Optic axon guidance during development and regeneration in the zebrafish

Directed regeneration of axons in the CNS has potential for the treatment of CNS disorders and injuries. In contrast to mammals, following optic nerve lesion zebrafish regenerate axons that navigate to their correct targets and form new synapses leading to functional recovery. Correct pathfinding is thought to rely on a range of molecular cues in the CNS which the growing axon expresses receptors for. However, the specific guidance cues are not well elucidated. It is likely that a proportion of them will be the same as during development, while some may be specific to regeneration. Alternatively, axons may simply retrace former trajectories guided by the molecular environment or mechanical constraints of degenerating tracts, as demonstrated in the mammalian PNS. To elucidate this, we investigated regeneration in the astray/robo2 knockout mutant which exhibits misprojection of optic axons during development leading to the establishment of ectopic tracts. We show that degenerating tracts do not provide a strong guidance cue for regenerating axons in the CNS as ectopic tracts in the astray mutant are not repopulated following lesion despite presenting a similar environment to entopic degenerating tracts. We also find that as astray mutant (knockout) and robo2 morphant (transient knockdown) projection and termination errors persist in the adult, it is clear that there is not an efficient correction mechanism for large-scale pathfinding errors of optic axons during development. In addition, we find a reduced importance of the axon guidance receptor Robo2 and its repellent ligand Slit2 for pathfinding during regeneration as specific developmental pathfinding errors of optic axons in astray mutants are corrected during adult optic nerve regeneration and global overexpression of Slit2 elicits pathfinding defects during development but not regeneration. To address regeneration-associated gene regulation in axotomised retinal ganglion cells, we carried out a microarray analysis. We found that many genes detected as a gradient in the adult retina during regeneration are not differentially expressed in the embryonic eye, despite having distinct expression patterns in other embryonic tissues. Of the genes which exhibit strong differential expression in the retina of both regenerating adults and developing embryos, foxI1 is one of the most interesting candidates as other fox genes have been implicated in axon guidance and due to its highly restricted retinal expression pattern. Surprisingly, further investigation has revealed that foxI1 knockout mutant embryos have retinotectal projections which appear normal in terms of axon pathfinding and mapping. Another family of genes indicated by the array, which are cytosolic phosphoproteins known to be involved in the signal transduction cascade of multiple inhibitory guidance cues during axon growth, are the crmps. Knocking down crmp2 with morpholinos during development resulted in a sparser innervation of the tectum with individual axons which trend towards having less complex arbors with shorter branches and reduced overall axon length. As a whole this work adds to our current knowledge of optic axon guidance during development and regeneration and the relative importance and effect of selected potential guidance cues, which may help toward informing future mammalian CNS regeneration research

Collisional Evolution of Irregular Satellite Swarms: Detectable Dust around Solar System and Extrasolar Planets

Since the 1980's it has been becoming increasingly clear that the Solar System's irregular satellites are collisionally evolved. We derive a general model for the collisional evolution of an irregular satellite swarm and apply it to the Solar System and extrasolar planets. Our model reproduces the Solar System's complement of observed irregulars well, and suggests that the competition between grain-grain collisions and Poynting-Robertson (PR) drag helps set the fate of the dust. Because swarm collision rates decrease over time the main dust sink can change with time, and may help unravel the accretion history of synchronously rotating regular satellites that show brightness asymmetries. Some level of dust must be present on AU scales around the Solar System's giant planets, which we predict may be at detectable levels. We also predict whether dust produced by extrasolar circumplanetary swarms can be detected. The coronagraphic instruments on JWST will have the ability to detect the dust generated by these swarms, which are most detectable around planets that orbit at tens of AU from the youngest stars. Because the collisional decay of swarms is relatively insensitive to planet mass, swarms can be much brighter than their host planets and allow discovery of Neptune-mass planets that would otherwise remain invisible. This dust may have already been detected. The observations of the planet Fomalhaut b can be explained as scattered light from dust produced by the collisional decay of an irregular satellite swarm around a 10 Earth-mass planet. Such a swarm comprises about 5 Lunar masses worth of irregular satellites. Finally, we consider what happens if Fomalhaut b passes through Fomalhaut's main debris ring, which allows the circumplanetary swarm to be replenished through collisions with ring planetesimals. (abridged)Comment: accepted to MNRA

