ESTROUS AND

MENSTRUAL CYCLES

ANSC 631

SPRING 2014

What are you expected to learn?

What is an estrous cycle?

How does it differ from a menstrual cycle?

What organs are involved?

What hormones are needed?

How/where estrogen and progesterone are synthesized?

What endometrial changes occur during the estrous and

menstrual cycles?

Menstruation: why and how

What happens in a fertile cycle

Outline for Presentations

• Estrous and Menstrual Cycles

• Gonadotropin Regulation of Follicular Recruitment and Development

• Follicular Steroidogenesis

• Growth Factors and Follicular Development

• Ovulation

• Corpus Luteum Formation, Function and Angiogenesis

• Luteal Peptides, Cytokines and Growth Factors

• Prolactin and Ovarian Function

• Luteolysis.

Reproductive cycles: Animals vs Women

Animals

Estrous cycle The physiological

events between successive

periods of sexual receptivity

&/or ovulation – Day 0 is day of

onset of estrus

Anestrus Without cyclicity -

caused by pregnancy, season,

lactation, stress (under-

nutrition, environment)

Women

Menstrual cycle The

physiological events between

successive menstruations

(~28d) – Day 1 in day of onset

of menses

Amenhorrea lack of menstruation

– caused by pregnancy,

lactation, stress, pathologies

Reproductive cyclicity provides females with repeated

opportunities to become pregnant

What was normal in ancient times?

If no conception in a cycle, another cycle begins to provide a new

opportunity to establish pregnancy

Estrus = heat = period of sexual receptivity

–Estrus is a noun. (estrus)

–Estrous is an adjective (estrous)

Cyclicity - categorized according to frequency of

occurrence throughout the year

Polyestrus

cattle, swine, rodents

Seasonally polyestrus

sheep, goat, mare,

deer

Monoestrus

dogs, foxes

Senger 2003

Classifications of Estrus

Physiological Estrus – Follicle Growth, Estrous behavior,

LH surge and ovulation with outcome being synchronized

mating and ovulation to maximize chances for fertilization of

oocytes and establishment of pregnancy.

Characteristics

- Increase in estrogens from mature Graffian Follicles

- Increase in GnRH synthesis by peptidergic neurons in

hypothalamus

- Increase in GnRH pulse frequency

- Increase in GnRH Receptors on Gonadotrophs in Anterior

Pituitary

- LH surge and Ovulation

Psychological Estrus – Estrous behavior without ovulation

1. Estrogens – effects in area of hypothalamus (work with

cats identified nuclei for estrous behavior without ovulation)

Pre-optic area - +++

Arcuate Nucleus - ++

Mammalary Body - +

2. GnRH – Glu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-

GlyNH2 Receptor Binding Lordosis

3. Oxytocin – Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-GlyNH2

a. Smooth muscle contractions – sperm transport,

lactation, parturition

b. Bonding

mother and offspring

sexual partners

Yen 2004; Reprod Endocrinol 3-73

Hypothalamic Divisions

Characteristics of Psychological Estrus

Increased activity: walking, vocalization, mounting,

accept male for mounting/mating

Example: Post-partum Estrus in Sows

a. Estrous Behavior 2 to 3 days post-partum

b. No Ovulation

c. Cause: Likely prepartum estrogens

Post-Partum Estrus Sow

- 2-3 days – Psychological Esrus Only

- Post-weaning estrus – 72 to 96 h is fertile

Mare

7-10 days post-partum – fertile

Beef Cows

60-80 days postpartum due to suckling intensity

Dairy Cows

2X Day Milking – 14 Days Postpartum is short cycle usually

21-25 Days Postpartum for normal cycles

Ewes – Normally Lamb During Anestrus Season

Mouse and Rat – Day 1 postpartum – fertile and followed by delayed

implantation

Humans – Variable due to suckling intensity and nutrition

DELAYED IMPLANTATION

• Embryonic diapause, temporary suspension of

blastocyst development in mammals due to

suppression of cell proliferation.

