The study is the result of an international collaboration between scientists at Uppsala University, Huntsville Institute of Biotechnology, Stanford University, University of Copenhagen, and SLU (Swedish University of Agricultural Sciences). It provides new insight on horse domestication.
A camouflage paint
Black color means pale pigmentation and is a camouflage color makes wild horses less conspicuous for hunting predators. The vast majority of domestic horses are not drab but has a more intense color, most likely because we humans have preferred the darker individuals in our breeding of horses throughout history.
– What is particularly interesting with the gene for black color is that it does not have the same effect in all parts of the body, says Leif Andersson who led the genetic analysis. We were very curious to try to understand the mechanism that explains why the dark eel and other wild signs do not have hair that is washed out.
The researchers began by studying the distribution of pigment in the individual hairs.
– Different hair from the most well-studied mammals have light hair from drab horses uneven distribution of color around the hair. The pigment is conditioned on the outside of the hair, while the part of the hairs lying against the body has relatively little pigment, said Freyja Imsland nydisputerad researchers Leif Andersson group. The hairs from the dark parts of drab horses contrast pigmented around along the hair shaft.
Mutations in the gene that affects the hair follicles
Genetic analysis and DNA sequencing showed that the difference between drab and non-drab due to mutations in TBX3 gene. TBX3 protein is important during the development of the individual and total inactivation of the gene for this protein causes severe birth defects in humans. That is not the case in these horses because the mutations the researchers discovered only affects the function of the gene in hair follicles.
– Previous studies in humans and mice have shown that TBX3 has a critical role in the development of the skeleton, mammary glands and heart, says Carl-Johan Rubin, one of the researchers behind the study. We have now shown that TBX3 also has a critical role in skin and hair’s development.
Two different mutations remove the black ink
A surprise in this study was that there is two recessive mutations that remove black color and gives non-drab individuals. These are called non-dun1 (non-black1) and non-dun2 (non-Black2).
– Horses are non-drab have a much stronger and more intense pigmentation than black colored horses that have paler hue. The non-blackar having non-dun1 variant may nevertheless show wild characters, such as a variable clear eel and zebra stripes on the legs, while the non-blackar with non-dun2 rarely wild characters, said Freyja Imsland. This can sometimes lead to the horse owners who have non-blackar with wild characters think their highly pigmented horses are black colored.
To understand how TBX3 affect the coloring of researchers examined the prevalence of TBX3 protein in hair development of drab and not -blacka horses.
– The growing hair we found that TBX3 protein only found in the hair follicle of drab horses. This excludes pigment cells from the portion of hair where TBX3 occur and therefore cause an asymmetrical distribution of the pigment in the hair, said Freyja Imsland. Our results indicate that TBX3 affects the development of specific cells in the hair follicle and in this way creates a microenvironment in which pigment cells are shut out.
Hint to zebra stripes
Scientists believe these results may be a clue to understanding how the zebra stripes appear. It is worth noting that a zebra is totally black skin, it’s just the hairs are white. So, a zebra is black with white stripes.
– It would not surprise me if it eventually turns out that TBX3 plays an important role in inhibiting the production of pigment in the hair follicles of the white stripes of zebras, says Leif Andersson.
The results of this study show that non-dun2 mutation likely arose recently, probably after the horse domestication of around 6 000 years ago. However, the capability for black ink and non-dun1 mutation existed long before horse domestication, because scientists found both variants in the DNA of a horse that lived about 43,000 years ago.
– This shows that it must have been two färgmorfer, perhaps different races, wild horses, and both of these groups contributed to the horse domestication. Future studies of ancient DNA samples will be able to document the geographical distribution of the two morferna, concludes Leif Andersson.
Science for Life Laboratory (SciLifeLab) is a national center for molecular biosciences with a focus on research in health and environment. The center combines technical expertise and advanced instrument with a broad expertise in translational medicine and molecular biosciences .
Contact : Professor Leif Andersson of Uppsala University, SciLifeLab SLU & amp; Texas A & amp; M University, Phone: 070-514 4904, email: Leif.Andersson@imbim.uu.se
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