Download BIOL212DevelopmentPDF23MAY2012

22/05/12 Scholarships 2012- 2013
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applications for next year’s scholarships.
Please let returning students know that it’s a
simple one-page application for both meritand need-based awards, and direct them to
https://northseattle.edu/edfund-scholarships
to learn more! The deadline is May 31.
Commit to Complete
Signing Ceremony.
•  Phi Theta Kappa Alpha Epsilon Omega
Chapter and North Seattle Community
College
•  http://www.cccompletioncorps.org/
•  Today, Weds. 23 May at 1:15
•  in the hallway on the way to the cafeteria
•  President Mark Mitsui will lead this ceremony. •  Students are encouraged to attend!
Animal Development
Common themes
Differences
INTERCONNECTEDNESS
REDUCE – REUSE – RECYCLE
1 22/05/12 Figure 47.1
1 mm
Fertilization
•  Molecules and events at the egg surface play a
crucial role in each step of fertilization
–  Sperm penetrate the protective layer around the
egg
–  Receptors on the egg surface bind to molecules
on the sperm surface
–  Changes at the egg surface prevent
polyspermy, the entry of multiple sperm nuclei
into the egg
The Acrosomal Reaction
•  The acrosomal reaction is triggered when the
sperm meets the egg
•  The acrosome at the tip of the sperm releases
hydrolytic enzymes that digest material
surrounding the egg
© 2011 Pearson Education, Inc.
2 22/05/12 Figure 47.3-5
Sperm
plasma
membrane
Sperm
nucleus
Basal body
(centriole)
Sperm
head
Acrosome
Jelly coat
Sperm-binding
receptors
Fertilization
envelope
Acrosomal
process
Actin
filament
Cortical
Fused
granule
plasma
membranes
Hydrolytic enzymes
Perivitelline
space
Vitelline layer
Egg plasma membrane
EGG CYTOPLASM
•  Gamete contact and/or fusion depolarizes the egg cell membrane and sets up a fast block to polyspermy •  The Cortical Reaction
•  Fusion of egg and sperm also initiates the cortical
reaction
•  Seconds after the sperm binds to the egg, vesicles
just beneath the egg plasma membrane release their
contents and form a fertilization envelope
•  The fertilization envelope acts as the slow block to
polyspermy
•  The cortical reaction requires a high concentration of
Ca2+ ions in the egg
© 2011 Pearson Education, Inc.
•  Development occurs at many points in the life cycle of an animal •  This includes metamorphosis and gamete producEon, as well as embryonic development © 2011 Pearson Education, Inc.
3 22/05/12 Egg Ac&va&on •  The rise in Ca2+ in the cytosol increases the rates of cellular respiraEon and protein synthesis by the egg cell •  With these rapid changes in metabolism, the egg is said to be acEvated •  The proteins and mRNAs needed for acEvaEon are already present in the egg •  The sperm nucleus merges with the egg nucleus and cell division begins © 2011 Pearson Education, Inc.
Fer&liza&on in Mammals •  FerElizaEon in mammals and other terrestrial animals is internal •  SecreEons in the mammalian female reproducEve tract alter sperm moElity and structure •  This is called capacitaEon, and must occur before sperm are able to ferElize an egg © 2011 Pearson Education, Inc.
•  Sperm travel through an outer layer of cells to reach the zona pellucida, the extracellular matrix of the egg •  When the sperm binds a receptor in the zona pellucida, it triggers a slow block to polyspermy •  No fast block to polyspermy has been idenEfied in mammals •  In mammals the first cell division occurs 12-­‐36 hours aUer sperm binding •  The diploid nucleus forms aUer this first division of the zygote © 2011 Pearson Education, Inc.
4 22/05/12 Figure 47.5
Zona pellucida
Follicle cell
Sperm
nucleus
Sperm
basal body
Cortical
granules
Cleavage •  FerElizaEon is followed by cleavage, a period of rapid cell division without growth •  Cleavage parEEons the cytoplasm of one large cell into many smaller cells called blastomeres •  The blastula is a ball of cells with a fluid-­‐filled cavity called a blastocoel © 2011 Pearson Education, Inc.
Figure 47.6
50 µm
(a) Fertilized egg
(b) Four-cell stage (c) Early blastula
(d) Later blastula
5 22/05/12 Cleavage Pa6erns •  In frogs and many other animals, the distribuEon of yolk (stored nutrients) is a key factor influencing the paYern of cleavage •  The vegetal pole has more yolk; the animal pole has less yolk •  The difference in yolk distribuEon results in animal and vegetal hemispheres that differ in appearance © 2011 Pearson Education, Inc.