• Obligate diapause occurs in every gestation of

some species, e.g., season to time birth with

favorable time of year for nutrients

• Facultative diapause is associated with

metabolic stress, usually lactation, to prevent

concident lactation and pregnancy.

3) Delayed implantation (Chiroptera, Carnivora, Xenarthra, Cetartiodactyla)

Zona Pellucida

Mechanisms for Optimizing Timing of Birth

Obligate

Ursus americanus

Facultative

Many Rodents

4) Embryonic diapause (Macropodids)

Mechanisms for Optimizing Timing of Birth

DELAYED IMPLANTATION IN WALLABY

JANUARY BREED AND NEW YOUNG TO TEAT TO SUCKLE AND INDUCE

FACULTATIVE DELAYED IMPLANTATION (LACTATION/SUCKLING

INDUCED)

CORPUS LUTEUM PRODUCING LITTLE PROGESTERONE

TREATMENT WITH BROMOCRYPTINE TO DECREASE PROLACTIN AND

DELAYED IMPLANTATION CAN BE INTERRUPTED

JUNE-JULY OBLIGATE DELAY DUE TO SEASON/PHOTOPERIOD

DECEMBER POUCH YOUNG OUT + ABOUT 28 DAYS AND FEMALE RETURNS

TO ESTRUS

JANUARY BREED AND REPRODUCTIVE CYCLE BEGINS AGAIN

Figure 1 Strategies for photoperiodic modulation of diapause employ melatonin and prolactin for contrasting purposes.

Lopes F L et al. Reproduction 2004;128:669-678

© 2004 Society for Reproduction and Fertility

Figure 2 Summary of uterine influences that could be acting on the dormant embryo in the rodent model to terminate the mitotic arrest of diapause.

Lopes F L et al. Reproduction 2004;128:669-678 © 2004 Society for Reproduction and Fertility

LIF – Leukemia Inhbiting Factor

ErbB – EGF Receptor

EGF – Epidermal Growth Factor

Anandamide -

Types of Ovulation

A. Spontaneous Ovulators – Women, Domestic Animals – Endogenous

hormonal changes adequate to stimulate ovulatory surge of LH and ovulation.

B. Spontaneous Ovulator with Induced CL Formation – Rodents – Spontaneous

Ovulation; Mating Induced CL Formation

C. Induced Ovulator – Mating or stimulation of vaginal-cervical area results in

noradrenergic stimulation of hypothalamic GnRH centers to cause release of ovulatory

surge of LH - rabbit, mink, cats. In rabbits, ovulation about 10 h post-mating or

stimulation of vaginal-cervical area. In domestic cats, multiple matings usually

required for full ovulatory response.

D. Seasonal Ovulators

1. Monestrus – bears, dogs (most big breeds) ovulate once per year

2. Long-Day Breeders – horse is seasonally polyestrus species

3. Short-Day Breeders – ewe is seasonally polyestrus species

Hormones of the Estrous and Menstrual Cycles

A. Luteotropic Hormones – LH, hCG, prolactin that act directly on CL to

stimulate progesterone (P4) secretion.

B. Luteolyic Hormone – Prostaglandin F2-alpha (PGF) that acts on CL to

cause cessation of secretion of progesterone and physical destruction of luteal cells.

Luteolytic PGF is from uterine epithelia in subprimate mammals and from intra-

ovarian sources in most primates, so menstrual cycle in uterine independent while

estrous cycles are usually uterine dependent.

