Clocking the birth of neurons

摘要

Millions of nerve cells, of many different varieties, are generated in the central nervous system during development. The cells that give rise to this plethora of neurons, known as neuroblasts, follow certain temporal guidelines: they generate particular types of neurons early in development, and other types later. For example, the neurons in the lower layers of the brain's cerebral cortex are born early, and those in the top layers are born later. This sequence is thought to have something to do with a progressive loss of a neuroblast's intrinsic capability, or 'competence', because when, for instance, older neuroblasts are transplanted into a young cortex in ferret embryos, they cannot make lower-layer neurons. Thanks to the work of Pearson and Doe (page 624 of this issue), we now have some idea about the molecular basis of this change, at least for one particular neuroblast in fruit-flies. The authors show that the transient expression of a single protein, called Hunchback, regulates the progressive loss of competence.