Human Reproduction Update Advance Access published online on November 8, 2008
Human Reproduction Update, doi:10.1093/humupd/dmn052
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Pinopodes: a questionable role in endometrial receptivity
1 Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Institute of Medical Sciences, University of Toronto, Toronto, ON, Canada M5G 1X5 2 Toronto Center for Advanced Reproductive Technology (TCART), Toronto, ON, Canada M5S 2X9
To whom correspondence should be addressed at: 3 Correspondence address. 150 Bloor St W, Suite 210, Toronto, ON, Canada M5S 2X9. Tel: +1-416-972-0777; Fax: +1-416-972-0036; E-mail: rfcasper{at}aol.com
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Abstract |
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 TOP Abstract IntroductionMethodsPinopode morphologyDuration of pinopodesFunction of pinopodesPinopodes as a clinical...New avenues of researchSummary and conclusionsFundingReferences |
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BACKGROUND: A better understanding of endometrial receptivity is crucial to the creation and optimization of tests to assess the window of implantation in a clinical setting. Testing endometrial receptivity via scanning electron microscopy of endometrial samples reveals that pinopodes are a very good marker of endometrial receptivity in the rat. There is still disagreement in the literature as to their usefulness as a receptivity marker in both mice and humans.
METHODS: Publications related to the discovery, study and usefulness of pinopodes as a marker of endometrial preparation for implantation in both rodents and humans were identified through MEDLINE and other bibliographic databases.
RESULTS: There is substantial evidence that pinopodes are good markers of endometrial receptivity in the rat. Pinopodes are not useful in the mouse or human as consistent markers of endometrial receptivity for implantation. In the human, pinopodes have a prolonged (>5 days) presence in the luteal phase and fail to delineate the brief (24–48 h) window of receptivity.
CONCLUSIONS: While there are many publications arising from one group supporting the use of pinopodes as a reliable marker of human endometrial receptivity, few independent groups have been able to confirm these results. The clinical usefulness of pinopodes to delineate a period of endometrial receptivity seems unlikely following recent findings that pinopodes are present throughout the luteal phase of the menstrual cycle.
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Introduction |
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TOPAbstractIntroductionMethodsPinopode morphologyDuration of pinopodesFunction of pinopodesPinopodes as a clinical...New avenues of researchSummary and conclusionsFundingReferences |
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Embryo transfer techniques, following in vitro fertilization, are often carried out at an earlier stage than an in vivo embryo would reach the uterine lumen. This leads to the possibility of asynchrony between embryo and endometrial development. To synchronize the two events, reliable and repeatable method(s) of determining the stages of development of embryos and the endometrium are needed. Assessing embryo development is an independent challenge but cleavage rate and morphology have been carefully described (Gardner et al., 2004
). Determining the stage/receptiveness of the human endometrium to embryo implantation has proven to be more difficult (Creus et al., 2002; Ordi et al., 2003b; Quinn et al., 2007a).
In the rat, use of embryo transfer experiments has revealed that endometrial receptivity to embryo implantation occurs during a brief 24-h period, 5 days following mating (Psychoyos, 1973a, b, 1976). It has been suggested that a similar phenomenon occurs in the human between approximately days LH + 6 to LH + 8 (Nikas, 2000; Kao et al., 2002; Giudice, 2004). It is therefore of interest to develop a definitive method of identifying endometrial receptivity, prior to embryo transfer procedures, to optimize pregnancy rates. To achieve this, some investigators have proposed examination of the presence and timing of pinopodes in the human endometrium.
Pinopodes are smooth mushroom or balloon-like projections that arise from the apical surface of the luminal epithelium of the endometrium in mice, rats and humans, measuring several micrometers (µm) in diameter (Nilsson, 1958; Johannisson and Nilsson, 1972; Enders and Nelson, 1973; Singh et al., 1996) (Fig. 1).
