Mechanisms of Development Flashcards
What are the two different ways in which cytoplasmic components may separate during cell division?
Asymmetrically and symmetrically.
Describe how pre-implantation genetic diagnosis (PGD) works?
One cell is removed for genotyping, if it is normal then the rest of the embryo is transferred to the uterus for normal development.
At what stage does compaction occur?
8 cell stage, transforms us from behaving like single-celled organisms to metazoan.
What follows compaction?
The first differentiation event - cells on the surface of the embryo become TROPHECTODERM CELLS, a form of epithelium.
What does compaction lead to the fomation of?
The blastocyst, which is what implants into the wall of the uterus.
What is a blastocyst made up of?
Trophectodermal cells and the inner cell mass.
What do trophectodermal cells eventually become?
The placenta.
What does the inner cell mass become?
The growing child.
Compaction involves cell adhesion. Which CAM is necessary for this?
E-cadherin.
How does E-cadherin bind cells together?
E-cadherin on one cell binds to e-cadherin on another - these are trans-membrane proteins and exist across the cell membrane.
What does e-cadherin bind to inside cells?
E-cadherin binds to beta-catenin inside cells.
What are the two roles of beta-catenin within cells?
Beta-catenin binds to the actin cytoskeleton (aids cell structure and polarisation).
Beta-catenin is a part of a signalling pathway; binds to TCF/LEF and this complex acts as a transcription factor, regulates gene expression.
Name the three ways in which signals are passed between cells.
Diffusion through the inter-cellular space.
Direct cell-cell contact.
Passage through inter-cellular junctions.
Signals from one cell can induce changes in adjacent cell populations - for example, how is this useful in C.elegans?
The Anchor cell instructs a program of development in the underlying vulval cells in C. elegans.
Describe how vulval development occurs in C. elegans.
Anchor cell (Ac) expresses LIN-3. LIN-3 induces vulval precursor cells (VPCs) at close range, which adopt 1/2/3 degree fates. VPC closest to anchor cells signals to 2 degree cells instructing them NOT to generate the CENTRAL VULVAL LINEAGES - lateral inhibition. Only VPCs in a position to recieve info will become vulval cells (1 and 2) - 6 VPCs.
What determines if a cell will respond to signalling?
Molecular composition.
Define competence.
An actively acquired condition which may change over time - it is NOT a passive state within the cell.
Give an example of a gene that acts as a ‘master’ competence factor.
Pax6 - mutations in Pax6 cause aniridia (partial or complete loss of the iris).
What does over expression of eyeless (or the human orthologue Pax6) result in?
Ectopic eyes that are morphologically normal.
What is Pax6, essentially?
A transcription factor that changes patterns of gene expression, providing the conditions for cells to respond to various inducers of eye morphogenesis.
What is the term used to describe the facets found in compound fly eyes?
Ommatidia
What does a stereotypical facet within a fly eye consist of?
Core of 8 photoreceptor cells (R1-R8) 4 cone cells Pigment cells 1 sensory bristle The number of cells/their identities/functions within each ommatidia is invariant.
Which cell is responsible for the series of inductive steps used to specify the cells of the ommatidium?
The R8 cell.
How do the cells R1-7 become specified within the ommatidium, in relation to R8?
R7 - cell-cell contact with R8.
R1-R6 - diffusable signals from R8.
Which signal is LIN-3 from C. elegans evolutionarily related to in Drosophila?
Evolutionarily related to Boss - both encode proteins related to mammalian epidermal growth factor (EGF).
How does cell-cell signalling influence patterning within C.elegans eyes?
R8 cell prevents its neighbours from becoming R8 cells by secreting an inhibitory molecule, limiting R8 cell fate to one cell - LATERAL INHIBITION.
Where does ommatidia formation start?
In the morphogenetic furrow. Behind this, cells differentiate to become regularly spaced ommatidia.
What does the ‘French Flag Model’ of cell positioning suggest?
Explains how identical cells can adopt a pattern irrespective of how many there are. Relies upon ability of diffusible substances to induce different EFFECTS at different CONCENTRATIONS.
What type of molecule provides positional information?
Morphogens
What must a substance be capable of to be classed as a morphogen?
Capable of directly activating cells at a DISTANCE, and must produce CONCENTRATION-DEPENDENT responses in receptive cells.
Define INDUCTION.
Instructive cell interaction between adjacent cell populations (often in contact, usually produces a few responses).
Define COMPETENCE.
Ability to respond to a specific inductive signal.
Why is LATERAL INHIBITION important in development?
Can give rise to spacing patterns when cells produce an inhibitor that prevents formation of similar structures in area adjacent to them.
Why are SPATIAL SIGNALS important in development?
Act over a LONG SPATIAL RANGE, inducer/responder aren’t always in contact, effect of inducer depends on its concentration.
What accounts for the diversity of different cell types?
Not all genes expressed in every cell - subsets of genes that are expressed (RNA/protein) will differ, subset expressed confers unique properties to the cell.
How many protein coding genes are there in the human genome?
23,000
How does regulation of gene expression control heterogeneity?
Determines which genes are expressed where, when and at what level - they in turn determine cell function.
What can lead to ‘hidden’ diversity in proteins?
Alternative splicing - can generate many different isoforms, creating a large potential for heterogeneity.
Is it exons or introns that encode proteins?
Exons; introns are removed in the primary transcript.
How many different isoforms can a single gene make?
Up to 28,016 (minor differences)
What is responsible for transcriptional regulation?
DNA-binding proteins - bind DNA in sequence specific manner, act as transcriptional activators and repressors.
What are enhancer elements required for?
Gene expression.
What are enhancer elements bound by?
Bound by more than one transcription factor.
Why is a single transcription factor able to induce expression of many genes?
Many (often functionally related genes) share the same REGULATORY SEQUENCES.
What are homeotic gene?
Master control genes that confer identity to individual segments of an organism.
