This web page was produced as an assignment for Genetics 564, an undergraduate capstone course at UW-Madison.
Introduction
Depression, despite being a highly treatable disorder, is very prevalent around the world today. It is characterized by feelings of hopelessness, guilt, sadness, changes in appetite and weight, changes in sleeping patterns, and difficulty making decisions, among others. Approximately 7% of the US population over 18 and 12.5% of individuals between 12 and 17 are diagnosed with depression[1]. While many antidepressant treatments are available, such as various medications and cognitive behavioral therapy, these are not always effective. Sadly, every day, about 121 people take their life, many of which are suffering from depression[2]. Depression is often stigmatized, which can make it exceptionally difficult for those suffering to get the help they truly need. Even if help is found, most insurance plans do not comprehensively cover inpatient stays, psychiatry appointments, cognitive behavioral therapy, or medications.
While most individuals respond well to antidepressant treatments, not all do. The effects of suicide and depression have largely impacted my life, which led me to explore this topic. I hope that soon individuals suffering from depression and suicidal thoughts and actions will be able to have the help they need and the resources to properly treat their very real, very dangerous illness.
Depression has been thought to have a genetic component for quite some time, but little concrete evidence has suggested a clear mode of inheritance. Unlike disorders like Cystic Fibrosis or Huntington's, the presence of a single allele is not enough to determine that one has the disease. Rather, depression is a polygenic disorder, meaning that multiple genes and factors are thought to be involved in development of the disorder. One of the genes recently thought to have a part in causing depression is FKBP5, which I have focused on.
While most individuals respond well to antidepressant treatments, not all do. The effects of suicide and depression have largely impacted my life, which led me to explore this topic. I hope that soon individuals suffering from depression and suicidal thoughts and actions will be able to have the help they need and the resources to properly treat their very real, very dangerous illness.
Depression has been thought to have a genetic component for quite some time, but little concrete evidence has suggested a clear mode of inheritance. Unlike disorders like Cystic Fibrosis or Huntington's, the presence of a single allele is not enough to determine that one has the disease. Rather, depression is a polygenic disorder, meaning that multiple genes and factors are thought to be involved in development of the disorder. One of the genes recently thought to have a part in causing depression is FKBP5, which I have focused on.
FKBP5 is a rather highly conserved gene and protein throughout species. This conservation was determined through phylogenetic tree analysis and sequence alignment. It is involved in isomerase activity and protein folding in the cytoplasm of cells. FKBP5 is an important piece in hormone signaling, especially the glucocorticoid pathway. In the realm of model organisms, mice and zebrafish are very well conserved. I chose to use zebrafish during this project because of their ease of care, inexpensive maintenance, and simplicity of drug screening.
|
In regards to depression, researchers have previously identified a risk and protective allele of FKBP5. This is indicated by a red T for risk and a white C for protective in the above picture. In individuals with the risk allele, FKBP5 has increased transcription when compared to those with the protective allele. This leads to an increase in FKBP5 protein, which impairs glucocorticoid signaling. This is a main hypothesis as to how FKBP5 is linked to depression. Following a literature search, I posed the question: how does the FKBP5 risk allele regulate transcription, and how is this involved in depression and antidepressant response?
Specific Aim 1
The first aim is to link the presence of an allele to depression and antidepressant response. I hypothesize that the risk allele will lead to increased depression and decreased antidepressant response. To study this in a model organism, I would first align the genomic sequences of multiple organisms by using MEGA and ClustalW to identify the similarity within the intronic region the allele is in. This would aid in determining a model organism. Then, a nucleotide-specific transgenic zebrafish line would be generated via CRISPR in order to screen for phenotypes. These fish would then be utilized throughout the remainder of the experiment.
I would expect that these results would confirm previous studies involving depressive phenotype and antidepressant response in response to different FKBP5 alleles.
Specific Aim 2
In the second aim, RNA-seq will be conducted in order to determine allele-specific variations in transcription. I hypothesize that there will be an increase in FKBP5 mRNA in the fish with the risk allele when compared to the protective allele, and that this phenotype can be reduced with the addition of an antidepressant. I would also expect an increase in transcription of genes involved in glucocorticoid signaling and transcriptional activation in fish with the risk allele. These increases would lead to an increase in depression.
Specific Aim 3
The third aim would address FKBP5 protein abundance in response to antidepressants. First, affinity-purification mass spectrometry would be done on the fish from the first aim and levels of protein would be addressed. I would expect fish with the risk allele would have a higher abundance of FKBP5 than fish with the protective allele and those being treated with antidepressants. Second, the protein interaction networks in fish would be constructed for each fish set and the interacting partners would be sorted by gene ontology. I would expect fish with the risk allele would have increased interaction with the glucocorticoid signaling pathway and transcriptional activation when compared to the protective allele and those being treated with antidepressants. The behavior of each fish set would then be assessed. The fish with the risk allele would show increased depressive phenotype than those with the protective allele or with antidepressants.
|
Future Directions
Following this set of experiments, I would want to conduct an isoform study. FKBP5 has two distinct isoforms, one of which is lacking protein domains required for heat shock protein and glucocorticoid receptor binding. I would hypothesize that if these domains were knocked out, depression symptoms would reduce because of the lack of interaction with the glucocorticoid pathway.
Citations:
[1]Anxiety and Depression Association of America. (August 2016). Retrieved from https://www.adaa.org
[2] Suicide Facts. The American Foundation for Suicide Prevention. (2017). Retrieved from https://www.theovernight.org/?fuseaction=cms.page&id=1034.
[1]Anxiety and Depression Association of America. (August 2016). Retrieved from https://www.adaa.org
[2] Suicide Facts. The American Foundation for Suicide Prevention. (2017). Retrieved from https://www.theovernight.org/?fuseaction=cms.page&id=1034.
PDF/PowerPoint files - newest to oldest
|
|
|
moriarty_presentationrd.pptx |
moriarty_presentation_draft2_pdf.pdf |