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.


GRENIER Eric, ABADON Monique, LAUMOND Christian, ABAD Pierre

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.