2.5 Gene Regulation in Eukaryotes Flashcards
What is the purpose of RNAseq?
- Expression of genes can be revealed by RNA sequencing. RNA expressed in a cell is sequenced by Next Generation sequencing machines and is aligned to the genome.
- Look at mRNA to get complete idea of gene expression, create complimentary strand of DNA using reverse transcriptase
- mRNA gets sequenced and histogram shows how many molecules match which parts of the genome
What is spatiotemporal gene expression?
What is Twist?
- Twist is an activator that is expressed in presumptive mesodermal cells of the early fly embryo.
- Causes these cells to undergo a fundamental change in their nature (cell type).
- Change from stationary epithelial cells to dissociated and migratory cells
How can inappropriate expression of activators like Twist cause cancer?
- Tumors are caused by mutations that change expression of genes controlling proliferation and cell death.
- If the human orthologue of Twist (Twist 1) is turned on then it can activate a whole genetic network that cuases benign tumor cells to become migratory and invasive (undergo metastasis)
How are Twist target located?
Twist binding sites were mapped by isolating bound DNA using Chromatin-ImmunoPrecipitation and then hybridising this to a whole genome microarray
What are two of the genes twist activates?
How is the rhomboid expression pattern achieved?
- rhomboid = Twist - Snail
- The repressor Snail is also expressed in a ventral band but in a more restricted region within the Twist region
- The target gene rhomboid is activated by Twist but repressed by Snail, so only expressed where Twist is on and Snail isn’t
How do twist and snail both control rhomboid expression?
The enhancer region of rhomboid has two binding sites for Twist and three for snail. These sites even overlap in one area
Where are the clusters of globin genes for Haemoglobin?
There are two clusters of globin genes, a cluster of alpha globins on chromosome 16 and a cluster of beta globins on chromosome 11
How is spatio temporal regulation of the globin genes throughout development seen?
After birth fetal gamma chain goes down
Replaced by adult beta globin
What is the need to have foetal haemoglobin?
- At low to medium partial pressures foetal hemoglobin has a much higher affinity for oxygen than adult haemoglobin
- In the placenta the mother’s blood comes into close proximity to the bood vessels of the fetus
- Foetal hemoglobin is able to steal oxygen from the mother’s haemoglobin
What is an enhancer?
A regulator DNA sequence to which regulatory proteins (trans acting factors) bind, increasing the rate of transcription of a gene.
What is the role of the Locus Control Region (LCR) in the expression of globin genes?
- It enhances expression by interacting with regulatory factors present at the promoters of the globin genes
- Turn on certain hemoglobin only
- It does not control which gene gets expressed, just amplifies expression of it
How does LCR enhance expression of certaing globin genes?
- It interacts with regulatory factors present at the promoters of the globin genes.
- Loops over and interacts with transcriptional machinery
- When fetus it interacts with gamma and then later with beta
Given that enhancers can have an influence from a long way away – how is this influence confined to the correct genes?
- Insulator elements create loops in chromosomes which limit the region an enhancer can affect.
- This barrier stops heterochromatin from spreading to silence nearby regions
What prevents LCR from activating other genes?
- Insulator sequences HS5 and 3’HS1 create loops so LCR only interacts with its target
What is anemia?
A decrease in the number of red blood cells (RBCs) or less than the normal quantity of haemoglobin in the blood
What is thalassaemia?
An inherited form of anaemia caused by faulty synthesis of haemoglobin
What happens in sickle cell anaemia?
- It is an autosomal recessive disease which limits the level of oxygen reaching organs and causing organ damage
- Low red blood cell counts (anaemia)
- Reduced life of red blood cells (120 days down to 10-20)
Where is Sickle cell disease (SCD) more common?
SCD is most common among people from Africa, India, the Caribbean, the Middle East, and the Mediterranean. The high prevalence thought to be due to carriers of SCD are more resistant to malaria (heterozygote advantage).
What mutation brings about sickle cell anaemia?
Results from a single mutation in beta globin where A is changed to T so glutamic acid is changed to valine
What are the two classes of mutations in beta thalassaemia?
- B0 where there is no beta globin produced
- B+ where there are diminished beta globin levels (these alleles vary in severity depending on how much is produced)
- Patient’s severity of disease depends on what combination of what class of mutations they have
What happens if you have beta thalassemia major?
What happens if you have beta thalassemia intermedia?
What happens if you have beta thalassemia minor?
