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  1. #1
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    Default How bees gain resistance to viruses: New thinking

    Below is the abstract of a technical paper that examines aspects of GM studies that cast light on the processes by which bees gain resistance to viruses. That's followed by extracts from a second paper that seem to elaborate usefully.

    Some people think this understanding could lead to new and useful techniques that beekeepers could use. Its also probable that Monsanto (who appear to have bought some of the leading research) will try to exploit to their own sweet ends.

    In either case its probably worth having a working knowledge of what's going on.

    I think one useful thing to try to figure out (we don't get it here) is how often it occurs that a fragment of virus is absorbed into a bee genome in a way that confers resistance to that virus. (It would also be good if somebody could explain _how_ it confers that resistance.)

    In my view an important thing to remember, that is incorporated, but not elaborated in the text, is that when that happens it supplies a new mechanism that is then utilized in the normal adaptive/evolutionary processes.

    With that second point in mind, we could usefully try to discover a response to the first - how often does it happen. I think an indication is supplied by the extracts, but that's as far as I've got.

    Please feel free to pick these thoughts apart and correct me. I'm here to learn.

    Mike

    [Extracts]
    Maori E, Tanne E, Sela I: Reciprocal sequence exchange between non-retro viruses and hosts leading to the appearance of new host phenotypes.
    http://www.sciencedirect.com/science...42682206009287
    [Abstract only available]

    Abstract
    Divergence among individuals of the same species may be linked to positional retrotransposition into different loci in different individuals. Here we add to recent reports indicating that individual variance occurs due to the integration of non-retroviral (potyviral) RNAs into the host genome via RNA recombination followed by retrotransposition. We report that in bees (Apis mellifera), approximately 30% of all tested populations carry a segment of a dicistrovirus in their genome and have thus become virus-resistant. Reciprocally, segments of host sequences have been found within defective-interfering-like sequences of a dicistrovirus. Similarly, host sequences were found fused to potyviral sequences, previously described integrated into their host genome. A potential, continuous RNA exchange leading to divergence is discussed.

    ===========
    Isolation and characterization of Israeli acute paralysis virus, a dicistrovirus affecting honeybees in Israel: evidence for diversity due to intra- and inter-species recombination
    Eyal Maori, Shai Lavi, Rita Mozes-Koch, Yulia Gantman, Yuval Peretz, Orit Edelbaum, Edna Tanne and Ilan Sela
    http://jgv.sgmjournals.org/content/8...28.full#ref-22
    [Full paper available]

    Intra- and inter-species recombination of viral and viral-non-viral sequences

    A DNA version of a segment of IAPV RNA has been found integrated into the bee genome, and reciprocally, a host sequence has been found embedded in an IAPV-related DI RNA (Maori et al., 2007). Figs 1⇑ and 5⇑ indicate the presence, within the virions, of RNAs carrying IAPV sequences which are smaller than full-length.

    Although RNA recombination requires certain structural features, by and large, it is a random occurrence. Therefore, the amount and characteristics of encapsidated DI-like RNAs may change from one cycle of infection to the next, and viral populations may differ from each other in this respect. We showed different profiles in different viral preparations (Fig. 5⇑). Therefore, the reported quantitative values apply to that particular viral preparation, and may differ when other preparations are tested.

    In many instances, bee viruses are found as non-apparent infections in their host. This may result from competition between the viral RNA and the abundant DI-like RNAs, but also from the abundance of double-stranded RNA structures carrying viral sequences. In the latter case, the balance between host factors silencing viral sequences and the virus-induced silencing suppressors may shift in favour of viral silencing. Another postulated consequence inferred from the various types of DI-like RNAs is the modification of proteins resulting from deletions, engendering deleted or frame-shifted proteins. Thus, RNA recombination may elicit protein divergence with obvious evolutionary impact. Furthermore, a reciprocal exchange between host DNA and viral RNA (or a DNA version of a recombinant viral RNA) has been demonstrated (Tanne & Sela, 2005; Maori et al., 2007). Therefore, RNA recombination may engender divergence in host genes, and the evolution of both virus and host may be interrelated and linked to the very same eliciting process. "
    Last edited by mike bispham; 09-29-2012 at 04:11 AM.
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  2. #2
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    Default Re: How bees gain resistance to viruses: New thinking

