3b: egg and sperm cells general features and 3c

Question 1

what are the two fertilization functions

Answer 1

1. fusion of genentic material
2. activation of egg metabolism and initiation of development (fertilization triggers the beginning of emrbyononic development

Question 2

Spermatogenesis

Answer 2

-sperm are highly specialized cells
-lose their cytoplasm

Question 3

typical sperm structure

Answer 3

-haploid nucleus
-dna tightly compacted by protamines which replace histones
-nucleus in head of sperm
-acromosome infront of nucleus, derived from golgi and contains enzymes and sugars
-sometime between there is globular actin
-mitochondria before tail (flagellum)
-flagellum core 9+2 microtubule structure of axoneme is conxserved

exceptions: nematodes have aflagellate sperm (no tail)

Question 4

Protamines

Answer 4

small arginine rich nuclear proteins that replace histones in sperm and allow for denser packing of dna in sperm head

Question 5

Axoneme structure of flagellum

Answer 5

has dynein which attaches to axoneme for propelling of sperm action
-it uses atp to promote the sliding of the microtubules, causing flagellum to bend and move as waves of dynesins bend it along the length(read slide 31)

Question 6

Egg structure

Answer 6

-ovum(egg)-female gamete capable of being fertilized
-oocyte: developing egg that cannot bind sperm or be fertilized yet

Enormous cells:
hsbvbe proteins
ribosomes
mrna
morphogenic factors
protective factors

-large nuclues
-at fertilization might still be diploid, in some stage of meiotic metaphase or already haploid pronucleus
-extracellular matrix (involved in sperm egg recognition, mat around egg
-egg cell membrane: fuse wtih sperm membrane , regulations of ions across
-beneath cell mem: cortex- enriched in globular actin and polymerize actin microfilaments which protude from egg surface

Question 7

what stage is the egg at the time of fertiliztation for mammals

Answer 7

second meotic metaphase arrest

Question 8

what is the difference between the extracellular matrix of invertebrates and mammalians

Answer 8

Invertebrates:
thin layer caleld vitelline envelope
-many have glycoprotein meshwork surrounding this which attracts sperm

Mammalia: thick layer called zona pellucida
-surrounded by CUMULUS, a layer of cells that nurture the egg at the tine of release from ovary
-innermost cumuls cells are called corona radiata

Question 9

What are the substages of meiotic 1 prophase

Answer 9

1) leptonene: condensed chromosomes are seen
2) zygotene: homologous chromoseoms pair up and synaptonomeal complex gorms between homologous chrom
30 pachytene : recombination, crossing over occurs
4) diplotene: sister chromatids seperate and synaptonomeal complex breaks
5) diakenesis: further seperation of sister and condensing occurs but still together at chiasma (since this seperation occurs in meiosis 2)

Question 10

what is homologous onthe egg tothe acromosome vesicle of sperm

Answer 10

cortical granules

Question 11

General interaction of egg and sperm

Answer 11

1) sperm attracted to egg due to chemoattraction (molecules secreted by egg)
2) exocytosis of sperm acromosome (releasing enzymes)
3)sperm binds to ecm (either vitiline envelope or zone pellucida)
4) sperm makes its way thru ecm
5) egg and sperm membranes fuse

2 and 3 could exchnge

Question 12

why are sea urchins good models for developmental biology

Answer 12

-sexually mature entire year
-can produce large transparent eggs in considerable quantities

Question 13

Chemotaxis, chemoattractants

Answer 13

Chemotaxis: directed movement of a cell in response to a chemical gradient such as sperm following chemical secreted by egg,, from egg jelly

Chemoattractants are highly species specific- pepties released from on have receptors on other

-also called sperm-activating peptides since the chemoattracants activate the sperm to produce more atp to move more

Question 14

what is resact

Answer 14

14 AA peptide released from egg jelly of sea urchin, only works on sperm of the same species, only they have te receptor for it

Question 15

What is the acrosomal reaction in sea urchins

Answer 15

1) acrosomal mem and sperm call mem fuse (results ine exocysoe of acrosome content)
2) leads to extension of acrosomal process

-triggered by contact with egg jelly
-acrosomal enzmes released digest path through jelly layer
-once thorugh the jelly layer, acrosomal process adheres to vitiline envelope and can digest it where attached