Mercurian impact ejecta: Meterorites and mantle

We have examined the fate of impact ejecta liberated from the surface of Mercury due to impacts by comets or asteroids, in order to study (1) meteorite transfer to Earth, and (2) re-accumulation of an expelled mantle in giant-impact scenarios seeking to explain Mercury's large core. In the context of meteorite transfer, we note that Mercury's impact ejecta leave the planet's surface much faster (on average) than other planet's in the Solar System because it is the only planet where impact speeds routinely range from 5-20 times the planet's escape speed. Thus, a large fraction of mercurian ejecta may reach heliocentric orbit with speeds sufficiently high for Earth-crossing orbits to exist immediately after impact, resulting in larger fractions of the ejecta reaching Earth as meteorites. We calculate the delivery rate to Earth on a time scale of 30 Myr and show that several percent of the high-speed ejecta reach Earth (a factor of -3 less than typical launches from Mars); this is one to two orders of magnitude more efficient than previous estimates. Similar quantities of material reach Venus. These calculations also yield measurements of the re-accretion time scale of material ejected from Mercury in a putative giant impact (assuming gravity is dominant). For mercurian ejecta escaping the gravitational reach of the planet with excess speeds equal to Mercury's escape speed, about one third of ejecta re-accretes in as little as 2 Myr. Thus collisional stripping of a silicate proto-mercurian mantle can only work effectively if the liberated mantle material remains in small enough particles that radiation forces can drag them into the Sun on time scale of a few million years, or Mercury would simply re-accrete the material.Comment: 14 pages. Submitted to Meteoritics and Planetary Scienc

Fate mapping melanoma persister cells through regression and into recurrent disease in adult zebrafish

Melanoma heterogeneity and plasticity underlie therapy resistance. Some tumour cells possess innate resistance, while others reprogramme during drug exposure and survive to form persister cells, a source of potential cancer cells for recurrent disease. Tracing individual melanoma cell populations through tumour regression and into recurrent disease remains largely unexplored, in part, because complex animal models are required for live imaging of cell populations over time. Here, we applied tamoxifen-inducible cre(ERt2)/loxP lineage tracing to a zebrafish model of MITF-dependent melanoma regression and recurrence to image and trace cell populations in vivo through disease stages. Using this strategy, we show that melanoma persister cells at the minimal residual disease site originate from the primary tumour. Next, we fate mapped rare MITF-independent persister cells and demonstrate that these cells directly contribute to progressive disease. Multiplex immunohistochemistry confirmed that MITF-independent persister cells give rise to Mitfa(+) cells in recurrent disease. Taken together, our work reveals a direct contribution of persister cell populations to recurrent disease, and provides a resource for lineage-tracing methodology in adult zebrafish cancer models

Changes in admission thresholds in English Emergency Departments

YesBackground: The most common route to a hospital bed in an emergency is via an emergency department (ED). Many recent initiatives and interventions have the objective of reducing the number of unnecessary emergency admissions. We aimed to assess whether ED admission thresholds had changed over time taking account of the casemix of patients arriving at ED. Methods: We conducted a retrospective cross-sectional analysis of more than 20 million attendances at 47 consultant-led emergency departments in England between April 2010 and March 2015. We used mixed- effects logistic regression to estimate the odds of a patient being admitted to hospital and the impact of a range of potential explanatory variables. Models were developed and validated for four attendance subgroups : ambulance-conveyed children; walk-in children; ambulance-conveyed adults; and walk-in adults. Results: 23.8% of attendances were for children aged under 18 years, 49.7% were female and 30.0% were conveyed by ambulance. The number of ED attendances increased by 1.8% per annum between April 2010 – March 2011 (year 1) and April 2014 –March 2015 (year 5). The proportion of these attendances that were admitted to hospital changed little between year 1 (27.0%) and year 5 (27.5%). However, after adjusting for patient and attendance characteristics the odds of admission over the five year period had reduced by: 15.2% (95% CI 13.4% - 17.0%) for ambulance-conveyed children; 22.6% (95% CI 21.7%-23.5%) for walk-in children; 20.9% (95% CI 4%-21.5%) for ambulance conveyed adults; and 22.9% (95% CI 22.4%-23.5%) for walk-in adults. Conclusions: The casemix-adjusted odds of admission via ED to NHS hospitals in England have decreased since April 2010. EDs are admitting a similar proportion of patients to hospital despite increases in the complexity and acuity of presenting patients. Without these threshold changes, the number of emergency admissions would have been 11.9% higher than was the case in year 5

Assaying sensory ciliopathies using calcium biosensor expression in zebrafish ciliated olfactory neurons

