To determine the impact of a controlled loss of dopaminergic neurons on locomotor function, we generated transgenic zebrafish, Tg(dat:CFP-NTR), expressing a cyan fluorescent protein-nitroreductase fusion protein (CFP-NTR) under the control of dopamine transporter (dat) cis-regulatory elements. Embryonic and larval zebrafish express the transgene in several groups of dopaminergic neurons, notably in the olfactory bulb, telencephalon, diencephalon and caudal hypothalamus. Administration of the pro-drug metronidazole (Mtz) resulted in activation of caspase 3 in CFP-positive neurons and in a reduction in dat-positive cells by 5 days postfertilization (dpf). Loss of neurons coincided with impairments in global locomotor parameters such as swimming distance, percentage of time spent moving, as well as changes in tail bend parameters such as time to maximal bend and angular velocity. Dopamine levels were transiently decreased following Mtz administration. Recovery of some of the locomotor parameters was observed by 7 dpf. However, the total numbers of dat-expressing neurons were still decreased at 7, 12, or 14 dpf, even though there was evidence for production of new dat-expressing cells. Tg(dat:CFP-NTR) zebrafish provide a model to correlate altered dopaminergic neuron numbers with locomotor function and to investigate factors influencing regeneration of dopaminergic neurons. Behavioral changes and neurochemical deficiencies have been previously described in the zebrafish following administration of neurotoxins such as 6-hydroxydopamine and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) which target the catecholaminergic neuron populations. Although dopaminergic neurons have been shown to regenerate in both the planarian (Nishimura et al. 2011) and salamander (Parish et al. 2007) neurotoxin-based models, this has not been demonstrated in the zebrafish brain. This lack of information may be attributed, in part, to the fact that although 6-hydroxydopamine and MPTP induce both neurochemical and behavioral changes, no dopaminergic neuron loss and cell death are detected in zebrafish (Anichtchik et al. 2004). Indeed, in larval zebrafish, MPTP treatments results in a short-lived reduction in tyrosine hydroxylase (TH) immunoreactivity at 5 and 6 dpf which is recovered by 7 dpf and does not lead to signs of apoptosis or cell death.To address the events that take place following DA neuron loss and to determine whether the ablated neuronal population can be re-established in the brain of larval zebrafish, we have Received March 25, 2015; revised manuscript received May 20, 2015; accepted May 26, 2015. Address correspondence and reprint requests to Dr Marc Ekker, Center for Advanced Research in Environmental Genomics, Department of Biology, University of Ottawa Ottawa, K1N-6N5, Canada. E-mail: mekker@uottawa.ca Abbreviations used: BrdU, 5-bromo-2 0 -deoxyuridine; CFP-NTR, cyan fluorescent protein-nitroreductase fusion protein; EGFP, -enhanced green fluorescent protein; MPTP, 1-methyl-4-phenyl-1,2,3,6-tetrahydro...

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Fibrosis-driven solid organ failure is a major global health burden. Spiny mice (genus: Acomys ) are terrestrial mammals that regenerate severe skin wounds without scars to avoid predation. To test whether spiny mice can also regenerate internal organ injuries, we performed acute obstructive or ischemic surgeries on adult kidneys of Acomys cahirinus compared to Mus musculus. Despite equivalent acute tissue damage, Acomys fully regenerate nephron structure, vascular & lymphatic networks, and organ function without fibrosis by 14d while Mus (CD1 or C57BL/6) develop extensive interstitial fibrosis and progress to organ failure and death. Comparative transcriptomic, epigenetic, and single-cell assays revealed that the Acomys genome appears poised to initiate a regenerative response at the time of injury. In addition, we found the Hippo pathway effector protein YAP localized to the nucleus in renal tubular epithelial cells (RTEs) undergoing scarless wound healing in Acomys while it was either cytoplasmic or not detectable in Mus RTEs. Experiments in vitro revealed an accelerated PP2A-dependent YAP phosphatase activity that maintained nuclear YAP in Acomys RTEs and was not detected in Mus or human cells. Treatment of Acomys in vivo with the nuclear YAP-TEAD inhibitor verteporfin converted tissue regeneration to fibrosis in the dermis and similar experiments for the kidney are in progress. These results suggest that the spiny mouse genome evolved both transcriptional and post-translational adaptations important for scar-free regenerative wound healing in vivo .