mtDNA and female families

[brogers]

An interesting paper has been released on mtDNA and its relationship with elite athletic performance in humans.

http://physiolgenomics.physiology.org/c ... 1.abstract

mtDNA is inherited from the mother (maternally inherited), and is not subject to recombination like nuclear DNA (although there is some conjecture that it occurs in very rare cases), and as such enables researchers to trace maternal lineage far back in time. The most prominent roles of mitochondria are to produce ATP through respiration, and to regulate cellular metabolism.

A few key considerations/comments in regard to the paper

1) One of the main determinants of individual variation in endurance performance is the skeletal muscle metabolic properties, particularly its mitochondrial oxidative potential. mtDNA codifies 13 out of 83 polypepties implied in the respiratory chain and as such there is a strong rationale for identifying an association between mtDNA variants and aerobic/endurance exercise phenotypes.

2) The paper is based on humans. The trick is going to be working out in thoroughbreds if mtDNA based performance is regulated by nuclear genes and if so what genes (they may be different to humans, but most likely the same). The paper suggests that there are nuclear encoded mtDNA genes or nuclear genes themselves that depending on the mtDNA haplotype that regulate metabolic pathways resulting in 1) A greater increase in the number mitochondria in the muscle under exercise and 2) a better quality of mitochondria enabling better efficiencies of ATP production in aerobic work. This sort of leads us down the path of certain haplotypes or families being superior to others, at least in terms of staying/routing performance.

3) If these regulatory genes/pathways are nuclear encoded mtDNA genes or nuclear genes then they are subject to Mendelian inheritance which means that based on what they inherit from their sire and dam will regulate mtDNA, that is, you could have the mtDNA haplotype but because you didn't inherit the right variants from your sire and dam, they are not as efficient as they could be if you had inherited different variants.

4) It is unlikely that a single variant will make an effect on a metabolic gene pathway in regards to mtDNA, rather it is more likely to be the additive effect of a number of variants.

5) mtDNA is only going to form part of the way that a elite horse is found/created. There are going to be a lot of other variants within nuclear genes that look at other systems (oxygen transport, cardio, metabolism, etc) will be specific to elite performers as there will be proteome/protein expression and metabolic signatures. Because many genes are involved, there are interactions among different genes, and there are interactions among genes and the environment. It is going to be a complex picture and many ways of making an elite performer, so to seize on mtDNA as the answer over others is going to be shortsighted.

6) Finally, if the performance of the mitochondria was based just on mtDNA haplotype alone, breeders would have selected for this attribute by now. Indeed I have a feeling that we have already in that there are ~19 mtDNA families in the thoroughbred, rather than the 50+ we are led to believe under the Bruce Lowe/Goos/Bobinski system so I think that a lot of the inefficient mtDNA/female lines were selected out of the breeding pool a couple of hundred years ago when they were running 4 mile heats and quality mtDNA played a greater part in separating out the elites from the others.

Interesting stuff ....

[Shammy Davis]

Yes, it is very interesting. I'm not sure I understand it all.

[xfactor fan]

Thanks for posting this. It pretty much dovetails with the study that found that there were 5 energy profiles--three sprinting, and two staying, related to mtDNA.

Just another thing to think about, mtDNA is very active right after the egg is fertalized. Wonder what they are doing?

Shammy the gist is that in humans how effecient the cell take up oxygen, and produce energy is based on an interaction between mtDNA, and regular genes on the chromosomes. Would explain Secretariat and The Bride. Both had the same mtDNA, but got different sets of "energy helper genes" from their sire and dam.

So in breeding the trick is to figure out the base energy profile of the mtDNA, then make sure the correct "helper" genes are present. Ok, part of the trick.

[Shammy Davis]

Xfactor: Thanks for the explanation. I've been going over my copy of Bill Lathrop's Modern Conduit Mares since he has been such a good predictor of KD winners.

