Characterization of the doublesex gene within the Culex pipiens complex suggests regulatory plasticity at the base of the mosquito sex determination cascade

Abstract

BackgroundThe doublesex gene controls somatic sexual differentiation of many metazoan species, including the malaria mosquito Anopheles gambiae and the dengue and yellow fever vector Aedes aegypti (Diptera: Culicidae). As in other studied dipteran dsx homologs, the gene maintains functionality via evolutionarily conserved protein domains and sex-specific alternative splicing. The upstream factors that regulate splicing of dsx and the manner in which they do so however remain variable even among closely related organisms. As the induction of sex ratio biases is a central mode of action in many emerging molecular insecticides, it is imperative to elucidate as much of the sex determination pathway as possible in the mosquito disease vectors.ResultsHere we report the full-length gene sequence of the doublesex gene in Culex quinquefasciatus (Cxqdsx) and its male and female-specific isoforms. Cxqdsx maintains characteristics possibly derived in the Culicinae and present in the Aedes aegypti dsx gene (Aeadsx) such as gain of exon 3b and the presence of Rbp1 cis-regulatory binding sites, and also retains presumably ancestral attributes present in Anopheles gambiae such as maintenance of a singular female-specific exon 5. Unlike in Aedes aegypti, we find no evidence for intron gain in the female transcript(s), yet recover a second female isoform generated via selection of an alternate splice donor. Utilizing next-gen sequence (NGS) data, we complete the Aeadsx gene model and identify a putative core promoter region in both Aeadsx and Cxqdsx. Also utilizing NGS data, we construct a full-length gene sequence for the dsx homolog of the northern house mosquito Culex pipiens form pipiens (Cxpipdsx). Analysis of peptide evolutionary rates between Cxqdsx and Cxpipdsx (both members of the Culex pipiens complex) shows the male-specific portion of the transcript to have evolved rapidly with respect to female-specific and common regions.ConclusionsAs in other studied insects, doublesex maintains sex-specific splicing and conserved doublesex/mab-3 domains in the mosquitoes Culex quinquefasciatus and Cx. pipiens. The cis-regulated splicing of Cxqdsx does not appear to follow either currently described mosquito model (for An. gambiae and Ae. aegypti); each of the three mosquito genera exhibit evidence of unique cis-regulatory mechanisms. The male-specific dsx terminus exhibits rapid peptide evolutionary rates, even among closely related sibling species.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0386-1) contains supplementary material, which is available to authorized users.

Sexually dimorphic traits in the silkworm, Bombyx mori, are regulated by doublesex

“…In other insects, the dsx gene also been identified, such as in Anopheles gambiae (Scali et al, 2005), Aedes aegypti. (Salvemini et al, 2011), Lucilia cuprina (Concha et al, 2005), Culex pipiens (Price et al, 2015), Tribolium castaneum (Shukla and Palli, 2012), Nasonia vitripennis (Oliveira et al, 2009) Apis mellifera (Cho et al, 2007), Musca domestica (Hediger et al, 2004), Gnatocerus cornutus (Gotoh et al, 2016), Antheraea assama and Antheraea mylitta (Shukla and Nagaraju, 2010). These insects dsx displayed the same sex-specific splicing between two sexes.…”

The ubiquity and ancestry of insect doublesex

“…Three additional type-B OD1 motifs were recovered, however no hits shared a common genomic contig and thus we were unable to link them. The genome contig encoding the OD1 domain contains 3.6 kb of sequence downstream of the domain, and the contig encoding the OD2 domain contains 3.5 kb of upstream sequence; this is well within the range of intron sizes present between the two domains in dipteran dsx gene models 34 35 36 , thus it remains possible the two domains are linked and were recovered on separate contigs of a fragmented assembly.…”

“…Additional studies have supported a role of positive selection on the male-specific protein region, implicated in a system of “runaway evolution” due to its developmental influence on secondary sex characteristics and the response of female preference to genetic drift 46 . As the upstream regulators of dsx are diverse and differ even among closely related taxa 34 35 36 , the large variation in gene length reported here may be a product of evolution under lineage-specific sexual selective pressures balancing the above structural, phenotypic and regulatory factors. The degree of length heterogeneity in the common region makes homologous codon identification, saturation estimates and alignment extremely difficult even between congeners, and thus current formal tests for positive selection will be unable to test this hypothesis.…”

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

“…gambiae and Ae. aegypti [22–25,72–74]. While sex-specific splicing regulation of the fru orthologs in both mosquito species is very well conserved respect to Drosophila (Fig.…”