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In the rat endometrium, the appearance of pinopodes clearly demarcates the window of receptivity with a rise in numbers on Day 4 of pregnancy (pre-implantation), abundance on Day 5 (day of embryo implantation) (Psychoyos and Mandon, 1971
) and rapid decline on Day 6 (post-implantation) (Singh et al., 1996; Quinn et al., 2007b). However, whether pinopodes are also a marker of endometrial receptivity in the human remains controversial (Creus et al., 2002; Ordi et al., 2003a, b; Quinn et al., 2007a).
Many publications arising from one group support the use of pinopodes as a reliable marker of the brief window of human endometrial receptivity (Nikas et al., 1995, 2000; Nikas and Psychoyos, 1997). To examine this, a detailed description of pinopodes, beginning with morphology and ending with clinical relevance and new avenues of research, follows.
For clarification, it should be noted that the terms pinopods, pinopodes and uterodomes have all been used to describe the same morphological feature. Specifically, the term pinopod has been used in association with rodents (Enders and Nelson, 1973), pinopodes in association with humans (Martel et al., 1991) and uterodome as a proposed universal term to describe both (Murphy, 2000). For convenience sake the term pinopode will be used throughout this work.
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Methods |
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TOPAbstractIntroductionMethodsPinopode morphologyDuration of pinopodesFunction of pinopodesPinopodes as a clinical...New avenues of researchSummary and conclusionsFundingReferences |
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Publications up to June 2008 related to the discovery, study and usefulness of pinopodes as a marker of endometrial preparation for implantation in both rodents and humans were identified through MEDLINE and other bibliographic databases. Additional references were considered by referral.
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Pinopode morphology |
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TOPAbstractIntroductionMethodsPinopode morphologyDuration of pinopodesFunction of pinopodesPinopodes as a clinical...New avenues of researchSummary and conclusionsFundingReferences |
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Pinopodes arise from the apical surface of the luminal epithelium of the uterus during the window of receptivity in both rodents and humans. This is best viewed by scanning electron microscopy (SEM) (Develioglu et al., 2000
) and reveals that on average, one pinopode extends from or bulges out of the surface of one cell and covers the majority of that cell's surface (Psychoyos and Mandon, 1971; Nikas et al., 2000; Quinn et al., 2007b) (Fig. 2A–C).
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There are notable morphological differences in shape, size and content of pinopodes between rodents and humans. In the rat, pinopodes have been shown to contain one to two large vacuoles (Parr and Parr, 1974
; Lopata et al., 2002), no organelles (Nilsson, 1966, 1972) and to extend from the apical surface of the cell on an actin-rich stalk or pedicle (Parr and Parr, 1974) above the level of the microvilli (Warren and Enders, 1964; Enders and Nelson, 1973; Parr and Parr, 1974) (Fig. 2C). This is not the case in the human where pinopodes extend from the entire surface or apex of the cell (Murphy, 2000), contain multiple organelles including mitochondria, golgi complex, secretory vesicles, rough endoplasmic reticulum and nuclei, and are devoid of large vacuoles (Friedrich, 1967; Bentin-Ley et al., 2000) (Fig. 2A). The presence or absence of vacuoles in mouse pinopodes has yet to be determined.
There are also morphological differences in the shape of pinopodes with mice possessing smooth mushroom or balloon-shaped pinopodes during the window of receptivity (Quinn et al., 2007b) (Fig. 2B) in comparison to rats, where pinopodes are moderately wrinkled and more oblong in shape (Enders and Nelson, 1973) (Fig. 2C). In humans, pinopode morphology changes as the luteal phase of the menstrual cycle progresses. Three different stages of pinopode development have been identified and are referred to as developing, fully developed and regressing with each phase lasting approximately 24 h (Nikas et al., 1995, 2000). In brief, developing pinopodes possess short microvilli and are beginning to bulge into the uterine lumen, mature pinopodes are devoid of microvilli and bulge maximally into the uterine lumen and regressing pinopodes are slightly wrinkled, less bulging and again possess short microvilli (Nikas et al., 1999, 2000) (Fig. 2A).
