Chapter 8 Principles of Development Flashcards
Hans Spemann and Hilde Mangold
Tissue induction using salamander embyros
- Take dorsal lip from salamander gastrula, implant on another host salamander, get a brand new salamander
What happens with Spemann and Mangold?
Spemann wins Nobel Prize in 1935
Mangold dies from gas heater accident
Preformation
the entire organism was in a miniaturized version within a sperm or egg
Epigenesis
(origin upon or after) an egg contains building material, activated by sperm.
A cell which has committed to a fate it is determined by one of two processes
- Specification
- Induction (usually irreversible)
Morphogenetic Determinants
transcription and inducing factors, direct activation and repress genes at the correct times
oocyte maturation
the egg increases in size
germinal vesicle
nucleus grows rapidly in size during egg maturation, becoming bloated with RNA and changes in appearance
T/F In some organismsm, Fertilization occurs before the oocyte has undergone meiosis
True
timing of fertilization is highly variable among organisms with regard to oocyte maturity
fertilization
male and female gametes unite to form a zygote
- combination of male and female genes
- restores diploid chromosomal status
T/F sperm is not always required for egg activatio
true
species specific recognition proteins
prevent fertilization by another species (postmating, prezygotic isolating mechanism). Especially useful for gametes in water.
polyspermy
fertilization by more than one sperm
fast block
electrical potential charge change in the egg membrane that acts as an electrical fence preventing other sperms from fusing in
slow block
cortical reaction, thousands of enzyme capsules release their contents between the egg membrane and vitellene envelope. Creates an osmotic gradient, water rushes in, sperm washed away. Later, causes the vitellene membrane to harden and physically block sperm.
fertilization membrane
harden vitelline envelope, permanent physical barrier to sperm
Sea urchin fertilization
Why do we use them?
- Easy to find, cheap
- Fertilization external, easy in lab
- Embryo transparent, easy to see development
- Very historic, aristotle used them
blastomeres
small, maneuverable cells
cleavage
no growth, big mass dividing to a group of normal sized cells
polarity is established
- animal pole
- vegetal pole (yolk end)
4 basic ways of yolk distribution
- Isolecithal
- Mesolecithal
- Telolecithal
- Centrolecithal
Isolecithal
eggs with very little yolk, evenly distributed throughout the egg
cleave easily
Mesolecithal
moderate amount of yolk at vegetal pole
telolecithal
lots of yolk at vegetal pole
centrolecithal
large, centrally located yolk
meroblastic
lots of yolk, cells sitting on top of undivided yolk
incomplete cleavage
holoblastic
cleavage furrows extened completely through the egg
direct development
embryo to a miniature adult
indirect development
multiple developmental stages
matrotrophy
the mother norusishes the developing embryo (shortcut for both developments)
bastula
a cluster of cells, usually hollow (blastocoel)
blastocoel
one layer of germ cells (one tissue layer)
gastrulation
the conversion of the spherical blastula into a two or three layered embyro
archenteron
the internal pouch formed in gastrulation
blastopore
the opening to the archenteron
three primary germ cell layers: triploblastic
ectoderm, endoderm, mesoderm
ectoderm
outermost germ layer; becomes integument and nervous system
endoderm
most of the GI tract, most of the internal organs
mesoderm
most connective tissues, fluids, and muscles
coelom
a body cavity completely surrounded by mesoderm, formed through one of two methods:
- schizocoely
- enterocoely
schizocoely
mesodermal band of tissue around gut forms before coelom. Splits mesodermal tissue. Coelom forms by ingression of mesoderm. in Protostomes
enterocoely
mesodferm forms two pockets of tissue, one on each side that eventually meet. coelom and mesoderm form at the same time. in deuterostome
protostomes
blastopore becomes mouth
spiral cleavage
deteurostome
blastopore becomes anus
radial cleavage
driesch experiment
sea urchin grinding and shaking
driesch and spemann/mangold
lead to the idea that every somatic cell contains the full genetic instructions for making an organism
- leads to cloning of cell lines and whole organisms (stem cell research)
conditional specification
The ability of cells to achieve their respective fates by interactions with other cells.
