title: Similarities to a LINE element shared by Anopheline and Culicine mosquitos map to the distal end of dihydrofolate reductase amplicons in Aedes albopictus mosquito cells.
abstract: To extend our understanding of amplicon structure in methotrexate-resistant Mtx-5011-256 Aedes albopictus mosquito cells, we examined a series of cosmids containing genomic DNA corresponding to the unique 3'-end of the Type 1 dihydrofolate reductase amplicon. Cosmid pWED118 contained five EcoRI fragments ranging from 2 to 5 kb (A, B, C, F, G) that hybridized to cDNA from methotrexate-resistant cells. Of these, fragments B and F hybridized weakly to first-strand cDNA from sensitive cells and shared considerable sequence identity. Fragment G occurred twice in the map of pWED118; one copy mapped within a 10 kb BssHII core fragment from the Type I amplicon and a second copy mapped downstream in the 48 kb BssHII core fragment. Hybridization signals among fragments contained in overlapping cosmids suggested that a branch point defining two or more subtypes of the Type I amplicon occurs within or near the 10 kb BssHII genomic DNA fragment. A 1.8 kb sequence common to fragments B and F included an approximately 0.4 kb region that shared sequence similarities with a LINE element from Aedes aegypti and with a repeated sequence from Anopheles gambiae. In addition, these elements shared amino acid similarity to a reverse transcriptase from the nematode, Caenorhabditis elegans. Shared sequence between Aedes and Anopheles elements supports the hypothesis that an ancestral LINE-like element was active in mosquito genomes prior to the divergence of the subfamilies Culicinae and Anophelinae. The presence of homologies to LINE-like elements near a branch point in the dihydrofolate reductase amplicon is consistent with a possible role of repeated sequences in amplicon shortening.
authors.affiliation: Department of Entomology, University of Minnesota, St. Paul 55108, USA.
authors.forename: Z H
authors.initials: ZH
authors.lastname: Wang
authors.forename: A M
authors.initials: AM
authors.lastname: Fallon
mesh_terms: D000818:Animals; D001483:Base Sequence; D003360:Cosmids / Q000235:genetics*; D009033:Culicidae / Q000235:genetics*; D018076:DNA, Complementary / Q000235:genetics; D019143:Evolution, Molecular; D008727:Methotrexate / Q000494:pharmacology; D008969:Molecular Sequence Data; D009693:Nucleic Acid Hybridization; D017386:Sequence Homology, Amino Acid; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics* / Q000378:metabolism; D014158:Transcription, Genetic / Q000235:genetics
chemical_list: D018076:DNA, Complementary; D013762:Tetrahydrofolate Dehydrogenase; D008727:Methotrexate