Notes

Radial Glia as Neural Stem Cells? How could you identify if these cells give rise to neurons within the developing cortex. It is done through Transgenic Fate Tracing.

Transgenic Fate Tracing It is a method used in developmental biology to study the development and differentiation of cells in an organism. It involves creating genetically modified organisms that express a certain gene or set of genes specifically in certain cell types of interest. The gene used for fate tracing are typically linked to a fluorescence or other type of reporter molecule, which allows the cells of interest to be visualized and tracked over time. The basic steps of transgenic fate tracing are:

• Identification of a gene that is specifically expressed in the cell type of interest.
• Creation of a transgenic organism that expresses the gene in the cells of interest.
• Observing the expression of the gene and the development and differentiation of the cells in the organisms. By tracking the cells that express the fate-tracing gene, researchers can gain insights into the origins and developmental pathways of different cell types.

In Malatesta 2003, it is done through Cre-recombinase, which are bacterial enzymes normally not present in the body that can cut DNA or recognize specific DNA patterns (loxp). You express this Cre-recombinase under GFAP (highly expressed in Glia cells), thus now driving also Cre-recombinase. The researchers generated transgenic mice that expressed a green fluorescent protein (h-GFAP) under the control of a promoter that was specifically active in neuronal precursors. Using these transgenic mice, the authors were able to visualize and track the development and differentiation of neuronal precursors in the hippocampus in real-time, and to demonstrate that these cells gave rise to both neurons and astrocytes.

Retroviruses Moloney murine leukemia (MML) viruses cannot cross nuclear membrane: specific for dividing cells. Then, when the cell divides, the retrovirus can enter the nuclear membrane and fluorescent protein (GFP) can be used to evidence it (Retroviral Labelling).

Radial Glia Divide and Generate Neuronal Progeny There are two main ways in which Radial Glia divides:

• Asymmetric: in this case, the radial glia cell divides into two daughter cells, one of which retains the characteristic of a radial glia cell and can continue to divide and support neuronal migration, while the other differentiates into a neuron. (Most common scenario).
• Symmetric: it generates a "daughter" which is a basal progenitor that can be divided again and it usually give rise to two neurons.