Lec63 Seaurchin - 
 Fertilization
and
Early
Development
 •  “ The
greatest
progressive
minds
of


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Unformatted text preview: 3/9/09
 Fertilization
and
Early
Development
 •  “ The
greatest
progressive
minds
of
 embryology
have
not
looked
for
hypotheses;
 they
have
looked
at
embryos.”
Jane
Oppenheimer
 •  “ The
questions
asked
by
developmental
 biologists
are
often
questions
about
becoming
 rather
than
about
being.”
Scott
Gilbert
 Simon
Wu
and
David
McClay,
Duke
Univ.
 Fertilization
and
Early
Development
 •  •  •  •  •  •  Phylogeny
 Sea
Urchin
Biology
 Sea
Urchins
as
Model
Organisms
 Fertilization
 Cleavage
 Gastrulation
 George
von
Dassow,
Univ.
of
Washington
 http://goblet.molgen.mpg.de/cgi‐bin/seaurchin‐insitubase.cgi
 George
von
Dassow,
Univ.
of
Washington
 http://goblet.molgen.mpg.de/cgi‐bin/seaurchin‐insitubase.cgi
 Simon
Wu
and
David
McClay,
Duke
Univ.
 Excavata
 Chromalveolata
 Rhizaria
 Archaeplastida
 Unikonta
 Animal
Phylogeny
(Metazoa)
 Animals
 Land
plants
 Fungi
 Basal
Metazoa
 Echinodermata
 Chordata
 Water
vascular
ser
‐
tem
 
 Janet
Pfeif ys wikimedia Radial
symmetry
in
adults
 Calcareous
endoskeleton
 Green
 algae
 Lophotrochozoa
 Ecdysozoa
 Deuterostomia
 Opisthokonts
 Protostomia
 Bilateria
 Bilateral
symmetry
 Three
germ
layers
 (triploblastic)
 Eukaryotic
Lineages
 Ancestral
Colonial
Flagellate
 Sea
Urchin
Biology
 •  Planet
Earth
–
BBC
video
(2007)

 •  Narrated
by
David
Attenborough
 Sea
Urchins
–
Model
Organisms
for
 Fertilization
and
Early
Development
 •  External
fertilizers
 •  Easily
produce
many
synchronously
 developing
embryos
 •  Transparency
of
eggs
and
embryos
 •  Closest
known
relatives
of
the
 chordates
(sister
group)
 •  Fate
map
known
for
60
cell
embryo

 •  Genome
sequenced
(2006)
 –  Science
10
Nov.
2006
Vol.
314
 1
 3/9/09
 Sea
urchin
genome
 •  23,300
genes,
814
megabases
 •  11,500
genes
turned
on
during
 first
2
days
of
development
 •  Possible
to
estimate
genetic
 repertoire
required
for
 formation
of
simple
embryo
 •  Complex
innate
immune
 system
(no
antibodies)
 •  Has
orthologs
of
genes
 associated
with
vision,
hearing,
 Light
sensing
 proteins,
yet
not
 balance
and
chemosensation
 sensing
light

 Science
News
‐
Dec.
6th,
2008
 No
Gene
Is
an
Island
by
Patrick
Barry
 Sequence
of
Events
 •  Fertilization
 Gametes
to
zygote
 Collecting
Sea
Urchins
 Discovery
News
–
2008
 http://www.youtube.com/watch?v=aVhI_zWSfa0
 •  Cleavage
 Zygote
to
blastomeres
to
 blastula
&
blastocoel
 Blastula
gastrulates,
 establishing
germ
 layers
&
archenteron
 in
the
gastrula
 •  Gastrulation
 Fertilization
in
the
Sea
Urchin
 Sperm
is
attracted
by
egg
jelly,
contacts
egg
 Acrosome
membrane
breaks
 Enzymes
released
to
 digest
jelly
layer
 Polymerization
of
actin
filaments
 forms
acrosomal
process
 The
Fast
Block
to
Polyspermy
 Bindin
proteins
on
acrosomal
 process
bind
to
vitelline
envelope
 Outpocketing
of
plasma
membrane
forms
 fertilization
cone
(due
to
actin
polymerization)
 Fusion
of
sperm
&
egg
plasma
membrane
 Na+
channel
in
egg
cell
membrane
opens;
influx
of
Na+
into
cell
–

 This
depolarization
causes
the
fast
block
to
polyspermy
(1
–
3
sec)
 Bindin
proteins
on
acrosomal
 process
bind
to
vitelline
envelope
 Outpocketing
of
plasma
membrane
forms
 fertilization
cone
(due
to
actin
polymerization)
 Fusion
of
sperm
&
egg
plasma
membrane
 Na+
channel
in
egg
cell
membrane
opens;
influx
of
Na+
into
cell
–

