Mouse Mating Activation of Follicular Estrogen Synthesis Expends Luteal Phase

Maternal Recognition of Pregnancy in the Mare

In the cyclic mare the CL starts regression on about 14 days post-ovulation.

CL regression and declining plasma progesterone concentrations are associatedwith increased plasma and uterine PGF2 secretion.

Stabenfeldt et al. In:Prostaglandins in Animal Reproduction, Acta Vet Scad. 1981, Suppl 77:159

Hysterectomy prior to Day 12 to 14 prolongs CL function for 70 to 140 days.

Removal of the equine conceptus by flushing the uterine horns prior to Day15 results in luteolysis, but after Day 15 the CL function is maintained.Therefore, Day 14 to 16 is the critical period for maternal recognition of pregnancy. Conceptus removal on Day 10, 15 and 20 resulted in interestrousintervals of 22, 38 and 46 days respectively, compare to 24 days in cycliccontrols.

Possible Mechanism for Maintenance of CL

1. Prevent PGF2 synthesis and release.2. Prevent PGF2 from entering the maternal vasculature.3. Prevent PGF2 from binding to luteal cell membrane receptors.4. Stimulate luteal gonadotropin receptors.

The pathway of PGF2 in reaching the ovaries in the mare differs fromcow and ewe. There is no direct unilateral effect of the luteolysin fromthe uterus to the ovaries.

The uterine artery is relatively straight and caudal to the ovarian vein,as it passes obliquely across the ovarian vein. In the mare, CL regressionappears to occur through a systemic pathway.

PGF2in the utero-ovarian venous plasma increaseson Day 14 in cyclic mares. However, PGF2 is much lower in pregnant mares.

PGF2Binding by CL

Day 14 luteal PGF2 receptors reach the highestlevel. PGF2binding rapidly declines after Day 14 in cyclic mares but continues to increase up toDay 18 in pregnant mares.

Ginther, 1998; AAEP Proceedings 44:73-104

Ginther, 1998; AAEP Proceedings 44:73-104

Endometrial Production of PGF2 Nonpregnant mares, PGF2endometrialcontent and synthesis increases on Day 14-16. Pregnant mares synthesis continuesto increase to Day 20, however content islower until Day 18-20.

There is a significant reduction PGF2luminal content inpregnant compared to cyclic mares. Evidence indicates that in the

presence of the conceptus, PGF2release or synthesis is inhibited

Collected bycervical lavage

Reproductive Biology of the Mare,Ed. O.J. Ginther, pp419-456

With systemic route of PGF2 in the mare the conceptus must migrate between the horns to inhibit oxytocin receptor

and the release and/or synthesis of PGF2.

Twining Tree

Ginther, IN: Reproductive Biology of the Mare, 2nd Ed. 1992

How is Embryo Reduction Accomplished?

Ginther, IN: Reproductive Biology of the Mare, 2nd Ed. 1992

Maternal Recognition in the Ewe

Uteroovarian Pathway

In comparison to the gilt and mare, regulation of the uterus on CL functionin the ewe and cow is exerted through a local utero-ovarian pathway.Experiments involving surgical anastomoses of a main uterine vein orovarian artery to the corresponding vessel on the opposite side have demonstrated that the local utero-ovarian pathway is the mechanism of CL regression in the cow and ewe.

Unilateral Hysterectomy: When the uterine horn is ipsilateral to CL, regression occurs more readily.

Unilateral Pregnancy: Establishment of pregnancy in one side of the uterus by surgical isolation of the uterine horns results in luteal maintenance on the gravid side more readily than on the nongravid side in sheep and cattle.

Ginther, 1998; AAEP Proceedings 44:73-104

A. Removal of the uterine horn maintains the CL in contrast to a intact uterine vein. Demonstrates utero-ovarian pathway.

B. CL will regress if the uterine vein of the intact uterine horn is anastomosed with the vein on the contralateral side. Note the fusion is above the ovarian artery!

C. Ovarian artery from the uterine intact side anastomosed with ovary from the side lacking uterine horn. Note anastomosed artery is cut at the region above were the artery touches the uterine vein.

O.J. Ginther, In:Prostaglandins in Animal Reproduction, Acta Vet Scad. 1981, Suppl 77:103

A. The presence of the conceptus prevents CL regression on the gravid side with loss of CL on the surgically isolated nongravid horn.

