A major quest in modem neurobiology is to understand how the brain controls behavior. To this end, the convergence of two traditionally separate fields, systems neuroscience and molecular neuroscience, is required. The delineation of brain regions responsible for different behaviors, and in particular, their underlying neural circuits should be accompanied by the appreciation of the molecules that compose such circuits.
I have taken two approaches toward unraveling the molecular signatures of specific neural structures.First, I conducted microarray-based RNA expression analyses to search, in a large scale and with no a priori constraints, for differentially expressed gene products in several brain regions, including the amygdala, cerebellum, hippocampus, olfactory bulb and periaqueductal gray. Interestingly, only 0.3% of the genes characterized to date showed restricted expression in distinct brain areas. Further characterization by in situ hybridization was performed for genes enriched in the amygdala, a structure that modulates emotional behavior. Remarkably, this revealed that most region-specific genes possessed expression domains whose limits respected subnuclear boundaries defined by classical cytoarchitectonic criteria.These analyses were not only informative about the molecular composition of distinct brain areas, but alsoprovided tools to genetically dissect the role of different brain nuclei in specific behaviors.
Second, I have used a genetic strategy to label all cellular derivatives of neural crest precursor cellsexpressing a particular gene, Ngn2. Such lineage tracing study uncovered a segregated cellular subpopulation in the developing peripheral nervous system, which was strongly biased for the generation of sensory rather than autonomic neurons. Despite this fate bias, Ngn2-derived cells in the dorsal root ganglion were equally likely to give rise to neurons or glia. This suggests that some neural crest cellsbecome restricted to sensory or autonomic sub lineages before becoming committed to neuronal or glialfates. In general, visualization of the behavior of neural progenitors during the formation of the nervoussystem may further our understanding of the generation of specific neuronal subtypes and, eventually,neuronal connections that shape the functioning brain.
The combination of strategies here described will enable the characterization of brain regions at the molecular level on a broad, systems-based approach.
