Postembryonic Development

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Postembryonic Development
BIOL 370 Developmental Biology Topic 18

• Lange

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The major thrust of this chapter is to highlight
more strenuously that development is NOT
something that occurs simply early in life.
Development and changes in development occur
THROUGHOUT the entire lifespan of an organism.
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Eye migration and associated neuronal changes
during metamorphosis of the Xenopus laevis tadpole
Note the difference in eye position for the frog
tadpole and the adult frog. The changes are
associated with changes in degree of binocular
vision.
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Changes in the Xenopus skull during metamorphosis
Blue stain is highlighting cartilage. Red stain
is highlighting bone.
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Development of the urea cycle during anuran
metamorphosis
The urea cycle shows the biochemistry behind the
process of cell waste release with limited water
loss (important for terrestrial animals). Notice
how this cycle develops as the aquatic tadpole
metamorphoses towards the adult stage.
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Metabolism of thyroxine (T4) and
tri-iodothyronine (T3)
In the body, Thyroxine (T4) and triiodothyronine
(T3) are the key players in regulating
metabolism. Thyroxine serves as a prohormone
a committed intra-glandular precursor of a
hormone. The enzyme Deiodinase II converts the
T4 into T3
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• Basics of Frog Metamorphosis
• Metamorphosis in frogs is where the body makes a
  transition into the adult form.and
• It is initiated by production of the hormone
  thyroxine.
• Thyroxine causes different tissues to develop in
  different ways in the frog
• development of the lungs and the disappearance of
  the gills and gill pouch
• the lower jaw transforms into the big mandible of
  the carnivorous adult
• the long, spiral gut of the herbivorous tadpole
  is replaced by the typical short gut of a
  predator
• nervous system becomes adapted for hearing and
  stereoscopic vision and for new methods of
  locomotion
• eyes are repositioned higher up on the head with
  eyelids and associated glands formed.
• eardrum, middle ear, and inner ear are developed
• skin becomes thicker and tougher

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Regional specificity during frog metamorphosis

• In this transplantation stuy, we can see that
  regional specificity is retained
• Regardless of normal or abnormal location of
  the tail tip, at this stage, it is reabsorbed
  (A).
• Regardless of location, eyecup transplants remain
  (B)

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Direct development of the frog Eleutherodactylus
coqui
While most frogs will undergo a fairly
traditional metamorphosis, there are exceptions.
Here we see a species that develops the adult
form while encased in the egg.
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Parental care of tadopoles
(A) Shows a poison dart frog carrying its
offspring on its back.
(B) Shows a moth brooding frog. The offspring
will not emerge until metamorphosis is complete.
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Modes of insect development
Ametabolous - insect development with no
metamorphosis. Immature stages appear very
similar to the adults, except that they lack
genitalia. Hemimetaolous - insect development in
which there is incomplete or partial
metamorphosis, typically with successive immature
stages increasingly resembling the
adult. Holometabolous - insect development in
which there is complete metamorphosis and the
immature stages, called larvae, are markedly
different from the adults.
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Regulation of insect metamorphosis
Hormones regulating metamorphosis include JH or
Juvenile hormone (also called neotenin) -
ensure growth and hinder metamorphosis PTTH or
prothoracicotropic hormone or metamorphosis
initiator hormone stimulates the prothoracic
gland to produce Ecdysone - the molting hormone
that causes ecdysis (molting) Hydroecdysone -
the hormone that stimulates ecdysis AND
metamorphic change in form.
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20E-induced puffs in cultured salivary gland
cells of D. melanogaster
Control Hydroxyecdysone stimulated (25
minutes) Hydroxyecdysone stimulated (1
hour) Hydroxyecdysone stimulated (2
hours) Hydroxyecdysone stimulated (4 hours)
The size differences in the puffs are an
indication of increased replication.
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Regeneration of a salamander forelimb
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Regeneration in the larval forelimb of the
spotted salamander Ambystoma maculatum
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Regeneration of newt limbs depends on nAG
(normally supplied by the limb nerves)

• nAG (neuroblastoma amplified gene) proteins are
  supplied by limb nerves
• The right limb in the image is denervated and
  then amputated.
• Following amputation, increased electrical field
  input (electroporation) along with nAG proteins
  induces the limb regeneration in the absence of
  the nerve.

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Effects of vitamin A (a retinoid) on regenerating
salamander limbs
Retinoic acid appears to help in regeneration in
a variety of ways. The limbs of these
salamanders had a more rapid regeneration when
the growing regions were bathed in this vitamin a
derivative.
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Proximalization of blastema respecification by
retinoic acid
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Grafting experiments demonstrating different
morphogenetic capabilities in different regions
of the Hydra apical-basal axis
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Grafting experiments providing evidence for a
head inhibition gradient
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Bud location as a function of head and foot
inhibition gradients
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Organisms must effect a compromise between the
energy allocated to reproduction and growth and
the energy allocated to the maintenance and
repair of bodily tissues
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Life span and the aging phenotype
The children in (B) have a condition called
Hutchinson-Gilford Progeria. This is a genetic
condition characterized by the dramatic, rapid
appearance of aging beginning in childhood.
Affected children typically look normal at birth
and in early infancy, but then grow more slowly
than other children and do not gain weight at the
expected rate.
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A possible pathway for regulating longevity
In these examples, insulin signaling is
associated with decreased cellular longevity.
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Survival curves for the U.S. population for the
periods 19001902, 19491951, and 19992001
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End.