Expression of Smac/DIABLO in mouse preimplantation embryos and its correlation to apoptosis and fragmentation

Regulation of early embryonal development during fertilization and implantation is crucial for mammalian reproduction. Several studies have described cell death during preimplantation embryogenesis in a range of mammalian species, both in vivo and in vitro. Therefore, apoptosis may be involved in early embryonic arrest and the characteristic cytoplasmic fragments are the equivalents of apoptotic bodies, the end-product of apoptosis. Although apoptosis is expected to associate with fragmentation in early preimplantation embryos, the mechanism through which this fragmentation occurs has not been elucidated. Recently, second mitochondria-derived activator of caspase/Direct IAP Binding Protein with Low pI (Smac/DIABLO) was identified as a mitochondrial protein that is released into the cytosol during apoptosis. Once released, the Smac/DIABLO blocks the anti-apoptotic activity of inhibitor of apoptosis proteins (IAPs). We hypothesized that the Smac/DIABLO may be involved in the fragmentation of mouse preimplantation embryos. Therefore, we investigated the expression of Smac/DIABLO mRNA and protein and its localization in mouse oocytes and preimplantation embryos. Smac/DIABLO mRNA was detected by RT-PCR in the oocytes and the preimplantation embryos. Immunohistochemistry studies showed that the Smac/DIABLO protein localized in mitochondria and was released into the cytosol in both fragmented embryos and embryos in which apoptosis was induced by staurosporine. These observations indicate that the Smac/DIABLO is involved in the fragmentation and apoptosis of preimplantation embryos.     

Proliferation of blastomeres from biopsied cleavage stage human embryos in vitro: an alternative to blastocyst biopsy for preimplantation diagnosis

Normally fertilized human embryos were biopsied at cleavagestages on the third day after in-vitro fertilization (IVF).One or two blastomeres at the 8-cell stage were removed andco-cultured with the biopsied embryos. Embryos and blastomereswere assessed daily for morphological development until day6, when the number of cells were counted by labelling the nuclei.In all, 53% of the biopsied embryos (25 out of 47) reached theblastocyst stage between day 5 and 6 and the proportion wasthe same irrespective of the number of cells removed. Therewas no significant difference between biopsied embryos fromwhich one or two blastomeres respectively had been removed withregard to total cell numbers at the blastocyst stage (56.2 ±3.0 and 64.7 ± 5.5), number of trophectoderm (45.4 ±3.5 and 44.0 ± 5.7) and inner cell mass cells (14.0 ±1.2 and 16.6 ± 1.8). Overall, 72% of the isolated blastomeresdivided at least once over 3 days in culture and 50% dividedmore than once. The mean overall cell number after 3 days inculture was 3.7 ± 0.48 per blastomere (range 1–8cells) if one cell was removed and 6.9 ± 1.0 if two cellswere removed. If the undivided blastomeres are excluded, themean cell number was 4.8 ± 0.51 and 8.3 ± 1.0respectively. Over this period, 55% of the blastomeres cavitated.Of the blastomeres taken from embryos that developed to theblastocyst stage, 92% divided and 76% cavitated. In those fromarrested embryos, 50% divided (P < 0.002) and 32% cavitated(P < 0.003). From the first group 8% of blastomeres and fromthe second group 41% of blastomeres neither divided nor cavitated(P < 0.008). We conclude that as a more consistent alternativeto blastocyst biopsy, cryopreserving biopsied cleavage stageembryos and culturing blastomeres would increase the numberof cells available for genetic analysis. This could facilitatepreimplantation diagnosis of inherited disease by improvingreliability and possibly allowing combined detection of chromosomaland single cell defects. Further studies will investigate thegenetics of proliferated blastomeres.     

