Gene Functions on the X-Chromosome of Drosophila melanogaster

Dr. Ulrich Schäfer
Max-Planck-Institut für biophysikal. Chemie
Abt. Molekulare Entwicklungsbiologie
Am Fassberg 11
D-37077 Göttingen Germany
telephone: (0551) 201-1798
fax: (0551) 201-1755
prestype: Platform
presenter: Dr. Ulrich Schäfer

Ulrich Schäfer, Annette Peter, Petra Schöttler, Meike Werner, Nicole Beinert, Gordon Dowe, Lore Dentzer, Foteini Mourkioti, Peter Burkert and Herbert Jäckle
Max-Planck-Institut für biophysikalische Chemie, Abt. für Molekulare Entwicklungsbiologie, D-37070 Goettingen

The genome of Drosophila melanogaster has recently been completely sequenced. Only 10% of the predicted 13,600 genes in this well studied model organism were up to now characterized at the functional level. To provide the tools for a functional analysis we performed a systematic screen in which vital genes of the Drosophila X-chromosome were tagged by the enhancer trap vector P-lacW. Towards this aim, we have so far screened over 50,000 individual females containing a new site of a P-lacW insertion in the genome. Out of 38,066 vials with progeny 501 lines were kept as l(1)G### (1.3%). In addition, we isolated 74 viable lines with a mutant phenotype from the same pool (0.2%). Sequences flanking the insertion site have been isolated from almost all the lines. BLAST searches have in most cases identified the affected gene. We found insertions in well analyzed Drosophila genes (e. g. Notch, armadillo), in known genes without a previously described mutation (e. g. dWnt-5, innexin-2) as well as in genes defined by a mutation where a molecular analysis has not been performed yet (e. g. trol, stardust). More importantly, there are many insertions in genes predicted by the Drosophila Genome Projects that may or may not have orthologues in other genomes.

It is known that over 60% of all the genes will not produce an easily scorable phenotype when mutated and thus will not be detected by a loss-of-function screen. Hence, we are complementing our ongoing work with a gain-of-function screen employing a specific P vector. We want to saturate the chromosome with insertions of P elements containing single upstream activating sequence (UAS). The UAS sites are oriented to transcribe flanking genomic sequences in response to a transgene-derived yeast transcription factor (GAL4) expressed in a tissue- and stage-dependent manner. This way we force GAL4-dependent misexpression, overexpression or even antisense expression of the tagged gene to cause mutant phenotypes that reveal "phenotypically silent" transcription units in addition to those carrying vital functions. The first results of this approach will be presented. Our collection of X chromosomal lethal lines has already proven to be a valuable tool for the Drosophila community. Based on the high degree of sequence conservation between human and fly genes one can expect that the data generated will also have an impact on the functional analysis of the human genome.

Supported by grants of the Deutsches Humangenomprojekt to H. J.

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