Untitled

Abstract

Three distinct types of Tc1-family transposable elements have been identified in the malaria vector, Anopheles gambiae. These three elements, named Tsessebe, Topi and Tiang, have the potential to encode transposases that retain most of the conserved amino acids that are characteristic of this transposon family. However, all three are diverged from each other by more than 50% at the nucleotide level. Full-length genomic clones of two types, Topi and Tsessebe, have been isolated and fully sequenced. The third, Tiang, is represented only by a 270 bp, PCR-amplified fragment of the transposase coding region. The Topi and Tsessebe elements are 1.4 kb and 2.0 kb in length, respectively, and differ in the length of their inverted terminal repeats (ITRs). The Topi elements have 26 bp ITRs, whereas the Tsessebe clones have long ITRs ranging in length from 105 to 209 bp, with the consensus being about 180 bp. This difference is due primarily to variation in the length of an internal stretch of GT repeats. The copy number and location of these elements in ovarian nurse cell polytene chromosomes varies greatly between element subtypes: Topi elements are found at between 17-31 sites, Tsessebe at 9-13 and Tiang at 20 euchromatic sites, in addition to several copies of these elements in heterochromatic DNA. The copy number and genomic insertion sites of these transposons varies between A. gambiae strains and between member species of the A. gambiae complex. This may be indicative of transpositionally active Tc1-like elements within the genome.

Intruder (DD38E), a recently evolved sibling family of DD34E/Tc1 transposons in animals

“…DD34E/ Tc1 is a classical family of Tc1/mariner transposons, first found in C. elegans in the 1980s [ 17 ], and displays extensive distribution in nature [ 28 ]. Diverse DD34E/ Tc1 transposons were discovered in multiple lineages of animals, including Topi and Quetzal in mosquitoes [ 48 , 60 ], Impala in fungi [ 30 ], Minos , S elements and Bari-3 in fruit flies [ 49 , 50 , 53 ], Frog Prince in frogs [ 32 ], and Passport in fish [ 26 ]. The DD34E/ Tc1 group was then divided into at least five distinct clusters based on the DD34E/ Tc1 elements identified from six teleost species in our earlier study, combined with previously reported elements of this family from other laboratories [ 58 ]; however, the intra-family diversity is still ambiguous.…”

Eight novel families of miniature inverted repeat transposable elements in the African malaria mosquito, Anopheles gambiae

“…A few samples in tier I are slightly more AT-rich than others. (21). § MER30 and MER44A are MITEs found in man (10).…”

Eight novel families of miniature inverted repeat transposable elements in the African malaria mosquito, Anopheles gambiae

“…The similarities to different DNA transposons at the insertion target and the TIRs support the hypothesis that MITEs may have been borrowing the transposition machinery from autonomous DNA transposons. As discussed above, Tsessebe I, a Tc1-pogo type DNA transposon in A. gambiae (21), share similar TIRs with some of the A. gambiae MITEs. However, it is not clear whether Tsessebe I had been involved in mobilizing these MITEs because the similarities between their TIRs are limited.…”

“…As shown in Table 2, more than half of the TA-specific MITEs in A. gambiae share similar terminal repeats with a TA-specific MITE in man and a Mimo element in a Culex mosquito (10,16). These MITEs also share similar TIRs with a few Tc1-pogo DNA transposons including Tsessebe I of A. gambiae (21). The phrase ''DNA transposon'' here refers to a DNA element that has the coding capacity for its transposase, which may or may not be still active.…”