ANS 3319C Reproductive Physiology and Endocrinology
Fertilization
Sperm Transport, Capacitation, & Fertilization 1) Site of semen deposition natural mating
♦ Cranial vagina :cow, sheep, rabbit, primates, dog, cat, rodents:
•
Rodents: gel plug for produce vagina, prevents retrograde sperm loss
♦ Cervix: Pig
•
Gel fraction: ê retrograde sperm loss
♦ Cervical lumen into uterus: horse
•
Gel fraction: ê retrograde sperm loss
2) Site of semen deposition artificial insemination (Fig 12-11 & 12-12)
♦ Transcervical: mare, cow, sheep
♦ Intracervical: sow
♦ Intravaginal: dogs & cats
3) Sequence of events post copulation (Fig 12-1)
Fig. 12-1
5
Fertilization
1
• acrosome reaction
• spermatozoon penetrates
oocyte
• male and female pronuclei form
Immediate Transport
• retrograde loss
• phagocytosis
• entrance into
cervix/uterus
4
2
Oviduct
Cervix
• capacitation completed
• hyperactive motility
• “privileged”
pathways
• removal of
non-motile
sperm
• removal of
some
abnormalities
3
Uterus
• capacitation initiated
• phagocytosis
117 ANS 3319C Reproductive Physiology and Endocrinology
Fertilization
4) Sperm loss from tract
♦ Retrograde transport
♦ Phagocytosis by neutrophils (WBC): vagina & uterus (Fig 12-2)
•
Due to é estrogen exposure
•
Prevent microorganisms from colonizing in tract
•
Digest some sperm (foreign to female)
♦ No real (-) effect on fertility
5) Cervix function
♦ Barrier: non-motile, abnormal, & dead sperm
♦ Sperm reservoir
♦ Mucous secretion (amount varies between species)
•
Cow: two types of mucous (Fig 12-3)
♦ Sialomucin : low viscocity, secreted by basal cells of crypts
•
“Privileged pathway” for sperm
♦ Sulfomucin: high viscocity, secreted by apical epithelial portions of crypts
•
Sperm washed out of tract with contact
∗
Filter non-motile sperm??
6) Sperm transport through tract (uterus/oviduct)
♦ é tone & motility
•
Estrogen (+) smooth muscle contractions
•
Seminal plasma PGF2α & PGE2
•
Unclear of what drives directionality of sperm flow
♦ Rapid phase: sperm at oviduct in minutes (Function??)
•
Typically non-viable & un-capacitated sperm
♦ Transport phase:
•
118 Sustained flow viable sperm to oviduct “trickle effect”
ANS 3319C Reproductive Physiology and Endocrinology
Fertilization
♦ Sperm capacitation (Fig 12-4)
•
Ejaculated sperm coated with proteins from seminal plasma
•
Capacitation : proteins striped away in female tract
♦ Biochemical changes - infer fertility on sperm
♦ Species differences in rate & location
7) Fertilization events
♦ Sperm acquisition of hyperactivity
•
Linear to frenzied activity (ampulla)
♦ Facilitates sperm/oocyte activity
♦ Sperm binding to zona pellucida (Fig 12-6)
•
Zona pellucida (ZP) glycoproteins
♦ ZP1 & ZP2: infer structural integrity
♦ ZP3: “receptor like activity” for sperm membrane
•
Specific sperm membrane proteins: bind to zona
♦ Primary zona binding region (ZBR): ZBR binds to ZP3
♦ Secondary zona binding region: acrosome reaction promoting ligand (ARPR)
•
ARPR binds to ZP3
∗
Binding initiates acrosome reaction
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Fertilization
♦ Acrosome reaction (Fig 12-7)
•
Sperm penetration of zona
♦ Sperm membrane fuses with outer acrosomal membrane
♦ Vesiculation: formation of vesicles due to membrane fusion
•
•
Acrosomal contents dispersed
•
Enzymes allow sperm to digest zona (small hole)
∗
Proacrosin: inactive form of acrosin, aids sperm binding to zona
∗
Acrosin: hydrolizes zona proteins (+) zona penetration
∗
Flagellar action of tail moves sperm through zona
Exposure of sperm equatorial segment
♦ Fuses with oocyte plasma membrane
♦ Fertilization (Fig 12-8)
•
Sperm enters perivitelline space
•
Sperm engulfed by oocyte plasma membrane
♦ Requires fusion of equatorial segment & oocyte plasma membrane
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Fertilization
121 ANS 3319C Reproductive Physiology and Endocrinology
Fertilization
♦ Cortical reaction
•
Granules on periphery of oocyte plasma membrane undergo exocytosis
♦ Contents released into perivitelline space è zona block
•
(+) biochemical changes to zona è prevents polyspermy
•
(+) vitelline block: prevents additional sperm binding oocyte plasma membrane
•
Species differences in absence/presence zona & vitelline blocks
♦ Decondensation of sperm nucleus
•
Reduction of disulfide cross links è nuclear material released
♦ Formation of male pronuceli
♦
8)
Syngamy: male & female pronuclei fusion
Sperm life span in female tract (Table 12-1)
♦ Domestic animals & humans (days)
Table 12-­‐1 Duration of fertilizing ability of sperm within female reproductive tract of various species Species Fertile Life (days) Bitch 9-­‐11 Camelids (Llama, alpaca, camel) 4-­‐5 Cow 1.5-­‐2 Mare 4-­‐5 Woman 5-­‐6 ♦ Superfecundation
•
Bitch mated by several males during estrus
♦ Sperm from all males can fertilize oocytes
♦ Litters of different breeds
♦ Probability of conception in women (Fig 12-9)
•
Oocyte lifespan; 24 hours
•
Conception occurs 6-7 d “Fertile period”
♦ 5 d preovulation + 2 days post ovulation
•
122 Closer copulation is to ovulation, é chance of pregnancy