1. Chapter 18- Metamorphosis/regeneration/aging
Most animals have a distinct larval stage
Massive changes often occur from larval to adult organism transition
Larva
Adult
Aquatic, tail fins
Gills
Herbivore
Excrete ammonia
Terrestrial, tail-less, ________
_________
___________
Excrete __________
Metamorphosis is dictated by _________ T4
In frogs- hormones __________ (T4) and _________________ (T3) are secreted from the ________ T3
Fig. 18.3

2. Thyroid stimulating hormone
A. Metamorphosis (cont.)
If remove thyroid from tadpole-
…becomes giant _______
The response to hormones is ____________ specific
The same stimulus can promote ___________in one tissue and ______________ in another
T3 promotes ____________ of tadpole head and body, but cell ___________ in the tail
The timing of hormone production is done by
1. The____________
2. The _________________ (which regulates thyroid
hormone production)
Thyroid stimulating hormone
___
Hypothalamus
_________
_______
_______
_______
___

3. A. Metamorphosis (cont.) A. Metamorphosis (cont.)
If transplant a second tail- it still degenerates by ________
Fig. 18.5
Transplanted
tail tip
Transplanted
tail tip regresses
But if transplant another eye cup, it ________________
How are these events of metamorphosis coordinated??
Need tail until have legs for locomotion
Need gills until lung muscles develop
One theory- “______________________________”
As _____________ levels increase, different events occur
If high levels of ________________ -tail regression prior to _________________ development
Go to morphogenesis on Vade Mecum

4. A. Metamorphosis (cont.) A. Metamorphosis (cont.) Fig. 18.7
Mechanism of thyroid hormone effects
Pre-metamorphosis
Early metamorphosis
Metamorphosis
_____ T3
____ T3r T3
T3r
____ T3
____T3r
T3 receptor gene
Activate ____________ genes
____T3,T4
______ T3,T4
_____ T3,T4

5. 3. ___________________ no _____________development
A. Metamorphosis (cont.)
Heterochrony
Definition- The phenomenon whereby animals change the ______________ and ____________________ of characters
Usually refers to creatures with _________ phases
1. __________- retention of juvenile form in body but germ cells/gonads mature _______________
2.___________- retention of juvenile form of body but germ cells and gonads mature ____________________________
3. ___________________ no _____________development

6. 1. ___________ (Salamander)
A. Metamorphosis (cont.)
1. ___________ (Salamander)
a. Mexican axolotl- body fails to mature do to lack of __________ from pituitary gland (hence no ___ produced by thyroid gland)
If treat axolotl with __________________, develops into creature not seen in nature
Normal
+ __________
Fig. 18.8

7. 1. ______________ (Salamander)
Heterochrony
1. ______________ (Salamander)
TSH-RF
TSH
T3, T4
No _______
No _________
No ________

8. 2. _________________ (Salamander)
A. Metamorphosis (cont.)
1. Neoteny (Salamander)
b. Tigrinum (salamander in Rocky Mtns) stays in larval form if cold
Metamorph into land-dwelling creature if _____
Why? Because can’t secrete ________________
___________ at low temps.
c. Other salamanders can’t respond at all to thyroid hormones
2. _________________ (Salamander)
a. Occidentalis (tree living salamander)
Remains in juvenile phase to retain _____________.

9. 3. ___________ Development
A. Metamorphosis (cont.)
3. ___________ Development
E. Coqui (frog) – In _____________ only
Develops directly into frog (no ____________ stage)
Egg is 20X larger than xenopus
Early development is similar to other frogs , but ____________ form right after __________ closure
Fig
Is larval stage only required for creatures with small eggs??
1998- Noisy problem when introduced into Hawaii- cluster can produce decibels
(75 decibels leads to hearing loss)

