CELL DIFFERENTIATION.pdf a ppt on cell differentiation

A ppt on cell differentiation

1. 6. Cell Differentiation

2. Fertilization
Adult
8 cell stage Zygote
Embryo

3. CellDifferentiation
❑Asinglecell,thefertilizedegg,givesrisetohundredsofdifferentcell
types;
musclecells,epidermalcells,neurons,lenscells,lymphocytes,blood
cells,fatcellsetc.
Thisgenerationofcellulardiversityiscalleddifferentiation.
❖Do every cell of the body contains the same set of genes?
❖How can this identical set of genetic instructions produce different
types of cells?
❖How can a single fertilized egg cell generate so many different cell
types?

4. Undifferentiated cells
Cell maturation
Cell Differentiation
Committed
to a Specific
cell lineage
Gene
expression
Cell fate
Determination
Cell Fate
Cell
Specification
Cell
Commitment
Cell
Differentiation
Cell
Determination
Cell Potency

6. It is the diversity of cell
types that a single cell can
become during Normal
development in an organism
Cell Fate
Cell
Commitment
Process of Deciding
the Fate of a cell
Cell
Specification
Cell
Determination
Process by which a cell
chooses any of the
specific development
pathway
The first stage of commitment
of cell or tissue fate
Varying ability of stem cells
to differentiate into
specialized cell types
Cell Potency

7. Cell differentiation is the process by which a cell
acquires the structural and functional properties
unique to a given cell type.
Cell differentiation
❖From an undifferentiated cell to a post-mitotic differentiated
cell type, a cell goes through a process of maturation
that experiences different levels of commitment
toward its end fate.
❖A cell is first specified toward a given fate, suggesting
that it would develop into this cell type even in isolation.
❖A cell is committed or determined to a given fate if it
maintains its developmental maturation toward this cell
type even when placed in a new environment.

8. ❑The process generation of specialized cell types during which
❖A cell ceases to divide,
❖Develops specialized structural elementsand
❖Distinct functional properties.
Undifferentiated
Cell
❖Fate determined
❖Committed
❖Specified
❖Differentiated
Cell type
Differentiation
Commitment Stages
Undifferentiated Differentiated
SpecificationDetermination

9. Commitment
Specification
The fate of a cell or tissue is said
to be specified when it is capable
of differentiating autonomously
(i.e., by itself) when placed in an
environment that is neutral with
respect to the developmental
pathway, such as in a petridish or
test tube.
A cell or tissue is said to be
determined when it is capable of
differentiating autonomously even
when placed into another region of
the embryo or a cluster of differently
specified cells in a petridish.
Determination
1 2
❖Capable of differentiating
autonomously when placed in a
neutral environment;
❖not when placed in non-neutral
environment
❖Capable of differentiating
autonomously even when placed
into another embryonic regionor a
cluster of differently specified cells
in a petri dish

10. Levels of differentiation
Undifferentiated
cell
❖Fate determined
❖Committed
❖Differentiated
cell type
Differentiation
Commitment Stages
Undifferentiated
Differentiated
SpecificationDetermination

11. Commitment
Labile (fate reversible)
Irreversible (fate irreversible)
Labile
Irreversible
Cell Fate deciding stage
Specification
Determination

12. Autonomous specification
❖Characteristic of mostinvertebrates (molluscs, annelids,and
tunicates).
❖Specification by differential acquisition of certain cytoplasmic
molecules present in theegg such as Morphogenetic determinants.
❖Invariant cleavages produce the same lineages in each embryo of
the species.
❖Blastomerefates are generallyinvariant.
❖Cell type specification precedes any large-scale embryonic cell
migration.
❖Produces “Mosaic” development: cells cannot change fate if a
blastomere islost.
.
In the absence of particular blastomeres, the
larva lacked just those structures normally
formed by those cells.

13. ❑if a particular blastomereis removedfromanembryoearlyinits
development,thatisolated blastomerewillproducethesametypesof
cells thatitwould have made if it were still part of the embryo.
❑Moreover, the embryo from which thatblastomereis taken will lack
those cells (and only those cells) that would have beenproducedby
themissingblastomere.
Whittakerremoved these two
cells and placed them in isolation,
they produced muscletissue

14. Conditionalspecification
❖Characteristic of all vertebrates and fewinvertebrates.
❖Specification by interactions between cells.
❖Relative positions of blastomeres areimportant.
❖Variable cleavages produce noinvariant fate assignments
to cells.
❖Massive cell rearrangements and migrations precede or
accompany specification.
❖Capacityfor“regulative”development:allowscells to
acquiredifferentfunctions.

15. ❖Ifablastomereisremoved fromanearlyembryothatuses
conditionalspecification,the remainingembryoniccellsaltertheir
fatessothattherolesof themissingcellscanbetakenover.
❖Theabilityofembryonic cellstochangetheirfatestocompensate
forthemissingparts is called regulation ( Regulative development)
❖Criticalinthedevelopmentofidenticaltwins.
❖Intheformationofsuchtwins the cleavage-stage
cells of a single embryo divide into two groups,
andeachgroupof cells producesafullydeveloped
individual

16. Conditional specification.
(A)What a cell becomes depends upon its
position in the embryo. Its fate is
determined by interactions with
neighboringcells.
(B) If cells are removed from the embryo,the
remainingcellscanregulate and
compensate for the missingpart.

