Development Flashcards
1
Q
Deuterostomes vs. Protostomes
A
- animal division based on -stome meaning mouth
- Protostomes: 1st opening that forms in embryos is mouth
- worms, mollusks, arthropods
- Deuterostomes: 2nd opening that forms in embryos is mouth; 1st is the anus
- all vertebrates - fish, amphibians, reptiles, birds, mammals
- echinoderms - invertebrates like sea urchins, sea stars
2
Q
4 differences between protostomes and deuterostomes
A
- Fate of Blastopore (embryo starts to divide until reaches in-folding which creates an opening called blastopore)
- blastopore becomes mouth in protostomes
- becomes anus in deuterostomes
- Cleavage - series of cell divisions
- protostomes - at 4 cells they jostle so max contact like soap bubbles - spiral cleavage
- deuterostomes - cells maintain their position called radial cleavage
- Fate of embryonic cells
- protostomes - determinate development/mosaic meaning each blastomere results in predetermined structure; if cell excised then development arrested
- each cell assigned a role in the individual
- deuterostomes - indeterminate development/regulative meaning cells in 8-16 cell stage aren’t fixed in dev potential yet, are flexible
- if take cell away other cells will compensate
- protostomes - determinate development/mosaic meaning each blastomere results in predetermined structure; if cell excised then development arrested
- Formation of coelom - body cavity that forms in developing organisms, forms in mesodermal layer and space in mesoderm is called coelom
- protostomes - mesoderm appears in corner and then spreads
- deuterostome - in-folding that happens and tissue that surrounds it creates a space as it folds
3
Q
Formation of Coelom
A
- coelom - body cavity lined w/mesoderm
- schizocoelous - splitting to get space for protostomes
- enterocoelous - extra folding that creates the space for mesoderm in deuterostomes
4
Q
Vertebrate Life Cycle/Stages of Development
A
- fertilization is before stages of development
- egg and sperm (haploid) give fertilized egg called zygote (diploid)
- Cleavage - formation of blastula (1000-3000 cells w/space in middle called blastocoel)
- Gastrulation - formation of gastrula (in-folding)
- Neurulation - formation of central nervous system w/Dorsel Hallow Nerve cord (spinal cord derived from this)
- Neural Crest Cell Formation - move from neural region to all parts of body; improved vertebrates (if sea urchin then don’t do much more after stage 3); more sophisticaed nervous system, > pigmentation
- Organogenesis - form organs to create a fetus (9-12 weeks of development); embryo all along and then here creates fetus
- Additional Growth and Development - form adult that produces egg or sperm to complete cycle and then die
5
Q
Fertilization
A
- first form haploid gametes and then fertilize to form zygote
- some animals have external fertilization (fish, protostomes in sea water)
- some animals have internal fertilization in specialized duct - oviduct/fallopian tube
6
Q
Gametogenesis - Spermatogenesis
A
- start w/diploid cells that are germ cells (sperm stem cells) in male
- go through meiosis I and II - one cell maintains population of stem cells and other diferentiates into sperm here
- after meiosis I they are haploid
- become primary and then secondary spermatocyte and then early spermatids
- toward end, sperms differentiate - shed extra cytoplasm and put all of their DNA in head of sperm
- mito is saved and packed away around long flagellum that forms
- modification lysosomes form acrosome at tip of head and holds digestive enzymes
- mito wrapped around midpiece w/9+2 arragement
7
Q
Sperm
A
- sperms break off and travel down the duct
- 100 million sperm a day in human male; similar hormones as those in female
- male cycles a bit as sperm levels fluctate
-
accessory cells that support development of the sperm
- ex. sustentacular and Leydig cells which produce testosterone
8
Q
Gametogenesis - Oogenesis
A
- diploid germ line cells in ovaries
- primary oocytes in female at birth (1/2 million - 1 mil cells), no new ones made
- primary oocyte is arrested in prophase I, until puberty
- puberty: 10-20 primary oocytes begin to mature into primary follicles each month - one gets ahead and 1 egg ovulates at a time
- 1st meiotic division occurs at time of ovulation: oocyte produced takes all the cytoplasm and leaves 1 set of chromosomes in polar body which degenerates (visible not functional) - 2ndary oocyte arrests in metaphase II
- first meiotic divition and ovulation are at same time
- primary oocyte travels in fallopian tube and when sperm enters it signals oocyte to complete second meiotic division
