Worm Breeder's Gazette 14(1): 26 (October 1, 1995)
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
INRA, Laboratoire de Biologie des Invertebres, BP 2078, 06606 Antibes cedex, France
The mariner transposable element is a small member of the transposable element class II. This element is thought to transpose through a DNA intermediate and shows short inverted terminal repeats (ITR) bordering the entire element. Originally described in Drosophila mauritiana, it has been identified in many other insect species representing ten insect orders. Mariner-like elements (MLE) have also recently been identified in the planarian Dugesia tigrina and in the nematode Caenorhabditis elegans. Using a polymerase chain reaction (PCR) strategy with degenerated oligonucleotides deduced from conserved sequences of the mariner central region, we have been able to detect the presence of MLE in the entomoparasitic nematode Heterorhabditis bacteriophora. These MLE appear to be either deleted forms or full-sized elements of 1279 bp with imperfect ITR of 30 bp. In a full-sized element, the transposase part codes for 358 amino acids including three stop codons and two frame shifts. Therefore, none of the sequences has an open reading frame encoding for a putative transposase. The H. bacteriophora sequences present a 5' transposase longer than those usually described in the Tc/mariner-like family (addition of 14 amino acids). Most of the MLE conserved mariner amino acids (Robertson H.M., 1995, J.Ins.Physiol., 41(2):99) are present and 90% of those missing result from a single nucleotidic mutation. Interestingly, the H. bacteriophora transposase shares more similarities with insect MLE transposase than with C. elegans one. Among the conserved H. bacteriophora amino acids, only 14% are typical C. elegans amino acids (compared with C. elegans PM and C. elegans ZK 370 MLE) while 28% are typical insect ones (compared with Drosophila mauritiana Mos 1 and Hyalophora cecropia MLE). When analysed with Genbank data system, the most important similarity has been found with a Carpelimus sp. mariner (Genbank accession number U04455). The H. bacteriophora MLE is 73% similar, at the nucleotidic level, to this coleopteran MLE, while it is only 52% similar to a C. elegans mariner. On another hand, the H. bacteriophora MLE ITR are more similar to C. elegans MLE ITR (up to 53%) than to insect ones (about 38%). The distribution of H. bacteriophora MLE has been studied by Southern blot analysis. All the tested H. bacteriophora isolates contain MLE, while they seem to be absent from the Steinernema genus, a very closed genus of entomopathogenic nematodes too. These results, together with the fact that H. bacteriophora is an entomoparasitic rhabditid, strongly suggest a case of trans-phyla horizontal transfer. studies are still carried out to further caracterize this new mariner element and to understand the phylogenetic relationships between the mariner transposable elements isolated so far.