The chromosome constitution of human preimplantation embryos fertilized in vitro

The chromosome constitution of five haploid, 178 diploid and11 triploid embryos fertilized in vitro was determined afterfixation on day 2 or day 3 of development. Karyotype analysisof 178 diploid embryos revealed abnormalities in 40 (22.5%)cases: 34 (19.1%) aneuploids, four (2.2%) mosaic embryos andtwo (1.1%) structural anomalies were identified. The majorityof aneuploid karyotypes (28/34) involved a single chromosomebut six embryos had aneuploidy of two or three chromosomes.The E group was most frequently involved in aneuploid karyotypes(10/23 hyperdiploid embryos) and trisomy 16, the most commonsingle anomaly in diploid embryos, was detected in 2.2% (4/178)of cases. Only one case of sex chromosome monosomy was identified.An excess of female karyotypes was detected in abnormal cases(sex ratio 0.48); this ratio was significantly (p< 0.05)different from that observed in normal cases (74: 64, XY: XX).The incidence of aneuploidy increased with maternal age butthis did not reach statistical significance. Embryo morphologyand growth rate, assessed by embryo development rating (EDR),did not distinguish between normal (mean score 7.9; mean EDR96.1) and aneuploid (mean score 8.1; mean EDR, 92.1) embryos.Numbers of hyperploid (n = 17) and hypoploid (n= 11) embryos(non-mosaic cases involving single chromosomes) were not statisticallydifferent. The relative proportions of chromosomes involvedin trisomic karyotypes showed a remarkable similarity to thepattern in spontaneous abortions. Pronuclear status was an unreliablepredictor of ploidy. Small numbers of karyotyped triploid embryosrevealed equal proportions of XXX, XXY and XYY embryos     

Fertilization and early embryology: Undocumented embryos: do not trash them, FISH them

Pronuclei formation is routinely assessed 16–20 h afteroocyte insemination in in-vitro fertilization (IVF). Occasionally,the pronuclei disappear before this time, rendering them as‘undocumented’. Since the number of pronuclei detectedis used to distinguish normal from abnormal embryos in the contextof ploidy, the diploidy of undocumented embryos is questionable,and therefore they are routinely discarded. The introductionof fluorescent in-situ hybridization (FISH) technology allowsthe assessment of ploidy status in undocumented embryos thatcontinue to cleave to form blostomeres. In this study, we usedFISH to analyse the chromosomal status of 23 undocumented embryosobtained from 10 patients. Biopsied blastomeres were fixed andprobed for five chromosomes (X, Y, 13, 18, 21). Diploidy wasconfirmed in 13 (57%) embryos while the remaining 10 embryosdisplayed various chromosomal anomalies. Six of the diploidembryos were transferred subsequently to the patients. One ongoingpregnancy was achieved following transfer of an undocumented,analysed embryo, which was already cleaved when assessed 20h after insemination. We suggest that accelerated dismantlingof the pronuclear membrane and subsequent cleavage do not necessarilyindicate abnormal chromosomal content and may result in normalpregnancy. In a patient with a small number of embryos, FISHmay be used to ascertain diploidy of undocumented embryos, therebyincreasing the number of available embryos for transfer.     

Improvement of the culture conditions for the development of human preimplantation embryos

The culture of human preimplantation embryos from the 1-cell to the morula/blastocyst stage of development is not satisfactory at present. The success of various IVF laboratories ranges from 18 to 23%, therefore there is a requirement for improvement in the standard conditions used to culture the embryo. Using a limited number of 'spare' human embryos which were donated for research, in-vitro studies have been undertaken using various culture media. The results show that a significant improvement in viability is achieved using Ham's F-12 medium compared with other media presently used for culturing embryos.     

Non-invasive measurement of pyruvate and glucose uptake and lactate production by single human preimplantation embryos

The consumption of pyruvate and glucose and the production of lactate by 40 single human preimplantation embryos has been measured using a non-invasive technique. Twelve of the embryos showed abnormal fertilization. Of the 28 normally fertilized embryos, nine (32%) developed to the blastocyst stage in culture while the remainder degenerated or arrested during cleavage. In the normal embryos, pyruvate uptake exceeded that of glucose in the early developmental stages (days 2-5 post-insemination) before glucose became the predominant substrate in the blastocyst (day 6). Considerable quantities of lactate were formed throughout development, rising from a value of 43.6 pmol/embryo/h on day 2.5 to 95.4 pmol/embryo/h on day 5.5. The values of pyruvate and glucose uptake and lactate production of those embryos which arrested were below those which developed normally. On the basis that one mole of glucose can give rise to two moles of lactate, only 50% of the lactate produced could be accounted for in terms of glucose uptake from the medium. This figure rose to 90% in the blastocyst. The remaining lactate must be derived from endogenous sources, most probably glycogen. It is proposed that the high production of lactate by human preimplantation embryos in vitro is an adaptation to the conditions of culture.     

