title: Altered expression of testis-specific genes, piRNAs, and transposons in the silkworm ovary masculinized by a W chromosome mutation.
abstract: BACKGROUND
  In the silkworm, Bombyx mori, femaleness is strongly controlled by the female-specific W chromosome. Originally, it was presumed that the W chromosome encodes female-determining gene(s), accordingly called Fem. However, to date, neither Fem nor any protein-coding gene has been identified from the W chromosome. Instead, the W chromosome is occupied with numerous transposon-related sequences. Interestingly, the silkworm W chromosome is a source of female-enriched PIWI-interacting RNAs (piRNAs). piRNAs are small RNAs of 23-30 nucleotides in length, which are required for controlling transposon activity in animal gonads. A recent study has identified a novel mutant silkworm line called KG, whose mutation in the W chromosome causes severe female masculinization. However, the molecular nature of KG line has not been well characterized yet.
  
  
  RESULTS
  Here we molecularly characterize the KG line. Genomic PCR analyses using currently available W chromosome-specific PCR markers indicated that no large deletion existed in the KG W chromosome. Genetic analyses demonstrated that sib-crosses within the KG line suppressed masculinization. Masculinization reactivated when crossing KG females with wild type males. Importantly, the KG ovaries exhibited a significantly abnormal transcriptome. First, the KG ovaries misexpressed testis-specific genes. Second, a set of female-enriched piRNAs was downregulated in the KG ovaries. Third, several transposons were overexpressed in the KG ovaries.
  
  
  CONCLUSIONS
  Collectively, the mutation in the KG W chromosome causes broadly altered expression of testis-specific genes, piRNAs, and transposons. To our knowledge, this is the first study that describes a W chromosome mutant with such an intriguing phenotype.
authors.affiliation: Department of Agricultural and Environmental Biology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Japan.
authors.forename: Kahori
authors.initials: K
authors.lastname: Hara
authors.forename: Tsuguru
authors.initials: T
authors.lastname: Fujii
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Suzuki
authors.forename: Sumio
authors.initials: S
authors.lastname: Sugano
authors.forename: Toru
authors.initials: T
authors.lastname: Shimada
authors.forename: Susumu
authors.initials: S
authors.lastname: Katsuma
authors.forename: Shinpei
authors.initials: S
authors.lastname: Kawaoka
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D012831:Bombyx / Q000235:genetics*; D016000:Cluster Analysis; D004251:DNA Transposable Elements / Q000235:genetics*; D005260:Female; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D008297:Male; D009154:Mutation; D009928:Organ Specificity / Q000235:genetics; D010053:Ovary / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics*; D012730:Sex Chromosomes; D013737:Testis / Q000378:metabolism
chemical_list: D004251:DNA Transposable Elements; D034741:RNA, Small Interfering