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. 15.25
And 15.26
Morphallactic Regeneration: Hydra
• Basal disc/hypostome
• Head activation/inhibition
gradients
• Hypostome= “organizer”
• Basal disc
activation/inhibition
Fig. 15.25
And 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