C. Antiluteolytic Hormones – Interferon tau (ruminants), estradiol and

prolactin (pigs), prolactin and lactogenic hormones (mice)

D. Luteal Protective – Prostaglandin E2 may antagoinize luteolytic effects of

PGF2-alpha

Stages of the Estrous Cycle

A. Estrus: High Estrogens from Mature Graffian Follicles

and LH Surge

1. Follicle Maturation

2. Oocyte Maturation

3. Estrous Behaviour (Psychological Estrus) and

Mating

4. Estrogen-Induced Ovulatory Surge of LH

(Physiological Estrus)

5. Ovulation

6. Initial Luteinization of Granulosa and Theca Cells

7. Decreased Vaginal and Rectal Temperatures

0.25 to 0.75 degrees C

Increased blood flow to perineum area

Monitor time of ovulation

8. Increase in cervical mucus

Unique crystallization patter of mucus – ferning pattern

9. pH of vagina increases to 6.8 from 7.1 to 7.4

10. Increased antimicrobial actions

Increase in Lysozyme – bacteriacidal

Increase in Lactoferrin – bacteriostatic

11. Pheromones for attracting male

a. Cow – acetaldehyde (Bill Klemm, TAMU)

b. Rhesus Monkey

Copulin – short-chain fatty acids: acetic acid,

proprionic acid, isobutyric acid, butyric acid, and isovaleric acid

c. Microflora of vagina produce pheromones

12. Swelling of sexual skin - Vulva

http://www.pork.org/images/YouthProducers/Vulvas.jpg

Metestrus: Ovulation and Corpus

Hemmorhagicum (Corpora

Hemmorhagica)

1. Circulating Estrogens and

Progesterone are LOW

2. Uterine cells expressing

receptors for progesterone (PGR),

estradiol (ESR1) and Oxytocin (OXTR)

Diestrus: Corpus Luteum (Corpora Lutea) and Progesterone

1. Circulating Progesterone is HIGH

2. Large luteal cells of CL synthesize and store, depending on

species, oxytocin-neurophysin (ruminants) and relaxin (pig)

In sheep and cow: OXY production:

Days 0-3 transcription (maybe in response to LH surge

Days 4-7 translation of OXT-Neurophysin mRNA

Days 8-14 storage of OXY-Neurophysin

Days15-17 pulsatile release of OXT and Neurophysin

3. Steroid Receptors in Uterine Endometrium

Uterine epithelia and stromal cells: NO OXTR

Uterine epithelia lose ESR1

Uterine epithelia lose PGR after Days 11 to 12

Uterine stromal cells express PGR and low or no ESR1

4. Preparation of the Uterus for Pregnancy – Uterine luminal

and glandular epithelial cells begin to express proteins important to

development of embryo/conceptus (conceptus is embryo and its

associated membranes)

Late Diestrus – Corpus Luteum Regression

1. Steroid Receptors in Uterine Endometrium

Uterine Epithelia have increasing expression of ESR1

and then OXTR

2. Increase in estrogens from developing follicles stimulate

more ESR1 and OXTR in uterine epithelia

3. Oxytocin released from CL and/or Posterior

Pituitary in Ruminants and Posterior Pituitary and/or Uterus in

sows and mares

4. Oxytocin-induced luteolytic pulses of PGF2a

5. Corpus Luteum Regression

Proestrus – Corpus Albicans (Corpora

Albicantia) and Mature Graffian Follicles

1. Circulating Estradiol Increasing

2. Circulating Progesterone Decreasing

to basal levels

3. GnRH Pulse Frequency increasing

from 1 pulse/2 to 4 h to approximately hourly

pulses

Fig. 7-3

Regulation of Corpus Luteum Function

Species Luteotrophic Complex

Human LH

Sheep LH & GH

Pig Estradiol

Pseudopreg.

Rabbit Estradiol, LH

Pseudopreg.

