Gene silencing

Gene silencing is a general term describing epigenetic processes of gene regulation. The term gene silencing is generally used to describe the "switching off" of a gene by a mechanism other than genetic modification. That is, a gene which would be expressed (turned on) under normal circumstances is switched off by machinery in the cell.

Genes are regulated at either the transcriptional or post-transcriptional level.

Transcriptional gene silencing is the result of histone modifications, creating an environment of heterochromatin around a gene that makes it inaccessible to transcriptional machinery (RNA polymerase, transcription factors, etc.).

Post-transcriptional gene silencing is the result of mRNA of a particular gene being destroyed or blocked. The destruction of the mRNA prevents translation to form an active gene product (in most cases, a protein). A common mechanism of post-transcriptional gene silencing is RNAi.

Both transcriptional and post-transcriptional gene silencing are used to regulate endogenous genes. Mechanisms of gene silencing also protect the organism's genome from transposons and viruses. Gene silencing thus may be part of an ancient immune system protecting from such infectious DNA elements.

Genes may be silenced by DNA methylation during meiosis, as in the filamentous fungus Neurospora crassa.

Specific studies of gene silencing
There are several more terms related to specific topics of gene silencing:

Transcriptional Gene Silencing:
 * Genomic Imprinting
 * Paramutation
 * Transposon silencing
 * Transgene silencing
 * Transcriptional gene silencing
 * position effect
 * RNA-directed DNA methylation

Post-transcriptional Gene Silencing:
 * RNA interference
 * Nonsense mediated decay

Meiotic gene silencing:
 * Transvection
 * Meiotic silencing of unpaired DNA

Cellular components of gene silencing: Ribozyme and antisense technology are the two approaches used to exact post transcriptional gene silencing in order to suppress a gene of interest.
 * Histones
 * Chromatin and heterochromatin
 * MicroRNA
 * siRNA
 * dsRNA
 * Dicer
 * Transposons