Worm Breeder's Gazette 14(2): 25 (February 1, 1996)

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.

Tc7, a new family of transposable elements in C. elegans.

Rene Rezsohazy1, Richard Durbin2, Ronald H.A. Plasterk1

1 The Netherlands Cancer Institute, Division of Molecular Biology, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands
2 Sanger Centre, Hinxton Hall, Cambridge CB10 1RQ, UK

Six families of transposable elements (Tc1-Tc6) have been described until now in C. elegans. They are class II transposons which presumably transpose via a DNA intermediate, and are delimited by inverted repeat sequences. Using the terminal 24 bp of the Tc1 inverted repeats as a probe to screen the whole genomic dataset, we found 8 hits correeponding to a new family of elements, which we call Tc7. They are 921- to 923-bp elements made up of two 327-bp inverted repeats and a conserved middle section which contains no large open reading frame. The outer 38 bp of their inverted repeats show 36 matches with the last 38 bp of Tc1. Furthermore, like Tc1, they are flanked by TA dinucleotides which correspond presumably to the target duplication generated upon transposition. The elements show less than 1% sequence polymorphism, but three copies of Tc7 show one small deletion (6- to 45-bp long) at different locations. Extrapolating the number of these sequences to the entire genome, we expect approximately 30 copies of Tc7, which is similar to the copy number of Tc1 in Bristol N2.

The binding site of the Tc1 transposase (Tc1A) within Tc1 inverted repeats (Vos et al., Genes Dev. 7, 1244-1253,1993) is fully contained within the 38-bp sequence shared with Tc7, suggesting that Tc7 could be a parasitic family of elements using Tc1A for their transposition. To test the ability of Tc7 to jump upon Tc1A expression, we used an integrated line harbouring the Tc1A gene under the control of an heat-shock promoter (NL818, Vos et al., submitted for publication). Using Tc7 primers, we visualized by PCR Tc7 insertions in a defined genomic target (gpa-2). After heat-shock, several insertions were found in NL818, whereas no jumps were detected in Bristol N2. Comparison with control experiments using Tc1 specific primers suggest that Tc7 transposes at a slightly lower frequency than Tc1 when Tc1A is provided in trans in somatic cells.

Altogether these data support the idea that Tc7 is a hitch-hiking transposon whose mobility depends on Tc1A expression. However, whether or not Tc7, like Tc1, is able to transpose in the germ line of mutator strains remains to be investigated.

_______________________________________
Tc7 sequences:

Cosmid name              Coordinates
_______________________________________

ZK899		J9218-30142
C07D10		S83-13307
F02D10		9-8254
F23A7		N849-7775
F19H6		@92-10973
F42F12		-32552
D1009		y-997
F10D7		J9311-30229
_______________________________________