Insertional mutagenesis by transposable elements in the mammalian genome.

Several mammalian repetitive transposable genetic elements were characterized in recent years, and their role in mutagenesis is delineated in this review. Two main groups have been described: elements with symmetrical termini such as the murine IAP sequences and the human THE 1 elements and elements characterized by a poly-A rich tail at the 3' end such as the SINE and LINE sequences. The characteristic property of such mobile elements to spread and integrate in the host genome leads to insertional mutagenesis. Both germline and somatic mutations have been documented resulting from the insertion of the various types of mammalian repetitive transposable genetic elements. As foreseen by Barbara McClintock, such genetic events can cause either the activation or the inactivation of specific genes, resulting in their identification via an altered phenotype. Several disease states, such as hemophilia and cancer, are the result of this apparent aspect of genome instability.