Understanding birth defects

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The image shows cell with a defective meiosis I, leading to aberrant chromosome segregation and chromosome imbalance in progeny. Photo by Xuexian Li

At conception, parents provide an embryo with chromosome information—23 each, for a total of 46. But when there are extra copies of chromosomes, or fewer than the normal 46, birth defects can occur. UGA researchers have developed a model system for plants and animals that shows that the loss of a key structural protein can lead to the premature separation of one DNA copy called a chromatid.

The new model shows for the first time that the loss of this protein can lead to birth disorders caused by extra or too few chromosomes. Best known may be Down syndrome, which is caused by an extra copy of chromosome 21. Many errors in chromosome transmission are so severe that miscarriages usually occur.

“As we know, human females have all the eggs they will ever have from the time of birth, and so as they age, the protein structures on chromosomes also age,” said Kelly Dawe, UGA geneticist and plant biologist. “If an egg is fertilized late in life, the final stages of chromosome separation may not occur properly. The goal of the work, which was done in maize, is to find out which parts of the chromosomes are most sensitive to failure. We now believe that proteins in a structure called the kinetochore are among the most sensitive to degradation or mutation. That may be a clue as to why older women have more problems with these kinds of chromosomal disorders when giving birth than younger women.”

The research was published in the journal Nature Cell Biology. Co-author on the paper is Xuexian Li (PhD ’09).