Rat/Mouse Estradiol, Prolactin & LH

Organs involved in female reproductive

cycle

hypothalamus

anterior pituitary

Oviduct

endometrium

ovary corpus luteum

uterus

Ovarian Cycles: Uterine-Dependent

and Uterine-Independent

Major hormones regulating the female

reproductive cycle

Hormone

gonadotropin-releasing

hormone - GnRH

luteinizing hormone - LH

follicle stimulating

hormone - FSH

estradiol 17 (E2)

Progesterone (P4)

Site of production

hypothalamus

anterior pituitary

(gonadotrophs)

ovarian follicle

corpus luteum

After ovulation, cells of dominant follicle give rise to the CL

The female hypothalamo-pituitary ovarian

axis

GnRH

Inhibin

Activin

Follistatin

ovary

Pituitary

Gonadotrophins

(LH, FSH)

Steroids

Hypothalamus

Feedback hormones

Steroids

/ Uterus

Estrous cycles consist of two major

phases

Follicular phase

Ovarian FOLLICLES -

dominant structures in the

ovary

ESTROGEN is the

dominant hormone

Luteal phase

CORPORA LUTEA –

dominant ovarian

structures

PROGESTERONE is the

dominant hormone

Follicles grow Corpus luteum develops / regresses

The estrous cycle has 4 stages

Proestrus – formation of ovulatory follicles + E2 secretion

Estrus – sexual receptivity + peak E2 secretion + ovulation

Metestrus – CL formation + early P4 secretion

Diestrus – substantial secretion of P4

Phases / stages of the estrous cycle Most animals - short follicular phase

Senger 2003

GnRH, FSH and LH

• Pulsatile secretion

• Changing frequency

& amplitude

Hormone cyclicity in menstrual cycle

Positive feedback of peak

E2 induces preovulatory

LH surge

In Women – Menstrual cycle

Differs from estrous cycle

no defined period of sexual receptivity

a period of endometrial sloughing (menstruation)

timeline for the description of the cycle begins and ends with

menses, not ovulation or estrus

Lack of cyclicity = amenhorrea – absence of cyclicity for an

extended period of time in women of reproductive age (in

athletes-loss of body fat; lactation (prolactin ↓ GnRH frequency

and amplitude; menopause; undernutrition; stress)

Richardson et al., JCEM, 1987

Age in Years

1

10

100

1000

10000

100000

0 0 10 20 30 40 50 60

Women with regular

menses

perimenopausal

women

postmenopausal

women

B B

B B

B

J

F

F F

F

F

F

F

Prim

ord

ial F

olli

cle

s / O

va

ry

Ovarian follicle numbers with age

In women, the proliferative or follicular phase and the secretory or luteal phases of the menstrual cycle are of equal length.

The phases of the menstrual cycle are named for the changes that occur in the endometrium.

Follicular phase (estradiol dominated) = proliferative phase

Luteal phase (progesterone dominated) = secretory phase

Summary – comparison events that

occur between estrous and menstrual

cycles

Senger 2006

Steroidogenesis

• Ovary (Follicles and Corpus Luteum)

• Conceptus

• Fetal Adrenal

• Placenta

20a-Hydroxysteriod Dehydrogenase

20a-HSD

Progesterone 20a-dihydroprogesterone

NADPH NADP

H3C

O

O

H3C

OH

20a-HSD

Prolactin

Inhibits Enzyme

Does not support pregnancy

or decidualization in rodents

FSH is a glycoprotein. Each monomeric unit is a protein molecule with a sugar attached

to it; two of these make the full, functional protein. Its structure is similar to LH, TSH, and

hCG. The protein dimer contains 2 polypeptide units, labelled alpha and beta subunits.

The alpha subunits of LH, FSH, TSH, and hCG are identical, and contain 92 amino

acids. The beta subunits vary. FSH has a beta subunit of 118 amino acids (FSHB) that

confers its specific biologic action and is responsible for interaction with the FSH-

receptor.The sugar part of the hormone is composed of fucose, galactose, mannose,

galactosamine, glucosamine, and sialic acid, the latter being critical for its biologic half-

life. The half-life of FSH is 3-4 hours.

FSH

HORMONES FROM GRANULOSA CELLS OF FOLLICLE AND SERTOLI

CELLS OF TESTES THAT REGULATE FSH SECRETION

Inhibin: a peptide inhibitor of FSH synthesis and secretion

participates in regulation of estrous and menstrual cycles.

