Systemic loss of Sarm1 protects Schwann cells from chemotoxicity by delaying axon degeneration

Protecting the nervous system from chronic effects of physical and chemical stress is a pressing clinical challenge. The obligate pro-degenerative protein Sarm1 is essential for Wallerian axon degeneration. Thus, blocking Sarm1 function is emerging as a promising neuroprotective strategy with therapeutic relevance. Yet, the conditions that will most benefit from inhibiting Sarm1 remain undefined. Here we combine genome engineering, pharmacology and high-resolution intravital videmicroscopy in zebrafish to show that genetic elimination of Sarm1 increases Schwann-cell resistance to toxicity by diverse chemotherapeutic agents after axonal injury. Synthetic degradation of Sarm1-deficient axons reversed this effect, suggesting that glioprotection is a non-autonomous effect of delayed axon degeneration. Moreover, loss of Sarm1 does not affect macrophage recruitment to nerve-wound microenvironment, injury resolution, or neural-circuit repair. These findings anticipate that interventions aimed at inhibiting Sarm1 can counter heightened glial vulnerability to chemical stressors and may be an effective strategy to reduce chronic consequences of neurotrauma.Tian et al. showed that systemic elimination of Sarm1 in zebrafish increases Schwann-cell resistance to chemotherapeutics and protects axons from Wallerian degeneration. They use genetics, pharmacology, and high resolution intravital videomicroscopy to study Sarm1 in vivo

Afferent Neurons of the Zebrafish Lateral Line Are Strict Selectors of Hair-Cell Orientation

Hair cells in the inner ear display a characteristic polarization of their apical stereocilia across the plane of the sensory epithelium. This planar orientation allows coherent transduction of mechanical stimuli because the axis of morphological polarity of the stereocilia corresponds to the direction of excitability of the hair cells. Neuromasts of the lateral line in fishes and amphibians form two intermingled populations of hair cells oriented at 180° relative to each other, however, creating a stimulus-polarity ambiguity. Therefore, it is unknown how these animals resolve the vectorial component of a mechanical stimulus. Using genetic mosaics and live imaging in transgenic zebrafish to visualize hair cells and neurons at single-cell resolution, we show that lateral-line afferents can recognize the planar polarization of hair cells. Each neuron forms synapses with hair cells of identical orientation to divide the neuromast into functional planar-polarity compartments. We also show that afferent neurons are strict selectors of polarity that can re-establish synapses with identically oriented targets during hair-cell regeneration. Our results provide the anatomical bases for the physiological models of signal-polarity resolution by the lateral line

El peix zebra com a sistema model per a l'estudi de les malalties humanes

El potencial dels estudis de malalties humanes en organismes model ha crescut substancialment durant els últims anys. L'herència evolutiva compartida entre els vertebrats permet l'ús d'organismes genèticament modificables per modelitzar malalties humanes de difícil estudi in vitro, i també faciliten l'estudi de malalties multifactorials complexes que en humans es presenten amb diferències d'expressivitat i penetrància, cosa que en dificulta la caracterització. Estudis en diversos organismes model han demostrat que diversos gens el producte dels quals permet el desenvolupament i assemblatge de teixits i òrgans també estan involucrats en malalties hereditàries i congènites comunes. Els desenvolupaments tecnològics aconseguits durant els darrers anys també ens permeten modelitzar malalties rares en organismes model. En aquest article intentarem demostrar que el peix zebra és un sistema que presenta qualitats que el fan ideal per a aquests estudis. En particular, presentarem com a exemple algunes malalties neurodegeneratives i la pèrdua d'audició i equilibri. Finalment, també discutirem la utilitat del peix zebra per a estudis de regeneració de cèl·lules sensorials.The zebrafish as a model system for the study of human pathologies. The potential of studying human pathologies in model organisms has grown substantially over the past few years. The shared evolutionary history among all vertebrates allows the use of genetically modified organisms to model human diseases that cannot be studied in vitro. It also facilitates the study of multifactorial complex pathologies that in humans present differences in expressivity and penetrance, which complicates their characterization. Studies in several model organisms have demonstrated that genes products that direct the development and assembly of tissues and organs are also involved in common genetic and congenital diseases. Additionally, technological developments permit the modeling of rare diseases in model organisms. In this chapter we will try to demonstrate that the zebrafish is a model that presents several qualities that make it ideal for this kind of studies. In particular, we will present some neurodegenerative diseases and loss of hearing and balance as examples. Finally, we will discuss the use of the zebrafish for studies on the regeneration of sensory cells

Delaying Gal4-driven gene expression in the zebrafish with morpholinos and Gal80.

