Academic journal article Genetics

Transposable Element Dynamics of the hAT Element Herves in the Human Malaria Vector Anopheles Gambiae S.S

Academic journal article Genetics

Transposable Element Dynamics of the hAT Element Herves in the Human Malaria Vector Anopheles Gambiae S.S

Article excerpt

ABSTRACT

Transposable elements are being considered as genetic drive agents for introducing phenotype-altering genes into populations of vectors of human disease. The dynamics of endogenous elements will assist in predicting the behavior of introduced elements. Transposable element display was used to estimate the site-occupancy frequency distribution of Herves in six populations of Anopheles gambiae s.s. The site-occupancy distribution data suggest that the element has been recently active within the sampled populations. All 218 individuals sampled contained at least one copy of Herves with a mean of 3.6 elements per diploid genome. No significant differences in copy number were observed among populations. Nucleotide polymorphism within the element was high (π = 0.0079 in noncoding sequences and 0.0046 in coding sequences) relative to that observed in some of the more well-studied elements in Drosophila melanogaster. In total, 33 distinct forms of Herves were found on the basis of the sequence of the first 528 bp of the transposase open reading frame. Only two forms were found in all six study populations. Although Herves elements in An. gambiae are quite diverse, 85% of the individuals examined had evidence of complete forms of the element. Evidence was found for the lateral transfer of Herves from an unknown source into the An. gambiae lineage prior to the diversification of the An. gambiae species complex. The characteristics of Herves in An. gambiae are somewhat unlike those of P elements in D. melanogaster.

hAT elements comprise a large and prevalent group of Class II transposable elements found in a wide range of plants and animals (KEMPKEN and WINDHOFER 2001; KUNZE and WEIL 2002; RAY et al. 2007). hAT elements are not only of interest for their role in genome evolution but also as tools for genetically modifying organisms, with the elements Hermes and hobo being two examples of hAT element-derived insect gene vectors (BLACKMAN et al. 1989; O'BROCHTA et al. 1996). Transposable elements from other families such as piggyBac, Mos I, and Minos have also been developed into effective insect gene vectors that are now employed in a variety of applications (ATKINSON et al. 2001). Using these relatively new gene-integration tools, a novel form of biological control is being considered to stem the transmission of certain arboviruses (e.g., dengue fever) and parasites (e.g., Plasmodium) by mosquitoes and other arthropod vectors (ADELMAN et al. 2002; Alphey et al. 2002; Beard et al. 2002). This strategy involves the introduction of transgenic insects into natural populations of a target species with the intent of replacing the native population with genetically modified conspecifics (CRAIG 1963; World Health Organization 1991; JAMES 1992; MILLER 1992). Introduced transgenic mosquitoes will contain transgenes conferring incompatibility (refractoriness) or resistance to the target pathogen or parasite. An increase in the frequency of the transgene within natural populations of the vector will, under certain conditions, lead to a reduction or elimination of vector-borne disease transmission (BOETE and KOELLA 2002).

Designing gene vectors and effector transgenes for refractoriness such that they will increase in natural populations and eventually reach fixation is a considerable challenge, and transposable elements may provide a means by which this can be accomplished (BRAIG and YAN 2001). The replicative nature of transposable element movement (even by elements that move by a cut-andpast fashion i.e., Class II elements) results in elements acquiring a transmission advantage, resulting in their gradual increase in frequency in populations (RIBEIRO and KIDWELL 1994; KISZEWSKI and SPIELMAN 1998). The magnitude of that transmission advantage is determined by the rate of transposition; the degree to which transposition is conservative or replicative; the spatial patterns of element transposition within a genome; the biology of the transposable element and its interactions with the host insect; and the size, structure, and characteristics of the target population (RASGON and GOULD 2005). …

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