Neurofly 2008 abstracts : the 12th European Drosophila neurobiology conference 6-10 September 2008 Wuerzburg, Germany

This volume consists of a collection of conference abstracts

Epigenetic and transcriptional regulation of cortico-ponto-cerebellar circuit formation

The precerebellar system constitutes an array of nuclei located in the mammalian hindbrain and conveys movement and balance information from the cortex, spinal cord and periphery to the cerebellum (Sotelo, 2004). Within this system, the pontine nuclei (PN), including pontine gray and reticulotegmental nuclei, mostly relay cortical information (Schwarz and Thier, 1999). During the processing through the cortex, PN and cerebellum, continuous maps of sensorimotor information are transformed into a complex fractured map (Leergaard et al., 2006). To date, however, there is a paucity of knowledge on the molecular and cellular mechanisms organizing this complex circuitry. Previous work suggests an intrinsic topographic organization, according to rostro-caudal progenitor origin, that is maintained during migration and nucleation of the PN (Di Meglio et al., 2013). As a result, one of the hallmarks of the PN topography is a well-defined population of Hox paralogous group 5 (PG5) expressing neurons in the posterior part of the PN. However, the molecular mechanisms governing the spatial expression pattern of Hox PG5 genes in the PN and their functional impact on circuit formation remain largely unknown. The first part of this thesis focuses on the molecular mechanisms of Hox PG5 induction in the precerebellar system. We find that the precise spatio-temporal expression pattern of Hox PG5 genes rely on the integration of environmental signaling and the resulting modifications of the epigenetic landscape. Unlike transcripts of more anterior Hox genes, expression of Hox PG5 genes is entirely excluded from progenitors in the rhombic lip (RL) and only induced in a subset of postmitotic neurons. Mapping and manipulation of signaling pathways show that the restriction of Hox PG5 induction to the ventrally located (i.e. posterior RL-derived) postmitotic pontine neuron subsets is due to an interplay between retinoic acid (RA) and Wnt environmental signaling. Assessment of histone profiles at Hox loci indicate that the induction of Hox PG5 genes through RA is tightly linked to a depletion of the histone mark H3K27me3. However, conditional inactivation of Ezh2, a member of the polycomb repressive complex 2 responsible for setting the H3K27me3 mark (Margueron and Reinberg, 2011), does not result in a de-repression of Hox PG5 genes in the progenitor domain. In contrast, removal of H3K27me3 in Ezh2 depleted PN neurons leads to an ectopic induction of Hox PG5 in rostral PN neuron subsets of the migratory stream showing an enhanced response to RA (Di Meglio et al., 2013). Moreover, high levels of RA-induced Hox PG5 expression in postmitotic PN neurons require Jmjd3, one of the enzymes known to catalyze the removal of methyl groups at H3K27 (Agger et al., 2007; De Santa et al., 2007). We show that Jmjd3 is physically present at RA responsive elements in proximity to the Hoxa5 promoter supporting the direct involvement of Jmjd3 in Hox PG5 induction. Thus, a central function of H3K27me3 regulation during late stages of precerebellar development is the establishment of a threshold for RA mediated activation of Hox PG5 genes to allow for diversification of PN neurons. Finally, we show how the integration of environmental signaling on the epigenetic level results in distinct changes of the three dimensional (3D) organization of chromatin at Hox PG5 loci in vivo. Together, the late specification of PN neurons employs a sophisticated sequence of interactions between signaling pathways such as RA and Wnt, and histone modifying enzymes like Ezh2 and Jmjd3. The second part of the thesis addresses the functional significance of Hox PG5 genes in sub-circuit formation of PN neurons. Using multiple conditional overexpression strategies, we show that the expression of Hoxa5 is sufficient to shape the input-output relationship of PN neurons. Hoxa5 expressing neurons migrate into a posterior position in the PN and induce a distinct transcriptional program specific for topographic circuit formation. Together, this indicates a crucial role of Hoxa5 in the specification of the positional identity of PN subsets. We further describe a genetically identified Hox PG5 negative PN subset that primarily projects to the paraflocculus, a lobule in the cerebellum heavily concerned with visually related tasks. Conditional overexpression of Hoxa5 in this PN subset leads to the ectopic targeting of several other lobes in the cerebellum concerned with processing of somatosensory information. This matches with the input connectivity of the PN that has been shown to be antero-posteriorly patterned, such that visual/medioposterior projections target the anterior, Hox PG5 negative, and somatosensory projections target the posterior, Hox PG5 positive part of the PN (Di Meglio et al., 2013; Leergaard and Bjaalie, 2007). Consequently, Hoxa5 overexpressing PN neurons are largely devoid of input from the visual cortex and primarily engage in a somatosensory hindlimb specific circuitry. One single Hox gene is thus sufficient to position neurons in the posterior aspects of the PN, change their transcriptional program and rearrange both, output connectivity to the cerebellum and input connectivity from the cortex. These findings extend the function of Hox genes to orchestrating topographic circuit formation in the PN. Further, the presented results point towards an involvement of Hox genes in the longstanding problem of fracturing of the somatosensory map that is realized between the cortex and the cerebellum

Proceedings of Abstracts Engineering and Computer Science Research Conference 2019

