Chongqing - Recently, Professor Dai Fangyin's team from the State Key Laboratory of Efficient Breeding and Utilization of Resources Insects at Southwest University published a groundbreaking research paper titled Multiple Independent Origins of the Female W Chromosome in Moths and Butterflies in the prestigious academic journal Science Advances.

This study successfully decoded the complete genome sequence of the silkworm's W chromosome for the first time and unveiled novel mechanisms of origin and evolution for the W chromosome in Lepidopteran insects.

A screenshot of the research paper titled Multiple Independent Origins of the Female W Chromosome in Moths and Butterflies from the academic journal Science Advances. (Photo/Screenshot)

Silkworm genome research has been ongoing for over two decades, yet the W chromosome sequence, unique to female silkworms, has remained elusive. Professor Dai, head of the research team and director of the State Key Laboratory, elucidated, "The complexity of decoding the W chromosome sequence of silkworms is exceedingly high. It is not that scientists harbor a bias against females; rather, the W chromosome of female silkworms is exceptionally intricate. This achievement signifies that silkworms now possess a truly complete genome sequence."

The research team conducting their study. (Photo/Southwest University)

In silkworms, females have ZW sex chromosomes, while males have ZZ, indicating that the W chromosome plays a pivotal role in sex determination. For a long time, the molecular mechanism of sex determination in silkworms has been a focal point in academic research. Decoding the sequence information of the silkworm's W chromosome provides researchers with invaluable data resources.

The study utilized second-generation short-read, third-generation long-read, and Hi-C sequencing technologies to assemble the chromosome-level genome of female silkworms successfully. The study also developed tools to identify the W chromosome, which is rich in repetitive sequences, ultimately obtaining a W chromosome sequence of approximately 10.1 Mb. Han Minjin, the first author of the paper and associate professor at Southwest University, explained: "We discovered that the W chromosome of silkworms contains 137 copies of the female sex-determining factor Fem and 76 protein-coding genes, 11 of which are unique to the W chromosome. This information is crucial for understanding the mechanism of sex determination in silkworms."

The research team conducting their study. (Photo/Southwest University)

Moreover, given that the silkworm is a model organism designated by the Lepidopterists' Society, the study also compared the genomes of 21 Lepidopteran insects and 3 Trichopteran insects. This comparison revealed the independent origin mechanisms of the W chromosome in Lepidopteran insects and proposed a new evolutionary mechanism where the W chromosome evolved from a single Z chromosome. This discovery not only represents a breakthrough in understanding the origin and evolution of sex chromosomes in Lepidopteran insects but also offers new insights into the complex evolution of animal sex chromosomes.

The study proposed a new mechanism for the origin of the W chromosome. (Photo/Southwest University)

Professor Han Minjin stated: "With the release of the Thousand Silkworms' Pan-genome genetic resource in 2022, the silkworm now possesses a comprehensive genome sequence as a species. This marks a new milestone in silkworm genome research, providing essential theoretical and technical foundations for the future development of 'all-male silkworm' varieties." This research achievement holds significant implications in the fields of genomics and evolutionary biology, particularly in the application of molecular breeding based on the W chromosome, which will profoundly impact the sericulture industry.

The distribution of repetitive sequences and protein-coding genes in different chromosomes of the silkworm. (Photo/Southwest University)

This breakthrough enriches the content of silkworm genome research. It offers innovative solutions for future molecular design breeding and sex control in silkworms, advancing the application and development of science and technology in sericulture.