On average, pinopodes in the rat have been reported to have a diameter of 
3.0 to 4.0 µm (Ljungkvist and Nilsson, 1971; Enders and Nelson, 1973), mice 6 µm (Quinn et al., 2007b) and humans 6 µm (Acosta et al., 2000; Nikas et al., 2000; Quinn et al., 2007a). For reference, a range of pinopode shapes and sizes can be seen in Fig. 1. Much smaller spherical features (0.10 to 1.0 µm in diameter) have also been referred to as pinopodes on occasion (Bagot et al., 2001; Kimber, 2005; Panzan et al., 2006). These spherical features are too small to represent pinopodes and are most likely droplets (average diameter of 0.7 µm) (Martel et al., 1991), microvilli/blebs (diameter of <1 µm) (Quinn et al., 2007b) or the swollen tips of microvilli (diameter of 0.6 µm) (Nikas et al., 1999).
Percentage of the surface area covered in pinopodes
The percentage of the luminal epithelium covered in pinopodes during the window of receptivity varies from study to study and species to species (Parr and Parr, 1977; Nikas et al., 2000; Quinn et al., 2007a).
In the rat, between 5.5% (Parr and Parr, 1974; Quinn et al., 2007b) and 20% (Nilsson, 1972) of endometrial epithelial cells have a pinopode extending from their apical surface during the window of receptivity. In the mouse, reports range from 0.6% (Quinn et al., 2007b) to 20% coverage (Parr and Parr, 1977).
Reports in the human are much more variable with pinopode coverage ranging from 0% to confluent (Nikas et al., 1999; Creus et al., 2002). Multiple studies have examined pinopode formation during the luteal phase of both controlled ovarian hyperstimulation and natural cycles with reports of 2.3% coverage in pinopodes (Novotny et al., 1999), 0–12% coverage (mid-luteal phase) (Oborna et al., 2004), 4.4% coverage (Simon et al., 2005), 5.9% coverage (Simon et al., 2005), 5–10% coverage (Bentin-Ley, 2000), 7– 9% coverage (Novotny et al., 1999) and absent to confluent coverage (Creus et al., 2003).
In our experience, calculating pinopode coverage is difficult, due to the low number of fields examined and tissue heterogeneity, resulting in the percent coverage changing from field to field (Quinn et al., 2007a, b).
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Duration of pinopodes |
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TOPAbstractIntroductionMethodsPinopode morphologyDuration of pinopodesFunction of pinopodesPinopodes as a clinical...New avenues of researchSummary and conclusionsFundingReferences |
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Pinopode duration has been reported to range from hours to weeks (Nikas, 1999
, 2000; Quinn et al., 2007a, b). In the rat, there is little debate as to timing of pinopodes with numbers rising on Day 4 of pregnancy, peaking on Day 5 (day of embryo implantation) and virtually absent by Day 6 (Singh et al., 1996; Quinn et al., 2007b). Much less data are available on pinopode formation in the mouse with one study reporting a similar pattern to that seen in the rat (Parr and Parr, 1977) and another suggesting that pinopode numbers rise on Day 3.5 of pregnancy (1 day prior to embryo implantation) and remain elevated through to Day 8.5 (Quinn et al., 2007b).
There are conflicting reports as to the duration of pinopodes in the human. Some studies have shown that pinopodes persist for less than 48 h (Develioglu et al., 1999; Nikas et al., 1999; Nikas, 2000; Aghajanova et al., 2003) during the mid-luteal phase of the menstrual cycle, while other studies have shown that pinopodes are present from shortly after ovulation and persist to the end of the luteal phase (Creus et al., 2002; Ordi et al., 2003b; Quinn et al., 2007a). Examination of endometrial tissue collected during the first trimester of pregnancy, following hysterectomy or elective pregnancy termination, reveals an abundance of pinopodes suggesting that they also persist past the usual luteal phase (Johannisson and Nilsson, 1972; Quinn et al., 2007a) (Fig. 3).
