CELL BIRTH

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CELL BIRTH

• Section 22.1
• Grace Githunguri

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BIRTH OF CELLS

• Cell division
• Stem cells
• Properties
• Tissue maintenance
• Embryonic stem cells
• Cell Fate
• Cell lineage
• C. elegans

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Cell Division

• Symmetric
• The progeny do not change their properties
  (same).
• Differences arise when cells diverge by receiving
  distinct developmental or environmental signals.
• Asymmetric
• Size, shape, and/or composition, or genes may
  differ in their state of activity.
• Internal signals confer different fates on cells.

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Stem cells- properties

• Divides symmetrically
• Produce themselves indefinitely (Self renewing).
• Asymmetric division generates an identical copy
  and a stem cell with restricted capabilities.
• Pluripotent (Multipotent) Generate a number of
  different cell types, but not all e.g. blood
  cells.
• Unipotent Forms a copy of itself
• forms one cell type.

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Stem cells
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Stem cells

• Totipotent generate all the cells types of the
  body e.g Zygote.
• Zygote and neuron-glial cell precursor
• are not stem cells because they are incapable of
  self renewing.

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Embryonic stem cells

• Human Embryonic cells can be grown in Suspension
  Culture and in Solid culture.
• Suspension Culture
• ES cells differentiate into multicellular
  aggregates (embryoid bodies).
• Solid Medium
• They grow into confluent cell sheets with
  differentiated cell types.
• ES can also be induced to differentiate into
  precursors for various types of blood cells.

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Embryonic stem cells cont

• Treatment of Parkinsons disease
• Culture grown neurons that produce dopamine.
• Other conditions like Alzheimers disease.

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Stem cells

• Differentiated cells have a shorter life span
  than that of an organism.
• They are replenished from nearby stem cell
  populations.
• Skin epidermis
• Underlain by a layer of stem cells that give rise
  to more layers and keratinocytes.
• Epithelial lining of the small intestine.
• Regenerated from deep intestinal wall in pits
  called crypts.
• Plant stem cells
• Persist for life in the meristem.

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Stem cells

• Production of new cells is controlled.
• By specific signals e.g ?-catenin
• Overproduction leads to excess proliferation of
  the intestinal lining.
• Links certain cell-cell junctions to the
  cytoskeleton
• Signal transducer in the Wnt pathway.
• Moves cells from epidermis to hair cell fates.

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Cell Fate.

• Restricted during development.
• Gastrulation form germ layers
• Ectoderm
• Mesoderm
• Endoderm
• cell populations with different fates.
• Germ line
• Stem cells and precursor cells that give rise to
  eggs and sperm.
• They have reduced number of replications.

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Cell lineage

• Are identical in all individual of a species
  because Cell are under tight genetic control.
• Signals can direct identical cells to different
  fates.
• C. elegans produce six different founder cells.

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Cell lineage

• Genetic control of cell linage come from
  heterochronic mutants.
• Too early (precocious development)
• Too late (retarded development).
• Too early e.g C. elegans
• Mutation of lin-14 leads to premature formation
  of PDNB neuroblast.
• Prevent L2-type cell division.
• lin-14 and lin-7 are micro RNAs that serves as
  timers of gene expressions.
• Control translation of mRNAs by hybridizing them.

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Summary

• Plant stem cells
• Persist for life in the meristem.
• During development
• precursor cells are restricted in number of cell
  type they form.
• Animal development
• Germ layers- Ectoderm, Mesoderm and Endoderm
• Germ line- eggs or sperm
• C.elegans
• Asymmetric division of zygote
• Short regulatory RNAs
• Control timing of developmental division.

• Cell Divide
• Symmetrically
• Asymmetrically
• Pluripotent stem cells
• More than one type of cells
• Cultured Embryonic stem cells
• Differentiated cell types
• Population of stem cells
• Regenerate tissue cells
• Stem cells
• Are controlled from differentiating by specific
  signals.