Rat

‘Scientists have decoded the rat genome, the biochemical instructions in the rodent's cells that guide the building and maintenance of the animal's body. It is the third mammalian DNA sequence to be deciphered - humans and mice came first - and will be used by researchers to understand the causes of disease. It should also give valuable insights into the evolution of all mammals…The rat was made a priority species to decode because of its importance to medical research. For nearly 200 years, scientists have used the animal as a "model" on which to test ideas about human biology. Today, the rat, along with its rodent cousin the mouse, account for more than 80% of all laboratory experiments. Scientists have hundreds of strains of mice and rats that mimic human illnesses. Now, researchers say the information contained in the rat genome will help produce disease models that are an even closer match for the sick conditions found in humans. "Rats remain the dominant pre-clinical model of human disease for developing new drugs," said Professor Howard Jacob, from the Medical College of Wisconsin, US, and a senior author on the Nature paper. “Better rat models will decrease drug failure in clinical trials - currently standing at about 90% - which will decrease development costs and time to market." The Rat Genome Sequencing Project Consortium used a strain of a brown Norway rat (Rattus norvegicus) to obtain the genetic information. Two females and a male provided the biological samples for the study. More than 90% of the rat's DNA has been read, sorted and analysed in what the consortium describes as a "draft". The remaining less than 10% is not thought to contain significant data and no current plans are in place to try to retrieve this information. The research found the rat genome to be of a similar size to humans and mice - at 2.75 billion "letters", or bases, of DNA. It also contains a comparable number of genes - about 25,000. And it is clear that most of the genes found in the rat can be seen in the human code, too. "If one looks at genes that are basically equivalent, then nine out of 10 are the same," said Professor Chris Ponting, from the UK Medical Research Council's Functional Genetics Unit, who worked on the project. "The disease genes are nearly all within that 90% - they're conserved between rodents and humans. Therefore, in looking at the biology of human disease genes in rodents, it appears rodents make excellent models," he told BBC News Online. Some families of genes, though, have been greatly expanded in the rat, including, perhaps not surprisingly, those associated with the ability to emit and sense smells. There are significant distinctions, also, in the genes of the immune system. Comparison of the rat code with those of the human and the mouse should allow a remarkable view of mammalian evolution. The rat data shows about 40% of the modern mammalian genome derives from the last common mammalian ancestor that existed tens of millions of years ago. This "core" DNA encodes nearly all the genes and their regulatory signals, and accounts for the similarities among mammals, such as the basic body plan. More details about the fundamental biochemistry and evolution of mammals will become apparent when scientists get to compare the human and the rodent codes with those of the soon-to-be finished chimp and dog genomes. "What we know about the dog is that genetically speaking it is closer to humans than rodents, even though in terms of evolution it is further away," explained Professor Ponting. "That's to say, the dog lineage split off from the human lineage before rodents - it's just that the rodents' DNA has mutated like crazy since then." BBC, 2004

‘Mice and rats have been described as animal weeds.’ Richard Dawkins, Unweaving the Rainbow, Penguin, 1998

‘An international research team has announced that it has completed a high-quality, draft sequence of the genome of the Brown Norway strain of the laboratory rat (Rattus norvegicus)…For nearly 200 years, the laboratory rat has played a valuable role in efforts to understand human biology and to develop new and better drugs. Areas in which rat models have already helped to advance medical research include: cardiovascular diseases (hypertension); psychiatric disorders (studies of behavioral intervention and addiction); neural regeneration; diabetes; surgery; transplantation; autoimmune disorders (rheumatoid arthritis); cancer; wound and bone healing; and space motion sickness. In drug development, the rat is routinely employed to demonstrate therapeutic efficacy and assess toxicity of drug compounds prior to human clinical trials. The genome sequence will facilitate all of these studies, as well as help researchers better pinpoint the crucial areas of biological difference between rats and humans. The rat sequence draft, which covers more than 90 per cent of the genome, represents the third mammalian genome to be sequenced to high quality and described in a major scientific publication…The availability of a third mammalian genome sequence gives scientists the ability to triangulate data to better resolve details of human biology, as well as mammalian evolution. In their Nature paper, the researchers reported that, at approximately 2.75 billion base pairs, the rat genome is smaller than the human genome, which is 2.9 billion base pairs, and slightly larger than mouse genome, which is 2.6 billion base pairs. However, they also found that the rat genome contains about the same number of genes as the human and mouse genomes. Furthermore, almost all human genes known to be associated with diseases have counterparts in the rat genome and appear highly conserved through mammalian evolution, confirming that the rat is an excellent model for many areas of medical research.’ Wellcome Trust 2004

Brother to the Rat, Rattus norvegicus

So, we are Brother to the Rat, brain and body;

great gallumphin’ rodent brethren - despising

our kin, loving them as pets in equal measure,

‘cos that’s the kind of crazy species we are…

Now Rattus norvegicus, the Brown Norway,

glory of his cunning, intelligent evolution -

reduced to being called the ‘Laboratory Rat’ -

demonstrates he must be truly reconsidered;

known only now by his posh, noble Latin name,

equal animal to Nature who drove, adapted both -

making it easier for selfish human reasons, showing

his usefulness for studying cardiovascular disease -

hypertension, psychiatric disorder, addiction;

neural regeneration, diabetes, surgery, cancer,

rheumatoid arthritis, transplantation, healing

of wounds, knitting of bones - autoimmune

disorders, space motion sickness, drug toxicity -

he’s a very Wonder Rat!, squeaking laboratory.

