Under the genomic radar: the stealth model of Alu amplification.

Alu elements are the most successful SINEs (Short INterspersed Elements) in primate genomes and have reached more than 1,000,000 copies in the human genome. The amplification of most Alu elements is thought to occur through a limited number of hyperactive "master" genes that produce a high number of copies during long evolutionary periods of time. However, the existence of long-lived, low-activity Alu lineages in the human genome suggests a more complex propagation mechanism.

Alu retrotransposition-mediated deletion.

Alu repeats contribute to genomic instability in primates via insertional and recombinational mutagenesis. Here, we report an analysis of Alu element-induced genomic instability through a novel mechanism termed retrotransposition-mediated deletion, and assess its impact on the integrity of primate genomes. For human and chimpanzee genomes, we find evidence of 33 retrotransposition-mediated deletion events that have eliminated approximately 9000 nucleotides of genomic DNA.

Analysis of the human Alu Ya-lineage.

The Alu Ya-lineage is a group of related, short interspersed elements (SINEs) found in primates. This lineage includes subfamilies Ya1-Ya5, Ya5a2 and others. Some of these subfamilies are still actively mobilizing in the human genome.

Comprehensive analysis of Alu-associated diversity on the human sex chromosomes.

A comprehensive analysis of the human sex chromosomes was undertaken to assess Alu-associated human genomic diversity and to identify novel Alu insertion polymorphisms for the study of human evolution. Three hundred forty-five recently integrated Alu elements from eight different Alu subfamilies were identified on the X and Y chromosomes, 225 of which were selected and analyzed by polymerase chain reaction (PCR). From a total of 225 elements analyzed, 16 were found to be polymorphic on the X chromosome and one on the Y chromosome.

Alu elements and hominid phylogenetics.

Alu elements have inserted in primate genomes throughout the evolution of the order. One particular Alu lineage (Ye) began amplifying relatively early in hominid evolution and continued propagating at a low level as many of its members are found in a variety of hominid genomes. This study represents the first conclusive application of short interspersed elements, which are considered nearly homoplasy-free, to elucidate the phylogeny of hominids.

Non-traditional Alu evolution and primate genomic diversity.

Alu elements belonging to the previously identified "young" subfamilies are thought to have inserted in the human genome after the divergence of humans from non-human primates and therefore should not be present in non-human primate genomes. Polymerase chain reaction (PCR) based screening of over 500 Alu insertion loci resulted in the recovery of a few "young" Alu elements that also resided at orthologous positions in non-human primate genomes. Sequence analysis demonstrated these "young" Alu insertions represented gene conversion events of pre-existing ancient Alu elements or independent parallel insertions of older Alu elements in the same genomic region.