- chromosomes frozen metaphase II until sperm enters
- finishes the division and produces 2nd polar body - fertilized egg and sperm not quite zygote since separate nuclei
- nuclei have nuclear fusion and then its officially a zygot
9
Q
Follicle
A
- cell is inside a follicle in the ovary
- bunch of cells surround developing oocyte that secrete estrogen
- as follicle grows larger the oocyte stays the same and follicle becomes mature when called vesicular follicle w/fluid filled space in layers of follicle cells and makes buldge at side of ovary
- at ovulation, wall of ovary breaks open and so does follicle, get hole where ovulated oocyte w/assoc follicle cell as it travels down fallopian tubes
- when ovulation occurs, egg is released right near cilia of fallopian tube
- if egg misses fallopian tube can get ectopic pregnancy in abd
- if fertilized in tube can get tubal pregnancy
- uterus is specialized for growth and support of embryo
10
Q
Zona Pellucida
Vitelline Membrane
A
- Zona Pellucida - clear membrane that is semi-transparent that surrounds oocyte as travels down fallopian tube (seen in mammals)
- Vitelline Membrane - equivalent that surrounds egg in other deuterostomes
- as egg waits to be fertilized there is a clear membrane surrounding it
11
Q
Sea Urchin Fertilization
A
- head of sperm has nucleus and acrosome and some membrane-bound protein markers, and depolymerized G actin monomers
- fertilize externally
- eggs have jelly coat w/vitelline membrane
- acrosome breaks open jelly coat and dumps digestive enzymes and goes through jelly coat
- to facilitate contact, when acrosome breaks open, the active monomers form actin filaments and start producing actin which pushes out membrane w/bindin protein markers
- bindin receptors on vitelline membrane so egg and sperm meet and allows fusion of sperm and egg membranes
- when membranes have fused then DNA can push through and into cytoplasm of egg
- receptors on vitelline membrane and then plasma membrane fuses w/sperm membrane
12
Q
Fertilized vs. Unfertilized Egg (Sea Urchin)
A
- when sperm gets into egg then tells vitelline membrane to jump up
- opens pores and allows water to stream into vitelline membrane and not egg membrane
- osmotic pressure
- water rushes into space between vitelline membrane and plasma membrane to prevent other sperms from entering
- cortical rxn when cortical granules near edge of egg and when 1st sperm enters there’s a signal for granules to dump stuff between plasma and vitelline membrane and that causes membrane to jump up
- exception - frogs allow multisperm into egg and degrade all but one
13
Q
Mammalian Fertilization
A
- egg has zona pellucida to prevent multispermy/triploid child and has polar body around somewhere
- bunch of cells that are remaining follicle cells stuck on surface (called corona radiate instead of jelly layer in sea urchins)
- when sperm makes it in, it interacts w/radiate cells and acrosome releases digestive enzymes and goes through zona pellucida (which doesn’t jump up)
- sperm meets receptors on plasma membrane probably
- head of sperm fuses w/membrane up to back of head of sperm and mito of sperm is left out
- maternal mito inheritance only
- tail of sperm never enters
- cortical granule (near surface is the cortex) - release chemicals that signal zona pellucida to become hard and impermeable so additional sperm can’t enter to prevent multispermy by hardening zona pellucida through cortical granule
14
Q
“Capacitation”
A
- make sperm more competent to fertilize (discovered during in vitro fertilization)
- saline wash of fallopian tubes and add to dish w/sperm and eggs, then sperm more likely to fertilize the egg
- some factor that is secreted in fallopian tubes that encourages the sperm to fertilize and this factor is called capacitation
15
Q
Stages of Fertilization
A
- Penetration - acrosomal rxn, drilling through zona pellucida and fusion (mostly sperm actions)
- capacitation - make sperm more competent to fertilize w/saline wash of fallopian tubes - some kind of factor secreted in fallopian tubes that encourages sperm to fertilize
- Activation (egg actions)
- cortical rxns - ion exchange in membrane, action potential causes Ca2+ to release which causes cortical granules to open and rxn to happen - fertilization occurs in fallopian tubes
- compled 2nd meiotic division since in ovulation egg went through 1st meiotic division and then down fallopian tube and chromosomes frozen in metaphase II
- when sperm enters the meiosis II completes and 2 polar body attached
- Fusion of pronuclei - make diploid zygote
