Download Lecture 27

12/10/2015
Fertilization
“N” polar body
mitosis
“N” polar bodies (2):
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reduction
division
“2N” pronucleus
(suspended in
meiotic metaphase)
disintegrate
membrane formation
migrate carrying nutrients
“N” sperm pronucleus
fertilization
“N” pronucleus
(after sperm
enters egg)
“2N” zygote nucleus
Early establishment of polarity in Drosophila eggs:
Maternal genes expressed in follicle cells produce “morphogens”
BICOID
Anterior
maternal effect
genes
NANOS
Posterior
gap genes (transcription factors)
-- a class of segmentation gene)
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Superficial (meroblastic) cleavage
yolk
ANT.
micropyle
cleavage nuclei
or energids
POST.
sperm
pronucleus
egg pronucleus
POST.
ANT.
cytoplasm
8-12 synchronized divisions (256-4096 energids)
“cleavage center”
cleavage cells
vitellophage
posterior
activation
center
P.
ANT.
primary dorsal organ
blastoderm
pole plasm & cells
(primordial germ cells)
differentiation center
(end of totipotency)
vitellophage
POST.
ANT.
germ band
(LONGITUDINAL SECTIONS)
posterior activation
(proliferation) center
(on a continuum)
Different types of later embryological development
1. Short germ band insects
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Apterygota
Orthoptera: Caelifera
some Coleoptera (e.g. Tribolium)
2. Intermediate germ band insects
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Odonata
Orthoptera: Ensifera
some Coleoptera
3. Long germ band insects (very distinct)
(Holometabola)
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Diptera (e.g., Drosophila)
Lepidoptera
Hymenoptera
some Coleoptera
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Embryonic membrane formation [cross-sections]
typical of short / intermediate germ band insects
blastoderm
yolk
amniotic
fold
serosa
germ band
(fusion)
amniotic
cavity
amnion
embryo
(CROSS-SECTIONS)
Four general pathways for dorsal closure
(puts the yolk inside the embryo)
Secondary dorsal
organ (serosa)
serosa
yolk
amnion
amnion
yolk
yolk
yolk
amnion
yolk
germ band
amnion
amnion
Secondary dorsal
organ (serosa)
yolk
yolk
embryo
yolk
(CROSS-SECTIONS)
yolk
serosa
amnion
embryo
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Types of “gastrulation” or
endoderm/mesoderm formation
1a. Invagination
(many Coleoptera, etc: short /
intermediate germ band insects)
2. Overgrowth
vitellophage
(Diptera, Lepidoptera, Hymenoptera,
& some Coleoptera: long germ band
insects)
blastoderm
inner layer
germ band
(lateral plates)
middle plate (inner layer)
1b. Proliferation or Delamination
(other short / intermediate germ band insects,
incl. many orthopteroids & Odonata)
yolk
inner layer
germ band
(lateral plates)
(CROSS-SECTIONS)
ventral groove
Blastokinesis in short / intermediate germ band insects
(Apterygota, Odonata, Orthoptera, some Coleoptera)
ANT.
yolk
serosa
“head”
amniotic
cavity
yolk
chorion
amnion
(dorsal
closure)
POST.
yolk
amniotic
cavity
amnion
“head”
(protocephalon)
chorion
serosa
abdomen
serosa
yolk
amnion
thorax
head
amnion &
serosa fused
head
head
abdomen
(LONGITUDINAL SECTIONS)
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Blastokinesis in an intermediate germ band insect
(Orthoptera: Gryllidae: Acheta)
ANT.
POST.
diagrammatic
summary
embryo revolution
dorsal closure
(see previous slide)
near
hatching
(LONGITUDINAL SECTIONS)
Segmentation & appendage formation, short germ band insects
(Apterygota, caeliferan Orthoptera, some Coleoptera)
Zygentoma (Petrobius)
Coleoptera
(Tribolium)
Each segment is added
sequentially
(Dark bands =
proliferation of
engrailed mRNA)
Posterior proliferation zone:
continually produces cells
immediately anterior to itself.
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Summary of segmentation & appendage formation in
short / intermediate germ band insects (e.g. Ensifera)
protocephalon
“Polypod” stage
labrum
labrum
antenna
protocorm
antenna
eye
mouthparts
mouthparts
(mandible, maxilla,
and labium)
legs
legs
abdominal
appendages
Loss of extra appendages late in embryo development
protocephalon
“Polypod” stage
labrum
labrum
antenna
protocorm
antenna
mouthparts
(mandible, maxilla,
and labium)
eye
mouthparts
legs
legs
too many
abdominal
appendages
morphs into “Oligopod” stage before hatching
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Parallel vs. serial/sequential segmentation
(long germ band insects)
(short / intermediate germ band insects)
initial
morphogen
gradient
gap genes
segment-polarity genes
(e.g. engrailed)
pair-rule
genes
14 post-cephalic
segments
segment-polarity genes
(e.g. engrailed)
14 stripes
No tissue growth
Sequential tissue growth
Fate map, Drosophila – a long germ band insect
Polarity, pattern formation, and appendage formation
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The eight Hox genes of Drosophila
(transcription factor genes)
Adult
Order of Hox genes
labial
proboscipedia
deformed
(regulate the development
and identity of each
region of the body)
antennapedia
ultrabithorax
abdominal-A, -B
Embryo
Summary of early tissue differentiation
oocyte
polar
nucleus
sperm
male
pronucleus
ovum with
female pronucleus
2 polar
bodies
zygote nucleus
vitellophage
cleavage nuclei
(resorbed)
pole cells
germ cells
oogonia or
spermatogonia
blastoderm
ectoderm:
mesoderm:
stomodeum & proctodeum,
neuroblasts & CNS,
epidermis & derivatives,
respiratory system
genital ridges
endoderm:
midgut
muscles,
fat body,
blood cells &
vascular system
gonads
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Hemocoelom, coelom, and mixocoelom
Hatching of the egg (eclosion)
Bedbug, Cimex sp.
(Hemiptera: Cimicidae)
Bollworm, Helicoverpa sp.
(Lepidoptera: Noctuidae)
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Hatching by means of a cap
Neuroptera: Ascalaphidae
Ululodes sp.
Post-embryonic development
AMETABOLOUS (Zygentoma)
(incomplete/complete metamorphosis)
HOLOMETABOLOUS
(Lepidoptera)
HEMIMETABOLOUS
(Hemiptera: Heteroptera)
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Pupal types (Endopterygota/Holometabola)
functional
mandibles
Decticous exarate
(Megaloptera: Corydalidae)
free appendages
Adecticous exarate
(Coleoptera, etc.)
free appendages
Adecticous obtect
(Lepidoptera: Sphingidae)
“glued”
appendages
Options: Decticous vs. Adecticous; Exarate vs. Obtect
Secondary return to adecticous exarate:
the puparium of higher Diptera and the coarctate pupa
Puparium
(larval skin)
Exarate pupa
inside puparium
Puparium after
eclosion
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Re-defining “instar”
Origin of the pupa
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3
4
Pharate adult
(monarch butterfly)
2
1
‘Pro-nymph’
(Truman &
Riddiford)
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