Download 4Fertilization, cell proliferation and differentiation

Fertilization, cell proliferation and
differentiation
www.sciencepicturecompany.com Molecular Cell Gene-cs 416451 Mingkwan Nipitwa6anaphon fertilization
•  Fusion of 2 haploid gametes to become diploid
zygote
–  Internal fertilization
–  External fertilization
•  Involved in many signaling process and cell division
•  In animals, there must be mechanisms to prevent
polyspermy
–  in mammals, the "cortical reaction" modifies the
extracellular coat of the egg (the zona pellucida), and
additional mechanisms modify the egg's plasma
membrane
fertilization
•  When the sperm bind to the egg before
fertilization, the egg become metabolically
active
–  Lots of transcription, translation and protein
synthesis
•  The fusion of the sperm to the egg continues
the meiotic process resulting in the releasing
of polar nuclei
fertilization
en.wikipedia.org fertilization
Click to see
fertilization video link
http://www.youtube.com/watch?v=BFrVmDgh4v4 h6p://humanphysiology2011.wikispaces.com/ fertilization
Proliferation
•  Cleavage - Rapid cell division
•  Gastrulation - Cell movements and 3 layers form
–  Ectoderm
–  Mesoderm
–  Endoderm
•  Organogenesis
–  Pattern formation
–  Cell differentiation
•  Endoderm -> digestive tract
•  Mesoderm -> support tissues, e.g. skeleton, muscle, connective tissues,
blood, urogential system
•  Endoderm - > epidermis, nervous system
www.stemcure.com Differentiation
•  A process by which individual cells
become specialized and distinct from other
groups of cells
•  Change in cell’s size, shape, membrane
potential, metabolic activity,
responsiveness to signals
•  Differentiation occurs at various stage of
development but mostly after fertilization
Different ways of differentiation
Determination & differentiation
•  Determination = the process of
establishing which genes will be expressed
and which will not.
•  Cells progressively lose their genetic
capacity (genes, or chromosomes) during
the development à cells become
determined?
•  In fact, determination is regulated by gene
expression
Control of gene activity
•  RNA level
–  Transcription regulation
–  RNA processing
–  RNA transport
–  Selection of mRNA for translation
–  mRNA degradation
•  Protein level
–  Translational control
–  Protein modification
–  Protein degradation
mRNA processing
apbio-­‐werle.wikispaces.com mRNA degradation
Specialized cells in different tissues
have large amount of certain mRNAs
Fraction No. Of different
mRNAs Copies per cell % of total
mRNAs Oviduct
I
1
100,000 50 II 8 3,750 15 III 14,000 5
35 1 32,800 16 II 106 750 40 III 11,600 7 44 Liver
I
Fraction I = highly abundant
Fraction II = moderately abundant
Fraction III = rare Cell potency
•  Developmental potency = ability of cell to
develop into different cell types
–  Unipotency
–  pluripotency
–  totipotency
h6p://163.16.28.248/bio/ac-velearner/16/ch16c4.html Pluripotency: stem cells can differentiate into many blood
cell types
Regeneration
•  A process of renewal, restora-on, and growth to repair the damage or maintain physiological and morphological stages •  Regulated by a sexual cellular process snowbio.wikispaces.com psi.wikia.com www.tutorvista.com Pattern formation
•  Cells need to know what they are and
what they do
•  A local group of cells organize into a
pattern of different cell types
–  Need communication between cells by
chemical signal
–  The signal can vary in concentrations
(gradient) resulting in different fate of cells
morphogen
•  A special type of chemical signal that
specifies development of particular pattern
•  There is a threshold of the morphogen
–  Reach the threshold -> cell become
determined -> differentiate
Pattern formation
Pattern formation
Pattern
formation
h6p://plantdev.bio.wzw.tum.de/index.php?id=58 Mutation of the homeobox (transcriptional factor) result in
developmental abnormality: antenapedia (fly that have legs
where the antena should be
Eyeless is a transcription factor
eyeless mutant has no eye while overexpression of this gene results in
developing eyes at the legs www.gehring.biozentrum.unibas.ch www.scienceforums.net Dedifferentiation
•  A cellular process that differentiated cells reverts to the earlier
developmental stage
–  Ex. worms and amphibians in which a partially or terminally differentiated
cell reverts to an earlier developmental stage, usually as part of
a regenerative process. Dedifferentiation also occurs in plants.
•  Cells in cell culture can lose properties they originally had, such as
protein expression, or change shape. This process is also termed
dedifferentiation.
•  Some believe dedifferentiation is an aberration of the normal
development cycle that results in cancer, whereas others believe it to
be a natural part of the immune response lost by humans at some
point as a result of evolution.
•  A small molecule dubbed reversine, a purine analog, has been
discovered that has proven to induce dedifferentiation in myotubes.
These dedifferentiated cells could then redifferentiate
into osteoblasts and adipocytes.
Terminal differentiation
•  Cells specilized
•  Post mitotic (stop dividing) -> die
•  Sometimes cell dead is a part of
differentiation, e.g. Progressive
keratinization of skin cell, progressive
lignification of xylogenic cells