Term
| Discontinuous development with larval stage (=growth and dispersal) followed by metamorphosis to juvenile adult form |
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Definition
| Indirect development aka complex lifecycle |
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Term
| Which life cycle is ancesterol and which is derived? |
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Definition
Ancesterol= indirect
Derived= direct |
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Term
| Describe direct development |
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Definition
Continuous development from fertilized egg to juvenile adult
***
Mother's investment much higher for direct!
All mammals, birds, and reptiles are direct!
Some amphibians make few dozen eggs rather than thousands and go straight from embryo to small adult (no tadpole stage). |
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Term
| T/F: Thyroid hormones, steroids, and GCs important for both indirect and direct development. |
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Definition
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Term
In early development, chemical signaling is...
In postembryonic development, chemical signaling is... |
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Definition
Paracrine
Paracrine and hemocrine - circulatory system developed - hormones from fetus, placenta, and mother. |
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Term
In humans, who do we study the roles/sources of hormones?
How do we do it in animal studies? |
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Definition
In humans, observe congenital glandular deficiencies.
In animal models:
- Fetal surgeries
- In vitro cultures
- Renal capsule grafting= fetal tissue implanted under kidney capsule and implanted cathaters yo deliver growth factors directly into kidney
- Transgenic animals (KO genes) |
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Term
Hormones involved in POSTnatal growth from:
Pituitary
Thryoid
Liver
Pancreas
Gonads |
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Definition
Pituitary GH, TSH
Thyroid Thyroid hormone
Liver IGFs
Pancreas Insulin
Gonads E2, T |
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Term
| Hormones involved in PREnatal growth and develoment (and what they do) |
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Definition
Thyroid hormone --> brain and skeletal development (maternal thyroid sufficient)
GCs--> lung development and brain development
Sex steroids--> CNS devlopment, genital tract, sex accessory organs
GH rises in fetus and peaks ~20wks
Others:
Insulin (anabolic hormone)
IGFs I&II (CRITICAL in fetal growth)
Placental polypeptides (PL, hCG)
Other peptide growth factors
***
Surfactant production induced by GCs
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Term
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Definition
| Dexamethasone= synthetic GC often given to premature infants (build of surfactant) |
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Term
| How does pituitary agenesis and pancreatic agenesis affect fetal growth? |
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Definition
Pituitary agenesis (no GH) - baby looks fine at birth but won't grow after birth
Pancreatic agenesis (no insulin) - small baby |
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Term
| How does the structure of IGF1 differ from insulin? |
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Definition
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Term
| What causes Leprechaunism? |
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Definition
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Term
| What gives us reason to believe that IGF1 is most important for postnatal growth? |
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Definition
| Pygmies have a deficiency in IGF1 but they give birth to normal sized babies |
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Term
| What is the importance of IGFI vs IGFII in growth? |
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Definition
IGFI important in later fetal devlopment/postnatal development
IGFII important in very early embryonic and fetal development |
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Term
| What are the affects of IGFI KO, IGFII KO, and IGFI/II double KO on mice? |
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Definition
IGFI KO smaller than wt
IGFII KO smaller than IGFI KO
IGFI/II double KO --> fatal |
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Term
What is Ecdysone?
What vertebrate receptor does EcR resemble?
What does EcR dimerize with? |
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Definition
Ecdysone= steroid in insects - induces gene expression changes that drive metamorphosis
EcR resembles vertebrate thyroid hormone receptors
EcR dimerizes with ultraspiracle (USP) - an RXR homolog |
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Term
| What hormone induces metamorphosis in echinodorms (e.g. sand dollars, sea urchins)? |
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Definition
Thyroid hormone
***
Amphioxus (the cephalochordate that looks like an eel/worm) has thyroid receptors (-->metamorphosis) |
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Term
| Common theme among aminal metamorphosis |
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Definition
| Animal metamorphoses are controlled by hydrophobic signaling molecules that bind to nuclear receptors (members of the nuclear hormone receptor subfamily) |
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Term
What is Pedomorphosis? and what is a nother name for it?