The modular Gal4/UAS gene expression system has become an indispensable tool in modern biology. Several large-scale gene- and enhancer-trap screens in the zebrafish have generated hundreds of transgenic lines expressing Gal4 in unique patterns. However, the early embryonic expression of the Gal4 severely limits their use for studies on regeneration or behavior because UAS-driven effectors could disrupt normal organogenesis. To overcome this limitation, we explored the use of the Gal4 repressor Gal80 in transient assays and with stable transgenes to temporally control Gal4 activity. We also validated a strategy to delay Gal4-driven gene expression using a morpholino targeted to Gal4. The first approach is limited to transgenes expressing the native Gal4. The morphant approach can also be applied to transgenic lines expressing the Gal4-VP16 fusion protein. It promises to become a standard approach to delay Gal4-driven transgene expression and enhance the genetic toolkit for the zebrafish

Inner Ear: Ca2+n You Feel the Noise?

AbstractThe death of hair cells in the inner ear as a result of exposure to loud noise can lead to irreversible deafness. New work shows that the mammalian cochlea can sense noxious sounds and use Ca2+ waves to rapidly propagate hair cell damage signals

Gal80 expression inhibits Gal4 activity.

<p>(<b>A–H</b>) Embryos resulting from a cross between <i>Tg[hsp70:Gal4]</i> and <i>Tg[UAS:Kaede]</i> fish were either non-injected (NI, A–D) or injected with 100 pg of mRNA encoding full-length Gal80 (E–H). Representative specimens are depicted at 24 hpf (A–B, N = 18 GFP<b>⁺</b>/72 fish; E–F, N = 0 GFP<b>⁺</b>/75 fish) and 5 dpf (C–D, N = 18 GFP<b>⁺</b>/77 fish; G–H, N = 19 GFP<b>⁺</b>/82 fish). In H, asterisks indicate the fish displaying GFP. (<b>I–N</b>) Embryos resulting from a cross of <i>Tg[UAS:Kaede]</i> fish were injected with a DNA encoding full-length Gal4 under the control of the HuC promoter either alone (NI, I–K, N = 32) or with 100 pg of mRNA encoding full-length Gal80 (L–N, N = 37). Representative specimens are depicted at 48 hpf, 3 and 7 dpf.</p

Temporal control of Gal80 expression.

<p>(<b>A</b>) Schematic representation of the construct hsp70:Gal80-myc. (<b>B</b>) Anti-myc western blotting of 48 hpf fish resulting from a cross of <i>Tg[hsp70:Gal80-myc]</i> fish after 0, 30 and 60 minutes of heat-shock. (<b>C</b>) Embryos resulting from a cross between <i>Tg[hsp70:Gal80-Myc]</i> and <i>Tg[UAS:Kaede]</i> fish were not submitted (a–c) or submitted to a one-hour heat-shock (d–f). Representative specimens are depicted for anti-Gal80 <i>in situ</i> hybridization at 30 hpf (a, d) or for Kaede expression at 2 dpf (b–c, d–e). (Scale bars: 150 µm). (<b>D</b>) Embryos resulting from a cross between <i>Tg[hsp70:Gal80-Myc]</i> and <i>Tg[UAS:Kaede]</i> fish were injected with a DNA encoding full-length Gal4 under the control of the β-actin promoter. At 24 hpf, the embryos were subjected to a 30-minute heat-shock at 39 degrees and immediately photo-converted. The following day, immunostaining anti-myc (c, g) was performed on fish expressing Gal80 (a–d) or not expressing Gal80 (e–h). The figure depicts muscle fibers for the expression of Kaede^red (a, e) and Kaede^green (b, f). (Scale bars: 20 µm).</p

Gal4 morpholino temporarily inhibits Gal4 expression in a dose-dependant manner.

<p>Embryos resulting from a cross of <i>Tg[hspGFF53A;UAS:EGFP]</i> double transgenic animals were either non-injected (A–E) or injected with 1 ng (F–J), 3 ng (K–O) or 5 ng (P–T) of Gal4 MO (N = 94). Representative specimens are depicted at 2, 4 and 6 dpf. White arrows indicate green fluorescence at the level of the posterior afferent lateralis ganglion. (Scale bars: 150 µm).</p