Neuroscience

The developing cerebral cortex of mammals is generated from nascent pyramidal neurons, which radially migrate from their birthplace in the ventral part of the neural tube to the cortical surface. Subtle aberrations in this process may cause significant changes in cortical structure and lead to developmental neurological disorders. During pyramidal neuron migration, we recently showed that the migrating neuron, which bypasses its last preceding neuron, is critical for its proper positioning and contributes to cerebral cortex thickness. Studying this process requires an imaging system with single-cell resolution and a prolonged observation window. Therefore, we built a system to maintain an organotypic brain slice on the stage of a Leica SP5 confocal microscope, which facilitated high-resolution imaging over a 12-hour time-lapse observation period of cellular events during neuron migration. Here, we share our protocol along with guidelines for overcoming difficulties during the setup. This protocol facilitates the observation of, but is not limited to, neurodevelopmental and pathological processes occurring during neuron migration.

The nematode Caenorhabditis elegans is a powerful genetic model that can be used to investigate neuronal death. Research using C. elegans has been crucial to characterize cell death programmes that are conserved in mammals. Many neuronal signaling components, such as those mediating dopaminergic neurotransmission, are preserved as well. Dopaminergic neurons are progressively lost in Parkinson’s disease and an important risk factor to develop this disease appears to be oxidative stress, the increased occurrence of highly reactive oxygen species. Oxidative stress-induced dopaminergic neurodegeneration is mimicked in animal models by treatment with 6-hydroxydopamine (6-OHDA), a dopamine analog, which is specifically taken up into dopaminergic neurons. After exposing C. elegans to 6-OHDA, the loss of fluorescently labeled dopaminergic neurons can be easily monitored. An organisms’ sensitivity to oxidative stress is thought to be influenced by basal levels of intrinsic oxidative stress and the ability to counteract oxidative stress and oxidative stress-induced damage. The C. elegans ‘6-OHDA model’ led to the discovery of novel genes that are required to protect dopaminergic neurons and it has helped to determine the effects of conserved cell death and cell engulfment pathways in dopaminergic neurodegeneration. Here, we describe a simple protocol that allows for the easy detection of dopaminergic neuron loss after 6-OHDA treatment in C. elegans.

The chick embryo has prevailed as one of the major models to study developmental biology, cell biology and regeneration. From all the anatomical features of the chick embryo, the eye is one of the most studied. In the chick embryo, the eye develops between 26 and 33 h after incubation (Stages 8-9, Hamburger and Hamilton, 1951). It originates from the posterior region of the forebrain, called the diencephalon. However, the vertebrate eye includes tissues from different origins including surface ectoderm (lens and cornea), anterior neural plate (retina, iris, ciliary body and retinal pigmented epithelium) and neural crest/head mesoderm (stroma of the iris and of the ciliary body as well as choroid, sclera and part of the cornea). After gastrulation, a single eye field originates from the anterior neural plate and is characterized by the expression of eye field transcriptional factors (EFTFs) that orchestrate the program for eye development. Later in development, the eye field separates in two and the optic vesicles form. After several inductive interactions with the lens placode, the optic cup forms. At Stages 14-15, the outer layer of the optic cup becomes the retinal pigmented epithelium (RPE) while the inner layer forms the neuroepithelium that eventually differentiates into the retina. One main advantage of the chick embryo, is the possibility to perform experiments to over-express or to down-regulate gene expression in a place and time specific manner to explore gene function and regulation. The aim of this protocol is to describe the electroporation techniques at Stages 8-12 (anterior neural fold and optic vesicle stages) and Stages 19-26 (eye cup, RPE and neuroepithelium). We provide a full description of the equipment, materials and electrode set up as well as a detailed description of the highly reproducible protocol including some representative results. This protocol has been adapted from our previous publications Luz-Madrigal et al. (2014) and Zhu et al. (2014).

This technique allows highly efficient and reproducible transfer of DNA/RNA into the embryonic neocortex of rodents across multiple ages. Ex utero electroporation compliments the more technically difficult in utero electroporation technique by maximizing the number of embryos for available for a given experiment, as well as increasing the variety of constructs used in each experiment, thereby helping to reduce their overall numbers. Ex utero electroporation followed by short term organotypic slice culture of embryonic brain sections allows immediate access to multiple slices for choosing optimal ones for live-cell imaging experiments, and characterization of various NSC manipulations in the intact stem cell niche. (see also “In utero Electroporation of Mouse Embryo Brains” (Ge, 2012); “Organotypic Slice Culture of Embryonic Brain Sections” (Calderon de Anda, 2013). Additionally, ex utero electroporated neocortices can be used for in vitro primary cell cultures with further dissection, dissociation into single cells, and plating on cover slips or in multi-well dishes according to standard techniques: note this procedure can be performed immediately after electroporation, prior to the onset of ectopic gene expression, or after overnight slice culturing to collect just the region of electroporated cells.

This is a non-invasive technique to introduce transgenes into developing brains. In this technique, DNA is injected into the lateral ventricle of the embryonic brains, and is incorporated into the cells through electroporation. Embryos then continue their development in normal conditions in vivo. The effects of genes of interest can be evaluated at certain time points after in utero electroporation. This technique allows acute knockdown or over expression of genes of interest. Compensatory effects from other genes are less likely to happen; it also circumvents possible chronic detrimental effects.