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Defect in production

Study detects chromosomal variation far higher than expected in neurons

STEVENS KASTRUP REHEN ArchiveAbnormal: there are three 2 (red) Chromosomes and only one 15 (light blue) and 17 (greenish). The normal karyotype of a rat neuroblast has 20 pairs of chromosomes STEVENS KASTRUP REHEN Archive

In a normal nervous system, the neurons should have one identical genome. Its karyotype should be made up of the same number of chromosomes. That is what the theory says. In practice, reality may be more complex, as it is shown by the results of a study carried out by researchers from the School of Medicine of the University of California, in San Diego, United States, in which Brazilian Stevens Kastrup Rehen took part. He is from the Federal University of Rio de Janeiro and doing post-graduate studies at the American institution. The work shows that one third of the neuroblasts, the precursor cells of neurons, of the mice embryos showed a variable quantity of chromosomes.

Instead of the expected 40 chromosomes, 33% of the more than 200 neuroblasts analyzed contained more or less chromosomes than standard. “This level of aneuploidy (variation in the number of chromosomes) is ten times higher than the accepted standard in conventional cytogenetics”, says Rehen, who is publishing the work in the Proceedings of the National Academy of Sciences magazine, of the National Academy of Sciences of the United States. In the lymphocytes, a kind of white blood globule, the rate of aneuploidy is 3%.

The measurements were taken during the mitosis of the neuroblasts, the process of the division of the nucleus, which splits and generates two daughter cells. When the mitosis is perfect, the daughter cells have the same number of chromosomes as the mother cell. From the research data, this process shows many imperfections in the case of neuroblasts. Fortunately, the fate of the majority of these neuroblasts with more or less chromosomes is to die as the organism grows. So much so that the levels of aneuploidy in neurons, the successors of the neuroblasts, in adult mice is significantly lower, in the order of 10%. Lower, but not to be disregarded. Rehen believes that the greater prevalence of aneuploidy in adult neurons may be an indication of greater predisposition to neurodegenerative diseases.