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.