Chapter 7: Fertilization (Mammals)

Question 1

fertilization usually takes place in the ___ region of fallopian tubes

Answer 1

ampulla region

Question 2

Oocytes in mammals released from the ovary is surrounded by a matrix containing ___ cells: ovarian cells of the follicle to which developing oocyte was attached

Answer 2

CMULUS CELLS

Question 3

Why are cumulus cells so important

Answer 3

salient for the oviduct fimbrae to pick up oocyte from ovary and propel it down female reproductive tract. No cumulus cells = no propelling

Question 4

3 components that allow sperm to move from vagina to oviduct

Answer 4

1) sperm motility: flagellar motion. In competitive species, sperm from the same male will form trans and aggregations where the combined propulasion of the falgella make the sperm swim faster

2) uterine muscle contractions
3) sperm rheotaxis: sperm get long-distance directional cues from the flow of liquid from the oviduct to the uterus

Question 5

rheotaxis

Answer 5

the process of migrating against current flow. Sperm use Catsper Ca2+ channels to sense calcium influx, and monitor the direction of the current.

Question 6

unlike sea urchins, mammalian sperm are immature and cannot undergo acrosommal reactions or sense directional cues outside of the vagina. They must first under go capacitation, or ___

Answer 6

competance.

Question 7

What happens if a sperm does not undergo capacitation in the female reproductive tract

Answer 7

sperm that don’t capacitate are unable to penetrate the egg, and remain in the cumulus matrix.

Question 8

3 molecular changes during capacitation of mammalian sperm

Answer 8

1) lipid changes: cholesterol is removed from the sperm head membranes in order to concentrate/shift the lipid rafts that allow proper binding of zona pellucida.
2) protein changes: proteins are LOST on the sperm surface. Some proteins can block the zona-pellucida recognizing sites on the sperm. Removing these proteins uncovers the recognizing sites and facilitates sperm binding
3) K+ also leaves the cell. Membrane potential becomes more NEGATIVE. allows Ca2+ channels to open. CA2+ and bicarbonate activate cAMP production, which is required for acrosomal membrane fusion and protein phosphorylation.

Question 9

although some proteins are lost, which phosphorylated protein migrates to the surface of the sperm head during capacitation (from acrosome)

Answer 9

Izumo : needed for sperm-egg fusion. Bicarbonate influx increases pH in sperm to activate Ca2+ channels: causes sperm to swim by acting on the microtubules and dynein in the flagella.

Question 10

during capacitation, K+ also leaves the cell. Membrane potential becomes more NEGATIVE. allows Ca2+ channels to open. CA2+ and ____ activate ____production, which is required for: acrosomal membrane fusion and protein phosphorylation.

Answer 10

K+ also leaves the cell. Membrane potential becomes more NEGATIVE. allows Ca2+ channels to open. CA2+ and BICARBONATE activate cAMP production, which is required for:

1) acrosomal membrane fusion
2) and protein phosphorylation. (IZUMO, which also helps with acrosomal membrane fusion)
3) bicarbonate opens Ca2+ channels by raisin gthe pH, allowing for More Ca2+ to enter the mammalian egg cell and trigger flagellar propulsion.–> hyperactivation

Question 11

before entering the ampulla, uncapacitated sperm bind to the membranes of the ___ cells. Why

Answer 11

oviduct cells. Allows the sperm to be capacitated before entering the ampulla where the egg is. Sperm are released when they are capacitated. Binding lengthens the sperm life span. Binding action functions as a block to polyspermy.
- slowing the rate of sperm capacitation maximizes the probability that sperm will be available to meet the egg in the ampulla.

Question 12

First “block” to mammalian polyspermy

Answer 12

binding of sperm to oviduct cells to allow them to undergo capacitation before going any further.

Question 13

How are capacitated sperm dislodged from the oviduct cells when they are done capacitating?

Answer 13

recall: the Ca2+ influx and bicarbonate raises the pH and activates flagellar motion. This causes hyperactivation and the asynchronous beating can dislodge the sperm from the membrane of oviduct cells.

Question 14

Capacitated sperm rotate around their ___ axis, where as uncapacitated sperm move ____.

Answer 14

Capacitated sperm rotate around their LONG axis, where as uncapacitated sperm move PLANARLY.

Question 15

___ and ___ enzyme found on the sperm surface enables the sperm to burrow and digest a path through the extracellular matrix of the ____ cells.

Answer 15

HYPERACTIVATION AND HYALURONIDASE enzyme found on the sperm surface enables the sperm to burrow and digest a path through the extracellular matrix of the CUMULUS cells. (TO REACH THE ACTUAL EGG).