•  The first two cleavage furrows in the frog form four equally sized blastomeres •  The third cleavage is asymmetric, forming unequally sized blastomeres •  Holoblastic cleavage, complete division
of the egg, occurs in species whose eggs
have little or moderate amounts of yolk,
such as sea urchins and frogs
•  Meroblastic cleavage, incomplete
division of the egg, occurs in species with
yolk-rich eggs, such as reptiles and birds
© 2011 Pearson Education, Inc.
Figure 47.7a-5
Animal pole
Gray crescent
Zygote
2-cell stage
forming
Blastocoel
Vegetal pole
4-cell stage
forming
8-cell stage
Blastula
(cross section)
6 22/05/12 Figure 47.7
Zygote
2-cell
stage
forming
Gray crescent
0.25 mm
8-cell stage (viewed
from the animal pole)
4-cell
stage
forming
Animal
pole
8-cell
stage
0.25 mm
Blastula (at least 128 cells)
Vegetal pole
Blastocoel
Blastula
(cross
section)
Regula&on of Cleavage •  Animal embryos complete cleavage when the raEo of material in the nucleus relaEve to the cytoplasm is sufficiently large © 2011 Pearson Education, Inc.
Concept 47.2: Morphogenesis in animals involves specific changes in cell shape, posiEon, and survival •  AUer cleavage, the rate of cell division slows and the normal cell cycle is restored •  Morphogenesis, the process by which cells occupy their appropriate locaEons, involves –  Gastrula:on, the movement of cells from the blastula surface to the interior of the embryo –  Organogenesis, the formaEon of organs © 2011 Pearson Education, Inc.
7 22/05/12 GastrulaEon •  Gastrulation rearranges the cells of a blastula into
a three-layered embryo, called a gastrula
•  The three layers produced by gastrulation are called
embryonic germ layers
–  The ectoderm forms the outer layer
–  The endoderm lines the digestive tract
–  The mesoderm partly fills the space between the
endoderm and ectoderm
•  Each germ layer contributes to specific
structures in the adult animal
Video: Sea Urchin Embryonic Development
© 2011 Pearson Education, Inc.
Figure 47.8
ECTODERM (outer layer of embryo)
• Epidermis of skin and its derivatives (including sweat glands,
hair follicles)
• Nervous and sensory systems
• Pituitary gland, adrenal medulla
• Jaws and teeth
• Germ cells
MESODERM (middle layer of embryo)
• Skeletal and muscular systems
• Circulatory and lymphatic systems
• Excretory and reproductive systems (except germ cells)
• Dermis of skin
• Adrenal cortex
ENDODERM (inner layer of embryo)
• Epithelial lining of digestive tract and associated organs
(liver, pancreas)
• Epithelial lining of respiratory, excretory, and reproductive tracts
and ducts
• Thymus, thyroid, and parathyroid glands
Gastrula&on in Sea Urchins •  Gastrulation begins at the vegetal pole of the
blastula
•  Mesenchyme cells migrate into the blastocoel
•  The vegetal plate forms from the remaining cells of
the vegetal pole and buckles inward through
invagination
•  The newly formed cavity is called the archenteron
•  This opens through the blastopore, which will
become the anus
© 2011 Pearson Education, Inc.
8 22/05/12 Figure 47.9a-5
Blastocoel
Animal
pole
Mesenchyme
cells
Filopodia
Vegetal Vegetal
pole
plate
Archenteron
Blastocoel
Archenteron
Digestive tube
(endoderm)
Ectoderm
Blastopore
Key
Mouth
Mesenchyme
(mesoderm forms
future skeleton)
Future ectoderm
Future mesoderm
Anus
(from blastopore)
Future endoderm
Figure 47.9b
Blastocoel
Filopodia
Mesenchyme
cells
Blastopore
Archenteron
50 µm
Variations
•  Frogs
•  Chicks
•  Humans
9 22/05/12 Gastrula&on in Frogs •  Frog gastrulation begins when a group of cells on
the dorsal side of the blastula begins to
invaginate
•  This forms a crease along the region where the
gray crescent formed
•  The part above the crease is called the dorsal lip
of the blastopore
•  Cells continue to move from the embryo surface
into the embryo by involution
•  These cells become the endoderm and
mesoderm
•  Cells on the embryo surface will form the
ectoderm
© 2011 Pearson Education, Inc.
