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Gene knockout is the total removal or permanent deactivation of a gene through inducing a targeted DNA damage. Knockout mice are commonly used in research to study the effects of genes that may have significance in human health.
Gene knockdown is the deactivation or suppression rather than deletion of the gene. Gene knockdown can be complete or partial, offering flexibility in studying the gene’s role in the biology of the organism. In gene silencing, or RNA interference (RNAi), small interfering RNA (siRNA) or short hairpin RNA (shRNA) are used to inactivate messenger RNA for a specific gene.
The Huntington faulty gene has increased trinucleotide repeats that leads to formation of a faulty protein with a long polyglutamine tail. This abnormal protein misfolds, precipitates, and causes the known pathological changes in the affected person.
Current approaches targeting the gene aim at silencing this faulty gene to decrease the synthesis of the abnormal protein. Antisense oligonucleotide therapy is leading the way. There are trials using micro-RNA and small interfering RNA for the same effect. The use of CRISPR technology obviously will aim at the same target, knocking out the faulty gene.
Here is a review of this subject: Gene Therapy for Huntington’s Disease: The Final Strategy for a Cure? – PMC (nih.gov)
Both mosaic and a chimera have more than one cell line. While a chimera results from fusion of two zygotes, a mosaic is monozygotic. A mosaic results from a somatic mutation leading to a different cell line. It occurs in different species including humans.
Since cancer results from a mutation that gives the cell different genetic constitution, cancer patients can be considered mosaic.
Now to the question “are human mosaic rare?”. Since all females carry double X chromosomes, only one is active in a cell, all females have two different cell lines and are considered mosaic. This brings natural mosaicism in humans to about 50% of the population.
Very rarely, a person can be dimeric with two different DNA fingerprints. In this person, a blood sample for example can have a DNA fingerprint different than that of a tissue sample. This can take place if one of two fraternal twin embryos dies and is absorbed by the other twin in utero.
In one episode of CSI, the rapist was acquitted based on a negative DNA fingerprint testing despite other evidence. He was discovered to be chimeric only after he had committed another crime, shocking the investigating team.
Metabolome is the total collection of metabolites present within an organism, a cell, or a tissue. Genome is the total collection of DNA in the cell of an organism. Similarly, the transcriptome is the total RNA and proteome is the total protein of a cell or tissue. While the genome is the same for all cells and tissues of an organism, the transcriptome, proteome, and metabolome are different from cell to cell or tissue to tissue. They are also different from one physiological state to another.