- called pronuclei when 2 haploid nuclei are in same cell but not diploid yet until fusion
16
Q
Amphibian fertilization - cytoplasmic rearrangement
A
- In frogs we see amphibian egg unfertilized, brown pigment on top and yellow bottom
- Sperm enters and pigmented top shifts to sperm entry point, creating grey pigment section called grey crescent
- Egg senses the sperm entering and shifts/rearranges factors within the egg so line down middle of egg where development occurs further
- Deuterostomes – regulated/non-determinate development, little less so in amphibians
- 1.5 mm egg
17
Q
Grey Crescent Experiments
A
- sperm enters and cell divides in half through middle of grey crescent which is normal, then you get normal tadpoles
- If turn egg and divide so L doesn’t get grey crescent then that side doesn’t develop but other side does
- If cleavage plain misses grey crescent then misses development, so factors that are distributed through that grey crescent and egg do seem to be important ; may be distribution effect in humans too but more subtle than this
18
Q
Cleavage –> Blastula in Echinoderms
A
- Cleavage is 1st stage of development – series of rapid (12 hours after fertilization) cell divisions, no transcription in between and no growth of cells, but do have to replicate the DNA using extra ORI
- Holoblastic cleavage since divide all the way through
- Radial cleavage so stay stacked as cells and not soap bubbles; hallowing out of the structure
- By around 1000-3000 cells have blastula stage which is end product of cleavage process - hallow space in blastula space but cells not differentiated into diff tissues yet, generalized ball w/space in middle ; space is the blastocoel
- More or less obvious which end is yolky end (animal pole is not so yolky) – more embryo forms at animal pole
- Bottom cells are absorbed in growing embryo
- In-folding occurs at vegetal pole, where the yolk is which is mix of proteins and lipids used for nutrition
19
Q
Cleavage in Amphibians (frogs)
A
- Amount of yolk makes a diff because yolk inhibits cell division
- Asymmetric holoblastic radial cleavage
- Embryos w/low yolk go through cell division unimpeded so doesn’t slow division
- Amphibian egg has lots of yolk at bottom – cell division occurs above and then slows drastically so second division occurs before 1st even finishes
- Transverse division slow; dense glob of yolk inhibits cell division
- End up w/many more and smaller cells at the top; fewer, larger cells at bottom
- Cells use up yolk as develops
- Blastocoel displaced to top since yolky cells at bottom are mess to deal with
20
Q
Discoid Cleavage in Chicks - Discal Cleavage (lots of yolk)
A
•yolk ball w/little cytoplasm; egg white is put on around there as source of additional nutrition by the mom and then shell gland;
yolky ball is released and then fertilization can happen, then white is added by mother
- One giant cell is egg white w/yolk
- Cell division can’t occur in giant yolky ball when sperm enters – start cleavage and then stalls around edges since yolk, then 4 cells not forming to membrane due to yolk ball; keeps dividing and dividing and group of cells becomes the embryo; abandons effort to divide through the yolk ball so divides where it can
- Cells are becoming the blastula of the chicken
- Analogous structure formed; 1000s of cells w/space called blastocoel that happens on top of giant yolk ball
- divides this way because of dense yolk ball – disc-like cleavage; all happens on top
- Sea urchins w/very little yolk, amphibians with medium amount of yolk, and birds and reptiles with ton of yolk, and very little yolk in mammals but acts like ancient reptile since derived from reptiles
21
Q
Blastulation in Mammals (very little yolk)
A
- Mammals have very little yolk – derived from reptiles so act little like there was yolk there even tho there’s not
- Early cleavage in mammal; Holoblastic cleavage means when divide they go all the way through
- Starts to form a ball and tight junctions between cells to create hallow space and not blastula yet – morula is intermediate phase w/tight junctions holding it all tightly together
- Blastula stage w/3000 cells and internal cells are inner cell mass and also a blastocoel under the cell mass
- Inner cell mass is part that will become embryo itself; outer cells are going to form extra embryonic structures called trophoblast cells like extra-embryonic membranes
- Embryonic stem cells from inner cell mass which become embryo proper
- We provide nutrition to offspring via placenta or mammary glands for lactation so don’t need tons of yolk to develop
- Animal pole at top and vegetal pole at bottom
