The transformer-2 and fruitless characterisation with developmental expression profiles of sex-determining genes in Bactrocera dorsalis and B. correcta

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 BddsxM splice variants are found in early embryos at the beginning of gastulation, but BdfruM 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.

Early embryonic transcriptomes of Zeugodacus tau provide insight into sex determination and differentiation genes

“…The male‐specific transcripts of Zttra encoded only truncated TRA proteins because there were several stop codons in the male‐specific exons that terminated translation, whereas the female‐specific transcript of Zttra encoded a full‐length TRA protein (Boggs et al ., 1987; Pane et al ., 2002; Concha & Scott, 2009; Arisa et al ., 2018). Male‐specifically spliced transcripts of Zttra were detected first at E5, which is consistent with the results of previous studies (Gabrieli et al ., 2010; Peng et al ., 2015; Luo et al ., 2017; Laohakieat et al ., 2020).…”

Identification and Functional Analysis of the Sex-Determiner Transformer-2 Homologue in the Freshwater Pearl Mussel, Hyriopsis cumingii

“…In Nasonia vitripennis, Nvtra2 was also found in early embryos (<3 h old), suggesting that the mother provides Nvtra2 to the egg and is critical for embryo viability (Geuverink et al, 2017). Studies of Bdtra-2 of Bactrocera dorsalis have shown that Bdtra-2 transcripts are contributed maternally and activated by the zygote in the developing embryos (Laohakieat et al, 2020). Therefore, we hypothesized that in H. cumingii, Hctra-2 might be provided by the mother and involved in embryo sex determination during cleavage.…”

The role of fruitless in specifying courtship behaviors across divergent Drosophila species

“…In Drosophila melanogaster, in which fru function was first described (11), splicing in the male pattern results in a functional protein called FruM in a subset (~2000, or ~2%) of male neurons, whereas splicing in the female pattern results in transcripts that are degraded, leading to no functional protein (3,12,13). Sex-specific fru splicing has since been found across many but not all insect species (14)(15)(16)(17)(18)(19)(20)(21)(22). Whether the role of fru in specifying sex-specific behaviors differs across species remains an open question.…”