Gene-rich and gene-poor chromosomal regions have different locations in the interphase nuclei of cold-blooded vertebrates.
In situ hybridizations of single-copy GC-rich, gene-rich and GC-poor, gene-poor chicken DNA allowed us to localize the gene-rich and the gene-poor chromosomal regions in interphase nuclei of cold-blooded vertebrates. Our results showed that the gene-rich regions from amphibians (Rana esculenta) and reptiles (Podarcis sicula) occupy the more internal part of the nuclei, whereas the gene-poor regions occupy the periphery. This finding is similar to that previously reported in warm-blooded vertebrates, in spite of the lower GC levels of the gene-rich regions of cold-blooded vertebrates. This suggests that this similarity extends to chromatin structure, which is more open in the gene-rich regions of both mammals and birds and more compact in the gene-poor regions. In turn, this may explain why the compositional transition undergone by the genome at the emergence of homeothermy did not involve the entire ancestral genome but only a small part of it, and why it involved both coding and noncoding sequences. Indeed, the GC level increased only in that part of the genome that needed a thermodynamic stabilization, namely in the more open gene-rich chromatin of the nuclear interior, whereas the gene-poor chromatin of the periphery was stabilized by its own compact structure.
Federico
Concetta
C
Dipartimento di Biologia Animale "M. La Greca", University of Catania, Via Androne 81, 95124, Catania, Italy.
Scavo
Cinzia
C
Cantarella
Catia Daniela
CD
Motta
Salvatore
S
Saccone
Salvatore
S
Bernardi
Giorgio
G
D000818:Animals; D002460:Cell Line; D002467:Cell Nucleus / Q000235:genetics; D002874:Chromosome Mapping; D002875:Chromosomes; D003080:Cold Temperature; D005796:Genes; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D007399:Interphase / Q000235:genetics*; D008116:Lizards; D011893:Rana esculenta; D014714:Vertebrates / Q000235:genetics*