[brogers]

Shammy

Just be aware that if the same applies to horses as it seems to humans, being out of a conduit mare family or from a certain Bruce Lowe/Goos/Bobinski family is irrelevant if you haven't inherited the right genes from your sire and dam to compliment the mtDNA that you get from your female family. You can do all the reading and theorizing you like about female families but it may mean nothing with the genetic role of the dice as explained above.

[karenkarenn]

OKay I'm game, who do I contact to get my mare tested?

[brogers]

Well so am I but until someone works out what variants within genes are required and how they relate to mtDNA in thoroughbreds we are not going to be testing anything

[Shammy Davis]

brogers: I assumed that. Conduit mare profiles, dosage, family, etc. for now only gets us in the ballpark.

As I enjoy the breed so much, it is fun for me to look at all the different aspects of the pedigree, especially those decades back. In the case of the conduit mare or dosage, I get a historical perspective also.

I wonder when the equine genome project is complete, if pedigree reseach will be as inviting as it is today.

[brogers]

I wonder when the equine genome project is complete, if pedigree reseach will be as inviting as it is today.

Shammy, the first draft of the horse genome was completed in 2007.

[xfactor fan]

Without testing you could:

Take the female family back several generations.The look at horses under each dam, and look for a pattern of conformation, and muscle structure. Do the winning horses like to run long, short? Are they better milers? Get a feel for what has worked in the past.Then look for a stallion from the same female family--by direct tail female -- so you have a mate to your mare that has the same mtDNA working. Cross you fingers and toes, and hope that the gene roll in your favor.

As for testing, try googling mitotyper, He's been collecting mtDNA for a while now, and I think that Dr Hill --one of the researchers on mtDNA in the TB has spun off a company and is doing mtDNA typing.

Take a good solid look at Bill from WA's work on conduit mares. He's looking at mtDNA by following female families from the 1900, and has come up with a way of bypassing all the historical errors that have crept into the stud book.

[Bill from WA]

Hello

Interesting topic. I'm sure that in the future science will answer all of these questions, but until then we are left with those of us who are researching ways of tipping the scales a little to the positive side of the equation. All of these methodologies are based on historical data, nicking, female families, conduit mares, et al. I have endeavored to eliminate female family errors by tracing only as far back as 1900, and have tried to establish racing aptitudes based on the racing records of individuals tracing back to circa 1900 (conduit mares of each target horse within a pedigree.) The Lowe or Bobinski families are irrevelent in this scenerio. I only care about the aptitudinal ranges achieved by the runners tracing to each conduit mare. I don't claim to predict racing talent, only aptitudinal ranges. Nicking is based on historical data as well, and even though a certain "nick" achieves a high rating, it doesn't guarantee that the A++ nick will produce a superior runner. As stated above, it all depends on how those genes shake out. George Smith's GSV scores seem to be on the right track, and will be even more effective when more foriegn runners are included in the data. I respect and appreciate all of the individuals who spend those countless hours researching and formulating their various applications. I know first hand what dedication it takes.

Respectfully,

Bill

[vineyridge]

How do mitochrondria apply to anaerobic performance and the shift to aerobic? As I seem to recall, the shift occurs between 90 seconds and 2 minutes and the anaerobic time has now been scientifically researched and shown to be affected by conditioning. Given that most US races come in under 2 minutes, if the anaerobic time can be lengthened, then won't almost all US races run on the anaerobic pathway? And if that's the case, how will MtDNA affect it?

[brogers]

My understanding is that more than 70% of the energy required to compete is supplied through the aerobic pathway during exercise in the horse regardless of distance so mtDNA plays a part no matter what.

[vineyridge]

I did some looking up literature after seeing this and found a 2004 article in a Czech journal citing studies showing that at 1600 meters the aerobic/anaerobic ratio in "gallopers" was 70% at maximal effort. At 1200 meters it was 60 to 70% . The research cited was published in 1994 and 1995. Apparently the authors felt the literature suggested that it might be different in trotters.

Thanks.

[Bill from WA]

http://www.nature.com/nature/journal/v4 ... ifferences