Structure: contains an alpha and beta subunit linked by disulfide

bonds. Two forms of inhibin differ in their beta subunits (A or B), while alpha

subunits are identical. Inhibin belongs to the transforming growth factor-β (TGF-

β) superfamily.

**********************************************************

Activin: a peptide stimulator of FSH synthesis and secretion

participates in regulation of estrous and menstrual cycles

Structure: two beta subunits identical to the two beta subunits (A or B)

of inhibin, allowing for the formation of three forms of activin: A, AB, and B;

linked by a single covalent disulfide bond.

**********************************************************

Follistatin: a single chain gonadal protein that inhibits FSH

synthesis and release by binding and antagonizing Activin.

LH is a dimeric glycoprotein with 2 polypeptide units, alpha and beta, connected

by two disulfide bridges

alpha subunits of LH, FSH, TSH, and hCG are identical, and contain 92 amino

acids.

beta subunits: LH beta subunit of 121 amino acids confers specific biologic

action and binding to LH receptor. This beta subunit identical to beta sub unit of

hCG and both bind LH receptor, but hCG beta subunit contains an additional 24

amino acids

half-life of LH is 20 minutes, shorter than that of FSH (3-4 hours) or hCG (24

hours).

LH

Prolactin is a single chain polypeptide of 199 amino acids with a molecular weight of

about 24,000 daltons. Its structure is similar to that of growth hormone and placental

lactogen. The molecule is folded due to the activity of three disulfide bonds.

PROLACTIN

Dopamine

pyroGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly CONH2

GnRH

Prolactin Inhibiting Factor

OXYTOCIN

Oxytocin-Neurophysin

Maturase

Oxytocin + Neurophysin

Circulation

To Target

Tissues

Copyright ©2004 The Endocrine Society

Sherwood, O. D. Endocr Rev 2004;25:205-234

Relaxin: A Hormone with Diverse Actions in Rats

Copyright ©2004 The Endocrine Society

Sherwood, O. D. Endocr Rev 2004;25:205-234

FIG. 12. Influence of immune neutralization of circulating R1 relaxin throughout the second half of pregnancy on nipple development in rats

The Ovary

Progesterone receptors, PGR

Androgen

Primary

Primordial

Secondary

Preovulatory

Corpus luteum

LH receptors Granulosa cell

Atresia

Developing

Follicles

Ovulation

Theca (androgens)

Oocyte

(progesterone

estrogen)

Androgen Estrogen FSH receptors

Estrogen

FSH

receptors

Estrogen receptor alpha, ESR1

Steroidogenesis Before LH Surge

A

GL

BM

TI

TE

Ch P A2

Ch P A2 E2

E2

A: Antrum; GL: Granulosas; BM; Basement Memb

TI: Theca Int. TE: T Ext.; C: Capillaries Ch: Cholesterol; P: Progesterone; A2: Endrogen; E2: Estradiol

17a-HSD

P450scc

3-HSD

Arom

LH

FSH

P450scc

3-HSD

FSHR

LHCGR

EP

EP

Luteal Steroidogenesis

17a-HSD Ch P A2 E2 Arom

17a-HSD Ch P A2 E2 Arom

Ch: Cholesterol; P: Progesterone; A2: Endrogen; E2: Estradiol

(Some Species)

Large Luteal Cells

Small Luteal Cells

P450scc

3-HSD

P450scc

3-HSD

LHCGR

LHCGR and FSHR EP

EP

Estrogen production in the ovary:

collaboration between two cell types

aromatase

Primary steps leading

to the pre-ovulatory

LH surge

• In early follicular phase GnRH pulse

frequency increases

• Causes LH & FSH secretion

• Increase in E2 production

• E2 stimulates:

• increase in GnRH Receptors on

Gonadotrophs;

•increase in GnRH pulse frequency

•surge in GnRH leads to ovulatory

surge of LH

• The follicle then starts to secrete inhibin

– negative inhibitor of FSH

Portal vessels

bovine human

CL

LH surge

Primates

Fig. 9-2

Stigma of Ovarian Follicle of Chicken

Fig. 9-2

Fig. 9-2

LH SURGE, OVULATION

AND FERTILIZATION

Fig. 8-6

Events in Proteolytic Cascade for

Ovulation • LH and PGE2 induce plasminogen activator

(PA)

