The Drosophila dosage compensation complex binds to polytene chromosomes independently of developmental changes in transcription.

In Drosophila, the dosage compensation complex (DCC) mediates upregulation of transcription from the single male X chromosome. Despite coating the polytene male X, the DCC pattern looks discontinuous and probably reflects DCC dynamic associations with genes active at a given moment of development in a salivary gland. To test this hypothesis, we compared binding patterns of the DCC and of the elongating form of RNA polymerase II (PolIIo).

The MSL complex levels are critical for its correct targeting to the chromosomes in Drosophila melanogaster.

In Drosophila, dosage compensation requires assembly of the Male Specific Lethal (MSL) protein complex for doubling transcription of most X-linked genes in males. The recognition of the X chromosome by the MSL complex has been suggested to include initial assembly at approximately 35 chromatin entry sites and subsequent spreading of mature complexes in cis to numerous additional sites along the chromosome. To understand this process further we examined MSL patterns in a range of wild-type and mutant backgrounds producing different amounts of MSL components.

Intercalary heterochromatin in Drosophila melanogaster polytene chromosomes and the problem of genetic silencing.

The morphological characteristics of intercalary heterochromatin (IH) are compared with those of other types of silenced chromatin in the Drosophila melanogaster genome: pericentric heterochromatin (PH) and regions subject to position effect variegation (PEV). We conclude that IH regions in polytene chromosomes are binding sites of silencing complexes such as PcG complexes and of SuUR protein. Binding of these proteins results in the appearance of condensed chromatin and late replication of DNA, which in turn may result in DNA underreplication.

Dosage compensation and intercalary heterochromatin in X chromosomes of Drosophila melanogaster.

Regions of intercalary heterochromatin (IH) are dispersed in the euchromatic arms of polytene chromosomes and share the main properties of heterochromatin, namely chromosome constrictions resulting from DNA underreplication. These constrictions are frequent on the paired X chromosomes of females, but are practically absent from the single X chromosome of males. These sex-specific differences have been proposed to reflect the different levels of transcription and chromosome compaction due to dosage compensation, which in turn may affect the degree of underreplication in IH regions.

Isolation and characterization of novel mutations of the Broad-Complex, a key regulatory gene of ecdysone induction in Drosophila melanogaster.

Seven new alleles of the Broad-Complex gene of Drosophila melanogaster, which encodes a family of four zinc finger protein isoforms BR-C Z1, Z2, Z3 and Z4, were generated by transposase-induced mobilization of a P[Zw] element inserted in either the first intron downstream from the P165 promoter or the exon encoding the Z2-specific zinc finger domain. They were characterized by genetic complementation tests, molecular mapping and cytogenetic analysis of their effect on ecdysone-induced puffing and BR-C proteins binding to polytene chromosomes. Four mutations that correspond to three overlapping deletions and one tandem insertion of the P[Zw] element are located in the intron.