Class 9: Fertilization

Question 1

Ampulla of the oviduct:

Answer 1

Top region of the oviduct where egg travels from ovary after ovulation (release from ovarian follicle)

Question 2

Prophase I arrest

Answer 2

Oocytes are arrested at prophase I until puberty when luteinizing hormone (LH) induces resumption of meiosis of follicle-enclosed oocytes. 2N 4C

Question 3

Metaphase II arrest:

Answer 3

oocyte (meiotic) maturation to Metaphase II arrest (progress through meiosis I into meiosis II.) The egg will remain in this arrest as 1N 2C, essentially frozen until fertilization occurs. The egg is poised here, waiting for hormones to kick off, and will not complete meiosis unless fertilized. NOTE: egg is never really 1N 1C because final metaphase doesn’t happen until sperm enters.

Question 4

Cumulus layer, cumulus cell (formerly granulosa cell)

Answer 4

cumulus cells are the granulosa cells from the follicle that are associated with and surround the egg

Question 5

Zona pellucida

Answer 5

the egg coat, synthesized and secreted by the oocyte during oogenesis. Composed of glycoproteins. Functions include: supports sperm interaction (the sperm can interact with the ZP glycoproteins), can help induce the sperm to undergo acrosome exocytosis, and later encases and protects the embryo during preimplantation development.

Question 6

Epididymal maturation

Answer 6

sperm in the testis are essentially “useless” they cannot swim yet or fertilize eggs. When sperm pass through the epididymis they mature and acquire motility and the ability to undergo capacitation.

Question 7

Seminal vesicle, prostate, bulbourethral gland

Answer 7

provide key components of semen which are mixed with the seminal fluids - nutrients, mucus and buffering components.

Question 8

Semen

Answer 8

composed of sperm, nutrients, mucus and buffering components.

Question 9

Capacitation

Answer 9

physiological changes in sperm that confer the ability/capacity to fertilize an egg, activated through second messenger cAMP and signal transduction cascade. Notable changes: loss of cholesterol from the sperm plasma membrane, “hyperactiviation” = different motility patterns, capable of undergoing acrosome exocytosis.

Question 10

Hyperactivation/CatSper

Answer 10

gained through capacitation, different/faster motility problems needed to access egg. CatSper (short for cation channel of sperm) is a protein in the sperm membrane that regulates the hyperactivated sperm motility.

Question 11

Lactobacilli, microbiome

Answer 11

microbes in the vagina and the collection of microbes respectively. A normal vaginal microbiome maintains vaginal health and prevents vaginal infections through a normal vaginal PH which is acidic (low PH.)

Question 12

Acrosome

Answer 12

organelle that develops over the anterior half of the spermatazoa - like the cap on the sperm. The contents include surface antigens and numerous enzymes which are responsible for breaking through the egg’s tough coating and allowing fertilization to occur.

Question 13

Acrosome exocytosis (or acrosome reaction)

Answer 13

When Sperm interacts with Zona Pellucida –> acrosome exocytosis. Release of acrosome contents out of the sperm, via fusion of outer acrosomal membrane with the plasma membrane. Calcium is a key second messenger that induces the sperm to undergo acrosome exocytosis.

Question 14

Egg activation

Answer 14

signal from the sperm triggers the egg-to-embryo transition - induces the egg to undergo the necessary physiological changes to become a one-cell-embryo (zygote). Calcium is also an important second messenger in the egg to trigger egg activation. Main results: 1. prevention of polyspermy 2. cell cycle resumption ie finishes meiosis and progresses to embryonic mitosis.

Question 15

PLC ( PLCzeta )

Answer 15

A sperm specific PLC which generates IP3 in the sperm-egg cytoplasmic fusion. –> release of calcium necessary for egg activation

Question 16

Cortical granules

Answer 16

small granules in the egg, just under the plasma membrane. Calcium increase induces exocytosis of the cortical granules. Cortical granules release enzymes that modify the components of the ZP, so that sperm can no longer bind the ZP on the fertilized egg → block polyspermy.

Question 17

Polyspermy

Answer 17

fertilization by more than one sperm. Egg activation blocks this from happening.

Question 18

Zygote

Answer 18

a one-cell embryo, reaches this stage after egg activation and completion of meiosis.

Question 19

Cleavage

Answer 19

cell division for embryos (mitosis and cell division to two cell, four cell, eight cell stages.)

Question 20

Blastomere

Answer 20

one cell of a multicellular embryo.

Question 21

Morula

Answer 21

After compaction, the embryo is in the morula stage.

Question 22

Blastocyst

Answer 22

embryonic stage formed through the processes of compaction and cavitation. Blastocyst reaches uterus and if endometrium is ready, implantation occurs → post implantation development including the formation of the placenta. The blastocyst hatches from the zona pellucida in order to implant.

Question 23

Compaction, cavitation

Answer 23

compaction is the first differentiation event in the embryo. During compaction the cells of the embryo bind tightly to each other, forming a compact sphere. Cavitation - the formation of a cavity in the embryo - along with additional cell divisions form the blastocyst.

Question 24

Inner cell mass, trophoblast

Answer 24

the two cell types in the blastocyst.

Question 25

Embryonic stem cell

Answer 25

the inner cell mass cells of the blastocyst can be isolated and cultured to perform stem cell research.

Question 26

2 Steps egg’s preparations for fertilization

Answer 26

(1) Egg changes location from ovary to oviduct following ovulation (release from ovarian follicle) and transits to top region (ampulla) of the oviduct. (2) Meiotic maturation to metaphase II

Question 27

The sperm’s preparations for fertilization (4 stages)

Answer 27

(1) Epididymal maturation - sperm change from the testis to the end of the epididymis, sperm mature during epididymal transfer and acquire motility and ability to undergo capacitation. (2) Mixture with seminal fluids - nutrients, mucus and buffering components (which neutralize the acidity of the vagina in order to pass through.) (3) Capacitation - the physiological changes in sperm that confer the capacity to fertilize an egg. Occurs in the female reproductive tract. (4) Storage in the female reproductive tract - sperm bind to the epithelial cells that line the oviduct. Sperm can live for several days in the female tract (this is why the timing of emergency contraception is important.)

Question 28

Steps to Fertilization (4 stages)

Answer 28

(1) Sperm-cumulus interaction - ovulated egg is surrounded by cumulus cells embedded in an extracellular matrix. Sperm binds to and works through the matrix. Motility is necessary for the sperm to get through the layers of cumulus cells of to the zona pellucida. (2) Sperm-zona pellucida (ZP) interaction - the ZP is the egg coat composed of glycoproteins, ZP helps induce the sperm to undergo acrosomal exocytosis, where the acrosome releases enzymes that can help to digest a hole in the ZP. (3) Sperm-egg plasma membrane interactions - making one cell out of two by merging the membranes of the sperm and the egg. (4) Egg activation - signal from the sperm triggers the egg-to-embryo transition.