Essential genes in proximal 3L heterochromatin of Drosophila melanogaster
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O R I GI N A L P A P E R
S. Schulze á D. A. R. Sinclair á E. Silva K. A. Fitzpatrick á M. Singh á V. K. Lloyd K. A. Morin á J. Kim á D. G. Holm á J. A. Kennison B. M. Honda
Essential genes in proximal 3L heterochromatin of Drosophila melanogaster Received: 16 March 2000 / Accepted: 1 September 2000 / Published online: 10 November 2000 Ó Springer-Verlag 2000
Abstract We have further characterized essential loci within the centric heterochromatin of the left arm of chromosome 3 (3L) of Drosophila melanogaster, using EMS, radiation and P element mutagenesis. We failed to ®nd any new essential genes, a result that suggests a lower-than-average gene density in this region. Mutations aecting expression of the most proximal gene [lethal 1, l1 or l(3)80Fj] act as dominant suppressors of Polycomb (Pc), behavior which is consistent with a putative trithorax group (trx-G) gene. The third gene to the left of the centromere [lethal 3, l3 or l(3)80Fh] is likely to correspond to verthandi (vtd), a known trx-G gene that plays a role in the regulation of hedgehog (hh) expression and signalling. The intervening gene [lethal 2, l2 or l(3)80Fi] is required throughout development, and mutant alleles have interesting phenotypes; in various allelic combinations that survive, we observe fertility, bristle, wing, eye and cuticle defects. Key words Essential heterochromatic genes á Position-eect variegation á Drosophila melanogaster
Communicated by D. Gubb S. Schulze á D. A. R. Sinclair á E. Silva á K. A. Fitzpatrick M. Singh á V. K. Lloyd1 á B. M. Honda (&) Department of Molecular Biology and Biochemistry, Simon Fraser University Burnaby, B.C., V5A 1S6 Canada E-mail: [email protected] Tel.: +1-604-2914804 Fax: +1-604-2915583 K. A. Morin á J. Kim á D. G. Holm Department of Zoology, University of British Columbia, Vancouver, BC V6 T 1Z4 Canada J. A. Kennison Laboratory of Molecular Genetics, National Institute of Child Health and Human Development, NIH, Bethesda, MD 20892-2785, USA Present address: Dept. of Biology, Dalhousie University, Halifax, NS B3H 3J5, Canada
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Introduction In the fruit ¯y Drosophila melanogaster, the position of a gene on a chromosome can have profound eects on expression. For example, rearrangements that place a euchromatic gene near heterochromatin at the centromere or telomere can result in a mosaic pattern of gene inactivation. This is referred to as position-eect variegation (PEV, see Spoord 1976; Weiler and Wakimoto 1995). Genetic screens for mutants that alter the extent of PEV have identi®ed genes that encode a number of modifying factors, including chromatin proteins and remodelling activities. These genes include Polycomb or trithorax group (Pc-G, trx-G) members, which are involved in the silencing of homeotic and other key regulatory loci through changes in chromatin structure. Paradoxically, in spite of its inactivating properties and apparently unusual chromatin architecture and/or nuclear localization, heterochromatin appears to contain a number of essential genes, whose structure and regulation rem
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