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HalfMooner
Dingaling
Philippines
15831 Posts |
 Posted - 02/17/2006 : 20:32:37
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I've a question or two about this, because I'm working on a novel that may touch on the subject. I've heard that retroviruses can carry genes between organisms.
Is this true? Is there a term for this? If it's real, could this work as a natural mechanism to carry traits across fairly wide divides, such as from dog to man, or vice versa?
Does such a mechanism have evolutionary implications, such as the idea that once first created, a useful trait might "accidentally" find its way into distantly related species, carried by viruses, incidentally making a bit of a hash out of traditional trees of descent?
Is the "external" genetic load that a retrovirus could carry limited by the virus' size? Would this limit, if any, affect how effective such transmisions could be?
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“Biology is just physics that has begun to smell bad.” —HalfMooner
Here's a link to Moonscape News, and one to its Archive. |
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H. Humbert
SFN Die Hard
USA
4574 Posts |
Posted - 02/17/2006 : 20:49:47 [Permalink]
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I think this thread might be of some help.
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"A man is his own easiest dupe, for what he wishes to be true he generally believes to be true." --Demosthenes
"The first principle is that you must not fool yourself - and you are the easiest person to fool." --Richard P. Feynman
"Face facts with dignity." --found inside a fortune cookie |
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Dave W.
Info Junkie
USA
26022 Posts |
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Dave W.
Info Junkie
USA
26022 Posts |
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H. Humbert
SFN Die Hard
USA
4574 Posts |
Posted - 02/17/2006 : 21:00:22 [Permalink]
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quote:
Originally posted by Dave W.
Damn, 25 seconds. I'm getting slow.
 I remembered that thread because it was one of the first I ever posted in over there.
edit: Ah, screw it, I corrected it anyway.
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"A man is his own easiest dupe, for what he wishes to be true he generally believes to be true." --Demosthenes
"The first principle is that you must not fool yourself - and you are the easiest person to fool." --Richard P. Feynman
"Face facts with dignity." --found inside a fortune cookie |
| Edited by - H. Humbert on 02/17/2006 21:25:26 |
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HalfMooner
Dingaling
Philippines
15831 Posts |
Posted - 02/17/2006 : 21:00:26 [Permalink]
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| Thanks much, fellas! I'm reading those now. : ) |
“Biology is just physics that has begun to smell bad.” —HalfMooner
Here's a link to Moonscape News, and one to its Archive. |
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Dave W.
Info Junkie
USA
26022 Posts |
Posted - 02/17/2006 : 21:16:42 [Permalink]
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quote:
Originally posted by H. Humbert
I remembered that thread because it was one of the first I ever posting in over there.
Emphasis mine, because obviously some of my 25-second shortfall was due to previewing my post. The rest I blame on a peculiar slowness of Wikipedia at the time. |
- Dave W. (Private Msg, EMail)
Evidently, I rock!
Why not question something for a change?
Visit Dave's Psoriasis Info, too. |
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H. Humbert
SFN Die Hard
USA
4574 Posts |
Posted - 02/17/2006 : 21:23:50 [Permalink]
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quote:
Originally posted by Dave W.
quote:
Originally posted by H. Humbert
I remembered that thread because it was one of the first I ever posting in over there.
Emphasis mine, because obviously some of my 25-second shortfall was due to previewing my post. The rest I blame on a peculiar slowness of Wikipedia at the time.
Yes, 'tis a fault of mine that I never preview. If you ever notice, almost all of my posts have edits, and almost always due to little misspellings I catch after the fact.
Ok, well, now I can't correct that one since you pointed it out. 
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"A man is his own easiest dupe, for what he wishes to be true he generally believes to be true." --Demosthenes
"The first principle is that you must not fool yourself - and you are the easiest person to fool." --Richard P. Feynman
"Face facts with dignity." --found inside a fortune cookie |
| Edited by - H. Humbert on 02/17/2006 22:12:49 |
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Dave W.
Info Junkie
USA
26022 Posts |
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H. Humbert
SFN Die Hard
USA
4574 Posts |
Posted - 02/17/2006 : 22:13:51 [Permalink]
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quote:
Originally posted by Dave W.
Well, you can always fix the one in the post above...
Fix what one? 
Dave, I can play this game all night.
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"A man is his own easiest dupe, for what he wishes to be true he generally believes to be true." --Demosthenes
"The first principle is that you must not fool yourself - and you are the easiest person to fool." --Richard P. Feynman
"Face facts with dignity." --found inside a fortune cookie |
| Edited by - H. Humbert on 02/17/2006 22:15:11 |
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Dude
SFN Die Hard
USA
6891 Posts |
Posted - 02/17/2006 : 22:54:25 [Permalink]
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Half said:
quote:
I've heard that retroviruses can carry genes between organisms.
Between organisms? I don't think they do. (tentative answer)
They can certainly add genetic info, your genome carries many thousand inert retroviral sequences, referred to as endogenous retroviruses.
These give us very strong evidence for common descent.
quote:
Is this true? Is there a term for this? If it's real, could this work as a natural mechanism to carry traits across fairly wide divides, such as from dog to man, or vice versa?
