Coordinate development of skin cells and cutaneous sensory axons in zebrafish.

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).

Wallerian degeneration of zebrafish trigeminal axons in the skin is required for regeneration and developmental pruning.

Fragments of injured axons that detach from their cell body break down by the molecularly regulated process of Wallerian degeneration (WD). Although WD resembles local axon degeneration, a common mechanism for refining neuronal structure, several previously examined instances of developmental pruning were unaffected by WD pathways. We used laser axotomy and time-lapse confocal imaging to characterize and compare peripheral sensory axon WD and developmental pruning in live zebrafish larvae.

Developmentally regulated impediments to skin reinnervation by injured peripheral sensory axon terminals.

The structural plasticity of neurites in the central nervous system (CNS) diminishes dramatically after initial development, but the peripheral nervous system (PNS) retains substantial plasticity into adulthood. Nevertheless, functional reinnervation by injured peripheral sensory neurons is often incomplete [1-6]. To investigate the developmental control of skin reinnervation, we imaged the regeneration of trigeminal sensory axon terminals in live zebrafish larvae following laser axotomy.

Fragile axons forge the path to gene discovery: a MAP kinase pathway regulates axon regeneration.

The nematode Caenorhabditis elegans is emerging as a promising model for studying the molecular control of axon regeneration. A forward genetic screen identified the DLK-1 (dual leucine zipper-bearing kinase 1) MAP (mitogen-activated protein) kinase pathway as a positive regulator of growth cone formation during axon regeneration. Although DLK-1 pathway mutant animals display a dramatic defect in regeneration, their axons have no apparent defects in initial outgrowth.

Two-photon axotomy and time-lapse confocal imaging in live zebrafish embryos.

Zebrafish have long been utilized to study the cellular and molecular mechanisms of development by time-lapse imaging of the living transparent embryo. Here we describe a method to mount zebrafish embryos for long-term imaging and demonstrate how to automate the capture of time-lapse images using a confocal microscope. We also describe a method to create controlled, precise damage to individual branches of peripheral sensory axons in zebrafish using the focused power of a femtosecond laser mounted on a two-photon microscope.