Basic Developmental Mechanisms and Principles Flashcards
Mechanisms of Developmental Patterning
Lacks Commitment
- Specification
- Determination
- Differentiation
This means that a cell can give rise to several different cell types
Pluripotent
Fate of cell/tissue is _______ when it is capable of differentiating autonomously when placed in a neutral environment
specified
The process of specification is (reversible, irreversible) if determined
irreversible
Modes of Specification
- Autonomous (mosaic)
- Conditional (regulative)
- Syncytial
Describe autonomous (mosaic) mode of specification
- morphogenetic determinants in the egg cytoplasm specify cell type
cells develop only according to early fate e.g. Tunicates, invertebrates
Principle
Depend on agents = transcription factors being locally placed in the egg by the mother.
Signaling molecules that control tissues development by diffusing from a source and creating a concentration gradient
Morphogens
mRNA for muscle development
Macho mRNA
Describe conditional (regulative) mode of specification
The fate of a cell depends on interaction with neighboring cells
The fate of cells depends on context. e.g. Vertebrates
If cells are removed from the embryo, the remaining cells can compensate for the missing part.
Principle
Depends in part on signals of positional information that trigger changes in cell identity in nearby neighbors
Describe syncytial mode of specification
Cell fate depends on exposure to cytoplasmic gradients of signaling molecules within a shared cytoplasm.
Interactions occur not between cells but between parts of one cell. Nuclei divide within the egg cytoplasm.
Morphogen
- Cytoplasmic proteins (TFs)
- Signaling molecules
- Form concentrated gradient (determinant)
- Provide positional information (TFs)
- Induce unique transcriptional responses
Both autonomous and conditional specification are at work during the embryo specification and development
tunicates - starts with mosaic
vertebrates - starts with conditional
plant - mosaic then conditional
> then adopts the other
Bicoid (anterior, posterior); Nanos (anterior, posterior)
Anterior; posterior
Mechanisms of Cell Differentiation [postulates]
- Genomic equivalence - DNA of all the differentiated somatic cells is identical
- RNA is specific for each cell
- only a small percentage of the genome is expressed in each cell. - Genes retain the potential to be expressed
- non-expressed genes in different cells are neither destroyed nor mutated
DNA methylation result
Turn off gene
DNA acetylation result
Turn on gene = exposes DNA, more accessible
Process leading to the formation of ordered form
is the construction of organized form
Morphogenesis
Local and long range mode cell-cell communication
a. Juxtacrine signaling = Local Mode
b. Paracrine signaling = Long-Range Mode
Cell to Cell Communication
- prerequisite for differentiation of development
- tightly regulated
- may be short-range or long-range
- occurs via direct contact or chemical signaling
four ways cells communicate through physical interaction (direct contact)
- [Connexin forming] Gap junctions (protein channels)
- Tunneling nanotubules (TNT - ex. microglial cells)
- Cell adhesion Molecules (CAM)
- Plasmodesmata
Transmembrane proteins that help cells bind to each other or to the extracellular matrix (ECM)
also provide an example
Cell adhesion molecules
Cadherins
Developing cells receive signals & in turn, signal the adjacent cells around them
Cell develop in the context of their environment.
Cell signaling
Mechanisms of cell signaling
- Gene expression
- Enzyme activities
- Protein-protein interactions
- Protein localization
Cell’s response to cell signaling
- divide or stop dividing
- differentiates
- cell death (apoptosis) or kills something phagocytoze
- moves somewhere or stops moving
- alter metabolism
- passes on the signal
Principle - Embryonic Induction
- Neighbors influence the development of cells
- Group of cells/tissues directs the development of another group of cells
Primary inductor in embryo
Notochord
Induction and Competence
- competent enough to respond to the signal
inducer and target/responder
refers to the process by which signaling molecules (paracrine factors) secreted by one cell diffuse over a short distance to affect the behavior of neighboring cells. This is essential in development, tissue repair, and cellular communication.
Paracrine induction
4 Major Paracrine Factors
- Fibroblast Growth Factor (FGF) Family
- Hedgehog Family
- Wnt Family
- Transforming Growth Factor-Beta (TGF-β) Superfamily (BMPs, Nodal protein, Vg1 family)
head cap-forming region in drosophila
Acron
Germ line in drosophila arise from
pole cells
Tail-forming region in drosophila
Telson
1) each region has a distinct Bicoid:Nanos ratio
2) Bicoid:Nanos determines anterior posterior identity
4 Ways Cell to Cell Communication
Direct contact
Paracrine signaling
Endocrine signaling
Synaptic signaling
§ Transmembrane proteins
§Important in tissue morphogenesis & homeostasis
Cadherins
Weak cadherin activity + α-catenin = Strong cadherin activity
Strong cadherin activity - α-catenin = Weak cadherin activity
Signaling pathway
Signal
Receptor
Transduction cascade
Output (change in cell behavior)
Which paracrine factor?
§ over 12 structurally related members
§ generate hundreds of protein isoforms
§ activate set of receptor tyrosine kinases (RTK)
FGF Family
Which paracrine factor?
§ Constitute PFs used by embryo to induce particular cell types
§ shh (notochord)
§ dhh (Sertoli cells)
§ ihh (gut and cartilage)
Hedgehog Family
Which paracrine factor?
§ cysteine-rich glycoproteins
§ name is from Drosophila polarity segment gene wingless
§ establish polarity of limbs
WNT Family
Which paracrine factor?
§ over 30 members
§ regulate cell division and formation of the extracellular matrix
TGF-β Superfamily