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To study the duration of pinopode presence, sequential endometrial biopsies during the luteal phase of the menstrual cycle have been utilized. In one study, two endometrial biopsies were collected per patient (one on ovulation Day +7 to +8 [speculated window of receptivity] and a second 4 days later [days LH + 11 to LH + 12]). Results showed that 73% (17/23) of the first biopsies and 56% of the second biopsies were positive for pinopodes. Thus, >50% of patients were positive for pinopodes from at least LH + 8 through to LH + 11 (Creus et al., 2002
). Another study showed similar results with pinopodes appearing on Days 20–21 of the cycle and persisting through to Day 28 (Acosta et al., 2000). Pinopodes have been found even earlier in the cycle with one study reporting 50% of biopsies dated as post-ovulatory Day 3 and 70–90% of biopsies dated as post-ovulatory Days 4–9 as positive for pinopodes (Creus et al., 2003). In order for pinopodes to be good markers of endometrial receptivity they would need to be present for <48 h, which for many of the publications cited here does not seem to the case. |
Function of pinopodes |
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TOPAbstractIntroductionMethodsPinopode morphologyDuration of pinopodesFunction of pinopodesPinopodes as a clinical...New avenues of researchSummary and conclusionsFundingReferences |
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It is important to note that the function of pinopodes is unknown. It has been suggested that blastocysts attach to them during the process of implantation but this has not been proven in vivo (Bentin-Ley and Lopata, 2000
).
The results of a small preliminary in vitro investigation suggested that human blastocysts attach to pinopode-presenting areas when cultured on human endometrial epithelial cells (Bentin-Ley et al., 1999). A subsequent study was less convincing with two out of 10 blastocysts attaching to areas free of pinopodes and seven more attaching to areas where <25% of the surface area was covered (Petersen et al., 2005). It is therefore unclear as to the necessity of pinopodes for the process of embryo implantation. It is also important to note that structures seen in vivo may or may not be pinopodes as no definitive test for these structures has been devised.
Another speculative function of pinopodes is pinocytotic uptake of fluid from the uterine lumen in the rodent (Enders and Nelson, 1973; Parr and Parr, 1974, 1977). In fact, the word pinopode is derived from the Greek words ‘pino podi’, which translates into ‘drinking foot’. It has been proposed that the process of pinocytosis helps to induce a phenomenon known as uterine closure whereby the two opposing walls of the uterine lumen come into close association with one another ensuring that implanting embryos are held tightly in place (Parr, 1983). The vacuoles inside rodent pinopodes are thought to be involved in this pinocytotic function and measure from 0.5 to 3 µm in diameter (Parr and Parr, 1974). After the introduction of ferritin (an electron dense tracer) into the uterine lumen of the rat, pinopodes can be seen to have engulfed the tracer into these large vacuoles (Enders and Nelson, 1973). Although pinopodes in the rat are pinocytotic, this is not the case in the human where pinocytosis is not observed (Adams et al., 2002).
Another possible function of pinopodes is the release of secretory vesicles full of leukemia inhibitory factor (LIF) into the uterine lumen. This was suggested following the discovery of periodically ruptured pinopodes in the human endometrium as seen by SEM (Kabir-Salmani et al., 2005). This was later verified using an antibody-based test to reveal the localization of LIF to the ruptured pinopodes. Few pinopodes in this study were shown to be ruptured (<1%) (Kabir-Salmani et al., 2005) and in our experience less than 1 in 500 (0.02%) (unpublished data, Quinn et al., 2007a) cells in the human endometrium and few if any in the rodent (unpublished data, Quinn et al., 2007b) are ruptured when viewed under SEM. This low level of rupture is potentially indicative of damage during processing or general apoptosis as opposed to a biologically relevant secretory function involving cellular rupture.
