Hermes transposon distribution and structure in Musca domestica

Abstract

Hermes are hAT transposons from Musca domestica that are very closely related to the hobo transposons from Drosophila melanogaster and are useful as gene vectors in a wide variety of organisms including insects, planaria, and yeast. hobo elements show distinct length variations in a rapidly evolving region of the transposase-coding region as a result of expansions and contractions of a simple repeat sequence encoding 3 amino acids threonine, proline, and glutamic acid (TPE). These variations in length may influence the function of the protein and the movement of hobo transposons in natural populations. Here, we determine the distribution of Hermes in populations of M. domestica as well as whether Hermes transposase has undergone similar sequence expansions and contractions during its evolution in this species. Hermes transposons were found in all M. domestica individuals sampled from 14 populations collected from 4 continents. All individuals with Hermes transposons had evidence for the presence of intact transposase open reading frames, and little sequence variation was observed among Hermes elements. A systematic analysis of the TPE-homologous region of the Hermes transposase-coding region revealed no evidence for length variation. The simple sequence repeat found in hobo elements is a feature of this transposon that evolved since the divergence of hobo and Hermes.

Figure 1

Structure and sequence of hobo and Hermes. (A) Diagrammatic representation of hobo and Hermes showing the location of the transposase-coding regions (open reading frame), the position of the 3′-NCR, the location of the priming sites, and the name of the primers. Primers 246F and 2600R were used to determine the structure of Hermes elements, and 1817F and 2073R were used to amplify the 3′-NCR in Hermes. The inverted terminal repeats (ITRs) are not drawn to scale. (B) An aligned amino acid sequence of hobo and Hermes transposases. Amino acids with a gray background indicate regions of amino acid identity. Sequences conserved within the hAT family (domains A–F) are outlined with a box and labeled A–F. The amino acids constituting the 3′-NCR between hobo and Hermes is outlined with a box and labeled 3′-NCR. The amino acids constituting the DDE motif are indicated with white letters on a black background. Residues (265–552) forming the α-helical domain in Hermes are indicated with a dashed line. The regions of the protein comprising the catalytic fold are indicated with a dotted line, whereas the insertion domain that splits the catalytic domain is indicated by a black line. The TPE repeat region within the 3′-NCR of hobo is shown in white letters on a black background.

Figure 2

Products of a PCR using Hermes primers 246F and 2600R using representatives of 11 of the 14 populations investigated in this study. MW refers to a molecular weight marker. Numbers along the left side of the figure refer to the size of the molecular weight markers measured in base pairs. The position of the 2454-bp PCR product resulting from the amplification of an intact element is indicated along the right side of the figure. K = Korea (sample K4); Th = Lampang,Thailand (sample Th16); S = Senegal (sample S38); U = Uruguay (sample U49); P = Panama (P52); Tx = Texas (sample Tx65); Mo = Missouri (sample M76); C = Lethbridge, Canada (sample L84); Z = Harare, Zimbabwe (sample Z93); G = Georgia (sample GA4); Md = Maryland (sample Md3).

Figure 3

Products of a PCR using Hermes primers 246F and 2600R using samples from Thailand (A) and Senegal and Uruguay (B). MW refers to molecular weight markers. The size in base pairs of selected markers is indicated on the left side of each figure. The 2454-bp PCR product arising from intact elements is indicated. Numbers associated with each lane refer to sample numbers. Thailand sample 17 is referred to in the text.

Figure 4

Summary of PCR results. PCR products were placed in 1 of 45 size classes, and the frequency distribution of each class is shown. n = 77.

Figure 5

Structure of the Hermes elements from natural populations of Musca domestica. Diagrammatic representation of the Hermes elements isolated from the natural populations of M. domestica shown in comparison with the intact Hermes element. Size and the region of the deletion are shown. Th16.1 = isolated from Lampang, Thailand (sample Th16), Z93.1 and Z93.2 = isolated from Harare, Zimbabwe (sample Z93), P52.1 = isolated from Panama (sample P52), Tx65.1 and Tx65.2 = isolated from Texas (sample Tx65).

Figure 6

Consensus nucleotide (A) and amino acid (B) sequence of the 3′-NCR of Hermes transposase. Boxed nucleotides and amino acids indicate sites of polymorphism. The observed polymorphisms and their frequency are shown above each sequence.