Development of Multicellular Organisms I: General Principles of Development Flashcards
What controls development?
gene expression
The genome of all cells in an organism are identical, but what makes us different?
Expression of genes are different.
Cells have “memory”. What is this referring to?
Retain record of signals their ancestors received during embryonic development.
What does the expression of genes by a cell depend on?
Environment, both present and past.
True or False:
Homologous proteins are functionally interchangeable.
True
What is the cells that cohere to form a sheet of epithelial cells facing the external medium known as?
This sheet constitutes the ectoderm.
What is ectoderm a precursor of?
Ectoderm - precursor of nervous system and epidermis.
What structures is endoderm a precursor of?
Endoderm - precursor of gut, lung, and liver.
What is formed when a group of cells move into the space between ectoderm and endoderm?
mesoderm
What structures is mesoderm a precursor of?
Mesoderm - precursor of muscles and connective tissue.
What is gastrulation?
Transformation of a hollow sphere of cells into a structure with a gut.
What is gene duplication?
Higher organisms have several homologs of the same gene.
What term describes higher organisms having several homologs of the same gene?
gene duplication
What are the two classes of proteins that are the most important for development?
- cell adhesion and cell signaling proteins
- gene regulatory proteins (e.g., transcription factors and DNA binding proteins)
Where are the instructions for producing a multicellular animal contained?
Non-coding regulatory DNA associated with each gene.
In development, what contains regulatory elements that serve as binding sites for gene regulatory proteins?
DNA
What does regulatory DNA define for development?
Regulatory DNA defines the sequential program for development.
The coding sequences in DNA are similar in most organisms, but what makes one organism different from another?
Non-coding sequences make one organism different from another and provide uniqueness.
the coding sequences in DNA are similar in most organisms
True or False:
Cells make developmental decisions long before they show any outward signs of differentiation.
True
What does a “determined” cell mean?
Cells that are fated to develop into a specialized cell type despite changes in environment.
Cells that are fated to develop into a specialized cell type despite changes in environment are called?
determined
What does a “completely undetermined” cell mean?
Cells that can change rapidly due to alterations in environment.
Cells that can change rapidly due to alterations in the environment are called?
completely undetermined
What does a “committed” cell mean?
Cells that have some attributes of a particular cell type but can change with environment.
Cells that have some attributes of a particular cell type but can change with environment are called?
committed
True or False:
Before acquiring a particular fate, cells express genes that are markers of their location (e.g., regionally determined).
True
What is the position specific character of a cell called?
positional value
cells retain “memory” of positional value
What does positional value of a cell refer to?
position specific character of a cell
cells retain “memory” of positional value
In cellular differentiation, what allows cells to become different?
asymmetric division (e.g., development of germ cells)
significant sets of molecules distributed unequally between daughter cells
How are significant sets of molecules distributed between daughter cells?
Significant sets of molecules distributed unequally between daughter cells.
How are cells born the same but can become different due to what?
Due to change in environment after birth (different molecules induced).
these molecules then directly or indirectly alter pattern of gene expression between the 2 cells
Cells born the same can become different due to change in environment after birth (different molecules induced). How do these molecules alter pattern of gene expression?
These molecules then directly or indirectly alter pattern of gene expression between the 2 cells.
What is asymmetric division?
Sister cells are born different.
What is symmetric division?
Sister cells become different as result of influences acting on them after their birth.
In inductive signaling, what is the most important environmental cues?
Signals from neighboring cells.
What is inductive signaling?
Induction of a different developmental program in select cells in a homogeneous group leading to altered character.
Induction of a different developmental program in select cells in a homogeneous group leading to altered character is known as what?
inductive signaling
What are the types of signals in inductive signaling?
- Short Range: cell-cell contacts
- Long Range: substances that can diffuse through the extracellular medium
Positive Feedback
- System starts off homogeneous and symmetrical.
- Environment imposes weak asymmetry.
- Positive feedback amplifies effect.
- Broken asymmetry is “all or none” phenomenon.
- Irreversible - once achieved external signal becomes irrelevant.
- Positive feedback provides cells with memory.
What does positive feedback provide cells with?
memory
Look over slide 27.
Asymmetry generated by positive feedback mechanism.
What is a morphogen?
A long range inductive signal that imposes a pattern on a field of cells.
exert graded effects by forming gradients of different concentrations
each concentration can direct the target cells into a different developmental pathway
What is the gradient of morphogens formed by?
(a) localized production of an inducer that diffuses away from its source
(b) localized production of an inhibitor that diffuses away from its source and block the action of a uniformly distributed inducer
What do morphogens need?
‘on’ and ‘off’ system
antagonists or extracellular inhibitors bind to the signal or its receptor and block interaction
What are signaling pathways the ultimate result of?
Ultimate result of inductive events is change in DNA transcription.
In signaling pathways, what does the response depend on?
Spatial and temporal expression of different sets of genes.
What are the proteins in the ligand family that bind to receptor tyrosine kinase (RTK)?
- EGF
- FGF (branchless)
- Ephrins
What are the proteins in the ligand family that signal TGF-beta superfamily?
- TGF-beta
- BMP (Dpp)
- Nodal
What ligand signals the Wnt signaling pathway?
Wnt (wingless)
What ligand signals the Hedgehog signaling pathway?
Hedgehog
What ligand signals the Notch signaling pathway?
Delta