Dave and HH already linked to some good sources on HGT.... I haven't read the PT link on the subject before, but am doing so now.
I can tell you that prokaryotes have a method of gene transfer that involves dropping small segments of DNA into the environment called plasmids. These are thought to play a large role in drug resistant bacteria, if a non-resistant bacteria picks up a plasmid from the environment that came from a resistant bacteria, it can gain the resistance.
Plasmids are not unique to prokaryotes either. Some species of eukaryote have them.
Side note: Plasmids and restriction enzymes are the main players in recombinant DNA technology, which allows us to produce several lifesaving drugs. Cool stuff.
quote:
Does such a mechanism have evolutionary implications
Major implications. Some prominent scientists have suggested that HGT will make it extremely difficult (if not impossible) to sort out the base of the phylogenetic tree. Things like endosymbiosis muddy that particular pond well beyond our current ability to look deeply into it.
quote:
Is the "external" genetic load that a retrovirus could carry limited by the virus' size? Would this limit, if any, affect how effective such transmisions could be?
The size of a virus definitely limits the ammount of DNA or RNA it can carry.
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Ignorance is preferable to error; and he is less remote from the truth who believes nothing, than he who believes what is wrong.
-- Thomas Jefferson
"god :: the last refuge of a man with no answers and no argument." - G. Carlin
Hope, n.
The handmaiden of desperation; the opiate of despair; the illegible signpost on the road to perdition. ~~ da filth |
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Hawks
SFN Regular
Canada
1383 Posts |
Posted - 02/18/2006 : 00:58:06 [Permalink]
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quote:
I've heard that retroviruses can carry genes between organisms.
Is this true? Is there a term for this? If it's real, could this work as a natural mechanism to carry traits across fairly wide divides, such as from dog to man, or vice versa?
They sure can. But they don't have to be retroviruses - any virus can do it via a process known as transduction. The reason that retroviruses are usually singled out is probably because they can insert themselves into the genome of the host organism. But ANY virus can potentially transfer ANY gene (providing that it's not too big) between organisms (limited only by the host range of the virus). When a virus invades an organism, it makes more copies of it's genetic material and packs this into protein shells - ie it makes more viruses. What actually goes into the protein shell does not have to be virus DNA, however. It could be anything - including DNA from the host organism. This allows for a mechanism whereby genetic material can be transferred between organisms.
Of course, this genetic material will have to be expressed in the new host organism. Often ,the DNA is probably never expressed because of the action of restriction enzymes or because this new DNA is not incorporated into the new hosts chromosome(s) or plasmids. BUT, for various reasons, some genes are very effective at being expressed if they should be transferred into a new organism. For example, "gene cassettes" contain a single gene (and it could be ANY gene) and a "recombination site". These gene cassettes can be proficiently transfered between any organism that contains an "integron" (and it seems that most bacteria do). The integron effectively recognises the "recombination site" of the gene cassette and inserts both gene and recombination site near itself, allowing for their expression. Some of these integrons contain over 150 gene cassettes! Integrons (and by extesion horizontal gene transfer) appears to be the most common process by which Esherichia coli acquires antibiotic resistance and virulence traits. From memory, it has been estimated that some 30% of the E. coli genome consists of horizontally transferred DNA (not necessarily integrons). As Dude pointed out, this will by necessity make it difficult to sort out phylogenetic relationships.
quote:
Does such a mechanism have evolutionary implications
Oh, yes. Organisms are not constrained to simple single-point mutations or additions/deletions within themselves to produce genetic variation. They instead have the ability to "easily" acquire whole working genes from their surroundings. Horizontal gene transfer is for bacteria what sex is for [insert you favorite sexually reproducing organism here].
Note also that you don't need viruses for this horizontal gene transfer to take place. Some bacteria do it between themselves via a process known as conjugation (this process can even happen between bacteria and fungi). Some organisms (including some bacteria and even some eukaryotes [such as worms]) can take up naked DNA from the environment (called transformation).
quote:
Is the "external" genetic load that a retrovirus could carry limited by the virus' size? Would this limit, if any, affect how effective such transmisions could be?
40 kilobases of DNA is not impossible for some (that can be quite a few genes by the way).
quote:
If it's real, could this work as a natural mechanism to carry traits across fairly wide divides, such as from dog to man, or vice versa?
The worm Caenorhabditis elegans acquire heritable changes when eating bacteria producing siRNAs (these can turn off the expression of genes whose sequence thay are complementary to).
If you are talking specifically about viral transfer then sure it can happen - as long as the virus can infect two fairly distantly related species. Some can of course. Just think about the current fear about bird flu.
