Tuesday, March 31, 2009

This Week's Sci-Fi Worthy Parasite

So you're sitting there, reading the paper, when you notice your head's a bit itchy. Dry skin? Maybe. Irritated scalp? It's possible. Of course it could be something far more sinister...

It could be every parent and school teacher's worst nightmare: Lice.

Lice, the kind that is the bane of elementary schools everywhere, are a kind of wingless insect. They're members of the order Phthiraptera, which is classically broken into two groups, the chewing lice and the sucking lice - the latter is where our lovely head louse, Pediculus humanus, belongs.

Why did I pick the measly little louse for my Sci-Fi worthy parasite?

Well, first off, they're vectors for a variety of terrible diseases that you just don't want to think about like Typhus or Relapsing Fever, and they're epidemic. Somewhere between 6-12 million people, mainly children, are treated annually for head lice in the United States alone. But, to be honest, that's not why I picked them.

I picked them because of a new study published in Genome Research which found that the sucking lice are unlike any other animal on the planet. In fact, you might even call them almost alien.

That's because instead of having one chromosome in their mitochondrial genome, they have 18 minichromosomes. While multiple mitochondrial minichromosomes have been found in plants and protists, this is the first report of an animal having highly fragmented mitochondrial DNA structure. And it's found in all the species of sucking lice they tested, but not in the closely related chewing lice. How did this fragmented DNA evolve? There aren't any transitional lice - none that have partially fragmented mitochondrial genomes, only not at all and completely broken apart. What purpose does it serve to have lots of little gene packages instead of one? It's a real science mystery, one which makes the common louse into a nifty, Sci-Fi enigma.

That, and I wanted to make your head itch. Don't pretend like you haven't scratched it at least once while reading this - you know you did.

Shao, R., Kirkness, E.F., & Barker, S.C. (2009). The single mitochondrial chromosome typical of animals has evolved into 18 minichromosomes in the human body louse, Pediculus humanus Genome Research DOI: 10.1101/gr.083188.108.


Anonymous said...

Wow, how interesting! No other animals are known to have that? How many animals have had their mitochondrial DNA examined?

Anonymous said...

Your nefarious plan succeeded - by the end of this post I was going at my scalp with both hands. (Memo to self: Don't read blog posts about ectoparasites near bedtime.)