Download - Gametogenesis & fertilization
Gametogenesis & fertilization
Lectured by
รศ.สิทธิชัย เอี่ยมสะอาด (Associate. Prof. Sitthichai Iamsaard, Ph.D.)
Department of Anatomy, Faculty of Medicine, Khon Kaen University
Official email: [email protected] 1
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Objectives
1. To know features of spermatogenic and egg cells
2. To describe and compare the events of
spermatogenesis and oogenesis
3. To understand the ovarian follicle development and
ZP structure
4. To explain the fertilization process, sperm
capacitation, acrosome reaction, and egg activation
5. To distinguish the fertilized egg from unfertilized one
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Resource: http://desertbruchid.net/4_GB1_LearnRes_fa10_f/4_GB1_LearnRes_Web_Ch10.html
1.Sexual interaction and intercourse
2. Internal fertilization
3. Gestation period (~ 9 months) 4. Childbirth
Involves:
- Creation of genetically novel individual
Requires: Gametogenesis - Spermatogenesis & Oogenesis
Sexual reproduction of human
-Sexual intercourse b/w a man and a woman
- Unity of sperm & oocyte at fertilization
The Human Life Cycle
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Sexu
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Note: Missionary Position
General structure and function of human reproductive organs
Origin of germ cells
Undifferentiate embryo at 4th weeks
Consideration of spermatogenesis (sperm forming)
At puberty (13-16 years old)
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Embryonic gonad (testis)
At week 4 of male embryo
Primordial
germ cells
(PGC)
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PGCs migrate to form gonad
Before puberty
PGCs remain dominant in testis
• PGCs differentiate into “spermatogonia” via mitosis
• Spermatogenesis plays (via meiosis) throughout male reproductive life
- produce sperm by spermatogenesis
2. Interstitial CNT
- contains Leydig cells which produce
testosterone
1.Seminiferous tubules
Microstructure of
adult testicular tissue
- Complex stratified epithelium
containing two basic cell populations:
(1) SPERMATOGENIC CELLS
(2) SERTOLI CELLS
- Non-replicating physical support cells
• LEYDIG CELLS
- Produce and release testosterone
In seminiferous epithelium
In interstitial CNT
1. Spermatogonia
Sertoli cells
4. Spermatids 5. Spermatozoa
Leydig cell
“5 spermatogenic cells”
Smooth muscle cell
2. Primary spermatocyte
3. Secondary spermatocyte
Cell members in testicular tissue
- Involved in spermatogenesis
(somatic cells)
Hormonal Control of Male Reproduction
Resource: http://philschatz.com/biology-book/contents/m44841.html
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3 PHASES
1. Spermatogonial Phase
(Mitosis)
2. Spermatocyte Phase
(Meiosis I&II )
3. Spermatid Phase
(Spermiogenesis)
Concept of SPERMATOGENESIS: formation of sperm (64 days, ~35 C)
Meiosis I (reduction division)
Meiosis II (equatorial division)
Spermiogenesis (differentiation)
DNA replication
(Diploid cell containing two sets of chromosomes (2n), one set inherited from each parent)
(embryo until puberty period)
Puberty
To Male RP life
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The “A pale & B spermatogonia” determined to be mature sperm
Resource: https://www.researchgate.net/profile/Ashok_Agarwal2/publication/259674480/figure/fig5/AS:296965855301640@1447813586084/Differentiation-of-a-human-diploid-germ-cell-into-a-fully-functional-spermatozoon.png
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Types of spermatogonia: stem cells (2N)
Primary spermatocyte
Type B spermatogonia
A dark A pale A long
12 http://journals.cambridge.org/fulltext_content/ERM/ERM3_03/S1462399401002319sup013.gif
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Pachytene primary spermatocyte: important for genetic recombination and genetic diversity
- Largest spermatogenic cells detected - Chromosomes clump during division
Leptotene: chromosome paring
Zygotene: chromosome condensation, double-strand breaks
Pachytene: synapsis and recombination begins
Primary spermatocytes (Pachytene stage)
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Spermatids differentiate to form sperm (structural maturation) via “spermiogenesis”
Secondary spermatocyte (n)
Meiosis II (equatorial division)
Meiosis I (reduction division)
A series of structurally
maturational changes of
spermatids to form sperm
14 Resource: https://www.researchgate.net/profile/Ashok_Agarwal2/publication/282917724/figure/fig7/AS:391465520910338@1470344061138/Diagrammatic-representation-of-the-steps-where-the-histones-are-replaced-with-the.jpg
Protamine used to replace for histone in packaging DNA of sperm during spermiogenesis
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How to condense sperm DNA?
