RNA Interference
The phenotypes of the following model organisms were determined by using a technique called RNA interference, or RNAi. RNA interference is a natural mechanism for targeted gene silencing, but can also be used as a genomic tool to knock down the expression of a specific DNA sequence (often times a gene) [4]. Once the gene is knocked down, scientists can observe the resulting phenotype to determine the function of the lost gene and its protein. The following video from Nature gives an excellent explanation of the cellular mechanism of RNAi [5].
Model Organisms and their Phenotypes
The term "genotype" refers to the genetic code of an organism. "Phenotype" refers to the manifestation of this code in physical characteristics or any other traits that are observable [1]. For example, a person may carry a mutation in the PER2 gene (genotype), resulting in depression or circadian abnormalities (phenotype). Mutations in the the PER2 gene may manifest themselves differently in model organisms. By observing the phenotypes of mutant PER2 organisms, we can learn more about the gene's function and associated diseases. You can find the phenotypes of mutant PER2 model organisms below, as described in organismal databases online.
Mouse:
Mice mutants with no working copies of PER2 (homozygous null) have a partially functioning circadian clock. In constant darkness, mutant mice experience a short circadian period followed by a loss of circadian rhythmicity. Mutants also lack full functioning DNA repair responses and are thus more susceptible to radiation and tumor formation [2].
Mice mutants with no working copies of PER2 (homozygous null) have a partially functioning circadian clock. In constant darkness, mutant mice experience a short circadian period followed by a loss of circadian rhythmicity. Mutants also lack full functioning DNA repair responses and are thus more susceptible to radiation and tumor formation [2].
Zebrafish:
per2 is involved in circadian regulation of gene expression, intersegmental vessels, and light stimulus response in zebrafish. period2 morpholino fish exhibited accelerated angiogenic vessel growth. Period2 is also involved with the pineal gland's (a photoreceptive organ) control of circadian rhythm. In zPer2 knock-downs, no rhythm was established, indicating that light-induced zper2 expression is necessary for establishing the rhythm [3].
per2 is involved in circadian regulation of gene expression, intersegmental vessels, and light stimulus response in zebrafish. period2 morpholino fish exhibited accelerated angiogenic vessel growth. Period2 is also involved with the pineal gland's (a photoreceptive organ) control of circadian rhythm. In zPer2 knock-downs, no rhythm was established, indicating that light-induced zper2 expression is necessary for establishing the rhythm [3].
Analysis
Even though PER2 has many homologues, my search through the online organismal databases only turned up phenotypes for two organisms, the mouse and the zebrafish. This may be because more research on PER2 needs to be done on model organisms or that the databases still need to be updated. From the mouse and zebrafish information that is available online, we can see that PER2 is important for circadian regulation. Model organisms like these are important tools for elucidating the function of a gene and may be useful for developing therapies for human disease.
References
[1] Science at a Distance. Genotype and Phenotype. http://www.brooklyn.cuny.edu/bc/ahp/BioInfo/SD.Geno.HP.html
[2] MGI. http://www.informatics.jax.org/marker/MGI:1195265
[3] ZFIN. http://zfin.org/action/marker/view/ZDB-GENE-011220-2
[4] NCBI. RNA Interference (RNAi). http://www.ncbi.nlm.nih.gov/projects/genome/probe/doc/TechRnai.shtml
[5] RNA Interference video animation from http://www.nature.com/nrg/multimedia/rnai/animation/index.html
[1] Science at a Distance. Genotype and Phenotype. http://www.brooklyn.cuny.edu/bc/ahp/BioInfo/SD.Geno.HP.html
[2] MGI. http://www.informatics.jax.org/marker/MGI:1195265
[3] ZFIN. http://zfin.org/action/marker/view/ZDB-GENE-011220-2
[4] NCBI. RNA Interference (RNAi). http://www.ncbi.nlm.nih.gov/projects/genome/probe/doc/TechRnai.shtml
[5] RNA Interference video animation from http://www.nature.com/nrg/multimedia/rnai/animation/index.html