Gastrula&on in Chicks •  Prior to gastrulation, the embryo is composed of an
upper and lower layer, the epiblast and hypoblast,
respectively
•  During gastrulation, epiblast cells move toward the
midline of the blastoderm and then into the embryo
toward the yolk
•  The midline thickens and is called the primitive
streak
•  The hypoblast cells contribute to the sac that
surrounds the yolk and a connection between the
yolk and the embryo, but do not contribute to the
embryo itself
© 2011 Pearson Education, Inc.
Figure 47.11
Fertilized egg
Primitive
streak
Embryo
Yolk
Primitive streak
Epiblast
Future
ectoderm
Blastocoel
Migrating
cells
(mesoderm)
Endoderm
Hypoblast
YOLK
10 22/05/12 Gastrula&on in Humans •  Human eggs have very liYle yolk •  A blastocyst is the human equivalent of the blastula •  The inner cell mass is a cluster of cells at one end of the blastocyst •  The trophoblast is the outer epithelial layer of the blastocyst and does not contribute to the embryo, but instead iniEates implantaEon © 2011 Pearson Education, Inc.
Figure 47.12
Endometrial epithelium
(uterine lining)
1 Blastocyst reaches uterus.
Uterus
Inner cell mass
Trophoblast
Blastocoel
2 Blastocyst implants
(7 days after fertilization).
Expanding region of
trophoblast
Maternal
blood
vessel
Epiblast
Hypoblast
Trophoblast
3 Extraembryonic membranes
start to form (10–11 days),
and gastrulation begins
(13 days).
Expanding region of
trophoblast
Amniotic cavity
Epiblast
Hypoblast
Yolk sac (from hypoblast)
Extraembryonic mesoderm cells
(from epiblast)
Chorion (from trophoblast)
4 Gastrulation has produced a
three-layered embryo with
four extraembryonic
membranes.
Amnion
Chorion
Ectoderm
Mesoderm
Endoderm
Yolk sac
Extraembryonic mesoderm
Allantois
Developmental AdaptaEons of Amniotes •  The colonizaEon of land by vertebrates was made possible only aUer the evoluEon of –  The shelled egg of birds and other repEles as well as monotremes (egg-­‐laying mammals) –  The uterus of marsupial and eutherian mammals © 2011 Pearson Education, Inc.
11 22/05/12 •  In both adaptaEons, embryos are surrounded by fluid in a sac called the amnion •  This protects the embryo from desiccaEon and allows reproducEon on dry land •  Mammals and repEles including birds are called amniotes for this reason © 2011 Pearson Education, Inc.
•  The four extraembryonic membranes that form around the embryo –  The chorion funcEons in gas exchange –  The amnion encloses the amnioEc fluid –  The yolk sac encloses the yolk –  The allantois disposes of waste products and contributes to gas exchange © 2011 Pearson Education, Inc.
Organogenesis •  During organogenesis, various regions of the germ layers develop into rudimentary organs •  Early in vertebrate organogenesis, the notochord forms from mesoderm, and the neural plate forms from ectoderm © 2011 Pearson Education, Inc.
12 22/05/12 Figure 47.13a
Neural folds
Neural
fold
1 mm
Neural
plate
Notochord
Ectoderm
Mesoderm
Endoderm
Archenteron
(a) Neural plate formation
•  The neural plate soon curves inward, forming the neural tube •  The neural tube will become the central nervous system (brain and spinal cord) Video: Frog Embryo Development © 2011 Pearson Education, Inc.
Figure 47.13b-3
Neural
fold
Neural plate
Neural
crest cells
Neural
crest cells
(b) Neural tube formation
Outer layer
of ectoderm
Neural
tube
13 22/05/12 •  Neural crest cells develop along the neural tube of vertebrates and form various parts of the embryo (nerves, parts of teeth, skull bones, and so on) •  Mesoderm lateral to the notochord forms blocks called somites •  Lateral to the somites, the mesoderm splits to form the coelom (body cavity) © 2011 Pearson Education, Inc.
Figure 47.13c
Eye
SEM
Neural tube
Notochord
Coelom
Somites
Tail bud
1 mm
Neural
crest
cells
Somite
(c) Somites
Archenteron
(digestive
cavity)
14