Post Embryonic Development• Metamorphosis- Amphibians and Insects• Tissue Regeneration• Aging

Metamorphosis: Overview• Direct Developers• Indirect Developers

Metamorphosis: Amphibians• Hormones

– Thyroxine (T4)– triiodothyronine (T3)

• Hormones cause:– Growth– Death– Remodeling– Respecification

Hormones: Growth• Growth and rearrangement• Limbs• Eyes

Hormones: Cell Death• T3 and tail degeneration• Concomitant with adult leg

generation.

Hormones: Remodeling• Digestive tract• Skull and gills• Nervous system

Hormones: Biochemical Respecification• Tadpole is ammonotelic• After morphogenesis, Frogs

are ureotelic.

Hormone function during Metamorphosis• T4 secreted by Thyroid.• TRa= receptor for T3;

ubiquitous• TRb= receptor induced by

hormones• Stages of Hormone activity

in Metamorphosis– Premetamorphosis– Prometamorphosis– Metamorphic climax

Hormone function during Metamorphosis• T4 secreted by Thyroid.• TRa= receptor for T3;

ubiquitous• TRb= receptor induced by

hormones• TR/RXR complexes• Stages of Hormone activity

in Metamorphosis– Premetamorphosis– Prometamorphosis– Metamorphic climax

Metamorphosis: Insects

Insect Imaginal Discs

Metamorphosis: Fly and Leg formation• Wingless (Wg); Wnt

homolog• Decapentaplegic (Dpp);

BMP homolog• Distal-less and Dachshund• 20-hydroxyecdysone (20-E)

Metamorphosis: Fly and Leg formation• Wingless (Wg); Wnt

homolog• Decapentaplegic (Dpp);

BMP homolog• Distal-less and Dachshund• 20-hydroxyecdysone (20-E)

Metamorphosis: Fly and Leg formation• Wingless (Wg); Wnt

homolog• Decapentaplegic (Dpp);

BMP homolog• Distal-less and Dachshund• 20-hydroxyecdysone (20-E)

Imaginal Discs: Wing

Fig. 15.14

Imaginal Discs: Wing

Imaginal Discs: Wing• Figure 15.15

Hormonal Control of Insect Metamorphosis• Fig. 15.16

Regeneration• Stem-cell mediated regeneration• Epimorphosis• Morphallaxis• Compensatory regeneration

“I’d give my right arm to know the secret of regeneration”-Oscar E. Schotte (1950)

Regeneration: Epimorphic• Limb regeneration in

Salamanders• Regeneration blastema• Wound epidermis• Apical epidermal cap (AEC)

Regeneration: Epimorphic

Epimorphic regeneration requires nerves and AEC• Newt anterior gradient

protein (nAG). • Fig 15.22

Morphallactic Regeneration: Hydra• Basal disc/hypostome• Head activation/inhibition

gradients• Hypostome= “organizer”• Basal disc

activation/inhibition Fig. 15.25And 15.26

Morphallactic Regeneration: Hydra• Basal disc/hypostome• Head activation/inhibition

gradients• Hypostome= “organizer”• Basal disc

activation/inhibition Fig. 15.25And 15.26

Compensatory Regeneration: Liver

Aging

Genetics and Aging• How can evolution select for a way to

degenerate?• How can evolution select for phenotypes that

can postpone reproduction or sexual maturity?

Aging• DNA repair enzymes• p53• Insulin Signaling

We’re staying alive…

Fig. 15.35

DNA methylation and Early Bird Specials.

Fig 15.36 and 15.37