title: Eu-heterochromatic rearrangements induce replication of heterochromatic sequences normally underreplicated in polytene chromosomes of Drosophila melanogaster.
abstract: In polytene chromosomes of D. melanogaster the heterochromatic pericentric regions are underreplicated (underrepresented). In this report, we analyze the effects of eu-heterochromatic rearrangements involving a cluster of the X-linked heterochromatic (Xh) Stellate repeats on the representation of these sequences in salivary gland polytene chromosomes. The discontinuous heterochromatic Stellate cluster contains specific restriction fragments that were mapped along the distal region of Xh. We found that transposition of a fragment of the Stellate cluster into euchromatin resulted in its replication in polytene chromosomes. Interestingly, only the Stellate repeats that remain within the pericentric Xh and are close to a new eu-heterochromatic boundary were replicated, strongly suggesting the existence of a spreading effect exerted by the adjacent euchromatin. Internal rearrangements of the distal Xh did not affect Stellate polytenization. We also demonstrated trans effects exerted by heterochromatic blocks on the replication of the rearranged heterochromatin; replication of transposed Stellate sequences was suppressed by a deletion of Xh and restored by addition of Y heterochromatin. This phenomenon is discussed in light of a possible role of heterochromatic proteins in the process of heterochromatin underrepresentation in polytene chromosomes.
authors: Isituto di Biologia e Patologia Molecolari del CNR, Universitá di Roma La Sapienza, Rome, Italy I-00185.
authors: Yuri A
authors: YA
authors: Abramov
authors: Galina L
authors: GL
authors: Kogan
authors: Eugenii V
authors: EV
authors: Tolchkov
authors: Vanya I
authors: VI
authors: Rasheva
authors: Sergei A
authors: SA
authors: Lavrov
authors: Silvia
authors: S
authors: Bonaccorsi
authors: Irina A
authors: IA
authors: Kramerova
authors: Vladimir A
authors: VA
authors: Gvozdev
mesh_terms: D000818:Animals; D015139:Blotting, Southern; D002874:Chromosome Mapping; D004261:DNA Replication / Q000235:genetics*; D029721:Drosophila Proteins / Q000235:genetics; D004331:Drosophila melanogaster / Q000235:genetics*; D015321:Gene Rearrangement / Q000235:genetics*; D006570:Heterochromatin / Q000235:genetics*; D017403:In Situ Hybridization; D005810:Multigene Family / Q000235:genetics; D011494:Protein Kinases / Q000235:genetics; D012469:Salivary Glands / Q000737:chemistry; D014960:X Chromosome / Q000235:genetics*
chemical_list: D029721:Drosophila Proteins; D006570:Heterochromatin; D011494:Protein Kinases; C094331:Ste protein, Drosophila