BIOL 370 – Developmental Biology
Topic #18
Postembryonic Development
Lange
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.
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.
Changes in the Xenopus skull during metamorphosis
Blue stain is
highlighting cartilage.
Red stain is highlighting
bone.
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.
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
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
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)
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.
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.
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.
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.
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.
Regeneration of a salamander forelimb
Regeneration in the larval forelimb of the spotted salamander Ambystoma maculatum
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.
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.
Proximalization of blastema respecification by retinoic acid
Grafting experiments demonstrating different morphogenetic capabilities in different regions of the
Hydra apical-basal axis
Grafting experiments providing evidence for a head inhibition gradient
Bud location as a function of head and foot inhibition gradients
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
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.
A possible pathway for regulating longevity
In these examples, insulin signaling is associated with decreased cellular longevity.
Survival curves for the U.S. population for the periods 1900–1902, 1949–1951, and 1999–2001
End.