Eukaryotic Gene Regulation 2

Eukaryotic Gene Regulation Overview

• Gene Expression Regulation Levels:
  • Chromatin: Influences the genetic accessibility for transcription.
  • Transcription: Control of gene transcription into mRNA.
  • Post-Transcription/mRNA: Modifications and stability of mRNA.
  • Translation: Regulation of protein synthesis from mRNA.
  • Post-Translation: Modifications to proteins after synthesis.

Estrogen Receptor and Gene Regulation

• Estrogen's Role:
  • Converts the estrogen receptor from inactive to active form.
  • Binds to cis-acting sites near gene promoters.
  • Can activate or repress transcription depending on the tissue type.

Levels of Gene Regulation in Eukaryotes

1. Chromatin Regulation:

   • Histone modifications (acetylation, methylation).
   • DNA methylation.

2. Transcriptional Regulation:

   • Cis-acting Elements:
     • Core promoter and proximal promoter elements.
     • Distal elements like enhancers and silencers.
   • Trans-acting Factors:
     • Transcription factors: activators and repressors.
     • Influence from ions, hormones, and signaling molecules.

3. Post-Transcriptional Modifications:

   • mRNA splicing: removing introns and joining exons.
   • mRNA degradation mechanisms.
   • Non-coding RNAs (ncRNAs).

4. Translation Regulation:

   • Subcellular localization of mRNA affects translation.

5. Post-Translational Modifications:

   • Phosphorylation: Addition of phosphate groups to amino acids.
   • Ubiquitination: Tags proteins for degradation by proteasomes.

CREB Transcription Factor Signaling

• Function of CREB:

  • Activated by signaling molecules that bind to membrane receptors, initiating a signaling cascade.
  • CREB binds to CRE sites (enhancers) to activate transcription.
  • Must be phosphorylated and partnered with CBP proteins to bind effectively.

• Signaling Pathway:

  1. Signal binds to membrane receptor.
  2. G protein activated.
  3. Adenylyl cyclase converts ATP to cAMP.
  4. cAMP activates Protein Kinase A (PKA).
  5. PKA phosphorylates CREB.
  6. CBP proteins interact with phosphorylated CREB.
  7. Transcription is activated at CRE sites.

mRNA Regulation Mechanisms

• mRNA Splicing:

  • Typical Process:
  1. snRNPs bind to pre-mRNA.
  2. Assemble to form a spliceosome.
  3. Intron is cut and released; exons are joined together.
  • Alternative Splicing Types:
  • Cassette Exons: Some exons can be excluded.
  • Altering splice sites: Use of alternate 5' or 3' splice sites.
  • Intron retention: Some introns retained in the final mRNA.
  • Mutually exclusive exons: Either one or another exon included.

• Example:

  • Calcitonin/CGRP gene: Different splicing in thyroid cells (CT needed) vs. neurons (CGRP needed).
  • PolyA signal ends transcription affecting splicing.

• mRNA Decay:

  • Regulated by the rate of mRNA degradation after transcription.
  • Enzymes remove protective structures from mRNA, leading to degradation.

Non-Coding RNA Functions

• Non-coding RNAs (ncRNAs): Do not code for proteins; involved in regulation.

• Types:

  • siRNA: Targets mRNAs for degradation.
  • miRNA: Inhibits mRNA translation or promotes degradation.

• RNAi Mechanism:

  • Involved in efficiently silencing specific mRNAs, especially for therapeutic interventions (e.g., treating TTR amyloidosis).

Post-Translational Modifications

• Purpose: Alter protein function, localization, and stability after translation.
• Post-Translational Mechanisms:
  • Phosphorylation: Usually activates or deactivates proteins.
  • Ubiquitination: Marks proteins for degradation by proteasome, affecting protein lifespan.

Summary of Gene Regulation Levels

• Gene regulation involves complex interactions across multiple levels from chromatin structure to post-translational events, emphasizing the multifaceted nature of gene expression control in eukaryotic cells.