DMTR3 takes the lead!
Dictionary for the Equestrian Illiterate
Gait - The specific footfall pattern, timing, and cadence with which a horse moves
Types of Natural Gaits (in increasing speed) -The walk, the trot, and the canter/gallop. Some horses additionally have an ambling gate and/or a pace.
Types of Alternate Gaits - Pace, regular rhythm ambling, lateral ambling, and diagonal ambling
Pace - "Two-beat gait where the horse moves two legs on the same side of the body in a synchronized, lateral movement" (Fig 1a)
Trot - Gait in which "the diagonal front and hind legs move forward and backward together" (Fig 1b)
Ambling gait - "Four-beat gaits in which footfall pattern, foot placement and timing are often unique to specific breeds"
Tölt - "Regular ambling gait characteristic of the Icelandic horse"
Figure 1: (a) A pacing horse; fore- and hind-legs on the same side of the body are synchronized. (b) A trotting horse; the diagonal fore-
and hind-legs are synchronized. (Andersson et. al, 2012 Figure 1 permission pending)
Journal Article: Mutations in DMRT3 affect locomotion in horses and
spinal circuit function in mice Andersson et. al
Summary: For horse-owners, the genetic factors contributing to a horse's gait are particularly interesting. If a genetic test to screen for which horses were more likely to take home the grand prize at a competition existed, then horse-owners could selectively breed and train those horses destined for glory. Through a Genome Wide Association Study (GWAS) and a knockout mouse model, a team of Swedish scientists recently identified the gene, DMRT3, to have a major effect on a horse's gait. The investigators first determined a chromosomal region associated with the Gait locus (Figure 1d). Further genome sequencing of the candidate genes in this region revealed that DMTR3 was mutated in a large percentage of the horses with the ability to perform alternate gaits. The Swedish team used Dmtr3-/- mice to evaluate the role of this protein in locomotion. These knockout mice displayed normal motor coordination and balance, but demonstrated difficulties when running at higher speeds, a longer stride length, increased propulsion in all limbs, and decreased brake time in hind limbs. Heterozygous Dmtr3+/- mice did not differ from control mice. Analysis of Dmrt3 knockout mice showed this protein is critical for the development and configuring of the spinal circuits that control stride in vertebrates. From the combination of genetic linkage analysis, comparative sequencing, and analysis of a mouse knockout model, Andersson et. al conclude that the nonsense mutation in DMRT3 is a causative mutation that affects gaitedness in horses. This article tells a coherent story and impressively presents a massive amount of data in a digestible manner. However, the authors do not spend much time discussing future directions or alternative genetic or environmental factors that might affect horse gait.
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Figure 1d: Genome-wide association study (GWAS) demonstrating significant linkage between a horse’s ability to pace and the single nucleotide polymorphism (SNP) indicated by the arrow (SNP BIEC2_620109) on chromosome 23.This GWAS study used 30 four-gaited (walk, tölt, trot and gallop) Icelandic horses and 40 five- gated (walk, tölt, trot, gallop, and pace) to determine the locus associated with the ability to pace. (1e) Schematic of region associated with Gait locus. Shaded box indicates minimum region of Gait locus from linkage analysis. (Andersson et. al, 2012 Figure 1 permission pending)
Popular Press: Horses’ Ability to Pace Is Written in DNA Goldberg
Comparison to Journal Article
Kua points out that the public understanding of science depends not just on internalizing scientific facts, but also understanding research methods and the socioeconomic impacts of scientific discoveries. Reporters communicating scientific findings to the general public should provide readers with a context to give the audience a framework within in which to interpret the results. This context should include a past body of work, the methods used to obtain the scientific results, the big picture implications of the discovery, and any notable future directions the investigators might wish to pursue. Moreover, science reporters should strive to act as an “intermediary” (effectively and accurately translating the science), a “watch-dog” (discussing the ethical implications of scientific discoveries), and “tool-givers” (adequately explaining the science, posing questions of long-term significance, and providing readers with context). Clearly, translating a scientific journal article to the layperson is no small feat and reporters often fall into several pitfalls when attempting this. These errors can include omissions, generalizations, oversimplification, and overstating the generalizability of data. Thus, with Kua’s guide on how to effectively communicate scientific literature to the general public in mind, I will critique Goldberg’s news report. (Kua, 2004).
