Cell Differentiation

1
Cell Differentiation Tissue Maintenance

• Yuttana Mundee
• Department of Clinical Microscopy
• Associated Medical Sciences
• Chiang Mai University
• myuttana_at_hotmail.com

2
Theory of Cell Differentiation

• Differential gene loss
• Selective gene amplification
• Genetic equivalence with differential gene
  expression

3
Observation on Chromosomes

• Different cells from the same individual show the
  same sets of chromosomes.
• Polytene chromosomes of insects show the same
  banding pattern in different tissue.
• Chromosome elimination is associated with the
  dichotomy between germ line and somatic cells.

4
Molecular Data on Genomic Equivalence

• Techniques in molecular biology have confirmed
  the rule of genetic equivalence.
• Selective gene expression and amplification are
  found.
• DNA excisions and rearrangements in B-lymphocytes
  to produce enormous type of antibodies is
  exception.

5
Totipotency of Differentiated Plant Cells

• New whole plants can be grown from several cell
  types of differentiated plant cells.
• Calluses, embryoids, growth factors, protoplasts,
  hybrid protoplasts.
• This indicates genetic equivalence in most of
  plant cells.

6
Totipotency of Nuclei from Embryonic Animal Cells

• Nuclei from an animal cell can be developed to a
  complete animal when implanted and nourished into
  the cytoplasmic environment of an egg of that
  animal.

7
Totipotency of Nuclei from Embryonic Animal Cells
(continued)

• Newt blastomeres develop normally after delayed
  nucleation.
• Nuclei from embryonic cells are still totipotent.
• Nuclei can be transferred by cell fusion.

8
Pluripotency of Nuclei from Differentiated Animal
Cells

• Nuclei from older donor cells show a decreasing
  ability to promote the development of a new
  organism.
• Nuclei from mature cells are unprepared for the
  fast mitotic cycles of early embryos.

9
Pluripotency of Nuclei from Differentiated Animal
Cells (continued)

• At least some differentiated cells contain highly
  pluripotent nuclei.
• Cells change their differentiated state during
  regeneration.
• Cells express different gene at different times.

10
Control of Nuclear Activities by the Cytoplasmic
Environment

• Gene expression changes upon transfer of nuclei
  to new cytoplasmic environments.
• Cell fusion exposes nuclei to new cytoplasmic
  signals.

11
Conclusion and Outlook

• Most cells inherit complete and unaltered set of
  chromosomes.
• Chromosome loss or selective gene amplification
  seem to be exceptions to the rule.
• Loss, alteration or selective amplification of
  genomic DNA are part of normal differentiation.

12
Maintenance of the Differentiated State

• Most differentiated cells remember their
  essential character even in a new environment.
• The differentiated state can be modulated by a
  cellular environment.

13
Tissues with Permanent Cells

• The cells at the center of the lens of the adult
  eyes are remnants of the embryo.
• Most permanent cells renew their parts the
  photoreceptor cells of the retina.

14
Reneval by Simple Duplication

• The liver functions as an interface between the
  digestive tract and the blood.
• Regeneration requires coordinated growth of
  tissue components.
• Endothelial cells line all blood vessels.

15
Reneval by Simple Duplication(Continued)

• New endothelial cells are regenerated by simple
  duplication of existing endothelial cells.
• New capillaries form by sprouting.
• Angiogenesis is controlled by growth factors
  released from the surrounding tissues.

16
Reneval by Stem Cells Epidermis

• Stem cells can divide without limit and give rise
  to differentiated progeny.
• Epidermal stem cells lie in the basal layers.
• Different epidermal cells synthesize a sequence
  of different keratins as they mature.

17
Reneval by Stem Cells Epidermis(Continued)

• Epidermal stem cells are a subset of basal cells.
• Basal cell proliferation is regulated according
  to the thickness of the epidermis.
• Secretory cells in the epidermis are secluded in
  glands that have their own population kinetics.

18
Reneval by Pluripotent Stem Cells Blood Cell
Formation

• There are three main categories of white blood
  cells granulocytes, monocytes and lymphocytes.
• The production of each type of blood cells in the
  bone marrow is individually controlled.
• Bone marrow contains hematopoietic stem cells.
• Pluripotent stem cells gives rise to all blood
  cells.

19
Reneval by Pluripotent Stem Cells Blood Cell
Formation (Continued)

• The number of specialized blood cells is
  amplified by divisions of committed progenitor
  cells.
• The factors that regulate hemopoiesis can be
  analyzed in culture.
• Erythropoiesis depends on the hormone
  erythropoietin.

20
Reneval by Pluripotent Stem Cells Blood Cell
Formation (Continued)

• Multiple CSFs influence the production of
  neutrophils and macrophages.
• Hemopoietic stem cells depend on contract with
  cells expressing the stem cell (steel) factor.
• The behavior of a hemopoietic cell depends partly
  on chance.
• Regulation of cell survival is as important as
  regulation of proliferation.

21
Genesis, Modulation and Regeneration of Skeletal
Muscle

• New skeletal muscle cells form by the fusion of
  myoblasts.
• Muscle cells can vary their properties by
  changing the protein isoforms that they contain.
• Some myoblasts persist as quiescent stem cells in
  adult.

22
Fibroblasts and Their Transformations the
Connective-Tissue Cell Family

• Fibroblasts change their character in response to
  signals in the extracellular matrix.
• The extracellular matrix may influence
  connective-tissue cell differentiation by
  affecting cell shape and attachment.

23
Fibroblasts and Their Transformations the
Connective-Tissue Cell Family (Cont.)

• Different signaling molecules act sequentially to
  regulate production of fat cells.
• Bone is continually remodeled by the cells within
  it.
• Osteoblasts secrete bone metrics, while
  osteoclasts erode it.

24
Fibroblasts and Their Transformations the
Connective-Tissue Cell Family (Cont.)

• During development, cartilage is erode by
  osteoclasts to make way for bone.
• The structure of the body is stabilized by its
  connective-tissue framework and by the selective
  cohesion of cells.