Developmental biology Flashcards
(100 cards)
1
Q
What does developmental biology integrate?
A
Molecular and cellular biology, genetics and morphology/embryology.
2
Q
What does development involve?
A
Cell division, emergence of pattern, morphogenesis, growth, progressive cell commitment.
3
Q
What can cleavage division do?
A
Can set up asymmetries by segregating determinants.
4
Q
What is pattern formation?
A
The process by which a spatial and temporal pattern of cellular activities is organised within the embryo so that a well-ordered structure develops.
5
Q
What is an important early step in pattern formation?
A
Allocation to different germ layers.
6
Q
What are the different germ layers?
A
Endoderm (gut, liver, lungs), mesoderm (muscle, kidney, heart), ectoderm (epidermis of skin, nervous system).
7
Q
What is morphogenesis?
A
Creation of structure and form.
8
Q
What cell characteristics does morphogenesis control?
A
Differential proliferation, change in cell shape and size, cell movement, fusion and death.
9
Q
What does gastrulation do?
A
Moves the germ layers relative to one another.
10
Q
What can differential growth rates result in?
A
Change in body proportions.
11
Q
What does it mean by the zygote is totipotent?
A
It generates all the cell types of the body and extra-embryonic tissues.
12
Q
What does progressive cell commitment mean?
A
Early embryonic cells are pluripotent, over time potential restricted.
13
Q
What is differentiation the process of?
A
Cells becoming structurally and functionally specialised, reflecting activating and maintenance of a particular pattern of gene expression.
14
Q
What does cleavage produce?
A
A cluster of blastomeres.
15
Q
When do divisions occur in blastomeres?
A
In the absence of growth.
16
Q
What do spherical blastomeres form?
A
A loose clump.
17
Q
What forms three days after fertilisation and what does this undergo?
A
Morula, undergoes compaction.
18
Q
Where does E-cadherin become restricted to three days after fertilisation?
A
Regions of intercellular contact.
19
Q
What does increased cell-cell adhesion three days after fertilisation do?
A
Maximises contact between blastomeres, forming a compact ball of cells held together by tight junctions.
20
Q
What produces one polarised and one nonpolarised daughter cell after fertilisation?
A
Subsequent tangential cleavages.
21
Q
What do outer cells of blastomeres have?
A
Distinct apical and basal surfaces.
22
Q
What do the nonpolarised cells form from?
A
The inner cell mass.
23
Q
What do the inner cells communicate via?
A
Gap junctions.
24
Q
What is the exterior surface of blastomeres?
A
Apical, microvilli.
25
What is the internal surface of blastomeres?
Basal or basolateral, E-cadherin.
26
What two distinct lineages do the outer and inner cells of blastomeres give rise to?
Trophectoderm and inner cell mass (ICM).
27
What is the importance of segregation of trophectoderms and ICMs?
First step towards differentiation.
28
At what point can an embryo be termed a blastocyst?
After a fluid-filled cavity develops.
29
What is the role of the inner cell mass of blastocysts?
Will give rise to embryo proper (and some extra-embryonic structures).
30
What is the importance of the zona pellucida of blastocysts?
Prevents implantation in the oviduct.
31
What forms the extra-embryonic tissues in blastocysts?
Flattened epithelial cells of the trophectoderm.
32
What is the name of the important fluid-filled cavity that makes a blastocyst what it is?
Fluid-filled blastocyst cavity or blastocoel.
33
What does active transport of sodium ions lead to?
Fluid accumulation in the blastocoel.
34
How does the process of active transport of sodium ions lead to fluid accumulation in the blastocoel?
Tight junctions between outer cells act as a permeability barrier, Na+ actively transported into blastocoel, ion conc increases so water flows in by osmosis, hydrostatic pressure inflates it.
35
What causes the embryo to hatch?
Enzymes digest through the zona pellucida.
36
What are the key components of a hatching embryo ?
Zona pellucida, trophoblast (derived from trophectoderm), hypoblast (part of inner cell mass), blastocyst cavity, epiblast (part of inner cell mass).
37
What does implantation require?
