The national treasure giant panda has always been known for its iconic black and white fur color. However, a rare coat color mutant, the brown white giant panda (hereinafter referred to as the brown giant panda), has emerged in the wild population of giant pandas in the Qinling Mountains. In 1985, a female brown giant panda named "Dandan" was first discovered and rescued in the Foping Nature Reserve in Shaanxi Province. Dandan passed away in 2000 due to illness. In 2009, the male brown giant panda "Qizai" was discovered in the Foping Nature Reserve when it was young. It was later rescued and taken to the Shaanxi Louguantai Rare Wildlife Rescue and Breeding Center, where it lived normally in a captive environment. So far, there have only been seven cases of brown giant pandas with physical or photographic evidence. Among them, three cases are from Foping County, two cases are from Yang County, and there is one case each in Taibai and Zhouzhi counties. The formation of this brown white fur phenotype and why it has only been discovered in populations of the Qinling Mountains have always been an unknown mystery.
Wei Fuwen, an academician of the CAS Member, has paid long-term attention to the rare brown white coat phenotype of wild giant pandas in Qinling Mountains. Using the ecological and genetic data and captive breeding information of wild giant pandas collected in Foping Nature Reserve for a long time, two families related to the seven cubs of brown giant pandas have been established, and the autosomal recessive genetic model of brown white coat has been determined. Based on third-generation sequencing data, the team identified the 25bp deletion mutation in the first exon of the Bace2 gene as the most likely genetic basis for brown giant pandas, including genome assembly at the chromosome level, whole genome resequencing data from the two families of Qizai, and whole genome resequencing data at the population level. Furthermore, the study confirmed the integrity of the Bace2 gene structure using transcriptome sequencing data, and verified the true existence of this mutation in brown giant pandas at the RNA level. To explore the reliability of the association between this deletion mutation and brown variation, PCR and Sanger sequencing were performed on the Bace2 gene deletion mutation segment of 192 other Qinling, non Qinling, or hybrid black and white giant pandas. Combined with 35 whole genome resequencing individuals, a total of 227 giant pandas were identified. Finally, it was confirmed that only two brown giant pandas had a homozygous 25bp deletion, and four Qinling black and white giant pandas and one captive black and white giant panda were heterozygous, And other black and white giant pandas are wild-type homozygotes.
This study used CRISPR-Cas9 gene editing technology to construct a homologous knockout mouse model in C57BL/6J strain mice, and found that the fur color of all Bace2-/- mice was lighter than that of the wild-type. Microscopic observation revealed that compared to the 1-month-old growth period, the lack of pigment in the hair of mice in the 4-month-old resting period was more significant. A study on transmission electron microscopy observation of mouse back hair and statistical analysis of the number and cross-sectional area of melanosomes in individual cells revealed that Bace2-/- mice exhibited a significant decrease in melanosome quantity and cross-sectional area, similar to brown giant pandas.
On March 5th, the research findings were published in the Journal of the National Academy of Sciences (PNAS) under the title "Taking a color photo: A homizygous 25-bp deletion in Bace2 may cause brown and white coat color in giant pandas". This study was completed in collaboration with the Institute of Zoology and the Qinling Giant Panda Research Center. The research work has been supported by the National Natural Science Foundation of China, the Chinese Academy of Sciences strategic leading science and technology project (Class B), the key project of Jiangxi Provincial Natural Science Foundation and the Chinese Academy of Sciences Youth Innovation Promotion Association.
Paper link:
论文链接
Brown Giant Panda Family and Bace2 Mutation Candidate Sites
Hair traits of Bace2 knockout mice and wild mice
