Transposable elements in reptilian and avian (sauropsida) genomes.

Transposable elements (TEs) have profound effects on the structure, function and evolution of their host genomes. Our knowledge about these agents of genomic change in sauropsids, a sister group of mammals that includes all extant reptiles and birds, is still very limited. Invaluable information concerning the diversity, activity and repetitive landscapes in sauropsids has recently emerged from analyses of the draft genomes of chicken and Anolis and other preliminary reptilian genome sequencing projects. Avian and reptilian genomes differ significantly in the classes of TEs present, their fractional representation in the genome and by the level of TE activity. While lepidosaurian genomes contain many young, active TE families, the extant avian genomes have very few active TE lineages. Most reptilian genomes possess quite rich TE repertoires that differ considerably from those of birds and mammals, being more similar in diversity to that of lower vertebrates. The large amount of recently accumulated genome-wide data on TEs in diverse lineages of sauropsids has provided a remarkable opportunity to review current knowledge about TEs of sauropsids in their genomic context.