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Next Gen Exam 1 > Fertilization > Flashcards

Fertilization Flashcards

1
Q

In ruminants, primates, rodents and cats, Upon intromission and ejaculation, semen is deposited into…

A

The Vagina

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2
Q

In pigs and equids, Upon intromission and ejaculation, semen is deposited into….

A

The cervix to into the uterus

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3
Q

In dogs, Upon intromission and ejaculation, semen is deposited into…

A

The uterus

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4
Q

Retrograde transport of semen

A

60% lost in cattle 12 hours post-insemination

Gel fraction reduces in some species (pig, horse, primates, rodents)

forms a visible vaginal “plug” in rodents

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5
Q

Major barrier to sperm transport in the female tract

A

Cervix (except in pigs and dogs)

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6
Q

Cervical sperm transport description

A

Rapid phase:
Injection to uterus by ejaculatory force (especially mares)

Slow phase:
Sperm swim upgrade through “channels” in cervical crypts to avoid retrograde mucous flow

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7
Q

In the slow phase of cervical transport sperm swim through…

A

“channels” in cervical crypts to avoid retrograde mucous flow

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8
Q

In the uterus sperm is transported anterograde towards the…

A

Utero-tubule junction by peristaltic contraction (estrogen induced)

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9
Q

The uterus has peristaltic contractions induced by ________ that move sperm anterograde towards the UTJ

A

Estrogen

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10
Q

In the female tract the _____-________ _________ acts as a reservoir for sperm

A

Utero-tubule junction
Sperm accumulate and bind tot he epithelium in the folds and are released slowly to the oviduct

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11
Q

Sperm Capacitation definition

A

physiological changes that sperm undergo in the female tract to gain the capacity to undergo the acrosome reaction (AR) (gaining the capacity to fertilize)

Capacitation normally occurs in the female tract (uterus, uterine tube) but can also be induced in vitro

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12
Q

Capacitation of sperm normally occurs in the….

A

Female tract (uterus, uterine tube) but can also be induced in vitro

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13
Q

Sperm undergo the acrosome reaction when…

A

Triggered by binding to the zona pellucida (oocyte is present)

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14
Q

Fertilizing capacity of an ejaculate can be stretched out over many hours, thereby increasing the odds of fertilization since….

A

It will not undergo acrosome reaction unless bound to zona pellucida of oocyte

(Once sperm are capacitated and/or undergo AR, their lifespan is dramatically shortened)

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15
Q

Requirement for ____________ stretches out the fertilizing lifespan of an ejaculate

A

Capacitation

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16
Q

Sperm Changes in Capacitation

A

Removal of surface factors (DF) (seminal plasma):
-ASF, Caltrin, CRISP-1
-Changes surface charge
-Unmasking of binding sites

Binding of surface factors
-Modulators of AC/cAMP: Calcitonin, FPP, adenosine, angiotensin II
-Modulators of Ca++ influx: progesterone, GABA
-Adhesion molecules: SPAM1 from female tract, via clusterin

Ability to undergo membrane fusion event (acrosome reaction):
-Membrane cholesterol efflux
-Increased plasma membrane fluidity and movement of some surface protein (e.g., dopamine receptors)

Motility changes (faster!!!!)
-Progressive motility
-Hypermotility (aka hyperactivation)

Metabolic changes
-Influx of Ca++
-Increased metabolism

17
Q

Acrosome reaction steps

A

Sperm binds to zona pellucida via ligand-receptor interaction (ZP3)

Receptor on sperm triggers calcium influx
Intracellular [Ca++] (rises F-actin -> G-actin)

Ca++ induces membrane fusion
-Outer acrosomal and sperm cell membrane fuse
-Resulting pores permit escape of soluble acrosomal contents
-Exposure of inner acrosomal membrane, which binds to ZP2

18
Q

Zona penetration by sperm

A

Hyaluronidase digests hyaluronic acid secreted by cumulus cells

Acrosin digests a pathway through zona pellucida (ZP2-3 matrix, ZP1 x-links)

Hyperactivated motility provides motile force

19
Q

Sperm penetration depends on…

A

Acrosin-digested pathway

Hyperactivated motility to propel sperm through pathway

20
Q

Sperm-egg binding

A

Entire sperm enters perivitelline space

Motility diminishes or ceases

Sperm binds to oocyte cell membrane
-Binding domain restricted to post-acrosomal region of sperm

Sperm ligand (fertilin, PH-30) binds to oocyte surface receptor (integrin?)
-Binding event triggers surface depolarization event
-Momentary opening of calcium channels causes massive increase in oocyte [Ca++]
-Cortical granule exocytosis (Block to polyspermy)
-Sperm-egg fusion (PLC) and endocytosis
-Sperm nucleus decondensation
-Resumption of oocyte meiosis

21
Q

How the oocyte blocks polyspermy

A

Cortical reaction
Cortical granule exocytosis once sperm enters into the oocyte Perivitelline space and binds to oocyte surface receptor