• Plasminogen is in follicular fluid

• PA converts Plasminogen to Plasmin, a serine

protease

• Plasmin converts procollagenase to

collegenase

• Combined effects of plasmin and collagenase

lead to rupture of stigma and ovulation

Adamts1 -A Disintegrin-like and

Metalloproteinase with

Thrombospondin Type 1 motif1

TSG6 - TNF-Alpha-induced

Protein 6

PCAP – pituitary activating

adenyl cyclase

PROAPOPTOTIC CASPASE

ADAPTOR PROTEIN

Tumor Necrosis Factor-stimulated Gene 6

IαI- Inter-alpha trypsin inhibitor

SHAP – IαI + hyaluronan (HA)

Follicle Wall and Ovulation • Stigma of Follicle – Avascular area at apex of follicle

– Proteases act to cause rupture of basement membrane

– Follicular fluid exits and takes oocyte and cumulus cells with

it into oviduct – Bernoulli’s Law

– Contractions of ovary generated by actin and myosin fibers

in area of theca externa aids in expulsion of oocyte and

cumulus cells

• Alpha adrenergic receptors on theca externa respond to

norepinephrine to enhance contractions

– Mature Graffian Follicle MINUS oocyte and cumulus cells

becomes corpus hemmorhagicum and with hyperplasia and

hypertrophy of large and small luteal cells they give rise to

the corpus luteum that produces progesterone

MECHANISM OF OVULATION – SEE PAPER

BY ESPEY

• LH, FSH and PGE2 act via LHCGR, FSHR and EPs to increase cAMP and Protein Kinase A that: – 1. Stimulates production of plasminogen activator by GC

and plasminogen activator converts plasminogen into plasmin (serine protease) and procollegenase to collagenase

– 2. Plasmin and Collagenase act on basement membrane and extracellular matrix of follicle to cause rupture and release of oocyte and cumulus cells

– 3. Ovulation is due to softening of cell wall, decrease in pressure in follicle, rupture of cell wall and as follicular fluid escapes it creates a negative pressure that pulls oocyte and cumulus mass with it into the infundibulum of the oviduct

Fig. 8-13

Follicular

Pressure

Does Not

Increase

Ovarian Histology • Corpus hemorrhagicum

(CH)/Corpora hemorrhagica – newly ruptured follicle

– essentially a blood clot

• Corpus luteum (CL)/Corpora lutea – LH stimulates formation

from theca interna and granulosa

– temporary endocrine gland

• progesterone

• Corpus albicans (CA)/Corpora albicantia – remains after CL regresses

LH Surge- Induced Events: The

Oocyte and Follicle • Inhibition of androgen and estrogen production

– Inhibition of C21 steroid 17α hydroxylase

– Aromatase enzyme inhibited

– Progesterone production increases

– Loss of FSHR on GC

– TC and GC become small and large luteal cells, respectively

• Hyperplasia

• Hypertrophy

• Endoplasmic reticulum develops in complexity

• Mitochondria develop with complex cristae to enhance conversion of

cholesterol to pregnenolone for P4 production

• Increase in cholesterol esters

LH Surge-Induced Events: Oocyte and

Follicle

• LHCGR and Prolactin receptors increase in

luteal cells to enhance LDL and HDL

receptors for uptake of cholesterol

• Progesterone Production Increases

• Increased production of PGE2 by luteal cells

Structural Changes During Luteinization

Antrum

GC

TC LC

BV

O

Small versus Large Luteal Cells

• LARGE LUTEAL CELLS FROM GC

– GREATER THAN 22 MICRONS

– HIGH BASAL P4 OUTPUT

– LITTLE ABUNDANT ROUGH ENDOPLASMIC

RETICULUM

• OXYTOCIN-NEUOPHYSIN

• RELAXIN

– FEW LHCGR

– ABUNDANT FP (PGF RECEPTORS)

