Cell lineage and regional specification in the mammalian neocortex.

The cerebral cortex is the largest structure in the mammalian brain and shows compartmentalization of distinct functions into cortical areas. How does this compartmentalization arise during development? In studies of cell lineage, dividing progenitor cells are labeled to produce clones of labeled adult cortical neurons, so that patterns of clones can be related to the functional architecture of the cortex. A library, consisting of many genetically distinct retroviruses, distinguishable with polymerase chain reaction amplification, allows the cells of a clone to be tagged and traced even when they disperse widely. Recent results indicate that progenitor cells frequently give rise to cortical neurons with heterogeneous cytoarchitectonic locations and functional roles. This suggests that cytoarchitectonic areas arise through mechanisms requiring intercellular communication, rather than inheriting signals about their functional roles from progenitor cells.