Development Flashcards
Two major categories of animals
deuterostomes and protostomes
deuterostomes
First opening is the anus; mouth forms second
ex: echinoderms (sea urchins), vertebrates (fish, amphibians, reptiles, birds, mammals)
protostomes
First opening is the mouth; anus forms second
ex: worms, mollusks, arthropods
deuterostomes vs. protostomes
- Cleavage - protostomes undergo spiral cleavage; deuterostomes undergo radial cleavage
- Determinant vs indeterminate development - protostomes have determinate development; deuterostomes have indeterminate development
- Fate of blastopore - protostomes - blastopore becomes mouth; deuterostomes - blastopore becomes anus
- Formation of coelom - protostomes have no folding occur in the mesoderm layer to form the coelom; deuterostomes have extra folding that occurs to form coelom
determinate vs. indeterminate development
indeterminate development means the cells at the 8-16 cell stage are not fixed in their development; you can remove one and the other cells can make up for it.
determinate development - causes damage if you remove a cell
leydig cells
make testosterone
sperm structure
- head - acrosomal vesicle, nucleus
- mid piece - mitochondria
- tail - flagellum
oogenesis
- primary oocyte begins meiosis but is arrested in prophase 1
- when girls hit puberty, primary oocyte begins meiosis again
- secondary oocyte arrests in metaphase II
- meiosis II completes only if the sperm fertilizes the egg
zygote
is the result of nuclear fusion - egg and sperm fuse nuclei
zona pellucida
an egg membrane layer underneath the corona radiata . Found in mammals. When the sperm fuses with the egg membrane it causes a hardening of the zone pellucida, which prevents multispermy in mammals
corona radiata
outer layer of cells protecting the egg in a mammal.
Sea urchin fertilization
sperm acrosomal enzymes digest the jelly coat of the egg. Actin monomers in the sperm start polymerizing to form microfilaments that push further into the egg. This nose pushes out and binding in the sperm can bind to their receptors on the egg. The membranes can then fuse and sperm can dump DNA into the egg.
When sperm gets into the egg, it signals Vitellin membrane to jump up - the cortical reaction is how sea urchins prevent multispermy
vitellin membrane
the membrane in sea urchins that jumps up when sperm fuses with egg membrane. Vitellin membrane jumping up is what prevents multispermy in sea urchins.
cleavage
the second stage of development that produces a blastula. This process is characterized by rapid cell division without any growth.
sea urchin cleavage
radial and holoblastic
holoblastic cleavage
cells divide all the way through
blastula
cells are not differentiated into tissues yet. 1000-3000 cell stage. The embryo arrives in the uterus in blastula form.
blastocoel
hollow space within the blastula
mammalian cleavage
mammals undergo holoblastic and radial cleavage. Blastocoel forms underneath the inner cell mass.
inner cell mass
found in the blastula stage of mammals and this group of cells goes on to form the embryo
trophoblast cells
the outer cells of the blastula that go on to form extra-embryonic structures (as opposed to inner cell mass, which forms embryo)
gray crescent
found in amphibian stage of fertilization. We don’t know what it is or how it works exactly, but if you fuck up the gray crescent material, you fuck up development.
cleavage in amphibians
asymmetric holoblastic radial cleavage. The result of this type of cleavage is that you end up with many more and smaller cells at the top of the embryo (animal pole) than the bottom (vegetal pole).
blastocoel is offset in frogs due to yolk presence
archenteron
primitive gut
archenteron
primitive gut. Forms during gastrulation
gastrulation in chicks
- -process of infolding occurs with the primitive groove
- -primitive groove becomes primitive streak, which determines the axis of division
- -Hensen’s node directs the head processes
morula
Forms in mammals. an early stage embryo consisting of cells (called blastomeres) in a solid ball contained within the zona pellucida.
gastrulation
The process of forming 3 primary germ layers - endoderm, mesoderm, ectoderm. Once gastrulation is complete, the tissues have been differentiated and are fated to their respective structures.
endoderm fate
digestive structures
mesoderm fate
bone and muscle
ectoderm fate
skin and nervous system
Gastrula
Has 3 primary germ layers and the cells are committed to developing into the fated structures at this point.
