practical advice on these model organisms have become aconditio sine qua non for a modern education of advanced undergraduate students, graduate students and postdocs working on marine model systems. Model organisms are not only tools they are also bridges between fields – from behavior, development and physiology to functional genomics. Key Features Offers deep insights into cutting-edge model system science Provides in-depth overviews of all prominent marine model organisms Illustrates challenging experimental approaches to model system research Serves as a reference book also for next-generation functional genomics applications Fills an urgent need for students Related Titles Jarret, R. L. & K. McCluskey, eds. The Biological Resources of Model Organisms (ISBN 978-1-1382-9461-5) Kim, S.-K. Healthcare Using Marine Organisms (ISBN 978-1-1382-9538-4) Mudher, A. & T. Newman, eds. Drosophila: A Toolbox for the Study of Neurodegenerative Disease (ISBN 978-0-4154-1185-1) Green, S. L. The Laboratory Xenopus sp. (ISBN 978-1-4200-9109-0)