Molecular and genetic organization of Drosophila melanogasterpolytene chromosomes: evidence for two types of interband regions

Abstract

The 3A and 60E regions of Drosophila melanogaster polytene chromosomes containing inserted copies of the P[1ArB] transposon have been subjected to an electron microscopic (EM) analysis. We show that both inserts led to formation of new bands within the interband regions 3A4/A6 and 60E8-9/E10. This allowed us to clone DNA of these interbands. Their sequences, as well as those of DNA from other four interbands described earlier, have been analyzed. We have found that, with the exception of 60E8-9/E10 interband, all other five regions under study corresponded to 5' or 3' ends of genes. We have further obtained the evidence for 60E8-9/E10 interband to harbor the 'housekeeping' RpL19 gene, which is transcribed in many tissues, including salivary glands. Based upon the genetic heterogeneity of the interbands observed a revised model of polytene chromosome organization is discussed.

Functional analysis of Drosophila polytene chromosomes decompacted unit: the interband

“…We have recently shown that several regions corresponding to interbands of polytene chromosomes from salivary gland cells show extremely low transcription, if any, in this tissue (Demakov et al 2004), reinforcing the idea that banding pattern and transcription are not mechanistically linked. The question about the mechanisms responsible for generation of decompacted state of certain regions concerns their limits.…”

Dissection of open chromatin domain formation by site specific recombination inDrosophila

“…Data from the Zhimulev laboratory also suggest a transcriptionindependent mechanism for the formation of open chromatin by the 61C7-8 interband (Semeshin et al, 1989;Demakov et al, 1993;Demakov et al, 2004;Semeshin et al, 2008). DNA from the 61C7-8 interband was first cloned starting from a P-element insertion that formed a new band within this interband (Demakov et al, 1993).…”

“…Bands and interband domains differ in their state of condensation with interbands condensed at the level of the 10-nm nucleosome fiber and bands at a level of §30-nm fiber (Beermann, 1972, Rykowski et al, 1988. Bands are supposed to reflect domains in a transcriptional inactive state, interbands, by contrast, might be transcribed or have a more open chromatin structure because they contain control elements, promoters and enhancers for genes poised for transcriptional activation (Rykowski et al, 1988;Demakov et al, 2004;Demakov et al, 2011). The finding of paused RNA polymerase in many interbands favors such models.…”

Dissection of open chromatin domain formation by site-specific recombination in Drosophila

“…It simply could be the consequence of the state of transcriptional activity that differs between these domains. However, at least some interbands appear not to be transcribed (Rykowski et al, 1988;Demakov et al, 2004). Alternatively, but not mutually exclusive, there could be a local difference in the epigenetic state caused by local protein binding and histone modifications.…”