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METHINKS IT IS LIKE A WEASEL
It's a small, off-duty czechoslovakian traffic warden! |
| Edited by - Hawks on 02/18/2006 01:00:56 |
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beskeptigal
SFN Die Hard
USA
3834 Posts |
Posted - 02/18/2006 : 02:23:00 [Permalink]
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Bird flu reassortment was thought to be the means of species jump in the H1N1 1918 avian strain but recent analysis showed it likely was genetic drift and not reassortment. Reassortment occurs with flu virus when 2 viral strains infect the same cell at the same time. The genome breaks down into 8 segments (8 or 9, can't remember) then reassembles the segment copies before being released to infect new cells. During reassembly, genes from the two strains can be exchanged. Reassortment occurred in the last two milder flu pandemics.
The current bird flu strain may have taken a genetic step closer to adapting to humans. Some researchers have identified which part of the genome has to change to affect the virus's affinity for human cells over bird cells. And the sub-strain in Indonesia seems to have partially changed in that direction. At the same time, it's been pondered that the sub-strain in Turkey, which is spreading most widely, also has mutated to a virus that more easily infects human tissue giving rise to a sudden cluster of human cases. It has more changes to go before humans shed enough virus via the lungs or airway to become directly infectious. None of this rules out the possibility of reassortment still occurring.
On another note, researchers are using retro viruses on a regular basis to introduce foreign genes into plants and animals. It was tried on humans as well to correct a genetic deficiency. The first patient died suddenly and the human trials were stopped. |
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beskeptigal
SFN Die Hard
USA
3834 Posts |
Posted - 02/18/2006 : 02:32:07 [Permalink]
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Exerpt from Pub Med abstract:
The role of the virion shell in viral pathogenesis is relatively unknown yet the use of viral vectors in human gene transfer experiments requires an understanding of these interactions.
University of N. Carolina, Chapel Hill department on human gene therapy:
The Vector Core Lab was established in 1993 as part of the Gene Therapy Center to provide production services of viral vectors for both UNC and non-UNC investigators. In addition to providing complex and sometimes unique reagents, the Vector Core provides consultation with respect to the general advantages and disadvantages of different gene delivery vectors, strategies for vector construction, and the use and handling of viral vectors.
Exerpt from NIH position paper:
One method for inserting genes into cells is to link the genes with a virus that has been crippled and rendered harmless. As part of the modification, such a virus, sometimes called a vector or vehicle, has been deliberately altered so that it can carry genes into cells but cannot then escape to infect other cells. After the cells to be treated have been temporarily removed from a patient's body, the virus or vector is used to carry the desired gene into them. The final step will be to return the treated cells, which now contain the correct genetic information, to the patient's body. For example, bone marrow, liver cells, or white blood cells could be removed from the body of a patient, treated in the laboratory, and returned to the patient. |
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HalfMooner
Dingaling
Philippines
15831 Posts |
Posted - 02/18/2006 : 02:35:35 [Permalink]
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And thank you also, Dude and Hawks for your fulsome and useful replies.
The specific trait I'm interested in is somethng like the "theory of mind" possessed by Homo sapiens, and how this might have somehow been tranferred to early wolves to give the them human empathy that makes dogs so special. I'm imagining that a gene-packing virus could have carried these genes between the species, perhaps via flea bites.
Apparently, Homo sap. came "out of Africa" numerous times. From what I've read, the first time failed. The first group likely went into the Levant, and died out there, perhaps killed by bad conditions, probably by being out-competed or killed by local Neanderthals. The second wave, about 100,000 years ago, may have crossed the straits at the entrance to the Red Sea, from modern Djibouti to Yemen, then continued up the Arabian coast. There they may have met the Arab subspecies of Canis lupus, a small, short-coated, coyote-like wolf that still lives there. The human-wolf association probably began when either wolves began following the human bands to scavenge their leavings, or vice versa. Gradually, the wolves became more tame, and maybe they got a genetic gift from Homo sap. that completed their transformation into full-blown dogs.
Of course, it's certainly not known that the dog was domesticated that early. Many scientists think that happened in Neolithic times, once the first agricultural-pastoral setlements appeared in the Levant. I [i]suspect[i/] it happened much earlier, partly because most events in human prehistory have a habit of being pushed further and further into the past as more information is gathered. Essentially, a 10,000-15,000 year ago date is based upon digs and bones, while an approximate 100,000 years ago date is based on mitocondrial DNA genetic drift studies of dogs, to determine their divergence from wolves. I'll go with the genes, figuring the correct bones simply haven't been found yet. (The dates above aren't very accurate, I'm going by memory tonight.) The origin of the dog remains very contoverial, but it is now known that the wolf was its sole ancestor, not another canid such as the jackal.
Anyway, this genetic stuff all you guys have helped me with would go into a preface or first chapter of the book. The novel's main events would be set in the medium future.
After I get enough of this horizontal gene tranfer stuff into my head, I'm going to have to ask about the potential future practicality of "quantum teleportation" as a means of transportation . ; )
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“Biology is just physics that has begun to smell bad.” —HalfMooner
Here's a link to Moonscape News, and one to its Archive. |
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HalfMooner
Dingaling
Philippines
15831 Posts |
Posted - 02/18/2006 : 02:39:04 [Permalink]
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And thank YOU very much, too, B!
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“Biology is just physics that has begun to smell bad.” —HalfMooner
Here's a link to Moonscape News, and one to its Archive. |
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