Transvection in the Drosophila Abd-B domain: extensive upstream sequences are involved in anchoring distant cis-regulatory regions to the promoter

• Published in: Genetics (Austin) 1998-06, Vol.149 (2), p.1031-1050
• Main Authors: Sipos, L, Mihaly, J, Karch, F, Schedl, P, Gausz, J, Gyurkovics, H
• Format: Article
• Language: English
• Subjects: ABD-B GENE; ABD-B PROMOTER; ABDOMEN; Abdomen - embryology; Abdomen - innervation; ALLELES; ANIMAL CUTICLE; ANIMAL PROTEINS; Animals; Central Nervous System - embryology; CHEMISTRY; CHIMIE; CHROMOSOMAL REARRANGEMENTS; CUTICULA ANIMAL; CUTICULE ANIMALE; DELETIONS; DNA-Binding Proteins - genetics; Drosophila - embryology; Drosophila - genetics; DROSOPHILA MELANOGASTER; Drosophila Proteins; GEN HOMEOTICO; GENE; GENE HOMEOTIQUE; GENES; Genes, Homeobox; Genes, Insect; GENETIC REGULATION; GENETICA; GENETICS; GENETIQUE; Homeodomain Proteins - genetics; HOMEOTIC GENES; IMMUNOHISTOCHEMISTRY; IMMUNOLOGIE; IMMUNOLOGY; INITIATION; INMUNOLOGIA; Insects; INSERTIONAL MUTAGENESIS; Male; MUTACION; MUTATION; NUCLEOTIDE SEQUENCE; Phenotype; Point Mutation; POINT MUTATIONS; Promoter Regions, Genetic; PROTEINAS; PROTEINE; PROTEINS; QUIMICA; RECOMBINACION; RECOMBINAISON; RECOMBINATION; REGULATORY SEQUENCES; Regulatory Sequences, Nucleic Acid; SECUENCIA NUCLEOTIDICA; Sequence Deletion; SEQUENCE NUCLEOTIDIQUE; TRANSCRIPCION; TRANSCRIPTION; Translocation, Genetic; TRANSPOSABLE ELEMENTS
• ISSN: 0016-6731; 1943-2631; 1943-2631
• DOI: 10.1093/genetics/149.2.1031

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.