Postembryonic Development

Lange

BIOL 370 – Developmental Biology

Topic #18

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.