Study reveals widespread variation in ribosomal DNA structure across vertebrate species
Researchers analyzing chromosome-scale genomes from the Vertebrate Genomes Project found that ribosomal DNA (45S rDNA) organization varies dramatically across vertebrate lineages, with differences in chromosomal location, copy number, and sequence composition. While the genes encoding ribosomal RNA remain highly conserved across species, the spacer regions between them show rapid evolution and lineage-specific changes. The findings suggest rDNA functions as a flexible genomic system balancing deep evolutionary conservation with structural adaptability.
A comparative genomic analysis of 45S ribosomal DNA across vertebrates reveals substantial interspecies variation in how this essential genetic material is organized. Mammals and birds typically concentrate rDNA in a few chromosomal locations, often at chromosome ends, whereas amphibians and some fish species have highly dispersed rDNA across dozens of chromosomes. Copy number varies by more than tenfold among species and does not correlate simply with genome size or predicted ribosome production needs. At the sequence level, the ribosomal RNA-encoding genes (18S, 5.8S, 28S) remain tightly conserved across evolutionary time, maintaining strong phylogenetic signal, while the internal transcribed spacer regions diverge rapidly and show pronounced differences between species. The study demonstrates that constraint on evolution is strongest in functional rRNA regions and progressively relaxes in spacer sequences, establishing rDNA as a multi-layered system combining deep conservation with structural flexibility.
What's missing
The study does not discuss potential functional implications of the observed variation in rDNA copy number and chromosomal distribution, nor does it address whether these differences correlate with organism size, metabolic rate, or other phenotypic traits that might explain the lack of simple scaling with ribosome demand.
What different sources said
- bioRxivCenter
Interspecies variation of 45S ribosomal DNA in vertebrates
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