Hormonal control of pinopode formation
The formation of pinopodes in both the rodent and human endometrium appears to be progesterone (P4) dependent (Ljungkvist, 1971; Singh et al., 1996), while administration of estradiol (E2) results in their rapid loss (<24 h) (Martel et al., 1991). In fact, administration of E2 to pseudo-pregnant rats results in a loss of pinopodes within 18 h of exposure (Martel et al., 1991). Oddly, ovariectomized (OVX) mice show an increase in the number of pinopodes present, surpassing even the number seen during the window of receptivity, suggesting that perhaps the absence or withdrawal of E2, perhaps even down-regulation of estrogen receptor by P4, as opposed to the presence of P4 is required for pinopode formation in these animals (Quinn et al., 2007b).
The correlation of pinopode formation to serum/media E2 and P4 levels has been studied both in vivo and in vitro. In one study, endometrial biopsies were collected from fertile patients for use in cell culture experiments (Petersen et al., 2005). Half of the biopsies were cultured in media supplemented with P4, while the other half were cultured in media supplemented with both P4 and the anti-Progestin Org 31710 (Petersen et al., 2005). Donated human blastocysts were overlaid onto the cultures and allowed time to attach to the underlying cells (Petersen et al., 2005). While blastocysts did not attach to the Org 31710-treated cells (Petersen et al., 2005), the number of pinopodes seen in these cultures was not statistically different from control cultures, suggesting that anti-P4 does not directly inhibit pinopode formation in vitro (Petersen et al., 2005).
Correlation of gene expression to pinopode formation
Several molecular markers have been correlated to the presence of pinopodes, including LIF (Aghajanova et al., 2003), HOXA10 (Bagot et al., 2001), Integrin 
vβ3 (Itgavb3) (Creus et al., 2003), Heparin-binding EGF-like growth factor (Hbegf) (Stavreus-Evers et al., 2002a) and Glutaredoxin (Glrx) (Stavreus-Evers et al., 2002b).
Studies examining the correlation of LIF expression to pinopode formation have reported that; (i) maximal IHC LIF staining is strongly correlated to the presence of fully developed pinopodes (Aghajanova et al., 2003) and (ii) IHC LIF staining is weak and erratic throughout the luteal phase of the cycle and does not correlate with pinopode formation which begins on Days 20–21 of the cycle and persisted through to Day 28 (Acosta et al., 2000). From these two studies, it can be seen that there is a lack of agreement in the literature as to the correlation between LIF expression and the presence of pinopodes. Furthermore, it has also been suggested that LIF is required for pinopode formation in the mouse (Kimber, 2005). However, a subsequent study has shown that Lif-null mice display an equivalent number of pinopodes in the peri-implantation period as do outbred laboratory (ICR) mice (Quinn et al., 2007b).
Another gene that has been implicated in pinopode formation is HOXA10 (Bagot et al., 2001). Altered expression of Hoxa10 in the mouse uterus via transient transfection with an anti-sense Hoxa10 construct has been shown to dramatically reduce the number of pinopodes present. In contrast, over expression of Hoxa10 has been shown to increase their numbers. A subsequent study however has shown that Hoxa10-null mice display a normal number of pinopodes in the peri-implantation period in comparison to ICR mice (Quinn et al., 2007b).
In the case of Itgavb3, one study has shown a strong association between intense IHC Itgavb3 staining and pinopode formation (Nardo et al., 2003), while another has shown no temporal association between the two markers (Creus et al., 2002).
Obvious disagreements between publications can be seen with regards to the temporal co-expression of the above molecular markers thought to frame the window of implantation and pinopode formation. These discrepancies most likely represent both differences in the animal and patient populations used, as well as the techniques employed to analyze the endometrial tissue that was collected from them.
