Alpha and beta heterochromatin in polytene chromosome 2 ofDrosophila melanogaster |
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Authors: | Dmitry E Koryakov Elena S Belyaeva Artyom A Alekseyenko Igor F Zhimulev |
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Institution: | (1) Department of Cytology and Genetics, Novosibirsk State University, Novosibirsk 630090, Russia, RU;(2) Institute of Cytology and Genetics, Siberian Division of Russian Academy of Sciences, Novosibirsk 630090, Russia, RU |
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Abstract: | The formation of alpha and beta heterochromatin in chromosomes of Drosophila melanogaster was studied in salivary glands (SGs) and pseudonurse cells (PNCs). In SGs of X0, XY, XYY, XX and XXY individuals the amounts of alpha heterochromatin were similar, suggesting that the Y chromosome does not substantially contribute to alpha heterochromatin formation. Pericentric heterochromatin developed a linear
sequence of blocks in PNCs, showing morphology of both alpha and beta heterochromatin. In situ hybridization with Rsp sequences (H
o
clone) revealed that the most proximal heterochromatic segment of the mitotic map (region h39) formed a polytenized block
in PNCs. Dot analysis showed that the clone had a hybridization rate with PNC-DNA very close to that with DNA from mainly
diploid head cells, whereas the homologous SG-DNA was dramatically underrepresented. A similar increase of DNA representation
in PNC was found for AAGAC satellite DNA. The mitotic region h44 was found not to polytenize in the SG chromosome, whereas
in PNC chromosome 2 this region was partly polytenized and presented as an array of several blocks of alpha and beta heterochromatin.
The mapping of deficiencies with proximal breakpoints in the most distal heterochromatin segments h35 in arm 2L and h46 in
2R showed that the mitotic eu-heterochromatin transitions were located in SG chromosomes distally to the polytene 40E and
41C regions, respectively. Thus, the transition zones between mitotic hetero- and euchromatin are located in banded polytene
euchromatin. A scheme for dynamic organization of pericentric heterochromatin in nuclei with polytene chromosomes is proposed.
Received: 17 November 1995; in revised form: 10 April 1996 / Accepted: 18 September 1996 |
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