CAMBRIDGE, Mass. (January 13, 2012) The blood-brain barrier is essential for maintaining the brain's stable environmentpreventing entry of harmful viruses and bacteria and isolating the brain's specific hormonal and neurotransmitter activity from that in the rest of the body.
In addition to nerve cells, the brain contains glia cells that support and protect the neurons. In the fruit fly, the blood-brain boundary is made by glia joined into an envelope sealed around the nerve cells. As the brain rapidly expands during development, the glial envelope must grow correspondingly to remain intact. However, little has been known about how the blood-brain barrier maintains its integrity as the brain it protects develops.
Now Whitehead Institute scientists report that as the developing larval fruit fly brain grows by cell division, it instructs subperineurial glia (SPG) cells that form the blood-brain barrier to enlarge by creating multiple copies of their genomes in a process known as polyploidization. The researchers report their work this month in the journal Genes and Development.
"We think that this may be the same developmental strategy that's used in other contexts, where you need an outer layer of cells to maintain a seal, yet you also need the organ to grow during development," says Whitehead Member Terry Orr-Weaver.
Like the larval fruit fly's blood-brain barrier, cell layers in the human placenta and skin may employ polyploidization to respond to the need to expand while maintaining a sound boundary between the fetus and its surroundings, and the body and the outside world, respectively.
For preserving such barriers, polyploidy is ideal, as the cells forming the boundary enlarge without undergoing full cell division, a process that would break the tight junctions between cells.
In the larval fruit fly, polyploid SPG are necessary for maintaining the blood-brain barrier. When Yingdee Unhavaithay
|Contact: Nicole Giese Rura|
Whitehead Institute for Biomedical Research