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Nucleolar dominance: uniparental gene silencing on a multi-megabase scale in genetic hybrids 总被引:11,自引:0,他引:11
Pikaard CS 《Plant molecular biology》2000,43(2-3):163-177
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Members of a group of Australian Chironomus species in the pseudothummi complex show wide variation in number and location of nucleolar organizing regions (NORs). The structure of these regions has been examined by phase contrast microscopy and silver banding of salivary gland polytene chromosomes. Presence of nucleoli was also checked on other types of chromosomes in some species. The contribution of the silver banding technique to nucleolar studies in these chironomid chromosomes is discussed. Nucleoli often seem to emerge from groups of (up to 9) bands. Further studies are necessary to confirm the presence of rRNA cistrons in all of these bands. Banding differences, in particular absence of bands from homologous regions of some species which have smaller nucleoli or lack particular nucleoli, have been found. In the case of Ch. tepperi, however, little banding difference is apparent in the 16B region between the N(IV)+ and N(IV)– chromosomes, although in situ hybridization (Eigenbrod 1978) shows a deletion of rRNA cistrons in the N(IV)– stock. Differences in heterochromatin amount have also been observed at different NORs. A scheme for the evolution of nucleolar-producing regions in this Chironomus group in terms of these and other known chromosomal changes is presented and discussed. 相似文献
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Silver Staining as an Indicator of Active Ribosomal Genes 总被引:2,自引:0,他引:2
Howard R. Hubbell 《Biotechnic & histochemistry》1985,60(5):285-294
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Silver staining as an indicator of active ribosomal genes 总被引:1,自引:0,他引:1
H R Hubbell 《Stain technology》1985,60(5):285-294
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The silencing of one parental set of rRNA genes in a genetic hybrid is an epigenetic phenomenon known as nucleolar dominance. We showed previously that silencing is restricted to the nucleolus organizer regions (NORs), the loci where rRNA genes are tandemly arrayed, and does not spread to or from neighboring protein-coding genes. One hypothesis is that nucleolar dominance is the net result of hundreds of silencing events acting one rRNA gene at a time. A prediction of this hypothesis is that rRNA gene silencing should occur independent of chromosomal location. An alternative hypothesis is that the regulatory unit in nucleolar dominance is the NOR, rather than each individual rRNA gene, in which case NOR localization may be essential for rRNA gene silencing. To test these alternative hypotheses, we examined the fates of rRNA transgenes integrated at ectopic locations. The transgenes were accurately transcribed in all independent transgenic Arabidopsis thaliana lines tested, indicating that NOR localization is not required for rRNA gene expression. Upon crossing the transgenic A. thaliana lines as ovule parents with A. lyrata to form F1 hybrids, a new system for the study of nucleolar dominance, the endogenous rRNA genes located within the A. thaliana NORs are silenced. However, rRNA transgenes escaped silencing in multiple independent hybrids. Collectively, our data suggest that rRNA gene activation can occur in a gene-autonomous fashion, independent of chromosomal location, whereas rRNA gene silencing in nucleolar dominance is locus-dependent. 相似文献
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Kalmárová M Smirnov E Masata M Koberna K Ligasová A Popov A Raska I 《Journal of structural biology》2007,160(1):49-56
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Pikaard CS 《Trends in genetics : TIG》2000,16(11):495-500
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