Small versus Large Luteal Cells

• SMALL LUTEAL CELLS FROM TC

– 8 TO 22 MICRONS

– LOW BASAL P4 OUTPUT

– ABUNDANT LHCGR

– INCREASE P4 IN RESPONSE TO LH

– SMOOTH ENDOPLASMIC RETICULUM

• NO OXYTOCIN-NEUOPHYSIN

• NO RELAXIN

– FEW FP (PGF RECEPTORS)

Ovulation: Morphological and

Cytological Changes • Increase in Blood Flow to Follicle

– Histamines

– PGE2

– Increased Vascular Permeability to Proteins • Platelet Activating Factor

• Increased influx of plasminogen into follicular fluid

• Granulosa Cells – Loss of junctional complexes between corona radiata cells

and oocyte

– Increase in hyaluronic acid and water in cumulus GC

– High cAMP due to FSH, LH and PGE2

– Plasminogen Activator Enzyme activity increases to convert plasminogen to plasmin (active protease) and collegenase

Oocyte Maturation

• Pre-Meiosis: Prophase I arrest

– Oocyte-corona radiata cell communication via gap

junctions

– High cAMP in oocyte blocks meiosis

• Adenosine – Increases conversion of ATP to cAMP via

adenyl cyclase

• Hypoxanthine – decreases activity of phsphodiesterase that

converts cAMP to AMP

– Maturation Promoting Factor Inactive

– RNA synthesis – maternal RNA

LH SURGE-INDUCED EVENTS

• Changes in cytoplasmic mass

– Increase deposition of nutrients into oocyte by corona

radiata cell just before loss of gap junctions

– Nuclear Envelope Breakdown

– Breakdown of centrioles and chromosomes migrate to

periphery of oocyte

– Chromosomes individualize

– Chromosomes condense due to increase in histone I kinase

– Microtubule organizing center forms (Centriole and

Microtubules)

– Chromosomes align on equatorial plane at Metaphase I

– Polar Body I extruded

– Metaphase II arrest

– Nuclear Envelope Forms

Oocyte Maturation (Continued)

• Protein Synthesis

– Zona Pellucida Proteins

• ZP1 – Cross-linking

• ZP2 – Sperm Trap

• ZP3 – Sperm Receptor

– Cortical Granules

• Proteases – destroy sperm binding sites

• Colloidal Molecules: Hyaluronic Acid and

Glycosaminoglycans – bind water and increase space

between vitelline membrane and zona pellucida

• Structural Proteins – unknown function

Fig. 8-17

FERTILIZATION MEDIATED EVENTS

• Fertilization

– Increase in intracellular Ca++ in oocyte

– Germinal Vesicle Breakdown

– Microtubule Organizing Center with Spindle forms

– Metaphase II Completed

– Polar Body II extruded into perivitelline space

– Syngamy between male and female pronuclei

– Pairing of paternal and maternal chromosomes

– Nuclear envelope forms

– Zygote forms – 1- cell embryo

TIMING OF EVENTS AFTER LH

SURGE IN EWES

• 8-12H: PROPHASE I COMPLETED

• 12-20H: METAPHASE II

• 21-24H: POLAR BODY I EXTRUDED TO

PERIVITELLINE SPACE

• 24-30H: METAPHASE II AND OVULATION

• 30-36H: FERTILIZATION

Fig. 8-16

Summary

FSH & LH levels rise during early follicular phase stimulating

growth of early antral follicles

During mid follicular phase, selection and emergence of

dominant follicle occurs. Corresponds to an increase in E2

secretion.

Increasing estrogen levels stimulate GnRH, which results in

preovulatory surges of LH & FSH leading to ovulation.

Following ovulation, the corpus luteum secretes large amounts

of P4. The P4 inhibits GnRH synthesis and secretion by

neurons in the hypothalamus.