    The Maori et al article demonstrates that viral genetic information can be inserted into the honeybee genome and it is apparent that the bees then have intrinsic immunity to the virus. I don’t “know” the specific details at the molecular level of how this is done but will take a stab at an explanation.
    I am not an expert in insect immunology but recently had some courses in virology and immunology in veterinary school. The following is a copy of a slide during one of our courses:
    “Innate immunity is phylogenetically conserved
    For example, insects have several innate immune mechanisms comparable to those found in mammals
    2) Specific immunity is not as highly conserved
    3) Beware assuming too much similarity with regard to detailed information (e.g., in mice the normal percentage of neutrophils in the blood is about 15; in humans it is about 70). “

    In mammals, our innate immune system is set up to be on constant surveillance for pieces of protein or other material that is common to bacteria and parasites. This system is primed to react immediately when it detects these materials to remove them from the system or slow the invader down enough to allow the specific immune system time to respond. Effector function refers to the specific mechanisms the organism uses to remove the pathogen from the body without the need for further processing or differentiation. To put it another way, these mechanisms are like perimeter guards that have instructions to shoot anything (no questions asked, just BLAM) that matches any of the characteristics of known enemies. The catalog of characteristic that the guards are looking for are programed into the genetic structure of the organism. This catalog can be updated with some difficulty but the changes are then passed on to subsequent generations. One of the main mechanisms for the catalog to be updated is by having fragments of genetic material of the attacking organism becoming inserted into the genetic code of the host organism that is attacked. This requires that a piece of DNA be inserted in just the right spot in the host genome so that the information is transcribed with the rest of the catalog of characteristics. Furthermore, the changes have to be present in the germ cells that become the gametes so the characteristics are passed on to subsequent generations. This sequence of events doesn’t happen easily and typically requires a bunch of random insertions into the host genome before one of the insertions lands in just the right spot.
    The other big chunk of the immune system is the Adaptive immune system. This part of the system requires that pieces of the attacking organism be sliced and diced by the innate immune system cells and presented to special cells in the adaptive system. These cells then develop specific antibodies or receptors directed specifically against the invading organism. These changes are typically not inserted into the host genome and are not genetically passed to subsequent generations. As a side note, the antibodies that are produced are passively passed to the offspring in mammals, either through the placenta (humans) or via colostrum (the first milk made by the mother and consumed by the offspring) in many animal species. This transfer of antibodies provides protection to the offspring until the offspring’s own immune system has time begin functioning.
    Last edited by TooFarGone; 09-29-2012 at 04:12 PM.

  3. #3
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    Default Re: How bees gain resistance to viruses: New thinking

    Quote Originally Posted by TooFarGone View Post
    The Maori et al article demonstrates and it is apparent that the bees then have intrinsic immunity to the virus. I don’t “know” the specific details at the molecular level of how this is done but will take a stab at an explanation.
    I agree the article demonstrates that viral genetic information can be inserted into the honeybee genome, but not having access to it I've no idea how your 'apparent' is demonstrated. I would like to know - have field tests on real bees been done under controlled conditions, or are there good reasons to believe this is not necessary? Do you have access to the article?

    As you say later:
    Quote Originally Posted by TooFarGone View Post
    This (Innate immune system) catalog can be updated with some difficulty but the changes are then passed on to subsequent generations. One of the main mechanisms for the catalog to be updated is by having fragments of genetic material of the attacking organism becoming inserted into the genetic code of the host organism that is attacked. This requires that a piece of DNA be inserted in just the right spot in the host genome so that the information is transcribed with the rest of the catalog of characteristics. Furthermore, the changes have to be present in the germ cells that become the gametes so the characteristics are passed on to subsequent generations. This sequence of events doesn’t happen easily and typically requires a bunch of random insertions into the host genome before one of the insertions lands in just the right spot.
    That 'doesn't happen easily' sounds like a cover for 'not very often at all' - was it you who offered odds of 1 in 10,000? Was that a guess, or something better?

    The event would have to have occurred in a queen, to be passed down via her direct contribution to the egg making the next queen, or via one of her (subsequent) drones - or it could occur in any drone that subsequently mates. Its happening in a worker won't make any difference.

    Lets see if we agree the following:
    The fragment would then, if it did its work well (and was needed at that time) be spread into future generations by natural selection. It would function as an advantage in the population all the while that particular virus (and perhaps closely related viruses) were present. If and when that ceased to be the case it would lose any function, and might slip out of the population genome.