Background: Primary cilia mediate signal transduction by acting as an organizing scaffold for receptors, signalling proteins and ion channels. Ciliated olfactory sensory neurons (OSNs) organize olfactory receptors and ion channels on cilia and generate a calcium influx as a primary signal in odourant detection. In the zebrafish olfactory placode, ciliated OSNs and microvillus OSNs constitute the major OSN cell types with distinct odourant sensitivity. Methods: Using transgenic expression of the calcium biosensor GCaMP5 in OSNs, we analysed sensory cilia-dependent odour responses in live zebrafish, at individual cell resolution. oval/ift88 mutant and ift172 knockdown zebrafish were compared with wild-type siblings to establish ciliated OSN sensitivity to different classes of odourants. Results: oval/ift88 mutant and ift172 knockdown zebrafish showed fewer and severely shortened OSN cilia without a reduction in OSN number. The fraction of responding OSNs and response amplitudes to bile acids and food odour, both sensed by ciliated OSNs, were significantly reduced in ift88 mutants and ift172-deficient embryos, while the amino acids responses were not significantly changed. Conclusions: Our approach presents a quantitative model for studying sensory cilia signalling using zebrafish OSNs. Our results also implicate ift172-deficiency as a novel cause of hyposmia, a reduced sense of smell, highlighting the value of directly assaying sensory cilia signalling in vivo and supporting the idea that hyposmia can be used as a diagnostic indicator of ciliopathies. Electronic supplementary material The online version of this article (10.1186/s13630-018-0056-1) contains supplementary material, which is available to authorized users

Portland Region Parks: Measuring Equity in Access

The goal of this Capstone project is to examine equity as it applies to the Portland region. CLF defines equity as “the right of every person to have access to opportunities necessary for satisfying essential needs and advancing their well-being” (CLF, 2007). Equity as it relates to parks is a difficult concept to define. Our project specifically focused on cataloging the amenities of ninety-three newly developed parks and making observations about park access in an effort to build a better picture of what equity looks like in the Portland region

Analysis of the astray/robo2 Zebrafish Mutant Reveals that Degenerating Tracts Do Not Provide Strong Guidance Cues for Regenerating Optic Axons

During formation of the optic projection in astray/robo2 mutant zebrafish, optic axons exhibit rostro-caudal pathfinding errors, ectopic midline crossing and increased terminal arbor size. Here we show that these errors persist into adulthood, even when robo2 function is conditionally reduced only during initial formation of the optic projection. Adult errors include massive ectopic optic tracts in the telencephalon. During optic nerve regeneration in astray/robo2 animals, these tracts are not re-populated and ectopic midline crossing is reduced compared to unlesioned mutants. This is despite a comparable macrophage/microglial response and upregulation of contactin1a in oligodendrocytes of entopic and ectopic tracts. However, other errors, such as expanded termination areas and ectopic growth into the tectum, were frequently re-committed by regenerating optic axons. Retinal ganglion cells with regenerating axons re-express robo2 and expression of slit ligands is maintained in some areas of the adult optic pathway. However, slit expression is reduced rostral and caudal to the chiasm, compared to development and ubiquitous overexpression of Slit2 did not elicit major pathfinding phenotypes. This shows that (1) there is not an efficient correction mechanism for large-scale pathfinding errors of optic axons during development; (2) degenerating tracts do not provide a strong guidance cue for regenerating optic axons in the adult CNS, unlike the PNS; and (3) robo2 is less important for pathfinding of optic axons during regeneration than during development

AgRP/NPY Neuron Excitability Is Modulated by Metabotropic Glutamate Receptor 1 During Fasting

The potential to control feeding behavior via hypothalamic AgRP/NPY neurons has led to many approaches to modulate their excitability—particularly by glutamatergic input. In the present study using NPY-hrGFP reporter mice, we visualize AgRP/NPY neuronal metabotropic glutamate receptor 1 (mGluR1) expression and test the effect of fasting on mGluR1 function. Using the pharmacological agonist dihydroxyphenylglycine (DHPG), we demonstrate the enhanced capacity of mGluR1 to drive firing of AgRP/NPY neurons after overnight fasting, while antagonist 3-MATIDA reduces firing. Further, under synaptic blockade we demonstrate that DHPG acts directly on AgRP/NPY neurons to create a slow inward current. Using an in vitro approach, we show that emulation of intracellular signals associated with fasting by forskolin enhances DHPG induced phosphorylation of extracellularly regulated-signal kinase (1/2) in GT1-7 cell culture. We show in vivo that blocking mGluR1 by antagonist 3-MATIDA lowers fasting induced refeeding. In summary, this study identifies a novel layer of regulation on AgRP/NPY neurons integrated with whole body energy balance