19 Stem Cells (DIY)

• Feature of Stem Cells (1)

  1. Stem cells are a group of undifferentiated and unspecialised cells

  • Specialised cells in tissues are differentiated and have tissue-specific structures that allow them to be adapted to perform unique roles
  • Stem cells do not have any tissue-specific structures and therefore cannot perform tissue-specific functions (No specific roles)
• Features of Stem Cell 2

  2. Stem cells can undergo extensive proliferation and are capable of self-renewal through mitosis

  • Symmetrical Division: Stem cells divide to produce 2 daughter stem cells that have the same characteristics as parent cells
  • enlarges the population of undifferentiated cells, maintains a pool of stem cells for further division
  • Asymmetrical Division: Stem cells divides to produce 1 daughter stem cell that is identical to the parental stem cell and 1 progenitor daughter cells
  • Stem cell is stimulated by molecular signals for differentiation
• • Progenitor daughter cell
  • increase/ renew population of specialised cells in a specific tissue - only capable of differentiating into related specialised cell type
• Myeloid Tissues

  • cells found primarily in bone marrow
  • cells that arise from the myeloid progenitor cell
  • gives rise to the platelets, red blood cells, basophils, neutrophils, eosinophils and monocytes
  • Haemotopoietic stem cells constantly proliferate and differentiate into various specialised blood cell types to replace the blood cells lost through normal cell death → maintains the immune and transport function of blood
  • Mainly involved in the innate immune system
• Lymphoid Tissue

  • cells found primarily in bone marrow
  • cells that arise from the lymphoid progenitor cells and gives rise to the natural killer cells and lymphocytes
  • Involved in the adaptive immune system
• Features of Stem Cell 3

  3. Stem cells can differentiate into various specialised cell types upon stimulation by the appropriate molecular signals

  • When a stem cell differentiates into a specialised cell, some of the genes in the resulting specialised cell are switched on, while others are switched off (different for each type of cell)
  • Occurs when a cell changes from being totipotent to pluripotent to multipotent (changes in differentiation potential)
  • May also result in synthesis of tissue-specific structures that enable these specialised cells to perform certain functions
• Totipotency (zygotic stem cells)

  • Has the ability to differentiate into all of the cell types that make up an entire organism including extra-embryonic tissue such as placenta, which nourishes the embryo
  • can give rise to an entire organism
  • also said to be pluripotent and multipotent
• Pluriotency (embryonic stem cells)

  • Has the ability to differentiate into all of the cell types that make up an organism except for extraembryonic tissue such as placenta
  • Alone cannot form the entire organism as extraembryonic tissues such as the placenta is required for foetal nourishment and development
  • Said to be multipotent
• Multipotency (lymphoid and myeloid stem cells)

  • Has the ability to differentiate into several related specialised cell types but far fewer types than the pluripotent embryonic stem cell
  • Main purpose is to produce specialised cells for growth and development, and for replacement of cells that are lost due to cell death and injury
  • Found in small numbers in diverse tissues after embryonic development
  • Neural stem cells can differentiate into nerve cells and neural support cells called glial cells
• Stem Cell Therapy

  (Multipotent and self-renewing nature of adult stem cells)

  • adult stem cells differentiate into the respective specialised cell type, thus restoring function of damaged or diseased tissue
  • transplanted stem cells constantly replicate in the patient to maintain a constant pool of stem cells
  • repeated treatment not necessary to sustain therapeutic effects
• Stem Cell Transplant

  • Adult stem cells can be obtained directly from the donor organ or tissue in which they are found
  • Carries the risk of donated cells being rejected
  • Unlike pluripotent embryonic stem cells which have the ability to differentiate into all cell types that make up an organism except for extra-embryonic tissues, adult stem cells are limited to differentiating into different cell types of their tissue of origin (Multipotent)
• Leukaemia (blood marrow cancer)

  • Abnormal increase in the number of immature white blood cells (blast cells)
  • Abnormal immature blast cells are not functional, frequently crowd the bone marrow and prevent the production of functional white blood cells
• Leukaemia Treatment

  • Bone marrow haematopoietic stem cell transplant
  • Patient is first irradiated to remove all existing haematopoietic cells and WBC from the body
  • Bone marrow haematopoietic stem cells from normal, healthy bone marrow donors are multiplied and infused into the patient
  • Transplanted haematopoietic stem cells will then populate the bone marrow and differentiate into normal blood cells
  • Restores function of blood

  (-) Found in small numbers and can be difficult to isolate

  (-) Possible immune rejection
• Genetically modified stem cell transplant

  • Can be used in gene therapy to treat genetic diseases - strategy involves removing stem cells from the patient, genetically modifying the genome of the stem cells by inserting a normal, functional allele and then reintroducing the modified stem cells back into the patient
  • Retroviruses are used as the vectors for gene therapy
  • risks involved - results in retroviruses insertional mutagenesis where retrovirus integration into the genome can transform cells by either oncogene activation or tumour suppressor gene inactivation
• Induced Pluripotent Stem Cells (IPSCs)

  • Used as an alternative to Embryonic Stem cells
  • Differentiated and specialised adult somatic cells can be reprogrammed to become pluripotent stem cells

  (+) iPSCs can be easily obtained from any type of adult without risk to the donor

  (+) derived from a patient’s own cells, will not be rejected by the immune system upon transplantation

  (-) Low efficiency since the conversion to iPSCs have been incredibly low

  (-) Genetic modification using retroviruses to deliver the reprogramming genes may pose cancer risk
• Explain why certain transcription factors are necessary for the production of iPSCs from adult cells

  1. The expression of the introduced genes allowed for the production of transcription factors which were able to promote the transcription of genes that were inactive/ silenced in adult cells
  2. The subsequent expression of proteins from these previously inactive genes allowed for the cells to convert from very differentiated adult cells to pluripotent stem cells
• How stem cells can continue to divide mitotically

  1. Stem cells express telomerase gene to produce telomerase and proliferate continuously (gene not expressed in other cells)

  2. Telomeres are shortened with each DNA replication

  3. No telomerase will result in telomeres being shrotened to critical length and cells undergo apoptosis/ replication senescene
• What happens during mitotic cell cycle

  Telomeres are shortened with each round of DNA replication