Snakes owe their long, slithery bodies to a single gene, UK research has shown.
The Oct4 gene regulates stem cells and affects the growth of the middle part, or trunk, of a vertebrate's body.
In snakes, a quirk of reptilian evolution has resulted in Oct4 remaining "switched on" for longer than usual during embryonic development.
"The formation of different body regions works as a strong-arm contest of genes. Genes involved in trunk formation need to start ceasing activity so that genes involved in tail formation can start working," Dr Rita Aires, from the Instituto Gulbenkian de Ciencia (IGC) in Lisbon, Portugal, said.
"In the case of snakes, we observed that the Oct4 gene is kept active during a longer period of embryonic development, which explains why snakes have such a long trunk and a very short tail."
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An evolutionary change caused the Oct4 gene to be placed next to a DNA region that kept it in an "on" state in the snake embryo, said the researchers.
The discovery was made while studying mice that had unusually long or short trunks.
Understanding the role of Oct4 in keeping the snake's body long may shed new light on spinal cord regeneration, the scientists claimed.
Study leader Dr Moises Mallo, also from IGC, said: "We identified a key factor that allows essentially unlimited growth of trunk structures, as long as it remains active.
"Now we will investigate if we can use the Oct4 gene and the DNA region that maintains its activity to expand the cells that make the spinal cord, trying to regenerate it in case of injury."