Showing a genetic genius for being human -

in all but species; fur, whiskers, ears and tail,

and it wouldn’t take much for us to grow them

too - but our old molecules were lucky, blessed,

to have fallen from stars to these arrangements -

when the Rat’s dust landed in Man’s laboratory.

Rat in Space

My feet left the floor – it was freaky -

exhilarating. I thought maybe I’d died

like some of my friends here, but instead

I left the ground – ha, ha! I squeaked, and

they thought I was afraid, but I don’t laugh

the same as them, is all. I began to wheel -

slowly, up and up, to the painted stars

I could believe in that state were real;

the picture of Earth the size of an orange -

I was flying as a fish flies in water, thickly.

I danced a little, spreading my hands and feet

into little pink stars among the white; happy,

I closed my eyes, on and on to a place beyond

I knew they thought I had no conception of -

just because I can only tell them with my eyes -

in mother space I would be able this time to say…

But suddenly I looked down,

violently barfed - (tee-hee).

Feeling Ratty

Our ghost is in the rat;

the rodent ghost in us -

when noise freezes -

blind noses still poised,

almost sniffing -

sense diluted over skin,

ice cube to water -

trembling whiskers

stubbed

to prickling hair.

We sense the malice

of our own cat -

scavenge cupboards

for stored treats;

scuttle to the bathroom

during the night - not sure

whether to be afraid of light

pools or dark.

Curl on the armchair,

clean, preened -

tucking our dressing gown

tails around.

‘Rats may not be able to talk but are capable of recognising different human speech patterns…. Rats were able to pick up enough clues from rhythmn and intonation of human speech to differentiate between spoken Japanese and Dutch. “It was very surprising, they could even recognise the languages when they were played backwards,” says Toro.’ The Guardian newspaper, 2004

Yeah, I’m a Rat

Yeah, I’m a rat -

D’you wanna make something of that?

You humans are quite beyond belief -

There’s no animal on Earth causes even a fraction of the grief;

But there you are sending out catchers,

When you’re breeding Archers and Thatchers!

So we like to poke around in rubbish, big deal -

Does everyone have to agree about what makes a good meal?

You’d think you’d be glad we live in sewers -

It’s not much of a home compared to yours -

And we’re far more intelligent than you think,

If only you could see further than the stink -

And now you’re learning we’re just like you,

It’s enough to make any rodent feel blue -

Our reputation among humans is completely unjust -

All that ‘Smell a rat’, ‘He’s a rat’, and that’s not the worst…

Gnawing babies in cradles, the feet of the poor, you think we’re scum,

It’s preposterous, distasteful - you don’t actually look very yum -

And it was the Pied Piper wot done it, OK;

We seem to be implicated, somehow, to our dismay -

And more than anything, just remember please,

It wasn’t us that had Bubonic Plague - it was the fleas.

‘Comparison of the rat genome to those of the human and mouse also opens a new and unique window into mammalian evolution. The rodent lineage, which gave rise to the rat and mouse, and the primate lineage, which gave rise to humans, diverged about 80 million years ago. Humans have 23 pairs of chromosomes, while rats have 21 and mice have 20. However, the new analysis found chromosomes from all three organisms to be related to each other by about 280 large regions of sequence similarity - called 'syntenic blocks' - distributed in varying patterns across the organisms' chromosomes. The sequence data also confirms that the rodent lineage split 12 to 24 million years ago into the separate lines that gave rise to the rat and to the mouse. Researchers estimate about 50 chromosomal rearrangements occurred in each of the rodent lines after divergence from their common ancestor. The number of chromosomal rearrangements, as well as other types of genome changes, was found to be much lower in the primate lineage, indicating that evolutionary change has occurred at a faster rate in rodents than in primates. The new analysis also underscores the fact that while rats and mice look very similar to the human eye, there are significant genomic differences between the two types of rodents. For example, some aspects of genomic evolution in the rat appear to be accelerated when compared to the mouse. According to the new analysis, due to the unusually rapid expansion of selected gene families, rats possess some genes not found in the mouse, including genes involved in immunity, the production of pheromones (chemicals involved in sexual attraction), the breakdown of proteins and the detection and detoxification of chemicals.’ Wellcome Trust, 2004

I know someone who looks like a rat

I am less astonished to find us relatives of the rat,

than the fly, pufferfish, blade of grass, lily flower,

because I know someone who looks like a rat -

wrong colouring, but right face; scrabbly hands,

pink-rimmed eyes with that reddish light,

sleekit, insinuating, sniffing, infiltrating -

always digging in the filth, enjoying sewage,

carrying disease but – typical, not made sick;

except in spirit, lack of generosity, any kindness.

I’ve always seen the way his wee nose twitches,

when he thinks nobody else is watching; probably