Fertilization and early embryology: The presence of multinucleated blastomeres in human embryos is correlated with chromosomal abnormalities

The purpose of the present study was to determine whether thepresence of one or more multinucleated blastomeres during earlyembryonic development is associated with chromosomal abnormalitiesIn sibling blastomeres of that embryo. Embryos with multinucleatedcells (n = 47) detected on day 2 or 3 of development were comparedto dividing embryos without multinucleation. Arrested embryoswere excluded from this study. Chromosome abnormalities weredetected using fluorescent in-situ hybridization (FISH) withX, Y, 18 and 13/21 chromosome- specific probes. Of 47 embryosincluded in this study, 76.6% were chromosomafly abnormal, comparedto 50.9% in the control group (P < 0.001). Excluding aneuploidy,which is originated in the gametes and not the embryo, the differenceswere even higher, with 74.5% of multinucleated embryos beingchromosomafly abnormal compared to 32.3% of non-multinucleatedembryos (P < 0.001). Day of multinucleation appearance, numberof nuclei per cell, number of multinucleated cells per embryoand developmental quality of the embryos as well as the typeof fertilization (intracytoplasmic sperm injection versus standardinsemination) were not found to affect the rate of chromosomalabnormalities In embryos with multinucleated cells. These resultssuggest that embryos with multinucleated cells may not be suitablefor replacement and should be excluded unless no other embryosare available.     

Amplification of X-and Y-chromosome-specific regions from single human blastomeres by polymerase chain reaction for sexing of preimplantation embryos

We describe a polymerase chain reaction (PCR) assay for thesimultaneous detection of X and Y chromosomes in human blastomeres.In a first round of PCR, both X- and Y-specific fragments areamplified with primers which are common to both chromosomesand are derived from the X-linked steroid sulphatase gene andthe Y-linked pseudogene. In a second round of PCR, fragmentsspecific to each chromosome are generated: both an X and a Yfragment in male embryos and, due to the absence of a Y chromosome,only an X fragment in females. The efficiency and accuracy ofthis assay are high; it generates no false positive amplificationsignals and allows sexing in 6h after embryo biopsy. We thereforebelieve that it is suitable for gender determination by preimplantationdiagnosis for couples at risk for X-linked genetic diseases.     

Growth rate of human preimplantation embryos is sex dependent after ICSI but not after IVF

BACKGROUND: There is concern that IVF and/or ICSI might have an adverse effect on embryonic development via epigenetic alterations. Such alterations might also be involved in the sex-related growth differences in preimplantation embryos found in some animal species. In the present study we analysed cell numbers of human male and female surplus embryos that developed to the blastocyst stage after either IVF or ICSI in order to investigate possible sex-dependent differential growth rates. METHODS: Blastocysts resulting from surplus embryos obtained after either IVF or ICSI during a 5 year study period were analysed using fluorescence in situ hybridization (FISH). RESULTS: The number of cells and sex could be determined in 330 blastocysts collected from 92 IVF cycles and in 322 blastocysts collected from 121 ICSI cycles. Whereas female and male embryos originating from IVF showed comparable mean log cell numbers per embryo +/- SEM (3.76+/-0.05 in 147 female and 3.72+/-0.04 in 183 male embryos), significant differences were observed in embryos originating from ICSI (3.57+/-0.05 in 162 female and 3.90+/-0.03 in 160 male embryos). The sex-related growth difference was significantly greater in ICSI than in IVF embryos. In a subset of 84 embryos, inner cell mass (ICM) and trophectoderm (TE) were analysed separately. A significantly higher mean log cell number of TE cells in ICSI male embryos was found as compared to their female counterparts (3.44+/-0.12 in 16 female and 3.90+/-0.11 in 29 male embryos), whereas this difference was not found in IVF embryos. CONCLUSION: A clear sex-related growth difference was found in human blastocysts originating from ICSI, but not in blastocysts originating from IVF. It is as yet unknown which mechanism is responsible for our findings. We hypothesize that the ICSI procedure might interfere with the process of imprinted X-inactivation.     

Zinc is a possible toxic contaminant of silicone oil in microdrop cultures of preimplantation mouse embryos

A batch of silicone oil (dimethylpolysiloxane) is describedwhich had differential effects on the development of 1- and2-cell preimplantation mouse embryos in vitro when used as amicrodrop overlay over two culture media: CZB and KSOM. A highrate of development into blastocysts was observed when usingCZB medium; in contrast, development was strongly inhibitedwhen KSOM was used. Other batches of silicone oil or paraffinoil permitted development from the zygote to the blastocystof an outbred strain of mouse without arrest at the 2-cell stage.Our results show that the higher concentrations of ethylenediaminetetraaceticacid (EDTA) and bovine serum albumin (BSA) in CZB medium, incomparison with KSOM, protect against the toxic component inthe oil. Observations also gave circumstantial evidence thatthe toxic component in the oil is zinc. The beneficial effectof including EDTA in a medium is usually attributed to its chelatingtoxic metals introduced as impurities in other components ofthe medium. Our results now show that EDTA also protects againstimpurites in the oil overlay.     

