While China’s black and white pandas are famous as symbols of diplomacy and conservation, their lesser-known and extremely rare brown and white relatives have remained a mystery since they were first spotted in 1985. There have been only seven documented reports of the species in the wild, and only one brown panda currently lives in captivity. Researchers have now used genetic analysis to better understand the origins of these animals’ distinct appearance.
Classified as a subspecies of the giant panda, brown Qinling pandas were named for the mountain range in the Shaanxi province where the first panda of its kind was found. That panda, a female named DanDan, was held in captivity until her death in 2000. Although DanDan has no surviving offspring, a stored tissue sample allowed the research team to study her genome.
Decoding the Genetic Mystery
In 2009, scientists found a young male brown panda in the same area where DanDan was discovered. Named Qizai, he now lives in the Louguantai Wild Animal Breeding and Protection Center in Xi’An, China, and is the only brown panda living in captivity. Researchers analyzed samples from DanDan, Qizai and pandas from the same region in comparison with genetic data from black and white pandas living in other mountain ranges. The results, published in the Proceedings of the National Academy of Sciences (PNAS), point to a missing sequence of DNA as the reason for the distinctive color.
To determine the genetic origin of the brown coloring, scientists sequenced the genomes of brown pandas and compared the results with those of nearly 200 black and white pandas from other regions. The study authors, from the Institute of Zoology at the Chinese Academy of Sciences (CAS), reported in PNAS that “the brown coat color is governed by autosomal recessive mutations.” That is, a brown panda results from a pairing of two parents that carry the mutation, even if they appear black and white.
The Bace2 Gene
From this finding, the researchers sought to identify the mutation responsible for the brown coloring. They found a deletion of 25 base pairs at the start of the Bace2 gene. None of the pandas from other mountain ranges had this mutation, while several from the Qinling Mountains and a hybrid of both populations carried the variation. Only Qizai and DanDan were homozygous, inheriting the mutation from both parents. This indicates that the mutation is recessive and explains the rarity of brown pandas.
To confirm the gene’s role in the brown panda’s coloring, scientists used CRISPR genetic editing to modify 78 black laboratory mice, deleting the same part of the Bace2 gene. The mutant mice grew brown fur, supporting the theory that the deletion in Bace2 is likely the genetic basis for the pandas’ brown-and-white coats. “This essentially means that the coding sequence for the protein is disrupted, which leads to a malfunction of the protein,” co-author Yibo Hu, explained. The Bace2 gene codes for a protein with various enzymatic functions. In humans, it has been linked to Alzheimer’s disease.
A “Brand-New Discovery”
Both the mutant mice and the brown pandas that have been observed in captivity have normal growth and reproduction, indicating no notable physical abnormalities. “The breakthrough of this paper is the finding that the missing of a gene or genetic segment could also lead to the change of color,” said Shi Peng, an evolutionary geneticist at the CAS Kunming Institute of Zoology. “From a genetics perspective, this is a brand-new discovery.”
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