 This
depolarization
causes
the
fast
block
to
polyspermy
(1
–
3
sec)
 2
 3/9/09
 Fertilization
in
Sea
Urchin
 Events of Fertilization (cont’d) Fusion
of
sperm
&
egg
plasma
membrane
 Entry
of
sperm
nucleus
into
egg
 Release
of
Ca++
from
ER
 Exocytosis
of
cortical
vesicles
 Fusion
of
sperm
and
egg
nuclei
 (Karyogamy,
t
=
20
min)
 Enzymes
released
into
 perivitelline
space
break
bonds
 between
plasma
membrane
and
 vitelline
envelope
 Vitelline
and
plasma
 membranes
separate
 Formation
of
fertilization
membrane
 Release
of
sperm
binding
receptors
 First
mitotic
division
of
zygote
 Further
development
 Fig.
47.3
 Fertilization
in
Sea
Urchin
 Calcium wave Fig.
47.3
 Clicker
Q:

You
want
to
find
a
way
to
predict
 whether
or
not
two
Sea
Urchin
species
can
 successfully
hybridize.

Which
of
the
following
is
 most
likely
to
give
you
information
about
 gamete
compatibility?

 A.  Mitochondrial
DNA
divergence
 B.  Geographic
Distribution
 C.  Bindin
Divergence
 D.  Pluteus
morphology
 E.  Cortical
granule
composition
 Zigler,
K.
S.,
McCartney,
M.
A.,
Levitan,
Don
R.
&
Lessios,
H.
A.
Evolution
59:
2399‐2404
(2005).
 Slow
block
to
polyspermy
t=~30
sec
 3
 3/9/09
 Sea
Urchin
Parthenogenesis
 •  In
1900,
Jacques
Loeb
claimed
that
you
could
 get
sea
urchin
eggs
to
form
blastula
by
placing
 them
in
sea
water
with
MgCl2


 •  This
was
a
very
controversial
claim
–
what
 alternative
hypothesis
did
others
propose?
 What
kind
of
controls
do
you
think
he
used
to
 support
his
claim
that
these
blastula
arose
via
 parthenogenesis
(in
the
absence
of
any
sperm)?
 Sea
Urchin
Cleavage
 •  First
cleavage
is
meridional
(N‐S)
 •  Second
cleavage
is
also
 meridional,
at
right
angles
to
the
 first
cleavage
plane

 •  Third
cleavage
is
equatorial
and
 produces
two
cell
size
classes
 •  The
4th
cleavage
results
in
three
 cell
size
classes
 ni h as 
W of v.
 on gt in 
 Ge or ge 
vo D n
 as 
U w, so http://www.luc.edu/faculty/wwasser/dev/urchdev.htm
 Cleavage in Sea Urchin up to Blastula Lytechinus
variegatus
 Ectoderm,
Mesoderm
and
Endoderm
 A) Before first cleavage B) First cleavage (2 cells) C) Third cleavage (8 cells - radial) D) 16 cells (cleavages unequal) E) 32-cell (morula) F) Hatched blastula From
Logan,
C.
Y.
and
McClay,
D.
R.
 Development
124:
2213
–
2223
(1997)
 •  The
mesomeres
at
the
animal
pole
become
 ectoderm
(blue)
 •  The
micromeres
at
the
vegetal
pole
become
 mesoderm
(red)
 •  The
cells
in
between
become
the
endoderm
(yellow)

 Gastrulation
Transforms
the
Blastula
 •  Involves
large
scale
cell
 movement
 •  Establishes
three
germ
 layers
 •  Creates
tube
that
 becomes
primitive
gut
 •  Gastrulation
is
complete
 when
the
tube
tip
touches
 the
top
epithelium
and
 fuses
to
form
the
 Deuterostome
–
mouth
second
 archenteron

 Gastrulation
 1
 2
 PMC
=

 primary
 mesenchyme
 cells
 3
 4
 From
TEMs
by
Hideki
Katow
and
Michael
Solursh
 worms.zoology.wisc.edu/urchins/SUgast_ingression2.html
 http://www.luc.edu/faculty/wwasser/dev/urchgast.htm
 4
 3/9/09
 Cell
Movement
by
Filopodia
 from
http://www.stanford.edu/group/Urchin
 Cell
to
urchin
animation
 5
 ...
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This note was uploaded on 10/20/2009 for the course BIO G 1102 taught by Professor Walcott during the Spring '08 term at Cornell University (Engineering School).

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