During brain development, one group of stem cells divides to produce progeny cells that finish up in different layers of the brain and have different functions.
The stem cells, called neuroblasts, produce their "daughter" cells in a specific order, and cells that are born at a particular time are destined to become a specific type of cell.
Understanding how this is brought about will be important to help us understand brain development.
Although there are some differences, the same sort of process seems to operate across a wide range of species, from mammals to insects.
In this week's issue of Cell, Chris Doe and colleagues show that in Drosophila, the underlying basis for the specification is a "memory" in the daughter cells of the genes being expressed by the neuroblast at the time the daughter is born.
The "parent" neuroblast undergoes a very specific sequence of changes in expression of a group of key regulatory genes (transcription factors called Hunchback, Kruppel, Pdm and Castor) during the time that it produces the daughter cells.
The daughter cell remembers the regulatory factor that was present at the time of its birth, and this determines which layer of the brain it goes to and what type of cell it becomes. Thus, the changing cycle in the parental neuroblast allows it to produce a set of distinct daughter cells that go on to form different nerve cells in different parts of the brain.
(Reference: Cell Volume 106 Number 4 August 24, 2001)
[Contact: Chris Q. Doe]