biol3010 lec 3/28/25

  • Overview of Today's Topic

    • Discussion of how the genome regulates gene expression across generations.
    • Focus on epigenetics and transgenerational inheritance.
    • Connection to transposable elements and their role in the genome.

  • Transposable Elements

    • Definition: Genes that can move (or "hop") within the genome, believed to have originated from viruses.
    • Types of transposable elements:
    • Retrotransposons:
      • Function: Copy-paste mechanism; replicates and inserts itself elsewhere in the genome.
      • Similar to retroviruses in replication.
    • DNA transposons:
      • Function: Cut-paste mechanism; cuts itself out and reinserts at a new location.
      • Occasionally behaves like copy-paste.
    • Autonomous vs Non-autonomous transposable elements:
    • Autonomous: Complete parts needed for movement.
    • Non-autonomous: Lacks necessary components; relies on autonomous elements.
    • Significance: Transposable elements constitute about 50% of the human genome but are largely non-functional or inert forms.

  • Epigenetics Defined

    • Heritable changes in gene expression that are not due to changes in the DNA sequence (mutations).
    • Mechanisms include:
    • Chemical modifications to nucleotides.
    • Chromosome packaging changes.
    • Inherited small regulatory molecules.
    • Key Forms of Epigenetic Change:
    • Programmed epigenetics: Normal developmental processes that are inherited through cell division (mitosis).
    • Plastic epigenetic inheritance: Epigenetic changes induced by environmental factors, especially prominent in plants.

  • Mechanisms of Epigenetics

    • Major processes discussed:
    1. Methylation of DNA: Commonly affects cytosines.
    2. Histone modifications: Important in chromatin structure and gene regulation.
    3. Inherited small RNA molecules: Involved in the suppression of gene expression (e.g., through targeting transposable elements).

  • Cytosine Methylation

    • Occurs at CpG islands: DNA regions with repeated cytosine (C) and guanine (G) sequences.
    • Mechanism:
    • Methyltransferases (DNMTs) recognize hemimethylated DNA and propagate methylation during DNA replication.
    • Effect on gene expression:
    • Methylated states: Prevent binding of regulatory proteins leading to reduced gene expression.
    • Unmethylated states: Allow for transcription factors to bind and promote gene expression.
    • Example: The dynamic methylation in gametes affecting gene expressions based on parental origin.

  • Transgenerational Effects of Methylation

    • Parent-of-origin effects: Maternal vs paternal contributions can dictate different gene expression patterns.
    • Example of conflict between maternal and paternal genomic interests in offspring growth, particularly during pregnancy.

  • Case Study: Insulin-like Growth Factors (IGF)

    • Discusses how methylation influences the expression of IGF and its receptor, contributing to the growth of animals.
    • Ligers vs Tigons: Explore the implications of cross-species hybrids on size and growth due to genomic conflicts and methylation differences between parents (lions vs tigers).

  • Inheritance of Small RNA Molecules

    • Focus on piRNAs:
    • Small RNA segments derived from truncated transposable elements.
    • Function: Suppresses transposable element activity in offspring, particularly in hybrid dysgenesis cases in flies.
    • Mechanism:
    • piRNAs bind to and target transposable element transcripts for degradation, thus preventing instability in the genome.

  • Conclusion & Reflection

    • Discussed interaction of various epigenetic mechanisms and their impact on gene regulation across generations.
    • Emphasized how these complex systems affect both normal development and evolutionary adaptations in various species.