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Pinopodes as a clinical marker of endometrial receptivity |
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TOPAbstractIntroductionMethodsPinopode morphologyDuration of pinopodesFunction of pinopodesPinopodes as a clinical...New avenues of researchSummary and conclusionsFundingReferences |
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For pinopodes to have clinical value they must be reproducibly and reliably predictive of pregnancy outcome. One group has devised a test for this purpose in which two consecutive endometrial biopsies were obtained during a mock cycle on Days 6 and 8 of P4 administration (Pantos et al., 2004
). The day of maximal receptivity, as established by the day on which mature pinopodes were detected, was then determined for each woman. Donor or frozen embryo transfers could then be timed so that the predicted most receptive day of the cycle coincided with embryonic Day 6 (Nikas et al., 2000).
To investigate the success of this strategy, 46 women with primary infertility and a history of three or more failed embryo transfers provided two endometrial biopsies during a mock cycle as described earlier. For 75% of the patients, a new ideal embryo transfer day was determined and used in a subsequent transfer cycle (Pantos et al., 2004). Of these women, 67% went on to deliver a healthy baby. For 25% of women with no indication for modification to their transfer protocol, only 25% went on to deliver a healthy baby (Pantos et al., 2004). The authors concluded that the results support the above described method of testing endometrial receptivity and modifying embryo transfer dates.
The assumptions associated with this test are that pinopodes last for <48 h per cycle, are predictive of receptivity and occur during the same window of time each cycle. All three assumptions, however, have been challenged. To examine between-cycle consistency, 15 infertile patients were asked to allow biopsies (one per cycle for three consecutive spontaneous cycles) on post-ovulatory Day 7 to examine pinopode formation by SEM. Analysis of the data from all 15 patients showed poor intra-patient consistency in pinopode scores between cycles with the status during one cycle not being predictive of what will occur in the next cycle (Ordi et al., 2003b). For one patient in particular all three endometrial biopsies were dated both histologically and hormonally (LH) as post-ovulatory Day 7 but pinopodes determination ranged from completely absent, to partially formed or to very prevalent for cycles 1, 2 and 3, respectively. Also many studies have shown that pinopodes persist through to the end of the luteal phase (Ordi et al., 2003b; Quinn et al., 2007a).
It is important to note that a post-biopsy healing response may affect the results of the second sample, which is retrieved 48 h following the first procedure. Examination of the human endometrium following a biopsy, as viewed under scanning and transmission electron microscopy, reveals that full repair of the luminal epithelium is completed in approximately 48–72 h (Ferenczy, 1976a, b; Ludwig and Metzger, 1976; Inoue, 1985; Kaitu'u et al., 2005). While complete, or nearly complete, repair may be achieved prior to re-sampling, it cannot be determined whether this process affects the presence, maturity or per cent coverage in pinopodes, even in non-biopsied regions.
An additional problem with this test is that the luminal surface of the endometrium is highly heterogeneous. Pinopodes are often found in clusters making any scoring system dependent on how many clusters randomly get included in the count. As well, in humans, the developmental stage of pinopodes changes from field to field with smooth, wrinkled and microvillous cells all visible throughout the sample, making it difficult to score.
Another intriguing observation is that infertile women regularly exhibit pinopode formation (Creus et al., 2002, 2003; Ordi et al., 2003a, b; Quinn et al., 2007a). To determine if fertile patients are more likely to have pinopodes then infertile ones, endometrial biopsies were collected from infertile patients with stage I or II endometriosis as their only cause of infertility, patients with unexplained infertility and patients undergoing tubal sterilization (controls) (Ordi et al., 2003a). Two separate endometrial biopsies were collected from each woman, one on post-ovulatory Day +7 to +8 and a second 4 days later. No statistically significant differences were found between the three groups with infertile patients showing an equivalent number of pinopodes as fertile controls (Ordi et al., 2003a). Another comparison of fertile and infertile patients showed similar results with no statistical differences between groups in relation to the presence of pinopodes or expression of Itgavb3 (Creus et al., 2002).