10. Insect morphogenesis
Instead of simply remodeling (e.g. amphibians), insects _______ tissues and ___________ new ones
Insects ______ (shed their cuticle)
Often go through multiple _________ (larval molts)
Each molt generates a ________ organism
Most of the previous body is destroyed by _________
_____________ lay dormant until needed to create adult

11. Recall Fruit Fly development
Imaginal discs
Fig
Imaginal discs lay dormant until needed to create adult

12. What dictates insect morphogenesis??
Answer: Primarily ________(actually 20-hydroxyecdysone)
But, ___________ (JH) levels dictate __________ effect
Low Ecdysone
Next _______ stage
High ___
_______ stage
High Ecdysone
_______ stage
Low ___
High Ecdysone

13. How does ecdysone work?
Ecdysone cannot bind _____
Must first bind the ecdysone _________
Fig
The _______________
______ binds DNA and creates “__________”
These puffs contain _________ that are _________
These genes encode _____________________ that promote _____________

14. B. Regeneration Three types-
1. ________ – e.g. a salamander growing back an entire limb
2. ____________ – the re-patterning of existing tissues, without requiring ____________
e.g. planaria regeneration of head and tail regions
3. _____________ – cells divide but maintain their ____________ phenotype
e.g. the mammalian ______- the removed lobe does not grow back, but the remaining _____ compensate by “___________________”

15. C. Aging
Definition- Time-related ______________of the physiological functions necessary for survival and function
Some developmental biologists tout that animals are only needed long enough to fill the need of ________________, then die (as occurs in ______ and __________)
Maximum life span- the _______________ number of years that a member of a species is known to have lived
Life ___________- the age to which __ of the population survives
In 1780 England- ___ yrs
In 1780 Massachusetts- ___ yrs
Today in Afghanistan, Cambodia, etc- ____ yrs
Today in America- ___ yrs (male) and __ yrs (female)
In 1935 America- ____ yrs (when Social Security was initiated)

16. 2. General ______________- the build up of__________________
B. Aging (cont.)
Theories of Aging
1. _____________- reactive oxygen species (ROS) in mitochondria progressively damage DNA, proteins, etc
Evidence- Drosophila and C. Elegans liver longer (up to 40%longer) if over-express catalase (which destroys ROS)
2. General ______________- the build up of__________________
Evidence- Species with more efficient DNA repair enzymes tend to live longer
Life span
3. _________________ genome damage
Leads to decreased ______ __________, increased ROS, and increased ____________
DNA repair efficiency
Fig

17. 4. ___________ shortening
15.3
15.2
15.1 14
13.3
13.1 12 11
11.1
11.2
13.2 15 21 22
23.1
23.3
31.1
31.2
31.3 32
33.1
33.3 34
35.1
35.3
35.2
33.2
23.2
B. Aging (cont.)
Theories of Aging
15.3
15.2
15.1 14
13.3
13.1 12 11
11.1
11.2
13.2 15 21 22
23.1
23.3
31.1
31.2
31.3 32
33.1
33.3 34
35.1 .3
35.2
33.2
23.2
4. ___________ shortening
Background- Telomere ends are normally maintained by the enzyme _____________ (not DNA polymerase)
Evidence-
a) Telomeres shorten as cells divide in culture until cell division stops, and cell division starts again if express telomerase
b) Telomerase-deficient mice show profound ________ defects
Problem with theory- _________________ between telomere length and life span of different species or even with a species

18. Fig. 18.37- 8 yr old children with progeria
B. Aging (cont.)
Fig yr old children with progeria
Theories of Aging
5. __________ aging programs
Evidence-
a) Known “old-age” genetic defects
Hutchinson-Gilford _______ syndrome in humans – 1/yr identified in US
Disease gene identified- Nature, April 24, 2003;Gordon et al.
Leslie Gordon is mother of progeria child
C to T transition in LMNA (Lamin A) gene (unknown function)
2) __________ gene mutation in mice
b) C. elegans- can extend lives __________ by altering genes involved in larva- to adult genetic pathway