Title:Polytene Chromosomes – A Portrait of Functional Organization of the <i>Drosophila</i> Genome
VOLUME: 19 ISSUE: 3
Author(s):Tatyana Yu Zykova, Victor G. Levitsky, Elena S. Belyaeva and Igor F. Zhimulev*
Affiliation:Institute of Molecular and Cellular Biology of the Russian Academy of Sciences, Novosibirsk 630090, Novoisibirsk State University, Novosibirsk 630090, Institute of Molecular and Cellular Biology of the Russian Academy of Sciences, Novosibirsk 630090, Institute of Molecular and Cellular Biology of the Russian Academy of Sciences, Novosibirsk 630090
Keywords:Polytene chromosomes, Bands and interbands, Drosophila, Genes, Promoters, Proteins of open chromatin, Origin
recognition complexes, P-elements.
Abstract:This mini-review is devoted to the problem genetic meaning of main polytene chromosome
structures – bands and interbands. Generally, densely packed chromatin forms black bands, moderately
condensed regions form grey loose bands, whereas decondensed regions of the genome appear as
interbands. Recent progress in the annotation of the Drosophila genome and epigenome has made it
possible to compare the banding pattern and the structural organization of genes, as well as their activity.
This was greatly aided by our ability to establish the borders of bands and interbands on the physical
map, which allowed to perform comprehensive side-by-side comparisons of cytology, genetic and
epigenetic maps and to uncover the association between the morphological structures and the functional
domains of the genome.
These studies largely conclude that interbands 5'-ends of housekeeping genes that are active across all
cell types. Interbands are enriched with proteins involved in transcription and nucleosome remodeling,
as well as with active histone modifications. Notably, most of the replication origins map to interband
regions. As for grey loose bands adjacent to interbands, they typically host the bodies of housekeeping
genes. Thus, the bipartite structure composed of an interband and an adjacent grey band functions
as a standalone genetic unit. Finally, black bands harbor tissue-specific genes with narrow temporal
and tissue expression profiles. Thus, the uniform and permanent activity of interbands combined
with the inactivity of genes in bands forms the basis of the universal banding pattern observed in various
Drosophila tissues.
