Abstract
BackgroundPrevious investigations from our laboratory were largely focused on the genome organization of vertebrates. We showed that these genomes are mosaics of isochores, megabase-size DNA sequences that are fairly homogeneous in base composition yet belong to a small number of families that cover a wide compositional spectrum. A question raised by these results concerned how far back in evolution an isochore organization of the eukaryotic genome arose.ResultsThe present investigation deals with the compositional patterns of the invertebrates for which full genome sequences, or at least scaffolds, are available. We found that (i) a mosaic of isochores is the long-range organization of all the genomes that we investigated; (ii) the isochore families from the invertebrate genomes matched the corresponding families of vertebrates in GC levels; (iii) the relative amounts of isochore families were remarkably different for different genomes, except for those from phylogenetically close species, such as the Drosophilids.ConclusionThis work demonstrates not only that an isochore organization is present in all metazoan genomes analyzed that included Nematodes, Arthropods among Protostomia, Echinoderms and Chordates among Deuterostomia, but also that the isochore families of invertebrates share GC levels with the corresponding families of vertebrates.
Highlights
Previous investigations from our laboratory were largely focused on the genome organization of vertebrates
This work demonstrates that an isochore organization is present in all metazoan genomes analyzed that included Nematodes, Arthropods among Protostomia, Echinoderms and Chordates among Deuterostomia, and that the isochore families of invertebrates share GC levels with the corresponding families of vertebrates
Recent investigations from our laboratory [1] showed that the isochore families of all vertebrate genomes explored are essentially conserved in GC levels and in isochore sizes
Summary
Previous investigations from our laboratory were largely focused on the genome organization of vertebrates. At least in eutherian mammals and birds, even the relative amounts of isochore families (i.e. the compositional patterns) are largely conserved It is well established by our previous work that a number of very basic genome properties, such as the distribution of genes and interspersed repeats, DNA methylation, gene expression, replication timing and recombination, are different in GC-poor and GC-rich isochore families (see [2,3], for reviews). These results obviously support the idea of isochores being a "fundamental level of genome organization" [4], at least in vertebrates. This is a pertinent question because evidence for a compositional heterogeneity was already obtained in our previous work on the genomes of trypanosomes, plasmodium and drosophila [see ref. [2]]
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