Developmentally-important
Genes in Drosophila
• Maternal effect genes:
Bicoid mRNA in egg
• Gap genes: basic
anterior/posterior
subdivisions; mutants have
gaps in segmentation
• Pair-rule genes: mutants
have 1/2 normal segment
number
• Homeotic genes: see next
slide
Homeotic Genes
• Set of genes expressed in different combinations along the
length of the body (anterior-posterior axis) and dictate the
fate of each segment
• Homeotic mutants: mutants in which normal body parts
are formed in inappropriate segments
• Bithorax mutant transforms 3rd thoracic segment, which
normally bears haltares, into the form of the 2nd thoracic
segment, which bears wings
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Hox Genes
• Class of homeotic
genes
• Extensively studied in
nematodes, insects &
mice
• Contain homeobox
(180 bp sequence)
• Arranged in same
order on each
chromosome as they
are expressed from
anterior to posterior in
the developing animal
New Topic: Chemical Signals in
Animals
• Hormone: chemical signal secreted into body
fluids (usually blood) which communicates
regulatory messages
• Hormones may reach all parts of the body but
only certain types of cells, target cells, are
equipped to respond
• Hormone secreting organs are called endocrine
glands, and, collectively, all of an animal’s
hormone secreting cells constitute the endocrine
system
• Study of hormones & endocrine system:
endocrinology
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Hormone Types
• Two Main Hormone
Types:
– Peptide
– Steroid
• Peptide Hormones
(water soluble), e.g.,
oxytocin &
epinephrine
• Don’t enter cells but
bind to specific
receptor on cell
membrane
• Initiate multi-step,
signal transduction
pathway
Non-Steroid Hormone Movie
3
Steroid Hormone Movie
Hormone Types cont.
• Steroid Hormones, e.g.,
testosterone, estrogen
• Passes through cell
membrane
• Binds with receptor
protein
• Hormone-protein
complex passes through
nuclear membrane and
binds to specific
regulatory site
• Stimulates transcription
of a specific gene
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Steroid Effects
East German Athletes 1970s 1980s
Men:
– Shrunken testicles
– Sterility
– Heart & Kidney damage
Women:
–
–
–
–
–
Increased body hair
Severe acne
Increased libido
Ovarian cysts
Uterine shrinkage
Components of Endocrine System
• Pineal Gland: secretes
hormone melatonin
(modified AA); contains
light-sensitive cells and
modulates biorhythms
associated w/ reproduction
• Hypothalmus: integrates
many functions of
vertebrate endocrine system
– Receives nerve input
from throughout body &
other parts of the brain
– Produces releasing and
inhibiting hormones that
control anterior pituitary
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Human Endocrine System II
Posterior Pituitary: ADH & oxytocin produced in
hypothalamus & stored in posterior pituitary
Stress &
Oxytocin
Women: Tend and
befriend;
oxytocin
promotes social
networking
Men: Fight or flight;
testosterone
mitigates effects
of oxytocin
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Human Endocrine System III
• Anterior Pituitary: Hypothalmus secretes releasing &
inhibitory hormones that control release of anterior
pituitary hormones
Hormones of Anterior Pituitary I
Growth hormone (GH):
• Protein of 200 AA
• Stimulates cells to take up AA
• Stimulates liver to produce somatomedins
which circulate in blood and stimulate
growth of bone & cartilage
• Primary determinant of stature:
– Overproduction of GH: gigantism
– Underproduction of GH: dwarfism
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Inserted Human Growth Hormone Gene
Hormones of Anterior Pituitary II
Endorphins
• Peptide
• Natural opiates: inhibit perception of pain
by acting as neurotransmitters in the brain
• Heroin & opiate drugs mimic endorphins
and bind to same receptors in the brain
• Endorphins: responsible for “runner’s high”
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Human Endocrine System IV
Thyroid Gland secretes hormones:
• Triiodothyronine, thyroxine
– Amines
– Stimulate & maintain
metabolism
– Regulated by TSH
• Calcitonin
– Peptide
– Lowers blood calcium
– Regulated by blood calcium
levels (negative feedback)
Parathyroid Gland secretes:
• Parathyroid hormone (PTH)
– Peptide
– Raises blood calcium
– Regulated by blood calcium
Human Endocrine System V
Thymus secretes hormones:
• Thymosin
– Peptide
– Stimulate T-lymphocytes
– Regulated by ??
Adrenal Glands
• Cortex: corticosteroids
• Medulla:
– Epinephrine (adrenalin)
– Norepinephrine
– Amines: catecholamines, i.e.,
made from AA tyrosine
– Raise blood glucose levels
– Increase basal metabolic rate
– Constrict blood vessels
– Regulated by nervous system;
secreted in response to stress
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Human Endocrine System VI
Pancreas
• Endocrine cells scattered in
clusters called the Islets of
Langerhans
• Secrete antagonistic hormones:
– Insulin
ß
ß
ß
ß
Produced by beta cells
Protein
Lowers blood glucose
Regulated by level of glucose in
blood
– Glucagon
ß
ß
ß
ß
Produced by alpha cells
Protein
Raise blood glucose levels
Regulated by level of glucose in
blood
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Diabetes
•
•
•
•
Disruption to blood glucose homeostasis
Diabetes--> copious urine production
mellitus --> honey (sweet urine)
Type I diabetes mellitus (<10% cases)
– Also called juvenile, early-onset or insulin-dependent diabetes
– Autoimmune disorder: immune system attacks cells of the
pancreas
– Requires frequent insulin injections
• Type II diabetes mellitus (>90% cases)
– Also called adult-onset or non-insulin-dependent diabetes (usually
after age 40)
– Usually due to reduced responsiveness in target cells due to
change in receptors
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