Dataset Information

Site-specific genetic engineering of the Anopheles gambiae Y chromosome.

ABSTRACT: Despite its function in sex determination and its role in driving genome evolution, the Y chromosome remains poorly understood in most species. Y chromosomes are gene-poor, repeat-rich and largely heterochromatic and therefore represent a difficult target for genetic engineering. The Y chromosome of the human malaria vector Anopheles gambiae appears to be involved in sex determination although very little is known about both its structure and function. Here, we characterize a transgenic strain of this mosquito species, obtained by transposon-mediated integration of a transgene construct onto the Y chromosome. Using meganuclease-induced homologous repair we introduce a site-specific recombination signal onto the Y chromosome and show that the resulting docking line can be used for secondary integration. To demonstrate its utility, we study the activity of a germ-line-specific promoter when located on the Y chromosome. We also show that Y-linked fluorescent transgenes allow automated sex separation of this important vector species, providing the means to generate large single-sex populations. Our findings will aid studies of sex chromosome function and enable the development of male-exclusive genetic traits for vector control.

SUBMITTER: Bernardini F

PROVIDER: S-EPMC4040617 | biostudies-literature | 2014 May

REPOSITORIES: biostudies-literature

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Site-specific genetic engineering of the Anopheles gambiae Y chromosome.

Bernardini Federica F Galizi Roberto R Menichelli Miriam M Papathanos Philippos-Aris PA Dritsou Vicky V Marois Eric E Crisanti Andrea A Windbichler Nikolai N

Proceedings of the National Academy of Sciences of the United States of America 20140512 21

Despite its function in sex determination and its role in driving genome evolution, the Y chromosome remains poorly understood in most species. Y chromosomes are gene-poor, repeat-rich and largely heterochromatic and therefore represent a difficult target for genetic engineering. The Y chromosome of the human malaria vector Anopheles gambiae appears to be involved in sex determination although very little is known about both its structure and function. Here, we characterize a transgenic strain o ...[more]

PMID: 24821795

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Project description:BackgroundThe African malaria mosquito, Anopheles gambiae, depends on availability of suitable surface water for oviposition. Short and long dry spells occur throughout the year in many parts of its range that limit its access to oviposition sites. Although not well understood, oviposition-site deprivation has been found to rapidly reduce egg batch size and hatch rate of several mosquito species. We conducted laboratory experiments to assess these effects of oviposition-site deprivation on An. gambiae and to evaluate the role of nutrition and sperm viability as mediators of these effects.MethodsAnopheles gambiae adults (1-2 d old) from the G3 laboratory colony were assigned to the following treatment groups: oviposition-deprived (fed once and then deprived of oviposition site for 7 or 14 d), multiple-fed control (fed regularly once a week and allowed to lay eggs without delay), and age matched blood-deprived control (fed once, three days before water for oviposition was provided). Egg batch size and hatch rate were measured. In the second experiment two additional treatment groups were included: oviposition-deprived females that received either a second (supplemental) blood meal or virgin males (supplemental mating) 4 days prior to receiving water for oviposition.ResultsAn. gambiae was highly sensitive to oviposition-site deprivation. Egg batch size dropped sharply to 0-3.5 egg/female within 14 days, due to reduced oviposition rate rather than a reduced number of eggs/batch. Egg hatch rate also fell dramatically to 0-2% within 7 days. The frequency of brown eggs that fail to tan was elevated. A supplemental blood meal, but not 'supplemental insemination,' recovered the oviposition rate of females subjected to oviposition-site deprivation. Similarly, a supplemental blood meal, but not 'supplemental insemination,' partly recovered hatch rate, but this increase was marginally significant (P?<?0.069).ConclusionsEven a short dry spell resulting in oviposition-site deprivation for several days may result in a dramatic decline of An. gambiae populations via reduced fecundity and fertility. However, females taking supplemental blood meals regain at least some reproductive success. If mosquitoes subjected to oviposition-site deprivation increase the frequency of blood feeding, malaria transmission may even increase during a short dry spell. The relevance of oviposition-site deprivation as a cue to alter the physiology of An. gambiae during the long dry season is not evident from these results because no reduction in hatch rate was evident in wild M-form An. gambiae collected in the dry season in the Sahel by previous studies.