Question 16

2 components that provide the sperm with directions

Answer 16

1) thermal environment: capacitated sperm respond to thermal gradients of 2 degrees. Ampullary region is warmer and preffered, which is why they swim to the ampula

2) chemical signals. Oocyte and cumulus cells secrete progesterone that can attract CAPACITATED sperm.
- in humans, progesterone has been shown to bind to a receptor that activates Ca2+ channels in the cll membrane of the sperm tail, leading to further cell hyperactivity.
- chemical gradients also form, perimtting sperm to move through cumulus, towards the egg. Progesterone provides direction and activates motility.

Question 17

chemical signals. Oocyte and cumulus cells secrete ____ that can attract____ sperm.

Answer 17

chemical signals. Oocyte and cumulus cells secrete progesterone that can attract CAPACITATED sperm.

Question 18

in humans, progesterone has been shown to bind to a receptor that activates Ca2+ channels in the cll membrane of the___ ____ leading to further ___ ___.

Answer 18

in humans, progesterone has been shown to bind to a receptor that activates Ca2+ channels in the cll membrane of the sperm tail, leading to further cell hyperactivity`

Question 19

3 Ca2+ induced sensing processes that get the mammalian sperm to the egg

Answer 19

1) rheotaxis: long range: vagina to ovariole
2) thermotaxis
3) chemotaxis, works within millimeters of the egg.

Question 20

When do cumulus cells release progesterone?

Answer 20

when the ovary releases and egg (during ovulation).

Question 21

zona pellucida is equivalent to ___ ___ of sea urchins

Answer 21

vitelline envelope. BUT ZP is denser with more glycoproteins.

Question 22

when does the acrosome reaction occur in mammals

Answer 22

often occurs wihtin the cumulus BEFORE sperm reaches the zone pellucida.

Question 23

in mammals, most sperm bind through ___ glycoproteins on the zona pelucida.

Answer 23

sperm bind through ZP2 glycoproteins on the ZP, and ZP3 is often seen too.

Question 24

in mammals, most sperm BIND through ___ glycoproteins on the zona pelucida.

Answer 24

sperm bind through ZP2 glycoproteins on the ZP, and ZP3 is often seen too.

Question 25

space between the acrosomal membrane and the sperm cell membrane

Answer 25

equatorial region

Question 26

the site of membrane fusion between sperm and egg occurs at the

Answer 26

equatorial region: site wehre the sperm actually binds to the egg.

Question 27

rather than binding of the TIP fo the sperm like in sea urchins, how does sperm bind to egg?

Answer 27

the side of the sperm head makes contact with the eg gmembrane. the equatorial region is the site where the sperm and egg fusion begins.

Question 28

Izumo is an ___-like protein originally in the membrane of the __- granules

Answer 28

Izumo is an IMMUNOGLOBULIN-like protein originally in the membrane of the ACROSOMAL- granules

Question 29

after the acrosome reaction occurs, Izumo becomes distributed along the surface of the sperm primarily along the ___ region. Izumo is not required for ___ but is required for ____

Answer 29

after the acrosome reaction occurs, Izumo becomes distributed along the surface of the sperm primarily along the EQUITORIAL region. Izumo is not required for BINDING but is required for FUSION.

Question 30

mechanism behind mammalian sperm-egg FUSION

Answer 30

Izumo protein on the equatorial region of the sperm bind to JUNO proteins on the oocyte surface. the Izumo-Juno complex recruits CD9 on the membrane of the egg to help with fusion.

Question 31

T/F there is a fast block in mammals

Answer 31

false. there is no fast block in mammals.

Question 32

T/F there is a fast block in mammals

Answer 32

false. there is no fast block in mammals.

Question 33

How does slow block occur

Answer 33

recall: sperm binds to ZP2 on zona pellucida of egg.

when block occurs, ZP2 gets cleaved by ovastacin so that binding to sperm cannot occur. This occurs when ovastacin is released from the cortical granules upon Ca2+ influx that occurs when sperm originally binds and activates the PIP2 pathway.

also, as sperm and egg fuse, JUNO is rleeased from the plasma membrane, effecitvely removing it from the Izumo docking site for sperm.
- Juno is now floating around in space between Zp and oocyte, the perivitelline space. Sperm can bind in this space, preventing them from meeting with any remaining Juno proteins that still reside on the oocyte membrane.