Cortical granule exocytosis release a variety of proteases (e.g., plasminogen activator)
Protease diffuse across PVS
Proteases alter zona structure (zona reaction), rendering zona resistant to acrosin digestion
Results in block to polyspermy

22
Q

Sperm-egg binding: the seminal fertilization event

A
  1. Sperm-egg binding
  2. Cytoplasmic [Ca++]
    a. Cortical Reaction (exocytosis)
    b. Fast Block to polyspermy
    c. Sperm endocytosis
    d. Sperm nucleus decondensation
    e. Resumption/completion of oocyte meiosis
23
Q

The Cortical reaction leads to a release of a variety of…

A

proteases (e.g., plasminogen activator)
Protease diffuse across Perivitelline space
(PVS)

Proteases alter zona structure (zona reaction), rendering zona resistant to acrosin digestion

Results in block to polyspermy

24
Q

Sperm endocytosis into the oocyte

A

Increase in cytoplasmic [Ca++]

Sperm and oocyte membranes fuse (endocytosis)

Decondensing sperm nucleus (1N)

Completion of oocyte Meiosis II
(extrusion of PBII)

25
Q

Resumption/completion of oocyte meiosis happens when….

A

Sperm endocytosis into the oocyte with increased cytoplasmic calcium

(Egg has already at metaphase and has extruded polar body and is ready to accept more DNA)

Sperm nucleus then decondenses and completion of oocyte meiosis II is complete and 2nd polar body is extruded- HAPLOID male and female pronuclei

26
Q

First zygotic cell cycle

A

After Meiosis II is complete there is formation of haploid male pronucleus (1N) and female pronucleus (1N)

27
Q

Sperm head decondensation

A

When the sperm head first enters the ooplasm, it immediately begins to swell

The dense chromatin “unpacks”, involving reduction of protamine disulfide bonds

Protamines are replaced by histones

Haploid genome becomes organized into chromosomes

28
Q

The enlarging sperm head is called the…

A

Male pronucleus

As it enlarges, it becomes surrounded by a pronuclear envelope/membrane and microtubules
It moves towards the center of the ovum.
It is also busy duplicating its chromosomes so that by the time it reaches the center, it is ready for the metaphase of mitosis.

29
Q

As the male pronucleus enlarges it becomes surrounded by…

A

a pronuclear envelope/membrane and microtubules

It moves towards the center of the ovum.

It is also busy duplicating its chromosomes so that by the time it reaches the center, it is ready for the metaphase of mitosis.

30
Q

In the oocyte, immediately upon extrusion of the second polar body, the remaining haploid genome forms…

A

a female pronucleus

It also forms a pronuclear envelope, duplicates its chromosomes, and moves towards the center of the fertilized ovum.

31
Q

In some species the female pronucleus is typically _______ than the male pronucleus.

A

Smaller

32
Q

Syngamy process

A

When the 2 pronuclei reach the center, the pronuclear envelopes disappear and the two genomes become one.

The chromosomes with duplicated chromatids line up on the metaphase plate for the first mitosis (first cleavage).

33
Q

First zygotic cell cycle

A

Interphase:haploid male and female pronuclei replicate chromosomes

Prophase: chromosomes condense; nuclear membrane breaks down

Metaphase: syngamy occurs as
maternal and paternal chromosomes align together on metaphase plate

34
Q

Cell stages of developing embryo

A

2, 4, 6, 12
At some point between 8 – 16 cells (depending on species), the cells produce a cell adhesion molecule on their surfaces, compaction process to create the MORULA

35
Q

Morula

A

At some point between 8 – 16 cells (depending on species), the cells produce a cell adhesion molecule on their surfaces
Uvomorulin, an E-cadhedrin
Forms tight junctions between adjacent cells, so that individual cell boundaries become difficult to see (morula becomes compacted; process is called “COMPACTION”.)
Some cells are now located in the interior of the ball of cells

Early morula- some cell boundaries still visible
Late morula- boundaries between cells not visible

Becomes blastocyst once fluid accumulates in cavities to form blastocoel

36
Q

Blastocyst description

A

multiple small fluid-filled cavities are formed. These coalesce into a single cavity – the blastocoel, marks the transition from morula to blastocyst

The cells on the inside form the Inner Cell Mass (ICM) which will eventually give rise to the embryo. The cells forming the periphery will eventually form the embryonic side of placental tissues (trophoblast).

Blastocyst is still surrounded by zona pellucida

37
Q

Blastocyst growth

A

ICM and trophoblast cells continue to multiply

Largest increase in blastocyst volume comes from accumulation of blastocoel fluid

This causes outward pressure on zona pellucida which stretches and thins

This pressure-caused thinning, together with proteases in the endometrium, eventually causes a zona rupture, through which the blastocyst escapes (hatches)

Next Gen Exam 1 (16 decks)

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