primary induction
from the dorsal lip (ectoderm) during gastrulation, last real chance to make a whole new organism
- gastrulation is really important
secondary induction
other cells types originate later from other induction events
primary streak
center of early embryonic growth in many animals
Synctial specification
a process that determines cell fates by involving interactions between parts of a single cell, rather than between cells
Synctium
single cell membrane surrounds multiple nuclei
Specification of body axes
Front/back (anteroposterior or top/bottom)
Left/right
Back/front (dorsoventral)
Very conserved genes
- hox
- sonic hedgehog
Hox genes
series of genes that controls the differentiation of cells and tissues in an embryo
Sonic hedgehog
signaling molecule released from neural tissue beneath spinal cord
segmentation (metamerism)
- division of the body into distinct segments
-Gap genes
-Pair-rule genes
gap genes
big segments
pair rule genes
divide the big segments into repeated segments
homeotic mutations
lead to the wrong body part forming in the wrong place
Protostomia clades
Lophotrochozoa and Ecdysozoa
Mosaic development
Pattern of animal embryonic development in which each blastomere contributes a specific part of the adult body. highly influence by distribution of cytoplasm
regulative development
A pattern of animal embryonic development in which the fates of the first blastomeres are not absolutely fixed.
spiral cleavage
blastomeres cleave obliquely at 45 degree angles, results in cells somewhat offset from their parent cell (P)
radial cleavage
blastomeres cleave evenly in relation to each other. Results in symmetrical looking embyro (D)
bilaterial cleavage
cleavage on one side is a mirror image of the other
example - ascidians
rotational cleavage
blastomeres divide at different times and some early blastomeres divide perpendicularly to others
example - mammals
discoidal cleavage
cleavage restricted to a small disk of cytoplasm on top of yolk
example - reptiles, most fish
Are all bilaterally symmetrical animals fundamentally similar?
yes
can we infere the anatomy of extinct ancestral species from developmetal genes?
no
is it possible that simple changes in developmental genes account for the wide diversity of organisms?
yes
amniotes
embryos form in a membranous sac, the amnion
four extraembryonic membranes
amnion, chorion, yolk sac, and allantois
amnion
fluid filled sac that encoses the embryo and provides an aqueous environment in which the embryo floats, protected from mechanical shock and adhesions
chorion
Outermost layer of the two membranes surrounding the embryo; it forms the fetal part of the placenta.
allantois
repository for metabolic wastes during development + functions as a respiratory sruface for exchange of oxygen and carbon dioxide
yolk sac
provides nourishment, very ancient
3 groups of mammals
monotremes, marsupials, placentals
monotremes
lay large, yolky eggs that closely resemble bird eggs
platypus and echidna
marsupials
pouched mammals
possums and kangaroos
placentals
94% class mammalia
have a placenta
placenta
modified version of an amnioticegg involving substantial modification to the utereus
why isn’t the placenta rejected by the mother’s immune system?
it produces proteins and lymphocytes that supress the mother’s immune system
placental development
- Allantois becomes incoporated into umbilical chord
- germinal period - (two weeks long in humans) embyro very resistant to outslide influence
- embryonic period - next eight weeks, all major organs forming, embryo extremely sensitive to outside influence
- fetal period - after two months, mostly growth and continued development
development of ectoderm
- Responsible for the nervous system
- Ectoderm thickens to form neural plate above notochord, edges join, form neural tube.
- Nerve cells grow and develop from cues exterior to the cell itself. They follow “road signs.”
development of endoderm
- Forms the digestive system
- Alimentary canal emerges from the primitive gut. Lungs, liver, pancreas emerge from foregut.
- Gill arches and their derivatives (jaws, ears) emerge from endoderm.
development of mesoderm
- Forms muscles (Arise from repeated segments called somites)
- Forms muscular organs such as heart