Question 34

Why is it beneficial the Juno sticks around in the perivitelline space after being released from the plasma membrane of the egg during slow block

Answer 34

Juno is now floating around in space between Zp and oocyte, the perivitelline space. Sperm can bind in this space, preventing them from meeting with any remaining Juno proteins that still reside on the oocyte membrane.

Question 35

Sperm bind to egg via ___ on the ZP, and then fuse to egg via ___-___ and ___ recruitment.

Answer 35

Sperm bind to egg via ZP2 on the ZP, and then fuse to egg via IZUMO-JUNO COMPLEX and CD9 recruitment.

Question 36

Fusion of genetic material takes a long time in mammals. DNA of sperm pronucleus is bound by ___

Answer 36

protamines: basic proteins that are tightly compacted through disulfide bonds

Question 37

how are the disulfide bonds of protamines broken in order to reduce the tightness of the DNA in the sperm?

Answer 37

Glutathione in the egg cytoplasm reduces the disulfide bonds and allows the sperm chromatin to uncoil.

Question 38

mammalian sperm enters the oocyte when the oocyte is stuck in ___

Answer 38

metaphase II. The egg is still diploid.

Question 39

Ca2+ surge brought by sperm entry inactivate ____ and allows for DNA synthesis. Additionally, Ca2+ also deactivates ___ and ___, allowing for the cell cycle to continue and finish meiosis.

Answer 39

Ca2+ surge brought by sperm entry inactivate MAPK and allows for DNA synthesis. Additionally, Ca2+ also deactivates CYCLIN and SECURIN (THOUGH MAPK DEACTIVATION/DEPHOSPHORYLATION), allowing for the cell cycle to continue and finish meiosis.

Question 40

Role of cyclin

Answer 40

prevents the cell cycle to continue. Ca2+ mediated deactivation in the egg allow for the cell cycle to continue.

Question 41

role of securin

Answer 41

protein that holds metaphase chromosomes together. inhibition of securin because of Ca2+ surge in egg allows for cell cycle to continue.

Question 42

T/F DNA synthesis as a result of MAPK deactivation occurs when the Egg and sperm DNA has wound together

Answer 42

false. DNA synthesis of both the sperm and egg DNA occurs separately in male and female pronuclei.

Question 43

the centrosome produced by the ____ generates asters from microtubule proteins stored in the ___. These microtubules join the ___ and allow them to migrate towards one another.

Answer 43

the centrosome produced by the MALE generates asters from microtubule proteins stored in the EGG. These microtubules join the PRONUCLEI and allow them to migrate towards one another.

Question 44

Once the pronuclei are joined by the asters, what happens?

Answer 44

the nuclear envelope of the sperm and egg breaksdown, but they do not yet form a zygote. The chromatin instead condenses into chromosomes and orient themselves on a common mitotic spindle (a true diploid nucleus is not seen until 2-cell stage rather than in zygote).
- The first cell isn’t really diploid because there has been no duplication.

Question 45

In addition to DNA, each sperm dispenses small amounts of __ , __ and ___. What portion gets degraded in the egg?

Answer 45

dispenses cytoplasm, mitochondria, and centriole.
mito from sperm gets degraded
sperm centriole survives to make a mitotic spindle.

Question 46

Sperm fertilization triggers Ca2+ intracellular rleease through ___ production by ____. What isoform is used? Which gamete contributes it?

Answer 46

IP3 production by PLC. PLC ZETA is used rather than PLC gamma seen in sea urchins. Also, the SPERM provides the PLC zeta. In urchins, PLCg is located alraedy in the egg. PLCz is transfered to egg during fusion, which causes Ca2+ influx from ER because IP3 binds to Ca2+ channels.

Question 47

Ca2+ released by IP3 in egg binds to:

Answer 47

1) MAPK: allows for DNA synthesis and resumed meiosis because cyclin and secretin are inhibited.
2) binds to calmodulin activated protein kinase: eliminates inhibitors of mRNA translation (ex/ eIF4E inhibitor is removed to allow for mrNA translation and protein production)
3) Synaptotagmin: initiates cortical granule fusion. Ovastacin in the cortical granule gets released to cleave ZP2 and prevent mroe sperm from binding

Question 48

Wh do we need multiple waves of Ca2_ in mammalian egg compared to sea urchin?

Answer 48

• egg must be active to undergo meiosis 2. Ca2+ is responsible for DNA replication and Meiosis. Meiosis occurs really SLOWLY in mammals, therefore, it needs more Ca2+ to keep activated. Sea urchin eggs are already diploid, and so the Ca2+ in EU eggs don’t need to be maintained for as long.