The transformer-2 and fruitless characterisation with developmental expression profiles of sex-determining genes in Bactrocera dorsalis and B. correcta
Kamoltip Laohakieat, Siriwan Isasawin, Sujinda Thanaphum
Abstract
Abstract Sex determination in tephritid fruit flies involves a signaling cascade of alternatively spliced genes. The Transformer (TRA) and Transformer-2 (TRA-2) complex establishes an autoregulatory loop switching sex-specific splicing of tra pre-mRNA in females. The TRA/TRA-2 complex also regulates the sex-specific splicing of downstream effector genes, doublesex ( dsx ) and fruitless ( fru ). In Ceratitis capitata , a Maleness-on the-Y ( MoY ) gene modulates sex-specifically spliced Cctra pre-mRNA and results in the breakdown of the Cctra autoregulatory loop in males. In this study, the tra-2 and fru genes were characterised in two key pests, Bactrocera dorsalis and B. correcta. The tra-2 genes showed high degrees of conservation among tephritids. The complex gene organisation for each of Bdfru and Bcfru were identified. There are sex-specific and non sex-specific transcripts generated by alternative promoters as found in Drosophila melanogaster and other insects. RNAi knockdown of Bdtra transcripts showed that BdTRA controls the sex-specific splicing of Bddsx and Bdfru pre-mRNAs. Developmental expression analysis shows that multiple splice variants of Bdtra and Bctra RNAs are present before and during cellular blastoderm formation and that the mature sex-specific variants become fixed later in embryogenesis. Furthermore, the Bddsx M splice variants are found in early embryos at the beginning of gastulation, but Bdfru M does not appear until the larval stage. We proposed that the zygotic tra loop is initiated in both female and male embryos before becoming automatised or abolished by MoY , respectively.