Question 16

what initiates the acrosomal reacton

Answer 16

-the receptors on sperm contact SPECIES SPECIFIC SULFATED POLYSACCHARIDES on egg jelly coat, iniates it

Question 17

what on the egg jelly of egg is species specific highly

Answer 17

the sulfated polysaccharides

-binding of thisto the receptors on the sperm membrane leads to acrosomal reaction by activating other sperm membrane proteins

Question 18

What are the species specfic reactions that happens on egg jelly with sperm

Answer 18

1) small peptides released from egg jelly lead to chemoattraction and sperm activation

2) sulfated polysaccharides on egg jelly can bind to sperm receptors and lead to acrosomal reaction

3)Acrosomal protein called BINDIN binds to dejellied eggs (eggs after acrosomal reaction and sperm digesting jelly) and will clump together
-also species specific

need specfici receptors for akk of these reactions

Question 19

Bindin receptors

Answer 19

in vitiline envelope
-limit the number of sperm that can bind to the vitiline envelope
-not highly concentrated on envelope, so there is still exposed area when sperm binds

EBR1 glycoprotein is a bindin receptor

Question 20

what are the species specific reactions simplified

Answer 20

1) find the egg (chemoattractins allow sperm to find and be activated)

2)penetrate coat (sulfated polysacharides allow sperm to bind and digest jelly coat)

3)adhere to viteline envelope (bindin ie EBR1 glycoprotein receptor allow sperm to bind to envelkpe)

Question 21

After the three species specific stesp what happens

Answer 21

sperm and egg membrane must FUSE and form fertilization cone (strucutre rich in filamentous actin)

-requires specific proteins like binidin bc hard to fuse two lipid bilayers
-can occur anywhere on egg membrane surface for sea urchins

Question 22

what is the two functions of bindin

Answer 22

1) attachment of sperm to vitiline envelope

2) fusion of sperm adn egg membrane due to the long stretch of hydrophobic AA’s near terminus called fusogenic region

Question 23

How do we know bindin is necessary for fertilization

Answer 23

when we used cas9-mediated inactivation of bindin gene, it showed that in a sea urhcin a perfectly normal looking embryo BUT the bindin lacking sperm never fertilized the egg

Question 24

What happens if more than one sperm enters the egg

Answer 24

polyspermy: more than one enters
leads to triploidy (three sets of chromosomes) then have two sets of spindles seperating three pairs of chromosomes, PROBLEM

-triploidy itself is not lethal but can cause lots of problems

Question 25

How does egg prevent polyspermy

Answer 25

PREVENTS ENTRY OF SECOND

1) Fast block: electrical change of egg membrane
before sperm: lots of NA outside, less inside, has resting membrane potential of -70
after binding of sperm mem: shifts to +20mv whcih prevents other sperm bc fusogenic region of bindin doesnt work on pos charged surface
-occurs in sea urchins not mamals
-only lasts one min so sperm needs to be removed from surface

2) slow block:
-sperm entry causes cortical granules of egg to fuse with egg membrane releasing the contents and proteins called CORTICAL GRANULE SERINE PROTEASE
-those proteins cleave protein posts that connect viteline envelope to egg membrane
-mucopolysaccharides push away the viteline envelope as well and absorb water to move it away from egg membrane
-protein cross link enzymes stabilize the fertilization membrane
-hyalin forms coat around the egg, egg ectends long microvilli into hyaline layer so it provides structural support

Question 26

What is apart of the cortical granules that is released after fast block

Answer 26

cortinal granules contain:
-cortical granule serine protease
-mucopolysaccharides
-portein crosslinking enzymes (TP and OVOP)
-hyaline

Question 27

How does the coritcal granule reaction occur

Answer 27

1) Ca conc increases in egg cytoplasm after fertilization: brief entry of CA from outside to inside
2)calcium wave
3) ca increase triggers the cortical granule membrane fusion
calcium ionophore triggers increase

where does Ca come from
calcium stored in endoplasmic reticulum

Question 28

How are calcium channels opened to be releaed to trigger cortical granule fusion

Answer 28

opened by IP3 (inositol 1,4,5-triphosphate )

Where does it come from:
PIP2
Membrane phospholipid phosphatidylinositol 4,5-bisphosphate (PIP2) is substrate of phospholipase C (PLC) yielding products IP3 and diacylglycerol (DAG).