Cell Differentiation Flashcards
1
Q
how cell development occurs
A
- all cells contain the same genes
- “genes are not gained or lost in the normal course of development”
- rather their expression is controlled
- Different cell types express different sets of proteins (differentiation)
2
Q
development
A
- In multi-cellular organisms, life begins as a single cell.
- With few exceptions, somatic cells contain the same genetic information as the zygote.
- In development, cells commit to specific fates & differentially express subsets of genes.
- Cells identify and respond to their position in developmental fields.
- Daughter cells may differ with respect to regulatory instructions and developmental fate.
3
Q
cell differentiation –> specialisation
A
- A cell changes or differentiates to carry out specialised functions
- Often marked by a change in cell appearance – morphology
- Differentiated cells produce specific proteins
- Differentiation is usually preceded by rapid proliferation
- Differentiation is a DNA-orchestrated set of cellular changes that normally occurs without error*
- Differential gene expression from the same nuclear repertoire
- Accomplished by regulation of gene expression at several levels
(phenotype: physical appearance of the cell)
4
Q
cells, tissues & organs
A
- Cell fate and differentiation are patterned in space (special)
- Also involves the intricate patterning & timing (temporal) of cell proliferation (temporal)
- Activation of cell division in some regions
- Imposition of cell cycle arrest in others ∴ controlled in a spatio-temporal manner
- The cell cycle, its control & checkpoints are of major importance in differentiation & development
- Cells not only have to proliferate & differentiate
- Sort into different tissues
- Segregate within tissues to form compartment boundaries
5
Q
cell asymmetry
A
Early Mammalian Development
- Symmetric division yields identical daughter cells that may have different fates if exposed to different external signals.
- Asymmetric cell division yields two different types of daughter cells with different fates.
- Mammalian embryo initial divisions yield equivalent totipotent cells;
- subsequent divisions give rise to the blastocyst inner cell mass and surrounding trophectoderm as the first differentiation event.
6
Q
building the embryo
A
Developmental decisions:
o made at specific times during development
o many are binary (yes/no), e.g., male or female
o most are irreversible
o many involve groups of cells rather than single cells
In animals decisions are made to:
o establish anterior-posterior and dorsal-ventral axes
o subdivide anterior-posterior axis into segments
o subdivide dorsal-ventral axis into germ layers
o produce various tissues and organs
- Most decisions involve changes in transcription
7
Q
developmental strategy
A
- Mother deposits material (mRNA and protein) that creates asymmetries - set up gradients that broadly define areas (basic body plan map!)
- Gene interaction subdivides these areas (cells differentiate)
- These identities are remembered
8
Q
features of cell polarity and asymmetric cell division (Common hierarchy of steps in generating a polarized cell before cell division)
A
- Cells exposed to a spatial cue – soluble signals from other cells/ECM
- Closest cell receptors bind extracellular signaling molecules
- Cell receptors locally activate an intracellular signaling pathway.
- Signaling pathway directs organization/orientation of the cytoskeleton (microtubules and/or microfilaments, depending on the system).
- Polarized cytoskeleton transports membrane-trafficking organelles and macromolecular complexes including fate and polarity determinants to one end of cell.
- Polarity –
o Reinforced by return of polarity determinants that have moved away from the site of concentration
o May involve endocytosis of membrane proteins and transport back to polarity site
(b) Cell polarity determinants – mRNAs, proteins, and lipids:
o Asymmetrically localized in mother cell
o Mitotic spindle – positioned so that polarity determinants are segregated differentially into daughter cells during cell division
9
Q
role of cytoskeleton in development
A
- Consists of highly organized rods and fibers
o microfilaments (actin)
o intermediate filaments
o microtubules - Such structures are polar, with distinct “+” and “–” ends
- Serve as highway system for intracellular transport
- Asymmetry of cytoskeletal elements plays fundamental roles
o directed transport of molecules - Cytoskeletal components give directional information - through orientation of filaments
- Multiple independent trafficking system … different cell components moved
10
Q
tissue identity
A
- Gradients of differentiation factors define a coordinated system for the entire embryonic body, then axial subunits such as limb buds
o Axial orientation (head /tail & anterior/posterior)
o Homeo-box genes (patterning)
o Dorso-ventral identity
11
Q
differentiation
A
The development of specialised cells/tissues recognised morphologically
- differentiated cells produce specific proteins
- all genes of the genome are present in every cell BUT only a small specific number are expressed (switched on) in each cell type
12
Q
the body plan
A
- The spatial pattern of tissues and body parts is influenced by:
o program of gene expression that specifies the pattern of the body
o local cell interactions that induce different parts of the program - The basic body plan of all animals is very similar
o preserves commonalities of molecular and cellular mechanisms controlling development - Structures during embryonic development very similar across species
13
Q
patterning genes
A
- Encode proteins that:
o Control expression of other genes (transcription factors bind to DNA)
o Cell adhesions molecules
o Signalling molecules, morphogens & more protein kinases - All expressed in a spatio-temporal manner that permits the integration and coordination of events in the developing embryo
- The precise timing of events is maintained by one group of cells inducing differentiation in a second group
- Mediated by:
o Direct cell-cell contact
o Soluble factors released by cells (morphogens)
14
Q
regulation of gene patterning
A
morphogen = a chemical agent able to cause or determine morphogenesis
- “genes are not gained or lost in the normal course of development”
- Therefore: Developmentally regulated and tissue specific gene expression must be very well regulated to enable differential gene expression in the right place at the right time.
15
Q
differentiation, division and new cell types
A
- Different cells have varying abilities to divide or differentiate.
- Cells in the embryo proliferate rapidly before differentiating
- Some adult tissues contain cells with a similar capacity to proliferate and regenerate tissue. These are called somatic stem cells.
- Most adult cells have a limited capacity to divide because they lack telomerase activity.
- Telomeres shorten with cell division
- Embryonic (& tumour cells) express telomerase
