AsianScientist (Nov. 11, 2016) – After female silkworms were made to express a male sex gene, they developed male reproductive glands and started producing sperm. Results from the Japanese study were published in PLOS Genetics.
Sex of the Bombyx mori silkworm is determined by small RNA molecules called piRNAs, a mechanism found only in silkworms. The piRNAs are produced by the Fem gene located on the female sex chromosome, or W chromosome, and repress the Masc gene believed to determine maleness. Thus, silkworms carrying Fem are thought to repress the male gene, thereby developing into females, but it was unclear whether Masc induced maleness.
The research group led by Associate Professor Masataka Suzuki at the University of Tokyo Graduate School of Frontier Sciences and their collaborators designed a gene called Masc-R, which is resistant to piRNAs, and observed what would happen if they introduced the Masc-R gene into the female silkworm genome. They found that transgenic females expressing Masc-R developed abnormal ovaries, and the number of eggs they produced fell drastically—close to zero.
The abnormal ovaries also contained male sex gland-like tissues and, more notably, the tissues contained a considerable number of sperm. External genital organs and external features of abdominal segments also showed signs of partial masculinization. The researchers concluded that the results strongly suggest the ability of Masc to induce maleness in the silkworm.
The number of genes identified thus far as determining maleness in silkworms is still limited; therefore, this study is valuable in showing the role of a gene in determining maleness in butterflies and moths. Also, these findings may eventually lead to the development of pesticides targeting the Masc gene and help pave the way for controlling agricultural pests through the sterilization of moths.
The article can be found at: Sakai et al. (2016) Transgenic Expression of the piRNA-Resistant Masculinizer Gene Induces Female-Specific Lethality and Partial Female-to-Male Sex Reversal in the Silkworm, Bombyx mori.
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Source: University of Tokyo; Photo: Pixabay.
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