    It appears to me that what is being explored is GM technology that bypasses the long odds governing this occurance in nature.

    Does that seem to you to amount to a fair outline of the nature and purposes of the technology?

    Mike
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    Default Re: How bees gain resistance to viruses: New thinking

    Mike,
    My comment on "apparent" is based on the observation that a previously lethal virus is not now killing the bees, and that this appears to be a heritable trate. It is my presumption that it is operating from the bees innate immune system ( I dont know this) but in mammalian system, this is frequently the case. I dont know if field tests have been done, but since bees in general no longer seem to be dying from this virus, it suggests that we are serving as th "beta testers" for the bees natural genetic experament!

    I will see if I can get the article through the library- I have not actually read the whole thing.

    Taking a wild stab at guessing the probability of this occuring naturally, I would have to say it is likely a lot MORE than 1 in 10,000 odds. While the honeybee has 10,000 genes, this genetic information would have to be placed at a specific spot within the gene to be functional. One of the reasons that this doesn't happen much in mammals is because it has such a low statistical probability. Historically, it is suspected that most of these peices of code were inserted into the genome during times of mass infection and die-off, effectively creating a bunch of opportunities for infection/reverse transcrioption/(random)transposon insertion into the host genome/and then the gene being preserved because of ongoing selective pressure. The bees apparently do not have as many reverse transcriptase families as mammals, so I might even happen less.

    Since the drone contribution is passed to the worker bees and subsequently to daughter queens, it would stand to reason that once a queen aquired the resistant gene, that she would pass it to her offspring including a bunch of drones that could pass the trait to other queens in the neighborhood.

    Genetic modification- this is a real can of worms... IMOH, yes they can, and I expect them too. It bothers me that Monsanto purchased the technology and know how to make it happen.
    Absolutely yes they could use genetic engineering to speed up the natural selection process and insert resistance genes into the genome. Just to tweek you a bit, I suppose they could insert "suicide genes" into the queens so they could not produce drones or somthing that would make us totally dependent on them for breeding stock...

  5. #5
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    Default Re: How bees gain resistance to viruses: New thinking

    Quote Originally Posted by TooFarGone View Post
    Mike,
    My comment on "apparent" is based on the observation that a previously lethal virus is not now killing the bees,...
    Hi Toofargone,

    My problem is; I haven't been shown any evidence of this. Where are the descriptions of trials showing that real bees really were made resistant?

    Quote Originally Posted by TooFarGone View Post
    .... and that this appears to be a heritable trate.
    I'm not sure if I should be worried about that. Usual GM conundrum I suppose.

    Quote Originally Posted by TooFarGone View Post
    It is my presumption that it is operating from the bees innate immune system ( I dont know this) but in mammalian system, this is frequently the case. I dont know if field tests have been done, but since bees in general no longer seem to be dying from this virus, it suggests that we are serving as th "beta testers" for the bees natural genetic experament!
    Do we have figures that demonstrate the infection rates over a relavant period? Can we trace the propagation of any such resistance?

    I'm not denying these things, but I would like to avoid building too far on foundations that might turn out to be non-existent! The idea of fast mechanisms protecting against new strains of fast-evolving viruses makes sense. I'm not sure how a selective beekeeper could make use of the understanding - though s/he'd be making use of it whenever it was advantageous without even knowing it!

    Quote Originally Posted by TooFarGone View Post
    I will see if I can get the article through the library- I have not actually read the whole thing.
    That would be grand!

    Quote Originally Posted by TooFarGone View Post
    Taking a wild stab at guessing the probability of this occuring naturally, I would have to say it is likely a lot MORE than 1 in 10,000 odds. While the honeybee has 10,000 genes, this genetic information would have to be placed at a specific spot within the gene to be functional. One of the reasons that this doesn't happen much in mammals is because it has such a low statistical probability.
    Even with huge odds, with a sufficiently large population the events could be expected to occur. But there would have to then be the means for the new advantage to establish itself - ie natural selection and propagation across the population. That all seems plausible in a natural population - though the chances of it happening the today's domestic populations seems unlikely.

    Quote Originally Posted by TooFarGone View Post
    Historically, it is suspected that most of these peices of code were inserted into the genome during times of mass infection and die-off, effectively creating a bunch of opportunities for infection/reverse transcrioption/(random)transposon insertion into the host genome/and then the gene being preserved because of ongoing selective pressure.
    That seems to me to make good sense.

