Production of H2O2 by injured zebrafish skin cells promotes the regeneration of nearby somatosensory axon terminals, thus coordinating wound healing of the skin with sensory reinnervation.

The upper rhombic lip, a prominent germinal zone of the cerebellum, was recently demonstrated to generate different neuronal cell types over time from spatial subdomains. We have characterized the differentiation of the upper rhombic lip derived granule cell population in stable GFP-transgenic zebrafish in the context of zebrafish cerebellar morphogenesis. Time-lapse analysis followed by individual granule cell tracing demonstrates that the zebrafish upper rhombic lip is spatially patterned along its mediolateral axis producing different granule cell populations simultaneously. Time-lapse recordings of parallel fiber projections and retrograde labeling reveal that spatial patterning within the rhombic lip corresponds to granule cells of two different functional compartments of the mature cerebellum: the eminentia granularis and the corpus cerebelli. These cerebellar compartments in teleosts correspond to the mammalian vestibulocerebellar and non-vestibulocerebellar system serving balance and locomotion control, respectively. Given the high conservation of cerebellar development in vertebrates, spatial partitioning of the mammalian granule cell population and their corresponding earlier-produced deep nuclei by patterning within the rhombic lip may also delineate distinct functional compartments of the cerebellum. Thus, our findings offer an explanation for how specific functional cerebellar circuitries are laid down by spatio-temporal patterning of cerebellar germinal zones during early brain development.

Paclitaxel (Brand name Taxol) is widely used in the treatment of common cancers like breast, ovarian and lung cancer. Although highly effective in blocking tumor progression, paclitaxel also causes peripheral neuropathy as a side effect in 60-70% of chemotherapy patients. Recent efforts by numerous labs have aimed at defining the underlying mechanisms of paclitaxel-induced peripheral neuropathy (PIPN). In vitro models using rodent dorsal root ganglion neurons, human induced pluripotent stem cells, and rodent in vivo models have revealed a number of molecular pathways affected by paclitaxel within axons of sensory neurons and within other cell types, such as the immune system and peripheral glia, as well skin. These studies revealed that paclitaxel induces altered calcium signaling, neuropeptide and growth factor release, mitochondrial damage and reactive oxygen species formation, and can activate ion channels that mediate responses to extracellular cues. Recent studies also suggest a role for the matrix-metalloproteinase 13 (MMP-13) in mediating neuropathy. These diverse changes may be secondary to paclitaxelinduced microtubule transport impairment. Human genetic studies, although still limited, also highlight the involvement of cytoskeletal changes in PIPN. Newly identified molecular targets resulting from these studies could provide the basis for the development of therapies with which to either prevent or reverse paclitaxel-induced peripheral neuropathy in chemotherapy patients.

Paclitaxel is a microtubule-stabilizing chemotherapeutic agent that is widely used in cancer treatment and in a number of curative and palliative regimens. Despite its beneficial effects on cancer, paclitaxel also damages healthy tissues, most prominently the peripheral sensory nervous system. The mechanisms leading to paclitaxelinduced peripheral neuropathy remain elusive, and therapies that prevent or alleviate this condition are not available. We established a zebrafish in vivo model to study the underlying mechanisms and to identify pharmacological agents that may be developed into therapeutics. Both adult and larval zebrafish displayed signs of paclitaxel neurotoxicity, including sensory axon degeneration and the loss of touch response in the distal caudal fin. Intriguingly, studies in zebrafish larvae showed that paclitaxel rapidly promotes epithelial damage and decreased mechanical stress resistance of the skin before induction of axon degeneration. Moreover, injured paclitaxel-treated zebrafish skin and scratch-wounded human keratinocytes (HEK001) display reduced healing capacity. Epithelial damage correlated with rapid accumulation of fluorescein-conjugated paclitaxel in epidermal basal keratinocytes, but not axons, and upregulation of matrix-metalloproteinase 13 (MMP-13, collagenase 3) in the skin. Pharmacological inhibition of MMP-13, in contrast, largely rescued paclitaxel-induced epithelial damage and neurotoxicity, whereas MMP-13 overexpression in zebrafish embryos rendered the skin vulnerable to injury under mechanical stress conditions. Thus, our studies provide evidence that the epidermis plays a critical role in this condition, and we provide a previously unidentified candidate for therapeutic interventions.aclitaxel is a microtubule-stabilizing chemotherapeutic agent that is widely used in the treatment of common cancers, including breast, ovarian, and lung cancer. Despite its promising anticancerous properties, paclitaxel also damages healthy tissues, most prominently peripheral axons of somatosensory neurons (reviewed in ref. 1). Paclitaxel-induced peripheral neuropathy initiates in the distal extremities and presents as neuropathic pain syndrome, temperature sensitivity, and paresthesia (tingling and numbness). Nerve biopsies from patients suggest that axon degeneration is the primary manifestation of this condition, followed by secondary demyelination and nerve fiber loss in severely affected patients (1, 2). Certain drugs have been shown in vitro and in vivo to protect against paclitaxel-induced nerve damage, including acetyl-L-carnitine, erythropoietin, alpha-lipoic acid, olesoxime, amifostine, nerve growth factor, and glutamate (reviewed in ref.3). However, so far, these agents have either not successfully passed clinical trials or merely alleviate symptoms such as pain without prevention (1). Thus, a better understanding of the underlying causes of paclitaxel-induced peripheral neuropathy is necessary and may help identify new candidate drugs with which to treat this condition.A widely...

Peripheral sensory axons innervate the epidermis early in embryogenesis to detect touch stimuli. To characterize the time course of cutaneous innervation and the nature of interactions between sensory axons and skin cells at early developmental stages, we conducted a detailed analysis of cutaneous innervation in the head, trunk, and tail of zebrafish embryos and larvae from 18 to 78 hours postfertilization. This analysis combined live imaging of fish expressing transgenes that highlight sensory neurons and skin cells, transmission electron microscopy (TEM), and serial scanning electron microscopy (sSEM). In zebrafish, the skin initially consists of two epithelial layers, and all of the axons in the first wave of innervation are free endings. Maturation of the epithelium coincides with, but does not depend on, its innervation by peripheral sensory axons. We found that peripheral axons initially arborize between the two epithelial skin layers, but not within the basal lamina, as occurs in other organisms. Strikingly, as development proceeds, axons become tightly enveloped within basal keratinocytes, an arrangement suggesting that keratinocytes may serve structural or functional roles, akin to Schwann cells, in somatosensation mediated by these sensory neurons.