B. The CL on the nongravid side is rescued if the uterine vein from the gravid horn is anastomosed to the vein on the nongravid horn.

C. The CL on the nongravid side is rescued if the ovarian artery from the gravid horn is anastomosed to the ovarian artery on the nongravid horn. Note: position of anastomoses.

O.J. Ginther, In:Prostaglandins in Animal Reproduction, Acta Vet Scad. 1981, Suppl 77:103

When the ovarian artery from the nongravidside was anastomosed with the ovary of thegravid horn the CL regressed. Indicatingthe conceptus factor to maintain the CL is not systemic.

When the ovarian artery of the nongravidside is anastomosed at a position wherethe conceptus factor can be transferredwith it to the ovary, the CL is maintained.Suggests a factor that can have a protectiverole to PGF2 which is a function of PGE.

O.J. Ginther, In:Prostaglandins in Animal Reproduction, Acta Vet Scad. 1981, Suppl 77:103

Maintenance of CL Function in Ewe and CowAlthough luteolysis occurs through PGF2 action, the effect of the embryo onPGF2 secretion in the uterus in early pregnancy is conflicting. Plasma levelsof PGF2 have been reported to be diminished, unchanged or higher duringearly pregnancy compared to the cyclic ewe.

Recent evidence by McCracken indicates rising spikes of PGF2 at Day 13 and14 in both pregnant and nonpregnant ewes. However, major luteolytic pulsesseen on Days 14, 15 and 16 are absent in pregnant ewes.

It takes five hour-long infusionsof PGF2 (0.4 to 1.2 g/h) over25 hours to cause complete CLregression in the ewe.

Nonpregnant

Pregnant

McCracken et al. 1981, Acta vet scand, Suppl 77:71

5 pulses within24 hours

Progesterone receptor in the endometriumNote presence of PR in epithelium, stroma and myometrium on Day 5.

Note absence of PR in epithelium onDay 15 of the estrous cycle orpregnancy

Day 0 Day 0

Day 15

Myometrium

McCracken Model of OxytocinControl of CL Regression

1. Because of declining progesterone action on the uterus towards the end of the luteal phase, estradiol-17is now able to stimulate formation of endometrial oxytocin receptors. (Takes 6 hours)2. Endogenous levels of oxytocin (posterior pituitary) interact with the receptor.3. PGF2 secretion from the uterus follows oxytocin stimulation.4. Progesterone secretion declines with luteolysis as result of secretion, locally transferred to the ipsilateral ovary.5. More oxytocin is released with PGF2 stimulation of the CL to reinforce more uterine PGF2 release.6. Since oxytocin receptors will down-regulate, subsequent hour-long episodes of PGF2 release at intervals of 6 h will allow replenishment of oxytocin receptor.

McCracken et al. 1981, Acta vet scand, Suppl 77:71

Custer et al. Reprod Dom Anim 31:449

1. Loss of P action occurs simultaneously in the hypothalamus and endometrium thus returning E action.2. E from follicles can then stimulate increase pulses of OT from hypothalmus with increase in endometrial OTR.3. Subluteolytic pulses of PGF2will be releasedfrom uterus following stimulation by post pit OT with uteine OTR.4. Subluteolytic levels of PGF2 will bind high affinity PGF2receptors (HFRR) on large luteal cells to release OT.5. Release of luteal OT will cause a luteolytic release of PGF2 from the endometrium.6. The high release of PGF2 now binds to low and high affinity receptors to cause inhibition of progesterone secretion and release of more OT. Positive feedback loop.7. Next release of luteolytic PGF2 depend on release of post pit OT, recovery of receptors for PGF2after 6-9 hours and recovery of uterine OTR.

McCracken Model of Oxytocin Control of CL RegressionMcCracken et al. 1981, Acta vet scand, Suppl 77:71

IFNAR

PR

ER

PR

ERE2 E2

ESTRUS MET-/DIESTRUS LATE-DIESTRUSP4 BLOCK

LUTEOLYSIS

OTROTR

P4

CL

GF

X

OTE2 P4 PGF

No ER

LATE-DIESTRUS

NO LUTEOLYSIS

OT

?