What kinds of animals is this seen in?
What are 2 subtypes of pedomorphs? |
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Definition
Pedomorphosis aka neoteny= animals become repoductively mature while retaining larval characteristics
Only seen in amphibians and salamanders
2 subtypes of Pedomorphs:
1. Obligate pedomorphs= NEVER metamorphose
2. Facultative pedomorphs= metamorphose if aquatic environment begins to deteriorate.
***
Obligate pedomorphs are RESISTANT to TH - Sirens and mudpuppies (salamanders) do not metamorphose when treated with TH. |
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Term
Flat fish metamorphosis:
Larvae are _____ and have bilateral symmetry.
Adults are ____ and right eye migrates to the left side of the body and become flat fish.
This metamorphosis is controlled by ___. |
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Definition
Larvae are pelagic (=live in open ocean) and have bilateral symmetry.
Adults are benthic (=migrate to bottom of the sea) and right eye migrates to the left side of the body and become flat fish.
This metamorphosis is controlled by thyroid hormone and corticosteroids. |
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Term
What initiates smoltification in salmon?
What occurs just prior to smoltification that is responsible for the transformation?
How does cortisol and GH change during downstream migration?
What is the freshwater adapting hormone? |
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Definition
Smoltification initiated by lengthening of photoperiod.
Just prior to smoltification, there is a thyroid hormone surge controlled by lunar cycle which is responsible for transformation.
Cortisol and GH increase during downstream migration - they are both salt-water adapting - affect gills and gut which are the main osmoregulatory organs in fish; change direction of salt transport.
PRL is the freshwater-adapting hormone |
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Term
What triggers amphibian metamorphosis (tail-loss, limb development)?
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Definition
Thyroid hormone
***
Feed tadpoles thyroid gland --> accelerated metamorphosis (Gudernatsch, 1914).
No thyroid, live as tadpole for years.
Cell proliferation, death, and differentiation all induced by TH (tissue remodeling) - true for humans too! |
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Term
What is the primary morphogen in amphibians?
What synergizes with this primary morphogen to speed up the process? |
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Definition
Thyroid hormone is the primary morphogen.
Corticosteroids synergize with TH.
***
Injection of TRH (tripeptide) does NOT promote TSH release in tadpoles.
CRF is a potent releaser of TSH and is now known the be the neuropeptide that controls amphibian metamorphosis. |
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Term
| T/F: Spike in thyroxin and cortocosterone in tadpole metamorphosis can be either spontaneous or elicited early by a stressor. |
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Definition
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Term
| How does PRL affect metamorphosis? |
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Definition
PRL is anti-metamorphic - may be important for tuning things off; otherwise, metamorphosis would occur twice rapidly followed by death.
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Term
| How do increasing levels of TRalpha mRNA affect metamorphosis in tadpoles? |
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Definition
TRalpha --> repression of adult-specific genes.
Presence of receptor but no hormone --> suppression of gene expression.
BUT also establishes tissue competance to TH when it finally IS expressed. |
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Term
| How does TRbeta mRNA expressed in tadpole metamorphosis? |
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Definition
TRbeta increases in parallel with thyroid hormone.
TRbeta is autoinduced= hormones induce expression of its receptor.
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Term
How does increased levels of T3 affect tadpole tail length?
How does increased levels of CORT affect tadpole tail length?
How does the combination of T3 and CORT affect tadpole tail length? |
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Definition
Increased levels of T3-->shrinking of tail
Increased levels of CORT-->deepening of tail
Increased levels of both T3 and CORT-->shrinking of tail even more than with only T3 (synergy) |
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Term
How is tissue sensitivity to T3 increased by the combination of thyroid hormones and glucocorticoids (synergy in metamorphosis)?
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Definition
TR-RXR + GR-GR --> more Thyroid hormone receptors (increases sensitivity to thyroid hormone)
AND
--> increased deiodinases (DII) (increases conversion of T4 to T3)
Same thing happens in human brains!
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