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Wednesday, January 28, 2009

Genetic research has confirmed what parents struggling to rid their school children of head lice already suspected - the little louse truly is a super bug.

In a paper to be published in Genome Research next month, the research team says head lice have one of the most highly evolved mitochondrial chromosomes of all multi-celled animals.

Lead author Associate Professor Stephen Barker, from the University of Queensland, says all animals have two types of chromosomes, the nucleic and the mitochondrial.

The mitochondrion is considered the "powerhouse of the cell", says Barker, because it is involved in the conversion of energy for the body.
Genome 'village'

On most animals the mitochondrial chromosome is a circular mass that contains 37 genes.

But genome sequencing of head lice has revealed the 37 genes are located on 12 or more mini-chromosomes that join and separate.

"Instead of living in one house it is like they are living in a little village of 12 houses," Barker says.

"It shows they are incredibly sophisticated and generally quite extraordinary."

Co-author Dr Renfu Shao, who Barker credits with the discovery, says the mini-chromosomes "seem to sit at the summit of mitochondrial chromosome evolution".

"The mitochondrial chromosomes of head lice, in this sense, are extreme genomes," Shao says.

Barker, of the parasitology section within the School of Chemistry and Molecular Biosciences, says the chromosome architecture is unique to the lice that infect primates.

"We've looked at all the major lineages [of lice]," he says. "These mini-chromosomes are only found in the lice that infect primates [including humans]."
No 'flash in the pan'

They pinpoint the first louse that had this unusual cell structure as branching from the evolutionary tree about 22.5 million years ago.

"The point of this is it's not a flash in the pan - [the chromosome structure] evolved about 20 million years ago and it still exists," he says.

Barker says the team is now investigating the implications of their find.

"We've described the pattern and now we are trying to understand how they use this and whether they so have some advantage to the insect."

Barker says head lice are incredibly successful at surviving, with 20% to 30% of school children likely to be infected at least once a year.

"We may be going to Mars and the moon, but we are still struggling with these head lice.

"Whether that is related to the genome structure we don't know."

For parents shampooing and combing their children's hair in an effort to rid them of lice, Barker's advice is: "Don't give up."

"Nothing kills the eggs, you will get rid of them [the lice] all today, but you have to do it [combing and shampooing] three weeks in a row."

by:ABC Science

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