    I wonder what the average period of value for these things is. How long do viruses last before mutating so far that the code no longer works? Is it always the same or do they differ. I wish I understood all this stuff a bit better.

    [QUOTE=TooFarGone;853953] Since the drone contribution is passed to the worker bees and subsequently to daughter queens,[/queen]

    Hmmm - how do workers have a role in this -beside acting as the 'body' of the colony in which an advantage can be expressed and passed on that is. There is no genetic pathway through workers.

    Quote Originally Posted by TooFarGone View Post
    it would stand to reason that once a queen aquired the resistant gene, that she would pass it to her offspring including a bunch of drones that could pass the trait to other queens in the neighborhood.
    Yes.

    Quote Originally Posted by TooFarGone View Post
    Genetic modification- this is a real can of worms... IMOH, yes they can, and I expect them too. It bothers me that Monsanto purchased the technology and know how to make it happen.

    Absolutely yes they could use genetic engineering to speed up the natural selection process and insert resistance genes into the genome. Just to tweek you a bit, I suppose they could insert "suicide genes" into the queens so they could not produce drones or somthing that would make us totally dependent on them for breeding stock...
    I suppose we'll have to try to work out at some point just what is likely to unfoldoccur under different scenarios of this kind.

    I wonder what the average period of value for these things is. How long do viruses last before mutating so far that the code no longer works? Is it always the same or do they differ. I wish I understood all this stuff a bit better.

    Mike
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  6. #6
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    Default Re: How bees gain resistance to viruses: New thinking

    'Isolation and characterization of Israeli acute paralysis virus, a dicistrovirus affecting honeybees
    in Israel: evidence for diversity due to intra- and inter-species recombination' Maori 2007.

    'IAPV, a bee-affecting virus assiciated with colony collapse disorder cab be silenced by dsRNA ingestion.' Maori, 2009.

    'Large-Scale Field Application of RNAi Technology Reducing Israeli Acute Paralysis Virus Disease in Honey Bees (Apis mellifera, Hymenoptera: Apidae)' Hunter 2010


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    Default Re: How bees gain resistance to viruses: New thinking

    Mike,
    I think the workers role in the situation where a queen is carrying the new resistance gene is that they survive and thrive, while adjacent colonies that do not have the gene die off- natural selection at its best. While the workers don't breed and pass the gene on, they do survive to allow the hive to reproduce itself.

    RNA viruses tend to mutate much faster than DNA viruses, because they have very little editing/ mistake correction capabilities carried within their genetic code. I believe that most of the honeybee viruses are RNA viruses. There are a huge number of variables that could enter into answering the question of how long a resistance gene could provide meaningful resistance. The genetic material in the innate immune system is highly conserved, likely because ongoing infective pressure culls the individuals that loose parts of this genetic code and subsequently die from the infection. Again, I state that I am not an insect specialist but infer a good bit from mammalian systems. Compared to our life spans, viruses tend to mutate with high speed. Just consider the influenza virus that has enough genetic drift (small mutations in its sequence) every year that many folks that had immunity last year will not have immunity this year when it recycles back through the population. About every 4 years, the virus re-assorts itself and becomes essentially a new virus that few people have resistance too.

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    Default Re: How bees gain resistance to viruses: New thinking

    A few things need to happen correctly. First, it needs to be the proper sequence in that it can inhibit the virus, secondly it needs to be translated to create RNA for that sequence. The mode is action is probably the same as RNAi (RNA-interference) or is nautral RNAi. The small RNA sequences bind to the viral sequences to create dsRNA strands which cannot be translated into the proteins for the virus or a certain component the virus needs to replicate.

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    Default Re: How bees gain resistance to viruses: New thinking

    There are known ping pong mechanisms between siRNA, Dicer/RISC (RNAi), and RdRP. Small interfering RNAs can persist because of this.

    DNA is transcribed into RNA.

    There are some real questions to be answered as to the vertical/germline vs horizontal/somatic transfer of RNAi in Honeybees. That's genetic (DNA) vs epigenetic (siRNA).

  10. #10
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    Default Re: How bees gain resistance to viruses: New thinking

    Let me start off by saying I use treatments and also have no plans to breed queens.

    Things are not as absolute some think. One queens mate with large numbers of drones that can be genetically diverse. Giving rise to workers that can have varying immune responses. Second hives that fail can produce drones from laying workers.

