Markers in vertebrate neurogenesis

Embryologists have long used morphological characteristics, and more recent ly marker genes, to identify neural tissue and to test the neural-inducing activity of specific cell populations and signalling molecules. These marke rs are also used to assess the function(s) of neural genes themselves. Prog ression from neural induction to terminal differentiation of neurons is a m ultistep process, and each step involves the activation and/or repression o f genes that can be used as molecular markers for these different events. H ere we briefly review these key steps in neurogenesis within the vertebrate central nervous system, and evaluate the markers used to define them. We e mphasize the importance of cellular context and an understanding of gene fu nction for interpreting the significance of marker genes.