Madalena Christiane Rodriguez Gutierrez, Amabis José Mariano, Stocker Ann Jacob, Gorab Eduardo
Departamento de Genética e Biologia Evolutiva, Instituto de Biociências, Universidade de São Paulo, Rua do Matão 277, Cidade Universitária, São Paulo, SP, Brazil.
Chromosome Res. 2007;15(4):409-16. doi: 10.1007/s10577-007-1127-0. Epub 2007 Jan 21.
The chromosomal localization of ribosomal DNA (rDNA) was studied in polytene and diploid tissues of four sciarid species, Trichosia pubescens, Rhynchosciara americana, R. milleri and Schwenkfeldina sp. While hybridization to mitotic chromosomes showed the existence of a single rDNA locus, ribosomal probes hybridized to more than one polytene chromosome region in all the species analyzed as a result of micronucleolar attachment to specific chromosome sites. Micronucleoli are small, round bodies containing transcriptionally active, probably extrachromosomal rDNA. In T. pubescens the rDNA is predominantly localized in chromosome sections X-10 and X-8. In R. americana the rDNA is frequently found associated with centromeric heterochromatin of the chromosomes X, C, B and A, and also with sections X-1 and B-13. Ribosomal probes in R. milleri hybridized with high frequency to pericentric and telomeric regions of its polytene complement. Schwfenkfeldina sp. displays a remarkably unusual distribution of rDNA in polytene nuclei, characterized by the attachment of micronucleoli to many chromosome regions. The results showed that micronucleoli preferentially associate with intercalary or terminal heterochromatin of all sciarid flies analyzed and, depending on the species, are attached to a few (Trichosia), moderate (Rhynchosciara) or a large (Schwenkfeldina sp.) number of polytene chromosome sites.
在四种菌蚊物种（柔毛菌蚊、美洲大蚊、米勒大蚊和施温克费尔德菌蚊）的多线和二倍体组织中研究了核糖体DNA（rDNA）的染色体定位。虽然与有丝分裂染色体的杂交显示存在单个rDNA位点，但由于微核仁附着于特定染色体位点，核糖体探针在所有分析的物种中都与多个多线染色体区域杂交。微核仁是小的圆形体，含有转录活跃的、可能是染色体外的rDNA。在柔毛菌蚊中，rDNA主要定位于染色体片段X - 10和X - 8。在美洲大蚊中，rDNA经常发现与染色体X、C、B和A的着丝粒异染色质相关，也与片段X - 1和B - 13相关。米勒大蚊的核糖体探针与其多线染色体组的近心端和端粒区域高频杂交。施温克费尔德菌蚊在多线核中显示出非常不寻常的rDNA分布，其特征是微核仁附着于许多染色体区域。结果表明，微核仁优先与所有分析的菌蚊的居间或末端异染色质相关，并且根据物种的不同，附着于少数（柔毛菌蚊）、中等数量（大蚊）或大量（施温克费尔德菌蚊）的多线染色体位点。