Goldberg does a nice job of providing a big picture. He gives the reader a historical background of harness racing, the different types of horses, and most importantly, the potential for this discovery to financially benefit horse-trainers. By providing a socioeconomic context to ground the findings, Goldberg enables the audience to understand the real-world applications of these results. Along a similar vein, Goldberg provides a nice background for the motivation that fueled Andersson et. al’’s research. He says, “These [Icelandic] horses have an ambling gait called tolt, a gait so calm for the rider that it is like sitting on a sofa…but only some horses can pace and they [Andersson et. al] wanted to find out why.” Goldberg effectively communicates the causative mutation that leads to a difference in horse gait, and avoids overstating the generalizability of the research. Importantly, he notes that this mutation “largely explained why some horses could trot or pace and why some could not,” (emphasis added) instead of attributing this difference to genetics alone. (Goldberg, 2013).
Despite providing a socioeconomic context to view the results under, Goldberg des not provide any reference to a past scientific body of work (i.e. the known function of Dmtr3 or previous genetic analysis of breeding horses) or the methods the researchers used to obtain their results. Goldberg simply states, “Scientists…recently discovered that a single gene, which they have called DMTR3, largely explained why some horses could trot…” He completely omits the methods the researchers used to arrive at this conclusion. Later in the article, Goldberg commits the same error and additionally oversimplifies the results in stating, “They found that a single gene differentiated pacers and nonpacers.” In this statement, Goldberg omits the fact that this gene is in fact in both types of horses, but a higher percentage of pacers have a mutation in that gene. Another poor translation occurs when Goldberg says, “By experimenting on mice, the Swedish researchers next determined that these genes were held in neurons in the spinal cored, which controls locomotion. That makes sense; trotting demands diagonal and coordinated movements.” Here, Goldberg lumps genes and proteins as one entity and reduces the battery of knockout mice experiments to two sentences. He fails to communicate how the researchers used mice to determine the location and function of the protein (not the gene as Goldberg indicates).
In summary, while Goldberg does a nice job providing a larger fame of real-world application for Andersson et. al'’s research, he does not provide a scientific context of previous work or detail how the researchers made these discoveries. Below is a review of how well Goldberg filled Kua’s recommended roles as “intermediary”, “watch-dog”, and “tool-giver”.
Intermediary: The job of an intermediary is to provide the reader with an effective translation of the research. Goldberg’s article contains several scientific errors (i.e. confusing the gene with the protein), thus weakening its power as a translation. Still, Goldberg adequately communicates the researcher’s main point – that DMTR3 predisposes horses to have multiple gaits. Overall, Goldberg does an average job as an intermediary between scientific research and the general public.
Watchdog: According to Kua, the primary role of the watchdog is to discuss the social and ethical implications of a finding. While Goldberg does a very good job commenting on the potential for this discovery to affect horse owners, he does not comment on ethically moral extension of these findings to human athletes – whether or not to pigeonhole someone’s future based on a genetic test. In doing so, Goldberg could have mentioned the other factors contributing to a horse’s success such as training and environment. Overall, Goldberg does a below average job of acting as a watchdog.
Tool-giver: A tool giver should provide the reader with enough context for them to think critically about a scientific finding and make connections between past, present, and future research. Although Goldberg provides his audience with a socioeconomic background of the real-world applications for this research, he fails at providing context on every other level. He does not mention any previous work that would act as a platform for this research, nor does he provide the methodology that the scientists used to come to their conclusions. Instead, he states that DMTR3 causes differences in a horse’s gait as if it was already an established fact. Furthermore, Goldberg does not provide the readers with any future questions the investigators might have about Dmtr3. Overall, Goldberg does a poor job at providing the reader with the necessary tools to think critically about the scientific findings.
Andersson, Lisa, Molly McCue, Jessica Petersen, Freyja Imsland, Martin Larhammar, Fatima Memic, Hanna Wootz, Doreen Schwochow, Carl-Johan Rubin, Kalicharan Patra, Thorvaldur Arnason, Lisbeth Wellbring, James Mickelson, Goran Hjalm, Klas Kullander, Gus Cothran, Nadav Ahituv, Lars Roepstorff, Sofia Mikko, Anna Vallstedt, Gabriella Lindgren, and Leif Andersson. "Mutations in DMRT3 affect locomotion in horses and spinal circuit function in mice.." Nature 488.7413 (2012): 642-646. Web. Jan. 2013. <http://www.nature.com/nature/journal/v488/n7413/full/nature11399.html?WT.ec_id=NATURE-20120830>.
Ryan. "Ability to Pace Is Written in DNA Of Some Horses." The New
York Times. The New York Times, 11 Sept. 2012. Web. 27 Jan. 2013. <http://www.nytimes.com/2012/09/11/sports/scientists-find-gene-could-explain-horses-ability-to-pace.html?_r=0>.
Kua, Eunice, Michael Reder, and Martha Grossel. "Science in the News: A Study of Reporting Genomics." Public Understanding of Science 13.3 (2004): 309-322. Print.
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