Abnormal tissue-dependent polytenization of a block of chromosome 3 pericentric heterochromatin in Drosophila melanogaster.

Dmitry E Koryakov,Igor F Zhimulev,Stepan N Belyakin,Elena V Domanitskaya

doi:10.1242/jcs.00283

Abstract

Heterochromatic DNA sequences in the polytene chromosomes of Drosophila melanogaster salivary glands are under-replicated in wild-type strains. In salivary glands of SuUR and in the nurse cells of otu mutants, under-replication is partly suppressed and a banded structure appears within the centric heterochromatin of chromosome 3. This novel banded structure in salivary gland chromosomes was called Plato Atlantis. In order to characterize the heterochromatic component of Plato Atlantis, we constructed a fine-scale cytogenetic map of deletions with break points within centric heterochromatin (Df(3L)1-16, Df(3L)2-66, Df(3R)10-65, Df(3R)4-75 and Df(3L)6B-29 + Df(3R)6B-29). Salivary gland chromosomes show that Df(3L)1-16 removes the complete Plato Atlantis, while Df(3L)2-66 deletes the most proximal 3L regions. These deletions therefore show a substantial cytological overlap. However, in the chromosomes of nurse cells, the same deficiencies remove distinct heterochromatic blocks, with the region of overlap being almost invisible. Satellite (AATAACATAG, AAGAG) and dodecasatellite DNAs mapped in a narrow interval in salivary glands but were found in three clearly distinguishable blocks in nurse cells. The 1.688 satellite was found at a single site in salivary glands but at two sites in nurse cells. We show that newly polytenized heterochromatic structures include blocks h47-h50d of mitotic heterochromatin in salivary glands, but the additional blocks h50p, h53 and h57 are also included in nurse cell chromosomes. Tissue specificity of the patterns of abnormal heterochromatic polytenization implies differential control of DNA replication in somatic and germline cells.

Highlights

The term ‘heterochromatin’ denotes chromosomal regions that remain condensed throughout most of the cell cycle, show late replication during normal cell cycles, under-replication in polytene chromosomes, extremely low gene density and high density of repeated sequences
Heterochromatin in mitotic chromosomes of Drosophila melanogaster has been divided into 61 regions according to H- and Nstaining (Gatti et al, 1994), which reflects heterogeneous contents of DNA
The very short 81F region of the 3R arm comprises several thin bands. These euchromatic regions are separated by unstructured diffuse β-heterochromatin (Fig. 2A)

Summary

Introduction

The term ‘heterochromatin’ denotes chromosomal regions that remain condensed throughout most of the cell cycle, show late replication during normal cell cycles, under-replication in polytene chromosomes, extremely low gene density and high density of repeated sequences. Heterochromatin in mitotic chromosomes of Drosophila melanogaster has been divided into 61 regions (designed h1-h61) according to H- and Nstaining (Gatti et al, 1994), which reflects heterogeneous contents of DNA. Sequences forming heterochromatin are divided into highly repeated (satellites), moderately repeated (mainly transposable elements) and occasional unique (genes). These sequences occur in fixed positions within the heterochromatic regions (Lohe et al, 1993; Pimpinelli et al, 1995; Carmena and Gonzalez, 1995; Makunin et al, 1999). The few heterochromatic genes are clustered within dull or moderately fluorescent regions after H-staining (Dimitri, 1991; Dimitri et al, 2003; Koryakov et al, 2002)

Results

Discussion

Conclusion