In-vitro studies on 'spare' human preimplantation embryos in culture

Methods previously used for the biopsy of preimplantation mouse embryos have been applied to individual 'spare' human embryos. Early cleavage-stage human embryos have been cultured and individual blastomeres removed following zonae thinning or drilling. Embryos have also been cultured to the blastocyst stage for the biopsy of three to five trophectoderm cells. Both the biopsied embryo and the biopsied cells have been allowed to develop and/or grow in vitro.     

Fetal abnormalities produced after preimplantation exposure of mouse embryos to ammonium chloride

BACKGROUND: The aims of this study were to determine whether preimplantation exposure of mouse embryos to ammonium resulted in abnormal fetal development and to evaluate similar risks to the outcome of human assisted conception. METHODS: Mouse embryos cultured from the 1-cell stage were exposed to 0.3 mmol/l ammonium chloride for 3 days. Embryos cultured from the 2-cell stage were exposed to 0.3 or 0.6 mmol/l ammonium for 2 days. After transfer to the uteri of pseudopregnant recipient females, post-implantation development was evaluated on embryonic day 15.5 (E15.5) or E18.5. RESULTS: There was no consistent effect of preimplantation exposure to ammonium chloride on fetal or placental weights. All 101 E18.5 fetuses were normal but 5/217 E15.5 fetuses were abnormal (three exencephalic and two polydactylous), which was significantly higher than the 0/363 for the pooled groups of E15.5 control fetuses (P = 0.007). The combined E15.5 and E18.5 frequency was also significantly higher than the controls (5/318 versus 0/433; P = 0.013). CONCLUSIONS: These results support the conclusion that abnormal preimplantation culture conditions can cause fetal abnormalities in mice, but the risks may be lower than previously suggested. Further work is needed to evaluate the risk more fully but this risk should be considered when designing new strategies for human assisted conception.     

Evidence that glucose is not always an inhibitor of mouse preimplantation development in vitro

A factorial experimental design was used to examine the effects of 16 combinations of four concentrations of glucose (0.20, 0.60, 1.8, 5.4 mmol/l) and four concentrations of potassium dihydrogen phosphate (KH(2)PO(4); 0.05, 0.15, 0.45, 1.35 mmol/l) on the development in vitro of outbred CF1 mouse zygotes. Three responses were measured: (i) the number of zona-enclosed blastocysts; (ii) the number of blastocysts that started to hatch; and (iii) the total cell counts in the blastocysts. General linear modelling was used to estimate the most parsimonious two-dimensional concentration-response surfaces that represent the three responses to the different concentrations of glucose and KH(2)PO(4). There were no significant interactions between the effects of glucose and KH(2)PO(4) in all cases. Thus, the effects of glucose and phosphate are independent. No significant effects of glucose on blastocyst formation and the initiation of hatching were observed. Increasing the concentration of KH(2)PO(4) inhibited slightly (相似文献   

Non-invasive measurement of glucose and pyrovate uptake by individual human oocytes and preimplantation embryos

Pyruvate and glucose uptake by 73 individual human oocytes andpreimplantation embryos was measured non-invasively, using anultramicrofluorescence assay to analyse changes in substratelevels in mkrodroplets of culture medium. The uptake of bothsubstrates was measured over successive daily incubations betweendays 1 (unfertilized oocytes) or 2 (‘spare’ embryoswhich were not transferred) and day 6 (day 0 = day of insemination).Under these conditions, 58% (25/43) of fertilized embryos withtwo pronuclei on day 1 developed to the blastocyst stage byday 6. The pyruvate uptake of these embryos increased from –28to a maximum of 40 pmol/ embryo/h between days 2.5 and 4.5.Similarly, glucose uptake increased from 8 to 14 pmol/embryo/hbetween days 2.5 and 4.5, but then increased further to 24 pmol/embryo/hon day 5 at the blastocyst stage. The pyruvate uptake of fertilizedembryos which arrested at cleavage stages was significantlylower than for those which developed to the blastocyst stage.Polyspermk and parthenogenetic embryos, and unfertilized oocytesalso had lower pyruvate uptakes at later stages. The glucoseuptake of unfertilized oocytes and abnormal embryos never reachedthe level of fertilized embryos at the blastocyst stage on day5.5. Non-invasive measurement of pyruvate uptake before embryotransfer may provide a valuable functional criterion for theselection of viable embryos capable of developing to the blastocyststage.     

