Repro physiology 6 - Sperm capacitation and fertilization of egg

What is covering the spermatozoa in the epididymis

Glycoproteins covering the acrosome surface

How is the activity low in the Spermatozoa in the epididymis

• Low pH

• Low HCO3-

Are Spermatozoa in the epididymis capable of motility

yes: Capable of motility

Spermatozoa in the epididymis is capable of secreiting what rapidly

Capable of rapid tyrosine phosphorylation

What is the first step of the sequence of events following deposition of spermatozoa in the female reproductive tract

Immediate transport

• retrograde loss

• phagocytosis

• entrance into the cervix /uterus

What is the second step of the sequence of events following deposition of spermatozoa in the female reproductive tract

Cervix

• “priviliaged pathway”

• removal of nonmotile sperm

• removal of some abnromailties

What is the third step of the sequence of events following deposition of spermatozoa in the female reproductive tract

Uterus

• capacitation initiated

• phagocytosis

What is the fourth step of the sequence of events following deposition of spermatozoa in the female reproductive tract

Oviduct

• docking to oviductal cells

• capacitation completed

• hyperactive motility

What is the fifth step of the sequence of events following deposition of spermatozoa in the female reproductive tract

Fertilization

• across reaction

• spermatozoon penetrates oocyte

• male and female pronuclei form

What are the Effect of seminal plasma on the female reproductive tract

• Increase uterine tone, contractility and sperm transport

• Non-motile sperm do not reach oviducts if suspended in saline

• Motility not required to reach oviduct in most species

• Regulating female’s local immune response

Post-mating immune response in vagina and cervix

• Clearance of abnormal/superfluous sperm and microorganisms

• Regulation of female immune response\

• Tissue remodeling

• Activation of cytokines and growth factors may be important for pre- implantation embryo development

Sperm lost primarily due to:

• Phagocytosis by neutrophils

• Retrograde transport

Site of deposition differs among species: what animal’s deposition is the cranial vagina

cow, sheep, rabbit, cat, dog, and primates

Site of deposition differs among species: what animal’s deposition is into the cervix

sow

Site of deposition differs among species: what animal’s deposition is Injected into cervical lumen

horse

Leukocyte infiltration helps prevent

reproductive tract infections

Cervix is the major barrier to the

spermatozoal transport, and it also serves as a reservoir for spermatozoa

What is the first phase of the spermatozoal transport:

• Rapid – due to motility of the tract

• Sustained – movement in trickle-like fashion from the reservoir to oviduct, where they get attached (docked) to the epithelium at the utero-tubal junction

Is docking important in the two phases of spermatozoal transport

yes: Docking crucial for survival

What are the factors for Capacitation of sperm

• Sperm must reside in the female genital tract before they acquire maximum fertility

• Hyperactivated movement (↑ motility)

• Removal of glycoproteins to enable the acrosome reaction

What are the molecular changes of the capacitation of sperm

• Cholesterol lost from sperm plasma membrane

• Increased membrane fluidity

• Hyperpolarization of the sperm plasma membrane

• Increased intracellular pH (through HCO3-)

• Increase in intracellular Ca2+ (leads to hyperactivation)

• Increased protein kinase A (PKA), and thus, tyrosine kinase (motility, acrosome reaction and membrane changes)

What are the factors of Chemotaxis post-capacitation

• Sperm move toward a concentration gradient of a chemoattractant released by oocyte (move toward follicular fluid)

• Poorly studied in mammals

• Chemoattractant?

• Progesterone (secreted by cumulus cells)

What is the first Sequence of post-capacitation events leading to fertilization

1. hyperactive motility

What is the second Sequence of post-capacitation events leading to fertilization

2. binding to zona pellucida

What is the third Sequence of post-capacitation events leading to fertilization

3. acrosomal reaction

What is the fourth Sequence of post-capacitation events leading to fertilization

4. penetration of zona pellucida

What is the fifth Sequence of post-capacitation events leading to fertilization

5. sperm oocyte membrane fusion

What is the sixth Sequence of post-capacitation events leading to fertilization

6. sperm engulged

What is the seventh Sequence of post-capacitation events leading to fertilization

7. decondensation of sperm nucleus

What is the eight Sequence of post-capacitation events leading to fertilization

8. formation of male pronucleus

What does the Acrosome contents contain

• Hyrdolytic enzymes (e.g., hyalonuridase, acrosin, + more)

acrosomal reaction Binding to

ZP3 initiates cause Ca2+ influx into sperm cell

↑ Ca2+ results in

fusion of outer acrosomal membrane (OAM) and plasma membrane (i.e., vesiculation)

Fertilization: consequence of ↑ in intracellular Ca2+ in the oocyte

• Initiates cortical reaction and zinc (Zn) blocking

• Resumption of meiosis II

• Extrusion of the second polar body

• A role in pronuclear formation

• Activation of embryonic genome

What is occuring Before sperm-oocyte fusion

When the spermatozoon completely penetrates the zone and reaches the perivitelline space, it settles into a bed of microvilli formed by the oocyte plasma membrane. the critical granules have migrated to the periphery of the oocyte

What is occurring During sperm-oocyte fusion

the plasma membrane of the oocyte fuses with the equatorial segment and the fertilizing spermatozoon is engulfed. the coritcal granule membrane fuses with the oocyte plasma membrane and the coritcal contents are released into to perivitelline space by exocytosis

What is occurring after sperm-oocyte fusion

after the fusion between the membrane of the equatorial segment and the oocyte plasma membrane occurs, the nucleus of the spermatozoon is within the cytoplasm. The sperm nuclear membrane disappears, and the nucleus of the sperm decondenses.

Although hundreds of spermatozoa reach an egg, which zones undergo alteration

the zona pellucida and vitelline membrane undergo alteration (cortical reaction) soon after the entry of the first spermatozoon, preventing polyspermy.

Concepton can occur within a what window prior?

It can occur within a 6-day window before ovulation. At 5 days before ovulation the probability of conception was 0.11, and the probability increases to about 0.33 two days before ovulation

Maximum duration of fertilizing ability of sperm within the female reproductive tract in a bitch

in a bitch its 9-11 days

Maximum duration of fertilizing ability of sperm within the female reproductive tract in a camelids

for a camelids its 4-5 days

Maximum duration of fertilizing ability of sperm within the female reproductive tract in cows

in cows its about 1.5-2 days

Maximum duration of fertilizing ability of sperm within the female reproductive tract in mare

in mare its 4-5 days

Maximum duration of fertilizing ability of sperm within the female reproductive tract in women

approxiately 5-6 days