Condensed nucleus (chromatins+protamines)
Summary of
Spermiogenesis
in details
1. Nucleus condenses
(chromosomes condense and nucleoplasm removed)
2. Flagellum or tail develops
3. Round spermatid elongates
4. Acrosome formed from golgi body
5. Mitochondria aggregates around base of forming flagellum
6. Mitochondria fuses to form supermitochondrion (in humans)
7. Most cytoplasm of sperm is shed and phagocytosed by Sertoli cell
1. Remove excess cytoplasm (residual body) from developing spermatid
2. Move spermatids toward the lumen of the seminiferous tubules - ectoplasmic
specializations
3. Cultivate and mediate maturation of spermatids
4. Segregate groups of developing gametes
5. Secrete fluid to transport sperm in reproductive tract
6. Secrete hormones and other factors
Summary of Sertoli cell’s function in details
Residual body
Blood-testis barrier or Sertoli cell barrier (SCB, now is a correct term)
Germinal epithelium of testis
Tight junction of
SCB
Sertoli
cell Sertoli
cell
Spermatogonia
1st Spermatocyte
2nd Spermatocyte
Spermatid
Sperm
Basal lamina
Divides the Semi. lumen into 2 compartments
Basal compartment
Adluminal compartment
-Prevent the passage of cytotoxic agents into semi. tubule.
Sperm has less cytoplasm
Human sperm structure
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“Required: the repetitive 5 mitotic divisions of spermatogonial cells
and followed by 2 meiotic divisions to gain 96 mature sperm”
How is the number of
spermatozoa increased?
Male fertility (depends on number and % motility of sperm)
- Average volume of ejaculated semen = 3.5 ml
- A concentration of about 100 million sperm/ 1 ml of semen (less than 20 million/ ml = sterile)
-Via entire “spermatogenic cycle (64 days)” of spermatogenesis
Spermatogenic cycle (~64 days) in human
1Ad
2Ad
1st Mitosis
3Ap 1Ad
2nd Mitosis
6B1
3rd Mitosis
12B2
5th Mitosis 24 primary spermatocytes
Reserved
48 secondary spermatocytes
Meiosis I
96 spermatids
Meiosis II
96 mature spermatozoa
Spermiogenesis
Reductional division (several weeks)
Equational division (about 8 hours)
4th Mitosis
Epididymis Transit
- Non-motile testicular sperm
Peristalsis
- Motile epididymal sperm
Spermatogonial mitotic divisions (5 times)
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Functional maturation &
storage of sperm produced by testes taking place at the
“Epididymis” before
ejaculation
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Fertility & capacitation factors produced in the epididymis
Associated reproductive glands of male
Epididymis
Vas deferens
- Head - Body - Tail
Ampulla
Seminal vesicle
Prostate gland
Cowper’s gland
Semen after ejaculation (ave, 3.5 ml )
Human sperm within seminal fluid/plasma observed under simple microscope
The sperm count varies from 20 to 150 million sperm per milliliter of semen.
25 Resource: http://www.tankonyvtar.hu/hu/tartalom/tamop425/0010_1A_Book_angol_05_termeleselettan/images/12a13.png
zygote
“Fertilization” takes place
• Sperm about 300-500 x 106 cells/ ejaculation (~10% abnormal sperm) will be deposited within posterior fornix of vagina
• Only 300-500 capacitated sperm can meet a mature egg at the
ampulla of oviduct and only one sperm can fertilize it.
