Principles In Animal Development Flashcards
1
Q
How do cells know what to become and
A
- how do cells know where to go
- is this fundamentally the same q?
2
Q
Positional fate mapping
A
Interactions in order to generate an adult plan, as well as progression of developmental shapes
3
Q
Process of cellular “becoming”
A
- Fate and lineage
- commitment (specification and determination) and differentiation
- organelle induction
- positional information, morphine and self-organisation
4
Q
How do cells know where to go?
A
Morphogenesis via cell migration and motility
5
Q
Fate and lineage
A
Label a blastomere and observe
6
Q
Fate
A
What a cell will (or has) become
7
Q
Lineage
A
Where/who a cell ce from
8
Q
Xenopus photoconvertible methodology
A
- inject protein @ zygote stage; integrated into every cell
- UV
9
Q
Lineage tracing
A
- label one cell and follow all descendants to create a Family Tree
- v difficult
- new system of inquiry
- facilitated by intestinal organoid microscopy
10
Q
Specification
A
Reversible
11
Q
Determination
A
Irreversible
12
Q
Differentiation
A
- When specific cells types are formed (e.g. muscle cells, neurons)
- an be inferred from morphology/ T profiles
- often come post-mitotic
13
Q
Committed?
A
- an experimental embryology approach
- do they do in culture what they would in vivo?
- yes: committed
14
Q
Specified/determined
A
- transplant!
- do they do what they would do in vivo in donor?
- yes: determined
- no: specified
15
Q
Induce
A
Change the fate
16
Q
Pattern
A
Generate an organised set of structures
17
Q
Induction
A
- tested using transplanted cells
- eye lens, heart
- the embryonic process in which one group cells, the inducing tissue, directs the development of another group of cells, the responding tissue
- first shown in newts
18
Q
When under the influence of a transplant, are surrounding cells
A
Induced to become something different
19
Q
Investigating induction
A
- interspecies transplants by dissection, under the prospective ectoderm of the blastopore lip in newts
- does the foetus develop finto in host/transplanted tissues?
20
Q
Newts
A
- tissue colour varies by species (light/pigmented)
21
Q
Induction results
A
- 2nd invagination site
- secondary axis with somites, neuronal plates
22
Q
Organisers
A
A region, or a group of cells in an embryo that can both induce, and cause pattern, adjacent embryonic structures
23
Q
Blastopore lip
A
An organiser in amphibian embryos, affects neighbour behaviour
24
Q
Experimental organisation of blatopore lip results in
A
Newts conjoined @ belly
25
Hensen’s node
- avian amniote organiser
- forms from primitive streak?
- analogous to blastopore lip
- grafting from quail embryo to chick host results in new axis induction
26
Pattern formation
The process by which distinct spatial territories are specified in a population of cells in a developing tissue
27
Territories
- defined by different molecular / T identities
- tend to precede morphological change ; embryonic complexity
28
Drosophila territories
Segment gene hierarchy
29
Gap
- broad, overlapping domains
- all happens in the blastoderm, before morphological appearance
30
Positional information
Proposes that cells acquire positional values as in a co-ordinate system, which they interpret by developing specific ways to give rise to spatial patterns
31
Questions regarding positional information
- how is it set up?
- how is it recorded?
- how is it interpreted? Cells read concentrations of a given signal?
32
The French Flag model
- morphogen conc changes by distance from source
- e.g. bcd
- graded signals across a field or cells would be read and interpreted
- adjust according to position in gradient
- size variation doesn’t affect proportions: scalable
33
Morphogens
Signalling molecules that emanate from a restricted tissue region, spreading away from their source to form a conc gradient
34
Fate and morphogens
As the fate of each cell in the field depends on the morphogen concentration, the gradient prefigures developmental patterning ; initial system conditions dependent on
35
Morphogen action
- act upstream
- affect pattern of genes in a concentration-dependent manner
- dynamic domains shift anteriorly over developmental time (unaccounted for by positional information; explains behaviour)
- measurable
36
GRNs
- gene interactions to interpret spatial inputs provided by morphogens, to output concentrations of different genes spatiotemporwlly
- explains why gene don’t overlap
- e.g. bistable switch
37
Changes between interactions have
- shaped evolution
- gap gene pattern changed across time in Diptera
- evolve GRNs for pattern generation; diverse phenotypes
38
Self-organising patterns
- found @ all levels
- not everything is directed by positional info/morphogens
39
In self-organising systems
1) pattern emerges at the global level from local interactions amoung components @ a lower level in the system’s organisation
2) without intervention by external directing influences
- emergent property of system
- can work in combination
40
Reaction-Diffusion model
- two molecular sp.
- diffusion is actively driving the formation of a pattern
- autoactivation, activation and inhibition
- inhibitor diffused faster than
41
Reaction-Diffusion process
- start with a homogeneous by fluctuating field of cells
- little fluctuations are large enough to generate peaks in auto-activation
- pattern propagation w cyclical dynamic
- stripes/dots
- you can get pattern from homogeneity
- you don’t pattern to generate pattern
42
Turing patterns
- changing the interaction parameters: stronger/weaker
- diffusion can be longer/shorter
- generated different patterns (larger/smaller dots; more/less stripes)
- tweaks pattern by tweaking global parameters
43
Turing patterns in nature
- skin cells in lizards
- feathers in birds
44
Combinatorial systems
- tweaking parameters of underlying Turing system to change patterning from same origin
- e.g. 2 fin patterning in dogfish
- e.g.2. Digit patterning in mice
45
Turing models
- produce a “consistent wavelength” controlled by global parameters
- wavelength of system depends on proximal-distal position across fin/limb bud
- increase distal, finger coherence
46
Fin
- only a “Turing space” in the middle
- no digits, just dots
- racpitulated by Sox9
47
Morphogenesis by cell migration and motility
- e.g. neural crest migration in zebrafish
48
Animal cells are motile
- animal embryos rely on cell motility and migration for the generation of form
49
Tissues are patterned
As they develop and grow
50
Pattern formation is an emergent property of
- GRNs (positional info and self-organisation)
- Morphogenesis
- coupled dynamics
51
Diversity can emerge from
The evolutionary tinkering of pattern formation
