Postembryonic growth Flashcards
1
Q
What are the 3 ways in which organisms can grow?
A
- Cell proliferation
- Cell enlargement
- Accretion (bone)
2
Q
What is accretion?
A
Depositing matrix between cells which causes growth
3
Q
Which molecules drive the cell cycle? (2)
A
- Cyclins
- Cdks
4
Q
What are the phases of the cell cycle? (4)
A
- G1
- S
- G2
- Mitosis
5
Q
What does the G in G1/G2 etc. stand for?
A
Gap
6
Q
What happens during S phase of the cell cycle?
A
DNA replication (synthesis)
7
Q
Which molecules control G1 phase? (3)
A
- Cdk 4/6
- Cyclin D
8
Q
Which molecules control S phase? (2)
A
- Cdk2
- Cyclin E
9
Q
Which molecules control G2 phase? (2)
A
- Cdk2
- Cyclin A
10
Q
Which molecules control mitosis? (3)
A
- Cdk1
- Cyclin A/B
11
Q
How does cell proliferation occur in drosophila during early development? (4)
A
- Egg is a syncytium
- Nuclei undergo rapid division without G1/G2 phases (S to M repeats)
- Division uses maternal String protein until cycle 14 where the zygotic genes kick in
- At cycle 14 division slows, G2 is included, cellularisation occurs
12
Q
What is String? (2)
A
- A phosphatase which activates CDKs resulting in cell division
- Controls mitotic domains
13
Q
What is String expression controlled by? (2)
A
- Patterning genes (Gap, Pair rule, segment polarity, Dorsal/Ventral genes)
- This links patterning to proliferation
14
Q
What is a mitotic domain?
A
Regions where cell division is occurring differently to form different tissues
15
Q
Which gene controls mitotic domains?
A
String
16
Q
Where is String action blocked in drosophila development? (2)
A
- String is blocked by Tribbles in the mesoderm
- Mesoderm needs to invaginate which requires cell migration not proliferation
17
Q
Is the control of the growth programme for limbs intrinsic or extrinsic? (2)
A
- Intrinsic control
- If you transplant a limb from a large newt to a small newt, the limb will grow to its correct size which is too large for the recipient newt
18
Q
Is control of organ size intrinsic or extrinsic? (4)
A
- Depends on the organ
- Thymus is intrinsic
- Spleen is extrinsic/systemic
- Growth programmes can be flexible e.g. liver regrowth
19
Q
How is organ/animal size determined? (3)
A
- Size is not determined by the number of cells in the organ/animal
- The absolute dimensions matter more than the number of cells
- Morphogens control the number of cells
20
Q
What are 2 important growth control pathways?
A
- TOR
- Hippo
21
Q
What does the TOR pathway control?
A
Cell size
22
Q
What happens to cells when TOR signalling is active?
A
Cells increase in size
23
Q
What does the Hippo pathway do?
A
Limits organ size
24
Q
How does the Hippo pathway work? (3)
A
- When Hippo is inactive, nuclear localisation of transcription factor Yki (drosophila)/Yap/Taz (mammals) which causes growth and survival of cells
- When Hippo is active, Yki/Yap/Taz is excluded from the nucleus
- Hippo signals to stop growth
25
What is the equivalent of the Hippo pathway in vertebrates?
Mst1/2
26
What activates Hippo? (2)
- Cell-cell contact
- Cell polarisation
27
What inactivates Hippo? (3)
- Mechanical stress
- Stiff ECM
- Signalling from GPCRs
28
What happens to cells when Hippo signalling is active? (2)
- Suppression of cell proliferation
- Promotion of apoptosis
29
What happens to cells when Hippo signalling is inactive? (2)
- Promotion of cell proliferation
- Suppression of apoptosis
30
What determines overall size in drosophila?
Insulin signalling affects the duration and rate of larval growth
31
Which hormones are involved in determining overall size in mammals? (2)
- IGF1, 2
- GH
32
What is GH?
Growth Hormone
33
How does GH signalling promote growth? (2)
- Stimulates IGF1 synthesis in the liver which circulates
- Stimulates local IGF1 synthesis in bone
34
How is negative feedback involved in GH signalling? (3)
- IGF1 inhibits GH production
- GH stimulates production of somatostatin which inhibits GH production
- GH blocks the production of GHRH
35
Where is GH produced?
Pituitary gland
36
What is GHRH?
Growth Hormone Releasing Hormone
37
How does the maternal environment influence growth? (2)
- Low birth weight is associated with coronary heart disease
- Severe caloric restriction during pregnancy puts babies at higher risk for obesity and diabetes
38
What is ecdysis?
The process of moulting
39
What is an instar?
The developmental stage between each moult
40
What is the process of ecdysis? (5)
- Stretch receptors in the epidermis signal to the CNS
- Prothoracicotropic hormone is released
- Causes ecdysone release from the prothoracic gland
- Activates enzymes which release the cuticle from the epidermis
- Shedding
41
What is the process of metamorphosis in insects? (2)
- Environmental cues stimulate release of prothoracicotropic hormone (PTTH) which causes ecdysone release from the prothoracic gland
- Ecdysone and juvenile hormone are balanced until an increase in ecdysone stimulates pupation
42
What is the process of metamorphosis in tadpoles? (4)
- Environmental cues act on the hypothalamus which releases corticotropin releasing hormone (CRH)
- CRH stimulates thyroid stimulating hormone (TSH) release from the pituitary
- TSH causes the thyroid to produce thyroxin (T4T3)
- Thyroxin and prolactin are balanced until there is increased thyroxin which drives metamorphosis and does positive feedback on the hypothalamus and pituitary
43
What are the tissue specific effects of thyroxin in frogs? (3)
- Promotes limb growth
- Promotes tail degeneration
- Modulates tissue responsiveness to oestrogen
44
Which tissues is cancer most common in?
Tissues that continue to divide throughout life e.g. epithelia and blood
45
What is a proto-oncogene?
A gene which becomes an oncogene after a mutation causes it to be inappropriately activated
46
What is a tumour suppressor gene?
A gene which normally suppresses cancer but can lead to cancer after inactivation
47
What are examples of tumour suppressor genes? (2)
- Retinoblastoma
- p53
48
What are examples of proto-oncogenes? (2)
- Ras
- Epidermal Growth Factor Receptor (EGFR)
49
How are developmental signalling pathways involved in cancer? (2)
- Proto-oncogenes/tumour suppressor genes are often involved in developmental signalling pathways
- Aberrant developmental signals can drive cancer
