Worm Breeder's Gazette 16(5): 20 (February 1, 2001)
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.
|1||Genetics Unit, Dept. of Biochemistry, University of Oxford, Oxford OX1 3QU, UK|
|2||The Sanger Centre, Wellcome Trust Genome Campus, Hinxton, Cambridge CB10 1SA, UK|
As pointed out by Mark Edgley et al. (WBG 15:5, p.20-21), chromosomes carrying integrated GFP transgenes are useful dominant chromosome markers. In the course of running the 24th and 27th Wellcome Trust Advanced Courses, on Methods for C. elegans, (held in November 1999 and September 2000), we made use of several different GFP insertions in order to demonstrate genetic mapping. The insertions were mapped using 3-factor mapping relative to established visible markers. The map positions of five insertions studied were confirmed, refined or corrected. Each of these has the useful properties of homozygous viability, good growth with no confounding phenotypes, male fertility and a strong GFP signal that can be easily scored using a dissecting microscope equipped with epifluorescence optics. Positions deduced were:
ccIs4251 LGI +4.0
ccIs9753 LGI +27.5
mIs13 LGI +27.5
mIs12 LGII +1.75
mIs11 LGIV +5.0
In the course of the mapping experiments, we made several incidental observations on these insertions:
1. mIs13 and ccIs9753 appear identical in map location, very close to the right end of LGI, and both also exhibit a weaker GFP signal than more central insertions of the same compound reporter at other locations. This might be the result of telomeric silencing or else of interference from the major rRNA cluster at this location.
2. ccIs4251 males have been reported as unable to mate, but we found that they are occasionally fertile (a him-8 strain, CB5600, has been deposited at the CGC). The males appear anatomically normal, and the reason for the low mating efficiency is not obvious.
3. The map position of mIs12 has been problematic, with data suggesting linkage either to LGIII or to LGIV. We obtained the original strain for mIs12 , DR2064, and found that the insertion in this strain is on neither of these chromosomes; instead, it has a convenient location close to unc-4 on LGII.
4. In mapping mIs11 on LGIV, we found that it exerts a significant suppression of recombination in its immediate neighbourhood. Map distance between the flanking markers unc-5 and dpy-20 was reduced from 3.3 cM to 1.3 cM. Local recombination suppression is not surprising, given that these insertions may consist of 100 kb or more of added DNA. However, such suppression may limit the usefulness of these inserts for detailed mapping. More extensive suppression of recombination may also result from rearrangement associated with insertion, as may have occurred in the case of mIs10, which suppresses recombination over a large part of LGV (Mark Edgley, pers. comm.)
Map data have been deposited in ACeDB. We encourage others to publish or deposit similar map data for inserted transgenes. Hitherto map data for only one GFP insertion has been published (ayIs4, Burdine et al. 1998) and none has been communicated to the CGC although many useful insertions have been constructed.
Participants in WTAC24 were: Patricia Berninsone, Marc Bickle, John Connolly, Rosane Curtis, Bill Gregory, Margorie Gurganus, Hisao Kondo, Dorota Kwasnika, Rowena Martin, Alison Motley, Rosa Estela Navarro, Karen Oegema, Tove Ostberg, Anastasia Papakonstantinopolou, Anna Salcini, Liora Shoshani, Anne Spang, Peter Tatnell.
Participants in WTAC27 were: Peter Askjaer, Alessandra Bodini, John Browne, Stefanos Christodoulou, David Clarke, Patrick Dekker, Maria Gravato-Nobre, David Lamb, Sara Mole, Patricia Murray, Sara Olson, Mark Petalcorin, Heike Schaurete, Stephen Stürzenbaum, Fiona Thompson, Jeremy Turnbull, Ross Waldrip.
We are grateful to the Wellcome Trust for supporting these courses, and to Leica Microsystems for lending MZII epifluorescence dissecting microscopes. Another course in this series will be taught in September 2001 (see announcement).