17. Syncytialspecification
❖Characteristic of most insectclasses.
❖Specification of body regions by interactions between
cytoplasmicregions prior to cellularizationof the
blastoderm.
❖Variable cleavage produces no rigid cell fates for
particular nuclei.
❖After cellularization, conditional specification is
most oftenseen.

18. ❖Interactions occurnotbetweencells,
butbetweenpartsofonecell.
❖Inearly embryosoftheseinsects,cell
divisionisnotcomplete.
❖Thenucleidividewithintheegg
cytoplasm,creatingmanynucleiwithin
onelargeeggcell.
❖Acytoplasmthatcontainsmany nuclei
is called a syncytium.

19. ❖The first evidence for genomic equivalence came from
embryologists studying the regeneration of excised tissues.
removal of the neural retina promotes
❖regeneration from the pigmented retina, and if the lens is
removed, a new lens can be formed from the cells of the dorsal
iris. The regeneration of lens tissue from the iris (called
Wolffianregeneration)
❖The formation of the lens by the differentiated cells of the
iris is an example of metaplasia(or transdifferentiation),
Genomic equivalence in cell and nuclei

20. Evidence that every cell in the body has the same genome originally
came from the analysis of Drosophila chromosomes, in which the DNA
of certain larval tissues undergoes numerous rounds of DNA replication
without separation such that the structure of the chromosomes can be
seen. In these Polytenechromosomes, no structural differences were
seen between cells; however, different regions of the chromosomes were
“puffed up” at different times and in different cell types, which
suggested that these areas were actively making RNA
Polytenechromosomes

21. Each cell's nucleus is identical to the zygote
nucleus, then each
Cell's nucleus should be totipotent(capable
of directing the entire development of the
organism) when transplanted into an activated
enucleated egg.
(1)A method for enucleating host eggs
without destroying them;
(2) a method for isolating intact
Donor nuclei;
(3) a method for transferring such nuclei into
the host egg without damaging
Either the nucleus or the oocyte.
Amphibian cloning:
The restriction of nuclear potency

22. ❖Cells from the mammary gland of an adult (6-year-old) pregnant ewe
and put them into culture.
❖The culture medium was formulated to keep the nuclei in these cells at
the resting stage of the cell cycle (g0).
❖They then obtained oocytes(the maturing egg cell) from a different
strain of sheep and removed their nuclei.
❖The fusion of the donor cell and the enucleated oocytewas
accomplished by bringing the two cells together and sending electrical
pulses through them.
❖The electric pulses destabilized the cell membranes, allowing the cells
to fuse together.
❖Moreover, the same pulses that fused the cells activated the egg to
begin development.
❖The resulting embryos were eventually transferred into the uteri of
pregnant sheep.
Cloning mammals

24. Totipotencyis the ability of a
singlecellto divide and
produce all of the
differentiated cells in
anorganism.
Able to differentiate into
anyembryoniccell, as well as
extraembryoniccells
Eg. Sporesandzygotes
Totipotency
Cell potency

25. Pluripotencyrefers to a stem cell that has the potential
todifferentiateinto any of the threegerm layers:
Endoderm(interior stomach lining, gastrointestinal tract, the
lungs),
Mesoderm(muscle, bone, blood, urogenital),
Ectoderm (epidermal tissues and nervous system),
but not into extra-embryonic tissues like the placenta.
Pluripotency

26. ❖Human development begins when
aspermfertilizes an egg and the
resulting zygote.
❖After reaching a 16-cell stage, the
totipotentcells of
themoruladifferentiate into cells
that will eventually become either
theblastocyst'sinner cell massand
the outertrophoblasts.
❖Four days after fertilization and
after several cycles of cell division,
these totipotentcells begin to
specialize.
❖The inner cell mass, the source
ofembryonic stem cells, becomes
pluripotent.

27. Multipotencydescribesprogenitor
cellswhich have the gene activation
potential to differentiate into discrete cell
types.
Eg. a multipotentbloodstem cell and this
cell type can differentiate itself into several
types of blood cell
likelymphocytes,monocytes,neutrophils,
etc.
Multipotency

29. A unipotentcell is the concept that one stem cell has the
capacity to differentiate into only one cell type.
A close synonym forunipotentcellisprecursor cell.
It is currently unclear if true unipotent stem cells exist.
Hepatoblasts, which differentiate intohepatocytes(which
constitute most of theliver) orcholangiocytes(epithelial cells
of the bile duct), are bipotent.
Unipotentand Bipotent

31. Dedifferentiation
Epimorphosis.
In some species, adult structures can undergo
dedifferentiationto form a relatively undifferentiated mass
of cells(a blastema) that then redifferentiatesto form the new
structure.
Such regeneration is characteristic of regenerating amphibian
limbs.

33. Hormones and Differentiation
srygene present in the short
arm of the Y chromosome
produces SRY proteins
SRY proteins responsible
for the development of
bipotentialgonads into
testes
Testes produces two hormones
1.Testosterone
2.Antimullerianhormone