One potential reason for poor agreement between studies in humans is that some publications calculate the ‘percent’ of the surface area covered in pinopodes, whereas others calculate the ‘stage’ (developing, developed or regressing) of pinopode development, and still others calculate both making it unclear as to what was calculated and what the results mean.
Animals and tissues in which pinopodes and pinopode-like structures have been identified
Endometrial pinopodes and pinopode-like structures have been reported in many different species during early pregnancy, including the viviparous lizard (Hosie et al., 2003), camel (Abd-Elnaeim et al., 1999), rabbit (Segalen et al., 1982), sheep (Guillomot et al., 1981), gerbil (Kress and Mardi, 1990), hamster (Blankenship et al., 1990), pig (Keys and King, 1990), deer (Aitken, 1975), monkey (Bhartiya and Bajpai, 1995) and cow (Guillomot et al., 1986; Murphy, 2000). It is of interest to note that many other different organs and cell types also possess pinopode-like (bulging microvillous free) cells. In fact, pinopode-like structures can be seen on the apical surface of the mouse trachea (Quinn et al., 2007b), canine cumulus–oocyte complex (Haenisch-Woehl et al., 2003), deep glandular lumen of the human endometrium (Kabir-Salmani et al., 2005), female turtle uterine tube (Alkindi et al., 2006) and lizard oviduct (Adams et al., 2004), to name a few showing the ubiquitous nature of this cell surface feature.
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New avenues of research |
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TOPAbstractIntroductionMethodsPinopode morphologyDuration of pinopodesFunction of pinopodesPinopodes as a clinical...New avenues of researchSummary and conclusionsFundingReferences |
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Review of the literature on endometrial receptivity suggests that morphological and single-gene approaches are not promising avenues of discovery (Horcajadas et al., 2007
). Research is now shifting towards microarray or global gene analysis. Many different endometrial-specific microarray studies have been performed and show good predictive value (Kao et al., 2002; Giudice, 2004; Talbi et al., 2006). For example, microarray analysis of endometrial tissue during the luteal phase of the menstrual cycle can now be used to repeatedly and reliably categorize samples within a day or two of their actual cycle date using biopsies collected via suction pipelle (Dominguez et al., 2003; Riesewijk et al., 2003; Horcajadas et al., 2007). This information is currently being used to form databases against which future biopsies can hopefully be compared to assist in patient management. The use of genome-wide arrays should eventually enable the verification of a cassette of genes that reliably predict or reflect endometrial receptivity as opposed to a single marker. |
Summary and conclusions |
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TOPAbstractIntroductionMethodsPinopode morphologyDuration of pinopodesFunction of pinopodesPinopodes as a clinical...New avenues of researchSummary and conclusionsFundingReferences |
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In conclusion, there is strong disagreement in the literature as to the timing, function and clinical value of pinopodes. The necessity of pinopodes in the implantation process has yet to be firmly established. We conclude that there is substantial evidence that pinopodes are good markers of endometrial receptivity in the rat. However, we believe that pinopodes are not useful in the mouse or human as consistent markers of endometrial receptivity for implantation. In the human, pinopodes have a prolonged (
5 days) presence in the luteal phase and fail to delineate the brief (24–48 h) window of receptivity. |
Funding |
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TOPAbstractIntroductionMethodsPinopode morphologyDuration of pinopodesFunction of pinopodesPinopodes as a clinical...New avenues of researchSummary and conclusionsFundingReferences |
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This work was supported by the Canadian Institutes of Health Research grant # HGG-62292.
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TOPAbstractIntroductionMethodsPinopode morphologyDuration of pinopodesFunction of pinopodesPinopodes as a clinical...New avenues of researchSummary and conclusionsFundingReferences |
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