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CELL BIRTH
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
Section 22.1
Grace Githunguri
BIRTH OF CELLS
Cell division
 Stem cells

 Properties
 Tissue
maintenance
Embryonic stem cells
 Cell Fate
 Cell lineage

 C.
elegans
Cell Division

Symmetric
The progeny do not change their properties (same).
 Differences arise when cells diverge by receiving
distinct developmental or environmental signals.
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
Asymmetric


Size, shape, and/or composition, or genes may differ
in their state of activity.
Internal signals confer different fates on cells.
Stem cells- properties
Divides symmetrically
 Produce themselves indefinitely (Self
renewing).
2. Asymmetric division generates an identical
copy and a stem cell with restricted
capabilities.
1.


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.
Stem cells
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.
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.
Embryonic stem cells cont…

Treatment of
Parkinson’s
disease


Culture grown
neurons that
produce
dopamine.
Other conditions
like Alzheimer’s
disease.
Stem cells


Differentiated cells have a shorter life span than that of
an organism.
They are replenished from nearby stem cell populations.

Skin – epidermis


Epithelial lining of the small intestine.


Underlain by a layer of stem cells that give rise to more layers and
keratinocytes.
Regenerated from deep intestinal wall in pits called crypts.
Plant stem cells
 Persist for life in the meristem.
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.

Cell Fate.
Restricted during development.
1.
Gastrulation form germ
layers;
Ectoderm
 Mesoderm
 Endoderm
cell populations with
different fates.


2.
Germ line


Stem cells and precursor
cells that give rise to eggs
and sperm.
They have reduced number
of replications.
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.
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.
Summary

Cell Divide
 Symmetrically
 Asymmetrically

Pluripotent stem cells
 More than one type of cells

Cultured Embryonic stem cells




Stem cells

Are controlled from
differentiating by specific
signals.
Persist for life in the meristem.
During development

Differentiated cell types
Regenerate tissue cells
Plant stem cells

precursor cells are restricted
in number of cell type they
form.
Animal development

Germ layers- Ectoderm,
Mesoderm and Endoderm
Population of stem cells



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C.elegans
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Germ line- eggs or sperm
Asymmetric division of zygote
Short regulatory RNAs

Control timing of
developmental division.