In their new research, scientists at Texas A&M University developed a highly contiguous chromosome-level reference genome for the North American bison (Bison bison). In doing so, they also discovered the gene responsible for albinism in this species.
Pelage color variation in the North American bison (Bison bison): (a) albino bison; note the white pelage, hypopigmented eyes, and hypopigmented skin particularly around eyes and nose; (b) typical wild-type bison pelage color. Image credit: Stroupe et al., doi: 10.1093/g3journal/jkad156 / National Buffalo Museum / Searle Swedlund of Jamestown, ND.
The North American bison is an iconic species due to their cultural and spiritual connection with Native American people, production potential to ranchers, and symbology of successful conservation efforts in federal and state parks and wildlife refuges.
In addition, the bison was officially named the national mammal of the United States in 2016.
Millions of bison once roamed the continent until they experienced a near extinction-level event reducing their census size by over 99% in the 1800s.
Their salvation is owed to various private herds established with wild caught calves across North America from Texas, United States to Alberta, Canada.
Today, most bison are privately maintained as production livestock, while a smaller portion are managed as wildlife on public, nongovernmental organization, or tribal lands where they continue to play a vital role as grazers and food sources.
“Because reference genomes can help researchers identify and characterize genes that are responsible for a large number of traits, this technology is used to do all kinds of things, including diagnosing health conditions and developing targeted treatments,” said co-senior author Dr. Brian Davis, a researcher at the Texas A&M University School of Veterinary Medicine and Biomedical Science.
The newest bison reference genome was developed using technology that allows researchers to create genomes based on DNA from hybrids, which are animals with DNA from two different species.
In this case, Dr. Davis and his colleagues used DNA from a type of bison-cow hybrid called an F1, or individuals with a perfect 50-50 split between its parents’ DNA.
In general, F1 hybrids between bison and cattle are rare but have historically happened, since we now know that most bison herds in North America contain descendants of hybrids between bison and cattle.
To create the new bison genome, the researchers first sequenced the genome of the F1 hybrid as well as the bison mom and the domestic cattle father.
With this information, they were able to separate bison DNA from the cattle DNA regions in the hybrid.
Since the cattle genome is already very advanced, it provided a reference for creating the new bison genome, helping to guide the researchers in developing the complete high-resolution reference bison genome.
To prove the utility of the new genome, the scientists set out to discover which gene mutation was responsible for albinism in bison and to create a genetic test that could be used to identify carriers of that mutation.
“Albinism, a rare condition characterized by a lack of pigment in an animal’s body, making them look white with red eyes, has historical significance in that albino bison have been recognized as a religious symbol for some Native American Indigenous tribes,” they explained.
The discovery is the first time anyone has successfully determined the gene mutation responsible for an observable trait in bison.
“We knew albinism was an inherited recessive trait, but we didn’t know which gene was responsible,” said first author Sam Stroupe, a graduate student at the Texas A&M University School of Veterinary Medicine and Biomedical Science.
“So, we sequenced the DNA from a few albino bison and compared them to those of normal coloration to find the mutation that causes albinism.”
“As it turns out, the mutation causes an important enzyme to cease functioning correctly, which leads to the lack of skin pigmentation.”
The team’s results appear in the journal G3: Genes, Genomes, and Genetics.
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Sam Stroupe et al. 2023. Chromosome-level reference genome for North American bison (Bison bison) and variant database aids in identifying albino mutation. G3: Genes, Genomes, Genetics 13 (10): jkad156; doi: 10.1093/g3journal/jkad156
