L6: Stem Cells & Cell Differentiation

• What are unspecialized progenitor cells capable of replication & differentiating to multiple different cell types?


  • Stem Cells
• What are partially differentiated intermediate cells capable of forming more differentiated cells?

  • Progenitor cells
• What is irreversible development of highly specialized cell types that generally do not divide?


  • Terminal differentiation
• What is symmetric cell division?


  • Produces daughter cells identical to parent
  • Differentiate upon receiving different development or environment clues
• What is asymmetric cell division?


  • Daughter cells have different composition & gene expression
• What tracks developmental fate of each cell?


  • Cell lineage
  • Cell fate progressively restricted

  
• Stem cells can undergo?


  • Symmetric or asymmetric division
  • Ability for self-renewal
• What are the 3 types of stem cells?

  1. Totipotent
  2. Pluripotent
  3. Unipotent
• Stem cell division

  
• What are the 3 somatic cell layers in development?

  1. Ectoderm
  2. Mesoderm
  3. Endoderm
• Somatic layers in development

  A) Ectoderm

  B) Mesoderm

  C) Endoderm

  
• Germ Cell Layers

  A) Ectoderm

  B) Central nervous system

  C) Retina

  D) lens

  E) Cranial

  F) sensory

  G) Ganglia

  H) nerves

  I) Pigment cells

  J) Head connective tissue

  K) Epidermis

  L) Hair

  M) Mammary glands

  
• Germ Cell Layers

  A) Mesoderm

  B) Skull

  C) Head

  D) Skeletal muscle

  E) Skeleton

  F) Dermis of skin

  G) Connective tissue

  H) Urogenital system

  I) Heart

  J) Blood

  K) Lymph cells

  L) Spleen

  
• Germ cell layers

  A) Endoderm

  B) Stomach

  C) Colon

  D) Liver

  E) Pancreas

  F) Urinary bladder

  G) Epithelial parts of trachea

  H) lungs

  I) pharynx

  J) thyroid

  K) intestine

  
• C. elegans Cell Lineage: What makes the cell lineage of C. elegans unique, and how many cells are formed after 10 rounds of cell division?


  • The cell lineage of C. elegans is completely defined, and the worm is transparent, allowing visualization of each cell during development.
  • After 10 rounds of cell division, approximately 1000 cells are formed.
  • Development can vary due to external signals.

  
• What are the key steps in generating and maintaining embryonic stem cells?

  • Cleavage-stage embryos are grown to the blastocyst stage.
  • The inner cell mass is isolated and grown on a feeder cell layer.
  • The cells are dissociated into individual cells to form ESC colonies.
  • ESCs can be maintained and/or cryopreserved.
  • They can be differentiated in vitro or injected in vivo.

  
• What factors regulate the fate of embryonic stem cells and how do they differentiate in culture?


  • ESCs form embryoid bodies in suspension culture and differentiate into various cell types on a solid surface.
  • Multiple factors regulate ESC fate, including:
  • Signaling proteins
  • DNA methylation
  • miRNAs
  • Transcription factors
  • Chromatin regulators (e.g., histone acetylation)

  
• ES Cells

  A) Mesoderm

  B) Cardiac Muscle

  C) Skeletal

  D) Tubule cell

  E) Red blood cells

  F) Smooth Muscle

  
• ES Cells

  A) Endoderm

  B) Lung cells

  C) Thyroid cells

  D) Pancreatic cells

  
• ES Cells

  A) Ectoderm

  B) Skin cells

  C) Neuron cells

  D) Pigment cells

  
• Development of Synthetic Embryos

  
• What factors are involved in transcriptional and post-transcriptional regulation?


  • Transcriptional Regulation:
  • Transcription factors
  • State of chromatin
  • DNA methylation
  • Histone acetylation
  • Post-Transcriptional Regulation:
  • Non-coding RNAs
  • RNA interference (miRNA)

  
• What are examples of extrinsic signaling proteins and intrinsic transcription factors?


