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The ability of fishes to adapt to any aquatic environment seems limitless. It is enthralling how new species keep appearing at the deep sea or in subterranean environments. There are close to 230 known species of cavefishes, still today the best-known cavefish is Astyanax mexicanus, a Characid that has become a model organism, and has been studied and scrutinized since 1936. There are two morphotypes for A. mexicanus, a surface fish and a cavefish. The surface fish lives in central and northeastern Mexico and south of the United States, while the cavefish is endemic to the "Sierra del Abra-Tanchipa region" in northeast Mexico. The extensive genetic and genomic analysis depicts a complex origin for Astyanax cavefish, with multiple cave invasions and persistent gene flow among cave populations. The surface founder population prevails in the same region where the caves are. In this review, we focus on both morphotype's main morphological and physiological differences, but mainly in recent discoveries about behavioral and metabolic adaptations for subterranean life. These traits may not be as obvious as the troglomorphic characteristics, but are key to understand how Astyanax cavefish thrives in this environment of perpetual darkness.

Background: Danio rerio is a powerful experimental model for studies in genetics and development. Recently, CRISPR technology has been applied in this species to mimic various human diseases, including those affecting the nervous system. Zebrafish offer multiple experimental advantages: external embryogenesis, rapid development, transparent embryos, short life cycle, and basic neurobiological processes shared with humans. This animal model, together with the CRISPR system, emerging imaging technologies, and novel behavioral approaches, lay the basis for a prominent future in neuropathology and will undoubtedly accelerate our understanding of brain function and its disorders. Objective: Gather relevant findings from studies that have used CRISPR technologies in zebrafish to explore basic neuronal function and model human diseases. Method: We systematically reviewed the most recent literature about CRISPR technology applications for understanding brain function and neurological disorders in D. rerio. We highlighted the key role of CRISPR in driving forward our understanding of particular topics in neuroscience. Results: We show specific advances in neurobiology when the CRISPR system has been applied in zebrafish and describe how CRISPR is accelerating our understanding of brain organization. Conclusion: Today, CRISPR is the preferred method to modify genomes of practically any living organism. Despite the rapid development of CRISPR technologies to generate disease models in zebrafish, more efforts are needed to efficiently combine different disciplines to find the etiology and treatments for many brain diseases.

Radial glial cells are a distinct non-neuronal cell type that, during development, span the entire width of the brain walls of the ventricular system. They play a central role in the origin and placement of neurons, since their processes form structural scaffolds that guide and facilitate neuronal migration. Furthermore, glutamatergic signaling in the radial glia of the adult cerebellum (i.e., Bergmann glia), is crucial for precise motor coordination. Radial glial cells exhibit spontaneous calcium activity and functional coupling spread calcium waves. However, the origin of calcium activity in relation to the ontogeny of cerebellar radial glia has not been widely explored, and many questions remain unanswered regarding the role of radial glia in brain development in health and disease. In this study we used a combination of whole mount immunofluorescence and calcium imaging in transgenic (gfap-GCaMP6s) zebrafish to determine how development of calcium activity is related to morphological changes of the cerebellum. We found that the morphological changes in cerebellar radial glia are quite dynamic; the cells are remarkably larger and more elaborate in their soma size, process length and numbers after 7 days post fertilization. Spontaneous calcium events were scarce during the first 3 days of development and calcium waves appeared on day 5, which is associated with the onset of more complex morphologies of radial glia. Blockage of gap junction coupling inhibited the propagation of calcium waves, but not basal local calcium activity. This work establishes crucial clues in radial glia organization, morphology and calcium signaling during development and provides insight into its role in complex behavioral paradigms.

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