Transvection in the Drosophila Abd-B domain: extensive upstream sequences are involved in anchoring distant cis-regulatory regions to the promoter.
The Abd-B gene, one of the three homeotic genes in the Drosophila bithorax complex (BX-C), is required for the proper identity of the fifth through the eighth abdominal segments (corresponding to parasegments 10-14) of the fruitfly. The morphological difference between these four segments is due to the differential expression of Abd-B, which is achieved by the action of the parasegment-specific cis-regulatory regions infra-abdominal-5 (iab-5), -6, -7 and -8. The dominant gain-of-function mutation Frontabdominal-7 (Fab-7) removes a boundary separating two of these cis-regulatory regions, iab-6 and iab-7. As a consequence of the Fab-7 deletion, the parasegment 12- (PS12-) specific iab-7 is ectopically activated in PS11. This results in the transformation of the sixth abdominal segment (A6) into the seventh (A7) in Fab-7 flies. Here we report that point mutations of the Abd-B gene in trans suppress the Fab-7 phenotype in a pairing-dependent manner and thus represent a type of transvection. We show that the observed suppression is the result of trans-regulation of the defective Abd-B gene by the ectopically activated iab-7. Unlike previously demonstrated cases of trans-regulation in the Abd-B locus, trans-suppression of Fab-7 is sensitive to heterozygosity for chromosomal rearrangements that disturb homologous pairing at the nearby Ubx locus. However, in contrast to Ubx, the transvection we observed in the Abd-B locus is insensitive to the allelic status of zeste. Analysis of different deletion alleles of Abd-B that enhance trans-regulation suggests that an extensive upstream region, different from the sequences required for transcription initiation, mediates interactions between the iab cis-regulatory regions and the proximal Abd-B promoter. Moreover, we find that the amount of DNA deleted in the upstream region is roughly proportional to the strength of trans-interaction, suggesting that this region consists of numerous discrete elements that cooperate in tethering the iab regulatory domains to Abd-B. Possible implications of the tethering complex for the regulation of Abd-B are discussed. In addition, we present evidence that the tenacity of trans-interactions in the Abd-B gene may vary, depending upon the tissue and stage of development.
Sipos
L
L
Hungarian Academy of Sciences, Biological Research Center, Institute of Genetics, H-6701 Szeged, Hungary.
Mihály
J
J
Karch
F
F
Schedl
P
P
Gausz
J
J
Gyurkovics
H
H
D000005:Abdomen / Q000196:embryology / Q000294:innervation; D000818:Animals; D002490:Central Nervous System / Q000196:embryology; D004268:DNA-Binding Proteins / Q000235:genetics; D004330:Drosophila / Q000196:embryology / Q000235:genetics*; D029721:Drosophila Proteins; D005801:Genes, Homeobox; D017344:Genes, Insect; D018398:Homeodomain Proteins / Q000235:genetics*; D008297:Male; D010641:Phenotype; D017354:Point Mutation; D011401:Promoter Regions, Genetic; D012045:Regulatory Sequences, Nucleic Acid; D017384:Sequence Deletion; D014178:Translocation, Genetic
C062393:Abd-B proteins, Drosophila; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D018398:Homeodomain Proteins; C060849:z protein, Drosophila