1. Eukaryotic Gene Regulation
Chapter 18

2. Overview
Eukaryotes can regulate gene expression at multiple stages from gene to functional protein
Regulation of chromatin structure
DNA methylation
Transcription initiation factors
Alternative RNA processing
Protein degradation

3. -- blue = DNA
-- orange = RNA
-- purple = protein
--Each of these is a possible site for regulation, but not all are used in any instance or cell

4. How do we get different cell types?
Red blood cells, muscle cells, neurons…
Every cell has the same genes
Different cells express only a fraction of their genes
20% of cell’s genes are expressed

5. Histone Acetylation -- DNA level of regulation
-- Histone proteins have protruding “tails”
-- Acetyl groups can be added to these tails
-- Acetylated histones lose their + charge, and are unable to bind to other nucleosomes
-- Acetylated histones = transcription more likely

6. Histone Code Hypothesis
Histone tails can be
Acetylated, methylated, or phosphorylated
Methylation = condensation of chromatin
Phosphorylation = separation of histones
So which determines the proteins produced: acetylation or the specific combination of these modifications?

7. DNA Methylation DNA itself can be methylated as well
Actually methyl groups are attached to the nitrogenous bases of nucleotides
Specifically cytosine
Methylated bases are not able to be expressed
Remember methylation from Inactivated X chromosomes?
Interfere with normal methylation = weird results

8. Important Difference…
Histone acetylation = INCREASED transcription
DNA methylation = DECREASED transcription

9. Why are identical twins different?
They have the same genome, so WTF?
Base-pair mutations are one way to get genetic diversity
Different DNA sequences may be methylated, this results in certain sequences being turned off
So same DNA but phenotypic variation
Identical twins, but one has schizophrenia while the other does not
Called epigenetic inheritance (traits that are NOT contained on nucleotide sequences)

10. Transcriptional Modification
Most important area of regulation or control of gene expression
Was this true in prokaryotes?
Involves Enhancer regions on the DNA
Activator proteins bind to mediator proteins
The complex is called transcription initiation complex
Transcription of the downstream regions is enhanced

12. -- Activator proteins bind to the enhancer region of DNA
-- Activator proteins also bind to Mediator proteins + Transcription factors
-- Forms transcription initiation complex
-- Almost guarantees that the gene will be expressed

13. -- Activator proteins bind to enhancer DNA region
-- Different activator proteins = different gene transcribed & expressed
-- Activator proteins = directors of transcription in eukaryotes

14. Alternative RNA Splicing
-- Spliceosomes can splice the primary RNA transcript differently
-- Creates different proteins
-- Fruit fly gene = 38,000 different combinations of proteins
-- Yet again, is phenotypic variation due to genetic sequences?

15. siRNA Cure for Ebola? 1.5% of genome codes for proteins
Even smaller amount codes for RNAs (tRNA, mRNA, rRNA)
So is any part of the 98% ever transcribed?

17. miRNA
microRNAs are capable of binding complementary sequences in mRNA molecules
Usually degrades the mRNA it binds OR blocks translation of the mRNA
1/3 of all genes regulated via miRNAs

18. RNA Interference (RNAi)
Inject dsRNA molecules into a cell
This turns off gene expression of those genes with same sequence as the dsRNA
Small Interfering RNA (siRNA) were the dsRNA responsible for the interference
How did this lead to a treatment for Ebola?
Ebola is an RNA based virus
What about HIV? Hepatitis A or C? common cold?
Dengue fever? influenza? H1N1, H5N1?

19. Skip 18.4

20. Cancer Genes Oncogenes = cancer-causing genes
Proto-oncogenes = genes that codes for proteins that promote normal cell growth
Proto-oncogenes can become oncogenes
Leads to an increase in protein production
OR an increase in the activity of normal protein production
Either leads to TOO MUCH mitosis

21. Tumor-Suppressor Genes
The produced proteins inhibit cell division
If a mutation decreases production of these products, cell division will accelerate
2 ways to get neoplastic growths (cancer):
Mutation which alters proto-oncogenes into oncogenes
Over-produces protein OR hyperactive protein production
This interferes with usual mechanism of cell cycle regulation
Mutation interferes with tumor-suppressor genes
Insufficient production leads to mitotic hyperactivity

22. Again…

23. Cell Cycle Stimulator Pathway Mutation in ras?
-- Activity even though no growth factor has been received by the RTK
-- Outcome = Excessive Mitosis

24. p53 gene
-- Commonly called the “guardian angel of the genome”
-- Halts cell cycle by binding CdK proteins
-- Allows time for DNA repair
--p53 is also directly involved in DNA repair
--p53 initiates apoptosis if DNA damage is beyond repair

25. MultiStep Model of the Development of
Colorectal Cancer