  • Extrinsic Signaling Proteins:
  • Growth factors that bind cell surface receptors
  • Examples: TGFβ, BMP, Notch, Wnt signaling pathways
  • Intrinsic Transcription Factors:
  • Proteins that bind DNA and regulate transcription

  
• What are the 3 key mechanisms of epigenetic regulation?


  1. DNA methylation
  2. Chromatin Regulators
  3. MicroRNA (miRNA) inhibit translation of specific mRNAs

  
• What is DNA methylation?


  • Methylation of cytosine in promoter CpG islands silences gene expression
• What are chromatin regulators?


  • –Acetylation/deacetylation of histones by HATs & HDACs
• What are the two primary uses of ES cells?

  • Therapeutic use to treat a wide variety of diseases.
  • Generation of mutant mice (e.g., SH2B1 knockout mice)

  
• What is the role of adult stem cells and where are they found?


  • Adult stem cells are found in multiple tissues, residing in specific microenvironments (niches) with intrinsic and extrinsic regulatory signals.
  • They are quiescent and non-dividing until stimulated, with little cell division in differentiated adult tissues.
  • Germ line stem cells are one type of adult stem cell.
• Adult Stem Cell Differentiation

  
• Pluripotency of Stem Cells

  
• Plasticity of Adult Stem Cells

  
• Induced Pluripotent Stem Cells:

  •Adult differentiated somatic cells treated with “cocktail” of transcription factors and growth factors to generate iPSCs

  
• Where do epithelial stem cells reside, and what regulates their division?

  • Epithelial stem cells reside in the hair follicle bulge.
  • They undergo asymmetrical division to replicate stem cells and produce precursors for keratinocytes and hair matrix precursors.
  • This process is regulated by BMP, Wnt, and TGFβ signaling.

  
• How do TGFβ and BMP signaling pathways regulate gene expression?


  • TGFβ Signaling:
  • TGFβ activates TGFBRs
  • Phosphorylation of Smad2/3
  • Smad2/3/4 complex translocates to the nucleus to regulate gene expression

  BMP Signaling:

  • BMP activates BMPRs
  • Phosphorylation of Smad1/5
  • Smad1/5 with Smad4 translocates to the nucleus to regulate gene expression

  
• How do intestinal stem cells regenerate, and what regulates their proliferation and differentiation?


  • Epithelial cells regenerate continuously from crypts in the intestinal wall.
  • Mesenchymal cells adjacent to stem cells produce Wnt (for proliferation) and BMP (for differentiation) signals.

  
• Intestinal cell turnover occurs in 2-3 days, and aberrant Wnt signaling can lead to colon cancer.
• How does normal and aberrant Wnt signaling affect colon cancer development?


  • Normal Wnt Signaling:
  • Wnt inhibitor SFRP binds to Wnt, preventing activation of the Wnt receptor FRZ.
  • APC destruction complex prevents β-catenin activation and downstream Wnt signaling.

  Colon Cancer (Aberrant Wnt Signaling):

  • DNA methylation in the SFRP promoter silences SFRP.
  • Inactivation of APC leads to increased β-catenin levels, which translocate to the nucleus and regulate gene expression.

  
• How does SFRP1 regulate Wnt signaling, and what happens when its transcription is blocked?


  • SFRP1 inhibits Wnt signaling, preventing colon stem cell proliferation.
  • Cystine methylation blocks SFRP1 transcription, leading to uncontrolled stem cell differentiation and epithelial cell proliferation.

  
• Into what cell types can neural stem cells differentiate, and what signaling pathways are involved?


  • Neural stem cells can differentiate into neuronal and glial progenitor cells.
  • Signaling pathways involved include FGF, BMP, TGFs, BDNF, and Notch.
  • BMP and Notch signaling specifically promote astrocyte formation.

  
• Where is the neural stem cell niche located, and what signals regulate NSCs?


  • The neural stem cell niche is located in the subventricle of the fluid-filled lateral ventricle.
  • Neural stem cells (NSCs) are a subset of astrocytes.
  • Blood vessel cells and ependymal cells provide signals that regulate NSCs.
  • NSCs produce dividing transit-amplifying (TA) cells that can form neuroblasts.
  • Adult brains contain NSCs.