Molecular mechanisms of secondary sexual trait development in insects

Bombyx mori histone methyltransferase BmAsh2 is essential for silkworm piRNA-mediated sex determination

“…Female flies carry two X chromosomes which activate the transcription of Sex-lethal ( Sxl ) and lead to female sexual development, while a single copy of X chromosome in male flies suppresses Sxl expression to determine male sexual fate [ 6 , 7 ]. Subsequently, the female-specific Sxl protein regulates splicing of transformer ( tra ), which cooperates with the product of the non-sex-specific transformer 2 ( tra2 ) gene to regulate the alternative splicing of doublesex ( dsx ) [ 8 , 9 ]. In contrast, the insect WZ sex determination system is found in most lepidopteran insects.…”

Sex differences in 20-hydroxyecdysone hormone levels control sexual dimorphism inBicyclus anynanabutterfly wing patterns

“…Previous studies on the developmental basis of sexual traits in insects have pointed exclusively to variation in cell-autonomous mechanisms involving the activation of members of the sex-determination pathway, such as the gene doublesex ( dsx ), in the cells that develop the trait [3, 13-15]. Therefore, we asked whether dsx was being expressed in the eyespot centers at the wandering stage of development.…”

“…This led us to ask whether the sexual ornaments could be under the control of sex-specific hormone titers. Previous studies have implicated insect hormones in the evelopment and maintenance of sexual traits in insects [3], but to date no study to our knowledge has ever shown sexual dimorphism in hormone titers leading to the development of sexual traits in insects. Furthermore, previous research in this species showed that levels of the molting hormone, 20-hydoxyecdysone (20E), were involved in regulating ventral eyespot center size in females during the Wr stages of development.…”

“…An important advance of this work is the demonstration that different levels of a steroid hormone in an insect control sexually dimorphic traits. Differentiation of male and female traits in insects has, so far, been attributed exclusively to cell-autonomous mechanisms involving the expression of sex-specific splice variants and factors from the sex determination pathway, such as Feminizer (Fem), Transformer (Tra), Fruitless (Fru), and Doublesex (Dsx), in cells that build the sexually dimorphic trait [3, 29, 30]. For instance, previous work showed that the sexually dimorphic mandibles of a stag beetle, Cyclommatus metallifer ,were regulated by Juvenile Hormone (JH) interacting with sex-specific isoforms of doublesex expressed in the mandibles, but levels in JH titers across the sexes were found to be similar [31,32].…”

“… Summary In contrast to the important role of hormones in the development of sexual dimorphic traits in vertebrates [1], the differentiation of these traits in insects is attributed exclusively to variation in cell-autonomous mechanisms controlled by members of the sex determination pathway [2], such as doublesex ( dsx ). Although hormones can shape the development of sexual traits in insects, and interact with dsx to create dimorphisms, variation in hormone levels are not known to cause dimorphism in these traits [3]. Here we show that butterflies use sex-specific differences in 20-hydroxyecdysone (20E) hormone titers to create sexually dimorphic wing ornaments, without the local involvement of dsx .…”