Lecture 16: Fertilization

Animal Science 434John J. Parrish

Capacitation

1951Austin - ratChang - rabbit Fertilization does not occur until several

hours after sperm are placed in the uterus or oviduct

Chang Experiment - 1951

0

20

40

60

80

100

-2 -1 0 2 4 6 8Time of Insemination (hr relative to

ovulation)

OvulationOvulation

Per

cen

t F

erti

liza

tio

n

AfterAfter BeforeBefore

Capacitation

The changes within sperm that confer upon the sperm the ability to acrosome react in response to the appropriate stimulus.

Zona Pellucida

Cumulus Cells

Follicular Fluid

Zona Pellucida

Cumulus Cells

Follicular Fluid

Effect of CapacitationEpididymal Ejaculated

SeminalPlasmaand/or

EpididymalSecretions

+

Capacitated

FemaleTract

+

Model of CapacitationD F

Plasma Membrane

Cytoplasm

Nucleus

AcrosomeAcrosome

D F

Plasma Membrane

Cytoplasm

Nucleus

AcrosomeAcrosome

GAG

Plasma Membrane

Cytoplasm

Nucleus

AcrosomeAcrosome

GAG

Cholesterol

Chol-Acceptor

Ca2+

Ca2+

pH

cAMPActivity ofEnzymes

Activity ofEnzymes

D F

Capacitation

No change in sperm morphologyMotility change

– hyperactivation

cAMP

Power output

cAMP

Power output

The Acrosome ReactionPlasma Membrane

Acrosome

Fused PlasmaMembrane and

Outer AcrosomalMembrane

Fused PlasmaMembrane and

Outer AcrosomalMembrane

Nucleus

AcrosinHyaluronidase

AcrosinHyaluronidase

Modificationof the

EquitorialRegion

Modificationof the

EquitorialRegion

The Zona PellucidaThe Zona Pellucida

Zona Pellucida

ZP3

Attachment

Binding

Acrosome ReactionInduction

Acrosome Reaction

Sperm Interaction with the Zona

Zona Pellucida

ZP2

ZP2

ZP2

ZP2

Secondary Binding

Zona Penetration

MotilityMotility

Zona Pellucida

Sperm tract through zona pellucidaSperm tract through zona pellucida

6-12 hr6-12 hr

18-24 hr18-24 hr

Maturation Promoting Factor(MPF)

Metaphase Promoting FactorMetaphase Promoting Factor

MPF MPF

MPFMPF

Primary Oocyte

GV-Intact

GVBD Metaphase I

PB-1

Secondary OocyteMetaphase II

Ovulation

LH Surge

Zona Pellucida

PerivitellineSpace

Oocyte

Ca2+

Ca2+

Ca2+

Ca2+

Zona Pellucida

PerivitellineSpace

Oocyte

Ca2+

Ca2+

Ca2+

Ca2+

Zona Pellucida

PerivitellineSpace

Oocyte

Ca2+

Ca2+

Ca2+

Ca2+

Zona Pellucida

PerivitellineSpace

Oocyte

Ca2+

Ca2+

Ca2+

Ca2+

Zona Pellucida

PerivitellineSpace

Oocyte

Ca2+

Ca2+

Ca2+

Ca2+

Calcium Transients During Bovine FertilizationCalcium Transients During Bovine Fertilization

Initiation of Calcium Pulse by Soluble Sperm Component

Endoplasmic Reticulum

Ca2+

PLCzetaPIP2

DAG

IP3

Ca2+

Oocyte

Sperm Receptor - Calcium Pulse Initiation

Ca++Ca++

ERER

IP3IP3

PLCPLC

Zona Pellucida

PerivitellineSpace

Oocyte

MII

AIIMPF X

Ca2+

Pronuclei

TII

PBII

Zona Pellucida

PerivitellineSpace

Oocyte

MII

AIIMPF X

Ca2+Ca2+

Pronuclei

Decondensation

Pronuclei

Zygote

TII

PBII

Zona Pellucida

PerivitellineSpace

Oocyte

Ca2+

CorticalGranules

Zona Block to Polyspermy

Zona Pellucida

PerivitellineSpace

Oocyte

Ca2+

CorticalGranules

Zona Block to Polyspermy

3

Blocks to Polyspermy

1

2

4

Species

1.Mammals

3.InvertebratesAmphibiansFishRabbits

4.AmphibiansAvians

Sperm acrosomalregion binds to spermreceptor on zona

Sperm penetrateszona

Initiates -Zona &VitellineReaction

Initiates completion ofMeiosis II and releaseof 2nd polar body

Zona and VitellineReactions blockpolyspermy

PerivitellineSpace

VitellineMembrane

CorticalGranule

ZP3

Binding

Initiation ofAcrosomeReaction

Continuation ofReaction

Acrosome-ReactedSperm

PenetrationExcluded Sperm

ZonaReaction

CorticalGranuleRelease

Fusion

1st Polar BodyZona

Pellucida

Redrawn fromWasserman, P.M. 1988 Scientific American. p78