Chapter 18- Metamorphosis/regeneration/aging

Metamorphosis is dictated by _________

Aquatic, tail finsGillsHerbivoreExcrete ammonia

Terrestrial, tail-less, ____________________________Excrete __________

Larva Adult

Most animals have a distinct larval stageMassive changes often occur from larval to adult organism transition

In frogs- hormones __________ (T4) and _________________ (T3) are secreted from the ________

T4

T3

Fig. 18.3

A. ___________________

The response to hormones is ____________ specific

A. Metamorphosis (cont.)

•If remove thyroid from tadpole- …becomes giant _______

• 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

______________

•But if transplant another eye cup, it ________________

•If transplant a second tail- it still degenerates by ________

Fig. 18.5

Transplanted tail tip

Transplanted tail tip regresses

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

A. Metamorphosis (cont.)A. Metamorphosis (cont.)

Mechanism of thyroid hormone effects

Early metamorphosisPre-metamorphosis Metamorphosis

____T3,T4 ______ T3,T4 _____ T3,T4

Fig. 18.7

T3 receptor gene

A. Metamorphosis (cont.)

____ T3r_____ T3 T3 T3r ____T3r____ T3

Activate ____________ genes

A. Metamorphosis (cont.)

Heterochrony

Definition- The phenomenon whereby animals change the ______________ and ____________________ of characters

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

Usually refers to creatures with _________ phases

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

A. Metamorphosis (cont.)

Heterochrony

No ________ No _______

TSH-RF TSH

No _________

T3, T4

1. ______________ (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

1. Neoteny (Salamander)

2. _________________ (Salamander)

a. Occidentalis (tree living salamander)

Remains in juvenile phase to retain _____________.

A. Metamorphosis (cont.)

3. ___________ DevelopmentE. Coqui (frog) – In _____________ only

Develops directly into frog (no ____________ stage)

Fig. 18.10

• Egg is 20X larger than xenopus• Early development is similar to other frogs , but ____________ form right after __________ closure

Is larval stage only required for creatures with small eggs??

A. Metamorphosis (cont.)

1998- Noisy problem when introduced into Hawaii- cluster can produce 70-90 decibels(75 decibels leads to hearing loss)

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

• Imaginal discs lay dormant until needed to create adult

Fig. 18.12

Recall Fruit Fly development

Imaginal discs

What dictates insect morphogenesis??

Answer: Primarily ________(actually 20-hydroxyecdysone)

But, ___________ (JH) levels dictate __________ effect

High ___

Next _______ stage

_______ stage

Low Ecdysone

High Ecdysone

Low ___High Ecdysone

_______ stage

How does ecdysone work?

• Ecdysone cannot bind _____• Must first bind the ecdysone _________

The _______________ ______ binds DNA and creates “__________”

Fig. 18.23

These puffs contain _________ that are _________

These genes encode _____________________ that promote _____________

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 “___________________”

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)

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

Fig. 18.36L

ife

span

DNA repair efficiency

3. _________________ genome damage

Leads to decreased ______ __________, increased ROS, and increased ____________

B. Aging (cont.)

Theories of Aging

4. ___________ shortening

Background- Telomere ends are normally maintained by the enzyme _____________ (not DNA polymerase)

Evidence-

Problem with theory- _________________ between telomere length and life span of different species or even with a species

a) Telomeres shorten as cells divide in culture until cell division stops, and cell division starts again if express telomeraseb) Telomerase-deficient mice show profound ________ defects

15.3

15.215.1

14

13.3

13.11211

11.111.2

12

13.113.213.3

14

15

21

2223.1

23.3

31.131.231.3

3233.133.334

35.135.3

35.2

33.2

23.2

13.2

15.3

15.215.1

14

13.3

13.11211

11.111.2

12

13.113.213.3

14

15

21

2223.1

23.3

31.131.231.3

3233.133.334

35.1.3

35.2

33.2

23.2

13.2

B. Aging (cont.)

Theories of Aging

5. __________ aging programs

Evidence-

1) 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

a) Known “old-age” genetic defects

Fig. 18.37- 8 yr old children with

progeria

b) C. elegans- can extend lives __________ by altering genes involved in larva- to adult genetic pathway