Interactions between trophoblast integrins and laminin/fibronectin extracellular matrix proteins expressed by epithelial cells of uterine mucosa.
38
What is the inner cell mass of the blastocyst called after implantation, between fertilisation and up to six days after?
The embryoblast.
39
What does the embryoblast form after implantation?
A flat disc of two layers, epiblast and hypoblast, with different fates.
40
What is the epiblast of the embryoblast and its role?
Columnar cells adjacent to newly formed amniotic cavity, will form embryo proper.
41
What is the hypoblast of the embryoblast and its role?
Small cuboidal cells adjacent to blastocyst cavity, will form extra-embryonic structures that will connect to mother’s circulation.
42
What forms after two weeks, after fertilisation and implantation, and where?
The primitive streak forms on the surface of the epiblast in the region that will become the posterior of the embryo.
43
What is the formation of the primitive streak the first sign of?
The anteroposterior axis.
44
What happens during gastrulation?
Epiblast cells migrate towards the primitive streak and invaginate, displacing the hypoblast.
45
What is the importance of the epiblast cells migrating through the primitive streak during gastrulation?
Creates the three germ layers.
46
What order of what epiblast cells invaginating during gastrulation forms what germ layers?
First cells to invaginate form endoderm, next cells form mesoderm, remaining cells form ectoderm,
47
What happens after gastrulation due to the germ layers being morphologically distinct and having different fates?
Flat embryo rapidly forms into a three dimensional body.
48
What happens during neurulation?
The ectoderm folds along its central axis to form the neural tube.
49
What are the steps causing the neural tube to form during neurulation?
Neural folds elevate and fuse, neural crest cells form near site of fusion and migrate away, epidermis fuses above neural tube.
50
What does the paraxial mesoderm do after neurulation?
Segments into somites.
51
What is the role of somites?
Generate trunk and limb muscles, dermis and vertebrae.
52
What is the important role of the endoderm in human development?
Is internalised so gives rise to epithelial lining of gastrointestinal tract.
53
Other than the gastrointestinal tract, what does the endoderm provide during embryo development?
Stomach, liver, pancreas and epithelial lining of respiratory tract.
54
What happens during the embryonic period (weeks 3-8) and what’s the scientific term for this process?
Germ layers give rise to tissue and organ systems - organogenesis.
55
What do stem cell populations do during organogenesis?
Establish each of the organ primordia.
56
What is organogenesis sensitive to?
Genetic and environmental influences.
57
What is the big issue during organogenesis?
Period when most structural birth defects are introduced.
58
What common stages does the development of most animals proceed through?
Fertilisation, cleavage to form blastula, gastrulation to reorganise structure of embryo and generate germ layers, neurulation, organogenesis.
59
What is the process known as epigenesis and what does this mean for development?
Simple embryo with few cell types in basic pattern is gradually refined to generate complex organism with many cell types showing highly detailed organisation, means development is progressive.
60
What are differentiated cells characterised by?
The proteins they contain.
61
What is genomic equivalence?
Somatic cell nuclear transfer shows that almost all somatic cells have a complete copy of the genome.
62
What can a differentiated cell’s nucleus do and what does this prove?
Can direct development of a new individual, proving it had not lost any of its genetic potential as it became specialised.
63
What underlies differentiation?
Differential gene expression.
64
How do cells become different from one another during cleavage?
By partitioning cytoplasmic determinants, which specify body axes and influence gene expression affecting cells developmental fate.
65
What happens once initial asymmetries have been established to further differentiation?
Subsequent interactions between cells influences their fate and bring about differentiation of specialised cells types.
66
What mediates inductions?
Diffusible signals or by cell-surface interactions.
67
What model organisms are suitable for experiments that address our questions about embryo development?
Mouse, zebrafish, fruit fly, frog, nematode worm, chick.
68
What is special to xenopus eggs?
Have visible and molecular polarity.
69
What is required for development of endoderm and mesoderm?
Vegetally-localised VegT.
70
As VegT binds to DNA what does it activate the expression of?
Transcription factors that mediate endoderm differentiation, nodal TGFbeta signalling factors that are secreted and induce reasoning cells to form mesoderm.