Project description:Two distinct site-specific retrotransposon families, named RT1 and RT2, from the sibling mosquito species Anopheles gambiae and A. arabiensis, respectively, were previously identified. Both were shown to occupy identical nucleotide positions in the 28S rRNA gene and to be flanked by identical 17-bp target site duplications. Full-length representatives of each have been isolated from a single species, A. gambiae, and the nucleotide sequences have been analyzed. Beyond insertion specificity, RT1 and RT2 share several structural and sequence features which show them to be members of the LINE-like, or non-long-terminal-repeat retrotransposon, class of reverse transcriptase-encoding mobile elements. These features include two long overlapping open reading frames (ORFs), poly(A) tails, the absence of long terminal repeats, and heterogeneous 5' truncation of most copies. The first ORF of both elements, particularly ORF1 of RT1, is glutamine rich and contains long tracts of polyglutamine reminiscent of the opa repeat. Near the carboxy ends, three cysteine-histidine motifs occur in ORF1 and one occurs in ORF2. In addition, each ORF2 contains a region of sequence similarity to reverse transcriptases and integrases. Alignments of the protein sequences from RT1 and RT2 reveal 36% identity over the length of ORF1 and 60% identity over the length of ORF2, but the elements cannot be aligned in the 5' and 3' noncoding regions. Unlike that of RT2, the 5' noncoding region of RT1 contains 3.5 copies of a 500-bp subrepeat, followed by a poly(T) tract and two imperfect 55-bp subrepeats, the second spanning the beginning of ORF1. The pattern of distribution of these elements among five siblings species in the A. gambiae complex is nonuniform. RT1 is present in laboratory and wild A. gambiae, A. arabiensis, and A. melas but has not been detected in A. quadriannulatus or A. merus. RT2 has been detected in all available members of the A. gambiae complex except A. merus. Copy number fluctuates, even among the offspring of individual wild female A. gambiae mosquitoes. These findings reflect a complex evolutionary history balancing gain and loss of copies against the coexistence of two elements competing for a conserved target site in the same species for perhaps millions of years.

Project description:In many species, males and females display differences in their physiology that are not limited to the gonads. Sex differences in adult insects can comprise body size and feeding behaviour, as only female, but not male mosquitoes are blood-feeding in order to produce eggs. This is relevant since the malaria-causing parasite Plasmodium is transmitted by a female mosquito through a previous blood meal from an infected individual. The initiation of sex-specific developmental programs can be often linked to heteromorphic sex chromosomes (XX/XY in Anopheles). In males, the X-linked genes are only present in a single copy. To counteract this hemizygosity, Anopheles, like other species, exhibits dosage compensation (DC). Anopheles DC manifests by upregulation of the single male X ensuring the equal expression of sex-chromosomal genes between males and females. To date, the sex-specific differences at the transcriptome level related to the X/Y chromosomes and DC have been characterized at post-embryonic stages. Their onset during embryogenesis, especially during the early stages where the embryo switches from the maternal to the zygotic transcriptome, is largely uncharacterized to date. Here, we generate a sex-specific transcriptome atlas across Anopheles embryogenesis ending at the first larval stage. Along with the transition from the maternal to the zygotic transcriptome, many transcripts switch isoform, where the 3’ untranslated regions (UTR) of zygotic transcripts are significantly extended compared to their maternal counterpart. We also identify stage- and sex-specific splicing events. Comparing male and female embryos, we identify 120 sexually dimorphic protein coding genes and non-coding RNAs, indicating that sexually dimorphic gene expression is not widespread during embryogenesis. Furthermore, the imbalance of X-linked genes between males and females after zygotic genome activation is corrected shortly after, where the majority of genes exhibit DC around 9 hours of embryogenesis with further fine-tuning later in development. Our atlas provides a framework to explore sex differences in development and evolution and thereby, enables future functional analyses of sex-specific expression patterns and isoform usage.

Dataset Information

Site-specific genetic engineering of the Anopheles gambiae Y chromosome.

Publications

Site-specific genetic engineering of the Anopheles gambiae Y chromosome.

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