    Say that a hive is infected with a virus that kills 90% of the bees in the hive including the queen. The surviving bees, that are resistant to that virus, can develop laying workers. The laying workers will then proceed to flood the area with drones that are resistant.

    If you are looking for a trait that resists something, you may be better off trying to breed from drones that come from the surviving laying workers. Same would be true if you wanted to select for bees that fly in cooler weather. Catch the bees that express a desired trait and try to get them to become laying workers to propagate that trait.

  11. #11
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    Default Re: How bees gain resistance to viruses: New thinking

    Tohya
    What an interesting idea. In our rush to "deal" with laying worker hives, we might be missing an opportunity here! Several ideas come to mind (please be aware that I am a functional newbe have not personally done any of the following things). The drones would be carrying the genetics of the (surviving) laying worker. I read on this site a discription by (i think) Michael Bush on how to produce queens from drone eggs that would have the same genetics as the mother queen. In this selected instance, it might be worth breeding a few test queens from the laying worker brood and see how they worked out. The method (if memory serves as I was unable to find the thread on this I read last week) involves collecting semen from a drone from this hive (one that hatched from a laying worker), mix it with some honey, and place a bit of this mix onto a freshly laid egg. Destroy the eggs around the selected egg and place the frame horizontally above the brood nest (blocked or secured in a way to allow the bees to work on the now vertical downward hanging comb. The bees will reportedly produce a queen cell from this fertilized drone egg. I would think that one might want to let another hive complete the queen-from-a-drone-egg project as the original hive might bee too weak to complete the process. The virgin queen would need to be placed in a mating nuc and then her own colony for performance monitoring. Might be all for naught, or maybe you get bees that are resistant to the virus! Just thinking.....

    I guess the bigger question is how badly do you want to preserve the genetics of a hive that failed? Are the laying workers really resistant, or just haven't died from the virus yet?? I don't see an answer to this question except by testing the new queen....
    Last edited by TooFarGone; 10-01-2012 at 12:35 AM. Reason: new thought, spellling (can't spell or type)

  12. #12
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    Default Re: How bees gain resistance to viruses: New thinking

    Quote Originally Posted by TooFarGone View Post
    There are a huge number of variables that could enter into answering the question of how long a resistance gene could provide meaningful resistance. The genetic material in the innate immune system is highly conserved, likely because ongoing infective pressure culls the individuals that loose parts of this genetic code and subsequently die from the infection.
    Perhaps we should look at this from the other side. How many active, or potentially active virus fragments might the genome carry? If there are any limiting factors here (it might be known for example that there is an average of x, or that if there are too many problems of some sort arise. Then again there might be a huge space for 'clutter' that might suddenly be useful at any time)

    Quote Originally Posted by TooFarGone View Post
    [...]Compared to our life spans, viruses tend to mutate with high speed. Just consider the influenza virus that has enough genetic drift (small mutations in its sequence) every year that many folks that had immunity last year will not have immunity this year when it recycles back through the population. About every 4 years, the virus re-assorts itself and becomes essentially a new virus that few people have resistance too.
    This sort of rate seems to me to make it unlikely that bees would store a great many different viral fragments indefinately - if there is no point its unlikely bees would have evolved that way. Does anyone know what (if any) the mechanism for de-cluttering is?

    Mike
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    Default Re: How bees gain resistance to viruses: New thinking

    In the rDNA site, there are literally hundreds of copies of ribosomal DNA available. So, this region can have quite a few insertions without having deleterious effects. In fact, it has been demonstrated in other insects that the rDNA sites, containing transposable element inserts, have their transcripiton supressed.

    The Isrealis found that 30% of the hives tested were positive for IAPV insertions. Hunter found DWV and KBV inserts. There are about 18 viruses known to infect Honeybees. It seems likely that most bees have virus derived inserts.

    How are these transposable elements cleared from bees?
    They have an RNAi system known as PIWI. Transposable element insertions are cleared during gametogenesis, but some will easily jump back in.

    Since the genome of the Honeybee is known to have less than 1% (very low) of its DNA as transposon derived sequences, we can say that PIWI is very effective in Honeybees. It would have to be so in a haploid/diploid species with one of the highest recombination rates of the higher eukaryotes (perhaps it's the highest).

    As I've said elsewhere, genes jump in the germline tissues (sex cells). This probably occurs because there's a switch from one RNAi system (Dicer/RISC) to another (PIWI).

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