71
What is the evidence for VegT’s function?
Proof that a molecule performs a function in development requires it to be expressed in right cells at right time, necessary for function to take place, sufficient for function to take place.
72
Where is the VegT gene normally expressed?
VegT mRNA and protein can be detected in cells that give rise to endoderm.
73
How is development affected by blocking VegT gene function via a loss of function experiment?
Removing VegT from oocyte interferes with endoderm development and mesoderm induction.
74
What are the consequences of ectopic VegT gene expression via a gain of function experiment?
VegT expression in ectoderm results in expression of endoderm-specific genes.
75
What does Wnt signalling cause?
Beta-catenin to accumulate in nucleus and activate target gene expression.
76
How do beta-catenin and GSK-3beta interact?
GSK-3beat destroys beta-catenin, if GSK-3beta is inactivated beta-catenin can enter the nucleus.
77
What does sperm entry trigger?
Cortical rotation which translocates dorsal determinants that initiate Wnt signalling and establish the dorsoventral axis.
78
How does cortical rotation initiate Wnt signalling specifically?
Redistributes determinants including Wnt11 and inhibitory GSK-3-binding protein to the prospective dorsal side where they activate the Wnt signalling pathway.
79
What effect do Wnt11 and GSK-3-binding protein have development?
Inhibit GSK3beta allowing beta-catenin to be stabilised in dorsal cells.
80
How is GSK-3 inhibited on future dorsal side?
Beta-catenin initially present throughout vegetal region, targeted for destruction by GSK-3, after cortical rotation dorsal determinants activate Wnt signalling and inhibit GSK-3 on future dorsal side.
81
What happens to beta-catenin after dorsal rotation?
Stabilised and enter nuclei on dorsal side, ventral nuclei do not receive it.
82
What shows that beta-catenin is required for normal development of dorsal axial structures?
Over-expression and depletion.
83
What does beta-catenin activate the expression of?
Dorsal transcription factors such as goosecoid.
84
How does beta-catenin activate goosecoid?
Interacts with Tcf-3 to activate expression of siamois, which activates expression of goosecoid.
85
What does activation of nodal expression due to VegT and B-catenin cause?
Nodal gradient across endoderm, high nodal plus b-catenin induces dorsal mesoderm, low nodal induces ventral mesoderm.
86
What does the organiser do?
Secretes signals that pattern mesoderm and neutralise dorsal ectoderm.
87
What does grafting dorsal organiser cells to ventral side of a host induce?
A secondary axis complete with head and nervous system.
88
What do host cells respond to?
Signals produced by grafted organiser, patterning mesoderm and inducing neural tissue.
89
What activates expression of genes needed for organiser function?
Goosecoid transcription factor.
90
What do cells differentiate in response to?
The signals they receive, patterning individual tissues and organs.
91
How do cells and signals interact?
Signals tell cells where they are in time and space, cells respond by activating transcription factors to turn target genes on or off.
92
What does the combination of transcription factors in a cell determine?
Which tissue specific genes it expresses and how it differentiates.
93
What do signals from surrounding tissues do to somites?
Pattern the mesodermal somites, instructing somite cells to differentiate into muscle.
94
What do signals from surrounding tissues induce?
Expression of muscle inducing transcription factors e.g. cells expressing MyoD (myoblasts) differentiate into skeletal muscle.
95
What can over-expression of MyoD cause?
Can convert non-muscle cells into muscle cells.
96
What can act as a master switch and what does this cause?
A single protein, initiating a complex programme of differentiation.
97
What is important to do to avoid master switches and how is this normally done?
Important to regulate regulatory proteins, normally combinations of signals and factors ensure cells differentiate appropriately.
98
What is cell lineage?
The developmental history of a differentiated cell, traced back to cell from which it arises.
99
What series of decisions leads to terminal differentiation of a particular cell type?
Cytoplasmic determinants and inductive signalling interactions establish and pattern germ layers by activating factors, combination of factors determines how cell differentiates.
100
What has a fundamental level of control on differential gene expression?
Transcription.
