Cell differentiation

• Each cell in the body contains the same instructions (genes) as all the other cells
• Specialised cells


  Cells that have specific functions in the body
• Process of producing specialised cells

  Differentiation
• Differentiation


  • Turning an undifferentiated, generalist cell into a differentiated, specialised cell
• Mitosis generally produces two identical daughter cells
• Stem cells are capable of producing many types of differentiated cells
• Stem cells


  Non-specialist (undifferentiated) cells that can produce differentiated cells
• Stem cell division


  • Asymmetric – producing two different daughter cells
  • Capable of self-renewal
• Types of stem cells

  • Totipotent
  • Pluripotent
  • Multi-potent
• Totipotent


  Capable of producing any cell type
• Pluripotent


  Capable of producing any cell within a major lineage (ectoderm, endoderm, mesoderm)
• Multi-potent


  Capable of producing a restricted set of related cells
• Differentiation is (normally) a one way process
• Stem cells receive instructions in the form of differentiation signals
• Differentiation signals


  Instructions telling stem cells what type of differentiated cell to produce
• Cell surface receptors


  Transmit the differentiation signal into the cell
• Chromatin


  Structure that determines whether a specific gene is expressed or silenced
• Euchromatin


  Lightly packed chromatin, accessible for transcription
• Heterochromatin


  Tightly packed chromatin, difficult to transcribe genes
• In stem cells, most of the DNA is found as lightly packed euchromatin
• As cells become differentiated, more genes become silenced in heterochromatin regions
• Only those genes needed to carry out the cell’s specialist function remain accessible in euchromatin
• Epigenetics


  Study of changes in gene expression that do not involve changes to the underlying DNA sequence
• Epigenetic control


  • Controlled by enzymes that attach methyl or acetyl groups to DNA or histone proteins
• DNA methylation


  Silences genes
• Histone acetylation


  Leads to euchromatin regions and increased gene expression
• Histone methylation


  Can either increase or decrease gene expression depending on modifications
• These epigenetic states can be inherited by daughter cells following mitosis