Lecture Notes on Epigenetics and Induced Pluripotent Stem Cells 9/30

Overview of Epigenetics and Induced Pluripotent Stem Cells (iPS Cells)

Lecture Outline

  • Finishing discussions on epigenetics.

  • Introduction to induced pluripotent stem cells (iPS cells).

  • Announcements regarding class schedule:

    • No class on Thursday (Fall break).

    • Quiz review next week, potentially replacing lecture.

    • Exam on next Thursday, October 9.

    • Revised syllabus posted with adjustments to quiz and exam dates.

Key Concepts in Epigenetics

  • Definition and Importance of Epigenetics:

    • Refers to modifications that change gene expression without altering the underlying DNA sequence.

    • Influence of environmental factors on gene expression.

  • Mechanisms of Epigenetic Modification:

    1. DNA Methylation:

      • Addition of methyl groups (–CH₃) to cytosine bases, particularly in CpG dinucleotides.

      • Plays a crucial role in gene expression regulation and cell differentiation.

    2. Histone Modifications:

      • Modifications such as acetylation and methylation of histones which can impact DNA accessibility and transcription.

  • Methionine Cycle and Methyl Donors:

    • S-Adenosylmethionine (SAM):

      • The primary methyl donor in methylation processes.

    • Diet can influence methylation through the availability of SAM precursors (folate, B12, betaine, choline).

  • **Examples of Epigenetic Impacts:

    • Agouti Mice Experiment:

      • Relationship between diet and coat color/obesity in mice.

      • Methylation of the Agouti gene leads to brown coat and slim phenotype whereas unmethylated gene leads to yellow coat and obesity.

    • Queen Bee Development:

      • Royal jelly feeding alters DNA methyltransferase action leading to activation of queen-specific genes.

    • Effects of Toxins on Methylation:

      • VPA (Valproic Acid) inhibits DNA methyltransferase leading to unmethylated gene expression, counteracted by a methyl-rich diet.

  • Behavioral Influences on Epigenetics:

    • Investigation into how anxiety in mother rats modifies DNA methylation and behavior in offspring.

    • Reference to Lamarckian inheritance concepts in behavior influencing phenotypic expression.

Notable Studies Discussed

Maternal Behavior and DNA Methylation by Moshe Zheff

  • HPA Axis Identification:

    • Examines how stress impacts the hypothalamus-pituitary-adrenal (HPA) axis.

    • Focus on glucocorticoid receptor expression and its implications in stress management.

  • Bisulfite Sequencing Methodology:

    • Used to examine DNA methylation.

    • Treats DNA with bisulfite to differentiate between methylated and unmethylated cytosines. Methylated cytosines remain unchanged, while unmethylated ones convert to uracil.

    • Allows analysis of regulatory areas affecting gene expression, particularly in stress response genes.

  • Findings and Conclusion:

    • Higher methylation levels in low-grooming mothers led to reduced glucocorticoid receptor expression affecting stress responses of the offspring.

    • Implications for understanding anxiety and behavior transmission across generations.

Transgenerational Inheritance Study by Diaz and Ressler

  • Study Objective:

    • Examine how fear experiences in mice can be inherited.

  • Method:

    • Conditioning mice to associate a specific odor (acetophenone) with a foot shock, then examining responses in F1 and F2 generations.

    • Analysis of DNA methylation patterns in both brain and sperm.

  • Key Findings:

    • Offspring exhibited heightened responses to the conditioned odor, indicating behavioral inheritance without direct exposure.

    • Methylation changes in olfactory receptor genes suggested mechanism for inherited trait.

Induced Pluripotent Stem Cells (iPS Cells)

  • Definition and Significance:

    • iPS cells are reprogrammed cells that regain pluripotency from differentiated somatic cells.

    • Developed as a tool for personalized medicine and regenerative therapies.

  • Yamanaka's Discovery:

    • Identified four transcription factors: Oct4 (O), Sox2 (S), Klf4 (K), and Myc (M) referred to as OSKM, that induce pluripotency.

    • Emphasizes moving beyond ethical issues surrounding embryonic stem cells.

  • Applications of iPS Cells:

    • Creation of patient-specific cells for research and potential therapies in diseases like diabetes and heart disease.

    • Models human diseases more accurately compared to traditional animal models.

    • Research on neurodegenerative diseases utilizing iPS cells derived from patients.

Organoid Technology and Microcephaly

  • Study Context:

    • Investigating the condition microcephaly using organoids developed from iPS cells.

  • Methodology:

    • Development of cerebral organoids from fibroblasts using various media, including Matrigel for three-dimensional growth.

    • Observation of developmental differences between control organoids and those derived from microcephaly patients.

  • Findings:

    • Microcephaly organoids displayed premature neuronal differentiation leading to a decreased size compared to controls.

    • Implications for understanding the underlying mechanisms of brain development disorders.

Summary and Implications

  • Ethical Considerations:

    • While iPS technology alleviates some ethical concerns, embryonic stem cell research remainsa critical area.

    • Advances in the field promise significant insights into human biology, disease modeling, and regenerative medicine.

Questions and Discussion

  • Engage in questions regarding the role of epigenetics, iPS cells, and their applications in modern biology.