An Unusual Role fordoublesexin Sex Determination in the DipteranSciara

Abstract

The gene doublesex, which is placed at the bottom of the sex-determination gene cascade, plays the ultimate discriminatory role for sex determination in insects. In all insects where this gene has been characterized, the dsx premessenger RNA (premRNA) follows a sex-specific splicing pattern, producing male-and female-specific mRNAs encoding the male-DSXM and female-DSXF proteins, which determine male and female development, respectively. This article reports the isolation and characterization of the gene doublesex of dipteran Sciara insects. The Sciara doublesex gene is constitutively transcribed during development and adult life of males and females. Sciara had no sex-specific doublesex mRNAs but the same transcripts, produced by alternative splicing of its primary transcript, were present in both sexes, although their relative abundance is sex specific. However, only the female DSXF protein, but not the male DSXM protein, was produced at similar amounts in both sexes. An analysis of the expression of female and male Sciara DSX proteins in Drosophila showed that these proteins conserved female and male function, respectively, on the control of Drosophila yolk-protein genes. The molecular evolution of gene doublesex of all insects where this gene has been characterized revealed that Sciara doublesex displays a considerable degree of divergence in its molecular organization and its splicing pattern with respect to the rest of dipterans as suggested by its basal position within the doublesex phylogeny. It is suggested that the doublesex gene is involved in Sciara sex determination although it appears not to play the discriminatory role performed in other insects.KEYWORDS sex determination; molecular evolution; Sciara; gene doublesex; genetics of sex M ALES and females are different at the morphological, physiological, and behavioral levels. This sexual dimorphism results from the integration of two processes: sex determination and sexual differentiation. Sex determination refers to the developmental program that commits the embryo to either the male or the female pathway. The genes underlying this phenomenon are the sex-determination genes. Sexual differentiation refers to the expression of the sex cytodifferentiation genes (which are controlled by the sex-determination genes), the expression of which gives rise to the formation of the sexually dimorphic structures that characterize the male and female adults.The animal kingdom possesses a wealth of mechanisms by which sex is decided (Bull 1983;Beukeboom and Perrin 2014). These mechanisms can be classified into three main categories, depending on the origin of the primary sexdetermination signal, which can be zygotic, maternal, or environmental. These three primary signals occur and are concatenated in the dipteran Sciara (for details see Sánchez 2010). Briefly, in Sciara, sex determination follows the XX/X0 mechanism: XX zygotes will develop as females and X0 zygotes will develop as males. Yet, the final chromosome constitution of the zygote, which start...

Mutation of doublesex in Hyphantria cunea results in sex‐specific sterility

“…The sex‐biased expression pattern of Hcdsx exhibited by H. cunea at late developmental stages may be responsible for establishing and maintaining sexually dimorphic traits in this species, but has not been reported in other Lepidoptera. However, sex‐biased expression of the dsx gene is reported in other insects, such as Sciara (Diptera), Nilaparvata lugens , Bemisia tabaci (Hemiptera), Daphnia pulex (Cladocera), Fenneropenaeus chinensis (Decapoda) and Gnatocerus cornutus (Coleoptera) . There are two possible explanations for this.…”

Genomics and transcriptomics to unravel sex determination pathway and its evolution in sand flies

“…In Ae. aegypti, dsx presents two female-specific exons, like in Sciaridae [73], that are escaped in males. In females, inclusion of both or only the second female-specific exon results in two isoforms.…”

Identification and characterization of doublesex from the pumpkin fruit fly, Bactrocera tau (Diptera: Tephritidae)

“…Since the Btau-dsx M2 transcript encoded a truncated protein without the OD2 domain and sex-specifi c region, the Btau-DSX M2 protein likely has no function, at least not in sex determination. Male dsx transcripts without the OD2 domain were reported in S. coprophila and S. ocellaris but in these two insects, male and female dsx transcripts were present in both sexes (Ruiz et al, 2015). However, Btau-DSX M2 contained the OD1 domain that functions as a DNA binding domain so the presence of the Btau-dsx M2 transcript in the adult stage could mean that this protein might be required for some other unknown function.…”

“…The splicing of the dsx pre-mRNAs to produce more than two transcript variants had been reported in many insect spe-cies, however, almost all additional dsx transcripts are female-specifi c transcripts, such as two in Aedes aegypti (Salvemini et al, 2011), Apis mellifera (Cho et al, 2007), Bombyx mori (Ohbayashi et al, 2001), Antheraea mylitta (Shukla & Nagaraju, 2010), three in Tribolium castaneum (Shukla & Palli, 2012), and six in A. assama (Shukla & Nagaraju, 2010). Two examples of a dsx gene producing more than one male-specifi c transcript have been reported in two insect species, a Japanese rhinoceros beetle, Trypoxylus dichotomus, 6 (F) female-specifi c transcripts, and 2 (M) male-specifi c transcripts (Ito et al, 2013), and a fungus fl y, Sciara ocellaris (2F and 2M) (Ruiz et al, 2015). Therefore, splicing of Btau-dsx pre-mRNA to produce two male-specifi c transcripts may be the fi rst multiple malespecifi c dsx pre-mRNA identifi ed in tephritid insects.…”