No OTR

NO PGF

(-)

JAK-STAT

Oocyte

Cyclic

Pregnant

No ERNo OTR

No PR

(-)

(-)

Day 0 1 4 10 13 14 15 16 17

LE

PPAP Ovary

(+)

OT

IFNARIFN

IFNARIFNARIFNAR

OT

Fertilization

Embryo

Trophoblast

Cloned gene sequence of oTP-1 and bTP-1 are homologous to bovinea II interferon family.

Interferons are antiviral, antiproliferative and immunomodulatory

The protein is now classified as ovine or bovine interferon-tau (oIFN)

IFNt increases the uterine expression of:

1) 2’, 5’ oligoadenylate synthetase 2) 2-microgolubin 3) Interferon regulatory factor-1 and -2 4) Ubiquitin cross-reactive protein 5) Mx protein 6) Graulocyte chemotactic protein-2 Binds to the IFN type I receptors on the surface and glandular epitheliumof the endometrium.

It clear that IFN is involved with maternal recognition of pregnancy inruminants.

Binds to cytosolic proteins to preventproteasomal degradation (prevent apoptosis)

Induced by type I IFN, antiviral protein - Possibly can act as GTPase

Schematic of current working hypothesis on cell-specific IFNT signaling in theendometrium of the ovine uterus. IFNT, produced by developing conceptuses ofruminants, binds to IFNAR present on cells of the ovine endometrium. (A) In the uterine luminal and superficial glandular epithelia (LE/sGE), IRF2, a potentand stable transcriptional repressor, increases during early pregnancy. Thecontinual presence of IRF2 inhibits classical IFN-stimulated genes or ISGs(STAT1, STAT2, IRF9, B2M, ISG15, MHC, and OAS) through direct ISRE andIRFE binding and coactivator repulsion. Thus, critical factors in the classical JAK-STAT-IRF pathway (STAT1, STAT2, and IRF9) are not present, resultingin the absence of ISGF3 or IRF1 transcription factors necessary to transactivateISGs. However, IFNT does activate an unknown cell signaling pathway that results in induction of WNT7A and stimulation of non-classical IFNT-stimulatedgenes (CST3, CTSL, and LGALS15) specifically in LE/sGE. (B) In cells of thestroma (ST) and middle to deep GE, the IRF2 repressor is not expressed. Thus, IFNT-mediated association of IFNAR subunits facilitates cross-phosphorylationand activation of JAK1 and Tyk2, which in turn phosphorylates the receptor andcreates a docking site for STAT2. STAT2 is then phosphorylated, thus creatinga docking site for STAT1 which is then phosphorylated. STAT1 and STAT2 arethen released from the receptor and can form two transcription factor complexes,GAF and ISGF3. ISGF3 is formed by association of a STAT1-2 heterodimer andIRF9 in the cytoplasm, translocates to the nucleus, and transactivates genescontaining an ISRE(s), such as STAT1, STAT2, IRF9, B2M, ISG15, MIC, and OAS. GAF is formed by STAT1 homodimers, which translocates to the nucleusand transactivates genes containing a GAS element(s) such as IRF1. IRF1 canalso bind and transactivate ISRE-containing genes as well as IRFE-containinggenes. The simultaneous induction of STAT2 and IRF9 by IFNT appears toshift transcription factor formation from GAF towards predominantly ISGF3.Therefore, IFNT activation of the JAK-STAT-IRF signal transduction pathwayallows for constant formation of ISGF3 and GAF transcription factor complexesand hyperactivation of ISG expression in the ST and GE. B2M, β-2-microglobulin; CST3, cystatin C; CTSL, cathepsin L; GAF, -activated factor;GAS, activation sequence; IFNAR, type I IFN receptor; IFNT, interferon; IRF1,interferon regulatory factor 1; IRF2, interferon regulatory factor 2; IRFE, IRF-response element; IRF9, IFN regulatory factor 9 (alias ISGF3G); ISG15, (ISG15 ubiquitin-like modifier; alias IFI15 or UCRP); ISRE, IFN-stimulatedresponse element; JAK, janus kinase; LGALS15, galectin 15; MIC, MHC classI polypeptide-related sequence; OAS, 2',5'-oligoadenylate synthetases; STAT1, signal transducer and activator of transcription 1, 91 kDa; STAT2, signal transducer and activator of transcription 2, 113 kDa; WNT7A, wingless-type MMTV integration site family, member 7A.Spencer et al. 2008; Reproduction135: 165 - 179.