Amnion formation
This occurs just prior to gastrulation in humans. The amnion is one of 4 extra-embryonic membranes (yolk sac, chorion, and allantois being the others).
syncytiotrophoblast
cells that form from trophoblast cells and they will help the egg implant in the uterus when the time comes. The amniotic cavity will fill with fluid.
neuralation
the last stage of development. Involves the formation of the neural tube through the process of primary induction.
neuralation
the last stage of development. Involves the formation of the neural tube through the process of primary induction. Neural crest cells are the other major developmental feature of this stage.
neural plate, neural tube, notochord
The layout of every vertebrate involves the formation of a dorsal hollow nerve cord with the notochord just underneath it
main methods of forming organs and structures in developing embryo after gastrulation
primary induction and secondary induction
FGF and macho1
fibroblast growth factor and macho1 are both signal molecules. With just these 2 signal molecules you can make 4 different types of tissue.
FGF and macho1
fibroblast growth factor and macho1 are both signal molecules. With just these 2 signal molecules you can make 4 different types of tissue. This shows the power of induction.
how can you tell if gastrulation is still occurring in part of the embryo?
the presence of the primitive groove
somites
little muscle blocks that form on either side of the neural groove and will develop into muscle and vertebrate. The number of somites gives you a way to detect how far along the embryo is.
fate of the notochord
the notochord becomes the centrum of each vertebrae
neural crest cells
Form only in vertebrates.
Just as the neural cord is about to round up and close, a bunch of cells break off - these are the neural crest cells
Neural crest cells migrate down into the embryo - they are responsible for faster, better functionality in vertebrates. They’re responsible for bigger frontal lobes, pigmentation in different areas, better eyesight.
secondary induction
A tissue or organ signaling a germ layer or another tissue. Something signaling something that is NOT primary germ layer signaling primary germ layer.
pharyngeal gill arches
are found in every vertebrate at an early stage of development - the gill arches go on to form different structures in different animals
geography genes
There are certain genes that differentiate head from tail and right from left. Different proteins express at the head end than at the tail end of an embryo.
toolkit of genes
Geography genes (including polarity genes) plus Homeobox genes
polarity and gap genes
Signal head vs tail - these are directional genes
Pair rule genes
establish segments in the developing embryo
Segment polarity genes
determine whether the segment is facing the head end of the tail end
Enhancer region modularity
- -Enhancer regions are responsible for different tissues developing
- -A brain-specific enhancer region may be activated by brain-specific transcription factors. The brain-specific enhancer region then interacts with RNAPII to enhance transcription of the mRNA that translates the brain protein in the brain tissue. That results in Gene A expressing in the brain while it doesn’t express in the limb, for instance.
- -Basically tissue-specific expression of genes is controlled by enhancers
Homeobox genes
Genes that control segment identity. ex: In a fly, tells the fly which thoracic segment it needs to be. ex2: mutant fly grows legs out of its eyes if it has a mutation in hox genes.
–The 9 Hox genes are present in the same order in all animals basically
Hoxc6
The hox gene that establishes the beginning of the trunk of the body - this is where the first set of limbs will come out.
stem cells
inner cell mass produces embryonic stem cells
cleavage types
deuterostomes undergo radial cleavage, whereas protostomes undergo spiral cleavage.
Within radial cleavage, you can have holoblastic cleavage or discoid cleavage. Echinoderms and mammals undergo holoblastic cleavage b/c we don’t have much yolk. Amphibians have a medium amount of yolk so they undergo asymmetric holoblastic cleavage, resulting in there are more and smaller cells at the top of the embryo than at the bottom. Chicks undergo discoid cleavage because of their huge amount of yolk.
Spemann Mangold Experiment
Showed the effects of primary induction.
They removed a chunk of mesoderm in one embryo that was not in the area that typically turned into the notochord. They removed an area of mesoderm from another embryo from the area that does normally form the notochord and placed it in the missing spot of the first one. The first embryo then developed two nervous systems - the mesoderm induces the overlying ectoderm to form the nervous system.
Primary Induction
When one primary germ layer induces another primary germ layer to form a structure. Our best example: the mesoderm induces the overlying ectoderm to form the neural crest —> dorsal hollow nerve chord, as well as the notochord.
