Most people know that DNA can mutate – genetic sequences can be altered and carried on by reproduction. Less well known is that DNA also changes, in a sense mutates, during the life cycle of a normal cell – with or without reproduction. There are sequences of DNA that can move about to different positions within the genome of a single cell in a process called transposition. These sequences are called transposons and a new study by the Johns Hopkins University School of Medicine released in the June 24 issue of the journal Cell [Mobile Interspersed Repeats Are Major Structural Variants in the Human Genome] indicates that are a lot more of them and they are more active than previously thought.
The thinking now goes that the transposons may be responsible for, or play a major role in, the differences between individuals. Body types, hair color, susceptibility to certain diseases may all be linked to the ability of transposons to move from one location in the genome to another, in effect inserting themselves to alter the genetic code – a mutation – which may play out even during the life of a single cell.
The research was carried out using a unique analytical tool that was developed by Johns Hopkins scientists; it’s a kind of biological testing chip (a very specialized semiconductor) designed to recognize DNA sequences and spot those which do not fit the known patterns. Using this tool, the researchers analyzed DNA from 15 unrelated people comparing the sequences found with known transposons and discovered about 100 new transposon sites in each person.
“We were surprised by how many novel insertions we were able to find,” says Jef Boeke, Ph.D., Sc.D., an author on the article, a professor of molecular biology and genetics, and co-director of the High Throughput Biology Center of the Institute for Basic Biomedical Sciences at Johns Hopkins.
“A single microarray experiment was able to reveal such a large number of new insertions that no one had ever reported before. The discovery taught us that these transposons are much more active than we had guessed.”
[Source: Cell News]
That there are more transposons and they are more active than thought, continues the gradual realization that the human genome is much more dynamic than just the occasional mutation that occurs at the time of cell division or reproduction. Once referred to as ‘jumping genes’ (and indication of how unserious they were thought to be), the identification of many more transposons opens doors to new areas of research. For example, how much genetic ‘mobility’ is provided by transposons during the development of an organism? What role can transposons play in the development of diseases such as cancer? How does transposition fit into the overall picture of epigenetics?
Scientists are a long way from answering these questions, in part because the nature of transposons – their properties, mechanics, and effects – is not fully understood. However, the transposon chip and related procedures provide very useful tools for delving into some of the open questions.