Investigators at St. Jude Children's Research Hospital have used the lowly yeast to gain insights into how a dividing human cell ensures that an identical set of chromosomes gets passed on to each new daughter cell. Errors in this critical part of cell division can cause one daughter cell to get extra copies of some chromosomes that should have moved into the other daughter cell, or no copies of other chromosomesa problem that is prevalent in cancer and can cause miscarriages or disease, such as Down syndrome.
St. Jude researchers made their discovery by tracking the activity of a small army of molecules with exotic names like argonaute (Ago1) and dicer; these molecules help maintain a specialized, tightly packaged form of DNA called heterochromatin at the part of the chromosome called the centromere. The investigators also showed the order in which certain critical events occur in setting up and maintaining this heterochromatin. The work is important because it gives scientists insight into how each daughter cell receives the normal number of chromosomes; and it offers important clues to understanding the genetic cause of certain catastrophic diseases. A report on this work appears in the May 25 issue of Molecular Cell.
All of the cells DNA is wrapped around a series of structures, called histone octamers, to generate chromatinmuch like thread wound around a spool. This chromatin is then further compacted to form the characteristic, thick structures commonly recognized in illustrations and photographs as chromosomes. At the centromere, DNA is packaged into an even more compact and specialized form of chromatin called centromeric heterochromatin.
The centromere is the last point at which the two identical chromosomes are joined before the cell divides. Centromeric heterochromatin helps to yoke together the sister chromatids of each chromosome pair as they line up in the center of the dividing cell before separating and moving into
Contact: Summer Freeman
St. Jude Children's Research Hospital