Nested genes: a gene within a gene

 Nested genes, i.e. two o more genes occurring in the same DNA filament but expressed in different ways, are under investigated. Nevertheless, growing body of evidences indicates an important role of nested genes, particularly in the respective regulation of expression of the pair, if any. In many examples, a gene of the pair is expressed in the opposite orientation, often within an intron. Frequently such intron has minor size that other introns present in the gene. It has been postulated the possible interaction between the two transcripts, and the possible mutual use of same enhancer elements. These and other possibilities of reciprocal regulation of a pair of genes such nested genes can be studied by atomic force microscopy, which allows visualization of the movement of RNA polymerase along a DNA template. A remarkable example is TIMP (tissue inhibitor of matrix metalloproteinases) that is “nested” within an intron of synapsin genes. Given that synapsin genes regulate neuronal differentiation in vitro, and that a possible important role might be played by metalloproteinases in pathfinding and growing of axons and dendrites for example, a reciprocal regulation of the genes could be a topic of research.