Oogenesis occurs within ovary
Consideration of oogenesis (oocyte forming) in ovary
At puberty (12-14 years old)
Embryonic gonad (ovary)
At week 4 of male embryo
Primordial
germ cells
(PGC)
PGCs migrate to form gonad
At birth
5th month of fetal life
PGCs differentiate into oogonia Mitosis
Meiosis I Oogonia divides to be
“primary oocyte” within “primordial follicle” of ovary
- No oogonia
- Primary follicles containing
only primary oocyte - Inactive ovary
Meiosis I (prophase arrested)
“Oogenesis begins at 5th mount of fetal life”
Menopause (45-50 years old)
- No oogenesis - No menstruation
- Follicular development
- Ovulation
- Fertilization and pregnancy (if any)
- Menstruation cycle
- Primary oocyte (Meiosis I completed)
during ovulation
- Secondary oocyte (Meiosis II completed )
after fertilization
Events: Follicle development, ovulation, and corpus luteal formation
Internal Structure of Adult Ovary
Anatomy of an ovarian follicle
1. A growing (primary) oocyte (ovum)
2. Follicular (granulosa) cell 3. Basal lamina
Graafian follicle
Follicular development within ovarian cortex
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ZP is firstly formed at the “unilaminar primary follicle”
Granulosa cells produce estrogen secreting into antrum
3. Secondary (antral) follicle 4. Mature (Graafian) follicle
A huge antrum More than one small antrum
Antral fusions
Days
FSH Ovarian follicles Estrogen Stimulates Grow
Produce
Before ovulation
Ovulation
Structures of mature Graafian follicle
ZP
Secondary oocyte present “during ovulation”
Presence of the first polar body
Oocyte structure
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Secondary oocyte (arrested in metaphase II) after ovulation present the 1st polar body
Primary oocyte in ovarian follicle
38 Recourse: https://canvas.instructure.com/courses/1021937/files/44221811/preview?verifier=xucOaEcu6uBIK5qikJZq8hUFzMSY4MoB6JaUxqce
Oogenesis
Vs
Follicular development
Perivitelline space
Secondary oocyte (completed
metaphase II ) or fertilized egg
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Summary of stages in oogenesis Phases
Multiplication
Growth
Maturation
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Chromosome No.
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Types of germ cells
Oogonium (2N)
Additional oogonium (2N)
Primary oocyte (2N)
Secondary oocyte (N) First polar body (N)
Second polar bodies (N)
(All degenerate)
Sperm (N)
Mitosis
Meiosis I
Meiosis II
Types of divisions
Zygote (2N)
Nuclei fuse
Mature ovum (N)
Events
Before birth: Takes place in fetal ovary
After puberty: occurs each month in ovary
Ovulation
Fertilization
Occurs as a result of fertilization
Male pronucleus
Female pronucleus
Note: Egg completes meiosis II after fertilization and second polar bodies present
Before puberty
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Fertilized egg (zygote)
Unfertilized egg
- Ovulation when LH surge (~day 14 of
1 menstrual cycle, 28 days)
- Corpus luteum formed after ovulation
- Progesterone production from corpus
luteum
- No fertilization, corpus luteum degenerated to be corpus albicans
LH surge Ovulation Corpus luteum Progesterone Triggers Forms Produces
High level of progesterone found at luteal phase of ovary
FOLLICULAR PHASE
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Resource: https://ars.els-cdn.com/content/image/1-s2.0-S0011224015002242-gr1.jpg
ZP3
- The receptor on the ZP - Binds sperm at the beginning of fertilization process
The human zona pellucida (ZP) is
composed of three major glycoproteins: ZP1, ZP2, and ZP3.
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Approximate number of oocytes in female RP life time
Primary oocytes
Secondary oocytes
At 5 months of fetal life ~ 7 million
At birth ~ 2 million (5 million degenerated)
At puberty ~ 40,000 cells (1.96 million more generated)
•12 secondary oocytes are ovulated per year
• Up to 480 oocytes over the entire reproductive life of the woman
(40 years x 12 oocytes per year = 480 oocytes )
Ovulation Cumulus oocyte complex (COC)
MII oocyte viability after ovulation for 72 hours
Ovulated oocyte will be successfully fertilized within 12-24 hrs.
If no fertilization occurs, oocyte will degenerate within the oviduct.
Ovulation: LH surge
Ovulated cumulus oocyte complex (COC)
48 Resource: http://bioserv.fiu.edu/~walterm/GenBio2004/new_reprostuff2/chapter_44.htm
Fallopian tube (oviduct)
- Internal fertilization takes place at 1/3 anterior or ampulla part - Gametes and zygote transport
Uterus
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Capacitation of sperm in oviduct
- Reduction in membrane cholesterols
- Hyperactiation: lateral movements
- Removal of coating factors
Note: only capacitated sperm
can bind to the ZP
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Comparisons between spermatogenesis & oogenesis
Outline of the fertilization process
Fertilization
Requirements: 2 steps of sperm
1. Sperm capacitation 2. Sperm acrosome reaction
7 steps of human fertilization
From: Yu’s thesis, 2008 (Queen’s university)
Histologic sperm acrosome reaction
Intact
Intermediate
Reacted
ZP3-INDUCED ACROSOME REACTION
“Supramicromolar calcium influx is essential for the induction of the
acrosome reaction”
Yanagimachi, 2009
Egg activation
“Supramicromolar calcium influx is also essential
egg activation”
Fertilization and implantation