Z. Tu

Transposable element (TE) display and rapid detection of TE insertion polymorphism in the Anopheles gambiae species complex

Transposable element (TE) display was shown to be a highly specific and reproducible method of detecting the insertion sites of TEs in individuals of the African malaria mosquito, Anopheles gambiae, and its sibling species, A. arabiensis. Relatively high levels of insertion polymorphism were observed during the TE display of several families of miniature inverted‐repeat TEs (MITEs) that have variable copy numbers. The genomic locations of selected insertion sites were identified by matching the sequences of their corresponding bands in a TE display gel to specific regions of the draft A. gambiae genome assembly. We discuss different scenarios in which TE display will provide powerful dominant and co‐dominant genetic markers to study the behaviour of TEs in A. gambiae populations and to illustrate the complex population genetics of this intriguing disease vector. We suggest that TE display can also provide tools for a phylogenetic analysis of the A. gambiae complex.

Characterization and expression of the odorant-binding protein 7 gene in Anopheles stephensi and comparative analysis among five mosquito species

Odorant‐binding proteins (OBPs) are important molecular players in insect olfaction, which has a great influence on the host‐seeking behaviour of mosquitoes and other disease vectors. The mRNA level of the Anopheles gambiae Obp7 gene (Agam‐Obp7) is higher in the adult female antennae and is slightly reduced in the female heads after blood‐feeding. Here we report the cloning, sequencing, chromosomal mapping and transcript analysis of Aste‐Obp7, the Obp7 gene from the Asian malaria mosquito Anopheles stephensi. Quantitative reverse transcription PCR showed that in adult female mosquitoes, Aste‐Obp7 was expressed abundantly in the antennae, much less in pooled maxillary palp and proboscis and at the lowest level in the legs. The Aste‐Obp7 level in female antennae was significantly higher than in male antennae and it slightly increased 24 h after a bloodmeal. The same pattern held for leg samples as well. The Aste‐Obp7 mRNA level dropped more than 10‐fold in the female maxillary palp and proboscis after a bloodmeal, although it was still significantly higher than in the males. Together, the above expression profiles suggest that Aste‐Obp7 probably functions in female olfaction and may possibly be involved in behaviour related to blood‐feeding. We also characterized the Obp7 gene from Anopheles quadriannulatus. Comparison among Anopheles Obp7 genes revealed conserved noncoding sequences that contain potential regulatory elements. The coding sequence and gene structure of Obp7 as well as local synteny of surrounding genes are conserved among the three Anopheles species and two divergent mosquitoes, Aedes aegypti and Culex pipiens quinquefasciatus. OBP7 protein phylogeny is congruent with the mosquito phylogeny and there is evidence of purifying selection acting on the mosquito Obp7 gene. Comparative genomics analysis will improve our understanding of the evolution and regulation of genes involved in mosquito olfaction.

Gambol and Tc1 are two distinct families of DD34E transposons: analysis of the Anopheles gambiae genome expands the diversity of the IS630-Tc1-mariner superfamily.

Tc1 is a family of DNA transposons found in diverse organisms including vertebrates, invertebrates and fungi. Tc1 belongs to the IS630‐Tc1‐mariner superfamily, which is characterized by common ‘TA’ target site and conserved D(Asp)DE(Glu) or DDD catalytic triad. All functional Tc1‐like transposons contain a transposase with a DD34E catalytic triad. We conducted a systematic analysis of DD34E transposons in the African malaria mosquito, Anopheles gambiae, using a reiterative and exhaustive search program. In addition to previously described Tc1‐like elements, we uncovered 26 new DD34E transposons including a novel family that we named gambol. Designation of family status to gambol is based on phylogenetic analyses of transposase sequences that showed gambol and Tc1 transposons as distinct clades that were separated by mariner and other families of the IS630‐Tc1‐mariner superfamily. The distinction between Tc1 and gambol is also consistent with the unique TIRs in gambol elements and the presence of a ‘W[I/L/V]DEDC’ signature near their N‐termini. This signature is predicted as part of the ‘RED’ domain, a component of the ‘PAI’ and ‘RED’ DNA binding domains in Tc1 and possibly mariner. Although gambol appears to be related to a few DD34E transposons from cyanobacteria and fungi, no gambol has been reported in any other insects or animals thus far. Several gambol and Tc1 elements have intact ORFs and different genomic copies with high sequence identity, which suggests that they may have been recently active.

Genomic and evolutionary analyses of Tango transposons in Aedes aegypti , Anopheles gambiae and other mosquito species

Tango is a transposon of the Tc1 family and was originally discovered in the African malaria mosquito, Anopheles gambiae. Here we report a systematic analysis of the genome sequence of the yellow fever mosquito, Aedes aegypti, which uncovered three distinct Tango transposons. We name the only An. gambiae Tango transposon AgTango1 and the three Ae. aegypti Tango elements AeTango1–3. Like AgTango1, AeTango1 and AeTango2 elements both have members that retain characteristics of autonomous elements such as intact open reading frames and terminal inverted repeats (TIRs). AeTango3 is a degenerate transposon with no full‐length members. All full‐length Tango transposons contain subterminal direct repeats within their TIRs. AgTango1 and AeTango1–3 form a single clade among other Tc1 transposons. Within this clade, AgTango1 and AeTango1 are closely related and share approximately 80% identity at the amino acid level, which exceeds the level of similarity of the majority of host genes in the two species. A survey of Tango in other mosquito species was carried out using degenerate PCR. Tango was isolated and sequenced in all members of the An. gambiae species complex, Aedes albopictus and Ochlerotatus atropalpus. Oc. atropalpus contains a rich diversity of Tango elements, while Tango elements in Ae. albopictus and the An. gambiae species complex all belong to Tango1. No Tango was detected in Culex pipiens quinquefasciatus, Anopheles stephensi, Anopheles dirus, Anopheles farauti or Anopheles albimanus using degenerate PCR. Bioinformatic searches of the Cx. p. quinquefasciatus (~10 × coverage) and An. stephensi (0.33 × coverage) databases also failed to uncover any Tango elements. Although other evolutionary scenarios cannot be ruled out, there are indications that Tango1 underwent horizontal transfer among divergent mosquito species.