Expression analysis of Drosophila doublesex, transformer-2, intersex, fruitless-like, and vitellogenin homologs in the parahaploid predator Metaseiulus occidentalis (Chelicerata: Acari: Phytoseiidae)

Abstract

Characterization and expression analyses are essential to gain insight into sex-determination pathways in members of the Acari. Little is known about sex determination at the molecular level in the western orchard predatory mite Metaseiulus occidentalis (Arthropoda: Chelicerata: Arachnida: Acari: Phytoseiidae), a parahaploid species. In this study, eight genes previously identified as putative homologs to genes involved in the sex-determination pathway in Drosophila melanogaster were evaluated for sex-specific alternative splicing and sex-biased expression using reverse-transcriptase PCR and quantitative real-time PCR techniques, respectively. The homologs evaluated in M. occidentalis included two doublesex-like genes (Moccdsx1 and Moccdsx2), transformer-2 (Mocctra-2), intersex (Moccix), two fruitless-like genes (MoccBTB1 and MoccBTB2), as well as two vitellogenin-like genes (Moccvg1 and Moccvg2). Single transcripts of equal size were detected in males and females for Moccdsx1, Moccdsx2, Mocctra-2, Moccix, and MoccBTB2, suggesting that their pre-mRNAs do not undergo alternative splicing in a sex-specific manner. Three genes, Moccdsx1, Moccdsx2 and MoccBTB2, displayed male-biased expression relative to females. One gene, Moccix, displayed female-biased expression relative to males. Two genes, Mocctra-2 and MoccBTB1, did not display detectable differences in transcript abundance in males and females. Expression of Moccvg1 and Moccvg2 were detected in females only, and transcript levels were up-regulated in mated females relative to unmated females. To our knowledge, this represents the first attempt to elucidate expression patterns of putative sex-determination genes in an acarine. This study is an initial step towards understanding the sex-determination pathway in the parahaploid M. occidentalis.

Hemimetabolous insects elucidate the origin of sexual development via alternative splicing

“…The dsx clade contained sequences from several basal insect orders, crustaceans, and chelicerates (Supplemental Figure 1), and included experimentally characterized dsx genes from the branchiopod crustacean D. magna (NCBI accession number BAJ78307.1), the decapod crustacean F. chinensis (AUT13216.1), and the mite M. occidentalis (XP003740429.2 and XP003740430.1). In these species, the dsx genes are not spliced sex-specifically, but are transcribed in a strongly male-biased fashion (53,54,57). dsx genes from holometabolous insects, which direct male and female differentiation via alternative spliceforms, are also present in this clade.…”

“…We propose that the canonical insect mechanism of sexual differentiation based on sex-specific splicing of dsx and tra evolved gradually in hemimetabolous insects, and may not have been fully assembled until the last common ancestor of the Holometabola (Figure 8). In crustaceans, mites, and non-arthropod animals, dsx and its homologs act as male-determining genes that are transcribed in a male-specific fashion and are dispensable for female sexual differentiation (53,54,57). One of the earliest events in insects was the evolution of sex-specific dsx splicing, where dsx is transcribed in both sexes but produces alternative isoforms in males vs females.…”

“…The D. magna tra gene is not spliced sex-specifically, does not differ in expression between males and females, and does not regulate dsx (Kato et al, 2010). dsx also shows male-biased transcription and no sex-specific splicing in the shrimp Fenneropenaeus chinensis (54) and in the mite Metaseiulus occidentalis (54). Thus, the origin of the transformer-doublesex splicing cascade was a key event in the evolution of sexual differentiation in insects.…”

Identification and characterization of doublesex in Bemisia tabaci

“…In Sciara spp., in contrast, dsx mRNAs are not sex‐specific, but the relative abundances of dsx transcripts are sex‐specific (Ruiz et al ., ). In the crustacean D. magna and the arachnid M. occidentalis , dsx pre‐mRNA regulates sexual dimorphism via sex‐biased expression in males (Kato et al ., ; Pomerantz et al ., ; Pomerantz & Hoy, ). The current study demonstrated that, like Sciara spp., B. tabaci lacks a sex‐specific dsx transcript and that the expression level of Btdsx , like the expression levels of dsx in D. magna and M. occidentalis , was significantly higher in males than females.…”

“…In most insects and as indicated earlier, male‐ and female‐specific sexual development occurs via the sex‐specific splicing of dsx pre‐mRNA (Baker & Wolfner, ; Scali et al ., ; Cho et al ., ; Shukla & Palli, ). In the crustacean Daphnia magna and the arachnid Metaseiulus occidentalis , however, dsx pre‐mRNA regulates sexual dimorphism via sex‐biased expression in males (Kato et al ., ; Pomerantz et al ., ; Pomerantz & Hoy, ).…”