© 2019 The Author(s). This is an open-access work distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. For further details please see https://creativecommons.org/licenses/by/4.0/. Note: Keynote: Fluorescence visualisation to evaluate effectiveness of personal protective equipment for infection control is © 2019 Crown copyright and so is licensed under the Open Government Licence v3.0. Under this licence users are permitted to copy, publish, distribute and transmit the Information; adapt the Information; exploit the Information commercially and non-commercially for example, by combining it with other Information, or by including it in your own product or application. Where you do any of the above you must acknowledge the source of the Information in your product or application by including or linking to any attribution statement specified by the Information Provider(s) and, where possible, provide a link to this licence: http://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/This book is the record of abstracts submitted and accepted for presentation at the Inaugural Engineering and Computer Science Research Conference held 17th April 2019 at the University of Hertfordshire, Hatfield, UK. This conference is a local event aiming at bringing together the research students, staff and eminent external guests to celebrate Engineering and Computer Science Research at the University of Hertfordshire. The ECS Research Conference aims to showcase the broad landscape of research taking place in the School of Engineering and Computer Science. The 2019 conference was articulated around three topical cross-disciplinary themes: Make and Preserve the Future; Connect the People and Cities; and Protect and Care

The Drosophila immunoglobulin gene turtle encodes guidance molecules involved in axon pathfinding

Background: Neuronal growth cones follow specific pathways over long distances in order to reach their appropriate targets. Research over the past 15 years has yielded a large body of information concerning the molecules that regulate this process. Some of these molecules, such as the evolutionarily conserved netrin and slit proteins, are expressed in the embryonic midline, an area of extreme importance for early axon pathfinding decisions. A general model has emerged in which netrin attracts commissural axons towards the midline while slit forces them out. However, a large number of commissural axons successfully cross the midline even in the complete absence of netrin signaling, indicating the presence of a yet unidentified midline attractant. Results: The evolutionarily conserved Ig proteins encoded by the turtle/Dasm1 genes are found in Drosophila, Caenorhabditis elegans, and mammals. In Drosophila the turtle gene encodes five proteins, two of which are diffusible, that are expressed in many areas, including the vicinity of the midline. Using both molecular null alleles and transgenic expression of the different isoforms, we show that the turtle encoded proteins function as non-cell autonomous axonal attractants that promote midline crossing via a netrin-independent mechanism. turtle mutants also have either stalled or missing axon projections, while overexpression of the different turtle isoforms produces invasive neurons and branching axons that do not respect the histological divisions of the nervous system. Conclusion: Our findings indicate that the turtle proteins function as axon guidance cues that promote midline attraction, axon branching, and axonal invasiveness. The latter two capabilities are required by migrating axons to explore densely packed targets

Maintenance of cell type-specific connectivity and circuit function requires Tao kinase

Sensory circuits are typically established during early development, yet how circuit specificity and function are maintained during organismal growth has not been elucidated. To gain insight we quantitatively investigated synaptic growth and connectivity in the Drosophila nociceptive network during larval development. We show that connectivity between primary nociceptors and their downstream neurons scales with animal size. We further identified the conserved Ste20-like kinase Tao as a negative regulator of synaptic growth required for maintenance of circuit specificity and connectivity. Loss of Tao kinase resulted in exuberant postsynaptic specializations and aberrant connectivity during larval growth. Using functional imaging and behavioral analysis we show that loss of Tao-induced ectopic synapses with inappropriate partner neurons are functional and alter behavioral responses in a connection-specific manner. Our data show that fine-tuning of synaptic growth by Tao kinase is required for maintaining specificity and behavioral output of the neuronal network during animal growth

Fluorescent and photo-oxidizing TimeSTAMP tags track protein fates in light and electron microscopy.

Protein synthesis is highly regulated throughout nervous system development, plasticity and regeneration. However, tracking the distributions of specific new protein species has not been possible in living neurons or at the ultrastructural level. Previously we created TimeSTAMP epitope tags, drug-controlled tags for immunohistochemical detection of specific new proteins synthesized at defined times. Here we extend TimeSTAMP to label new protein copies by fluorescence or photo-oxidation. Live microscopy of a fluorescent TimeSTAMP tag reveals that copies of the synaptic protein PSD95 are synthesized in response to local activation of growth factor and neurotransmitter receptors, and preferentially localize to stimulated synapses in rat neurons. Electron microscopy of a photo-oxidizing TimeSTAMP tag reveals new PSD95 at developing dendritic structures of immature neurons and at synapses in differentiated neurons. These results demonstrate the versatility of the TimeSTAMP approach for visualizing newly synthesized proteins in neurons

Interaction dynamics and autonomy in cognitive systems

The concept of autonomy is of crucial importance for understanding life and cognition. Whereas cellular and organismic autonomy is based in the self-production of the material infrastructure sustaining the existence of living beings as such, we are interested in how biological autonomy can be expanded into forms of autonomous agency, where autonomy as a form of organization is extended into the behaviour of an agent in interaction with its environment (and not its material self-production). In this thesis, we focus on the development of operational models of sensorimotor agency, exploring the construction of a domain of interactions creating a dynamical interface between agent and environment. We present two main contributions to the study of autonomous agency: First, we contribute to the development of a modelling route for testing, comparing and validating hypotheses about neurocognitive autonomy. Through the design and analysis of specific neurodynamical models embedded in robotic agents, we explore how an agent is constituted in a sensorimotor space as an autonomous entity able to adaptively sustain its own organization. Using two simulation models and different dynamical analysis and measurement of complex patterns in their behaviour, we are able to tackle some theoretical obstacles preventing the understanding of sensorimotor autonomy, and to generate new predictions about the nature of autonomous agency in the neurocognitive domain. Second, we explore the extension of sensorimotor forms of autonomy into the social realm. We analyse two cases from an experimental perspective: the constitution of a collective subject in a sensorimotor social interactive task, and the emergence of an autonomous social identity in a large-scale technologically-mediated social system. Through the analysis of coordination mechanisms and emergent complex patterns, we are able to gather experimental evidence indicating that in some cases social autonomy might emerge based on mechanisms of coordinated sensorimotor activity and interaction, constituting forms of collective autonomous agency