Structural heterogeneity of platelet-activating factor produced by murine preimplantation embryos.

Platelet-activating factor (PAF) is 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine with the alkyl moiety predominantly a mixture of saturated hexadecyl and octadecyl chains (C16:0 and C18:0 PAF, respectively). Previously, a PAF bioassay was compared with a radioimmunoassay for PAF (NEN Du Pont). Both assays were sensitive and quantitative, but the correlation between PAF measured by the bioassay compared to the radioimmunoassay was poor for murine embryo-derived PAF (r = 0.773, n = 88), while being completely adequate (r = 0.961) for a PAF standard which was an equimolar mixture of C16:0 and C18:0 PAF (C16:0/C18:0 PAF). This study compared a larger sample size of murine embryo-derived PAF (n = 154) and found that the poor correlation between the two assays persisted (r = 0.791). When dose-response curves were generated with C16:0, C16:0/C18:0 and C18:0 PAF (over a concentration range of 0.3-30 ng/ml), the concentrations which gave a 50% response were equivalent in the bioassay (i.e. 6 ng/ml), but differed in the radioimmunoassay (i.e. 1.5, 3 and 6 ng/ml, respectively). Following separation of murine embryo-derived PAF (from medium in which 30 two-cell embryos had been cultured for 24 h) into C16:0 and C18:0 PAF by reverse phase high performance liquid chromatography, 9/20 cultures produced 100% C16:0 PAF, 2/20 cultures produced 100% C18:0 PAF and the remaining 9/20 cultures produced varying proportions of both.(ABSTRACT TRUNCATED AT 250 WORDS)     

Human preimplantation development in vitro is not adversely affected by biopsy at the 8-cell stage

Normally fertilized human embryos biopsied 3 days after in-vitro fertilization (IVF) have been examined for effects on viability and development in vitro after removal of one or two cells at the 8-cell stage (1/8 and 2/8) from each embryo. A high proportion of 7/8 and 6/8 biopsied and unmanipulated embryos developed to the blastocyst stage between days 5 and 6 (79, 71 and 59%, respectively), and many biopsied embryos (56%) hatched from the zona pellucida in vitro. The viability of biopsied embryos which developed to the blastocyst stage was assessed by daily non-invasive measurement of the uptake of two energy substrates, glucose and pyruvate. Uptake of both substrates was generally lower in 7/8 and 6/8 biopsied embryos but only in proportion to the reduced cellular mass. The total cell number and the numbers of both trophectoderm (TE) and inner cell mass (ICM) cells in biopsied embryos at the blastocyst stage, counted by differential labelling of their nuclei, were also reduced in proportion but the ratio of ICM to TE cells was maintained in both 7/8 and 6/8 biopsied embryos. We conclude that removal of one or two cells at the 8-cell stage, while reducing the cellular mass, does not adversely affect the preimplantation/development of biopsied embryos in vitro and suggest that this approach could be used for preimplantation diagnosis of genetic defects.     

Variation in the dry mass of mouse embryos throughout the preimplantation period.

Information on the net balance of embryonic metabolism during the preimplantation period is provided by measurements of embryo dry mass. The dry mass of mouse embryos at 10 defined stages of preimplantation development was measured using the Vickers M86 scanning microinterferometer. The results demonstrate that there is an overall loss of dry mass from the unfertilized ovum (39.10 +/- 0.6 ng) to the late blastocyst stage (32.80 +/- 0.53 ng) with these differences being highly significant. However, there is a significant increase in embryonic dry mass from the 1-cell (36.88 +/- 0.34 ng) to 2-cell stage (40.48 +/- 0.40 ng). These results suggest that protein synthesis exceeds degradation during the 2-cell stage but that from the 4-cell to morula stage the reverse is true. In addition, the variation in dry mass between embryos at the same developmental stage is extremely small, suggesting that this may be a useful indicator of embryonic viability.     

Effect of damage to the zona pellucida on development of preimplantation embryos in the mouse

The effect on development of early mouse embryos of making ahair-line slit in the zona pellucida of approximately one-thirdits diameter was investigated. The rate of development to mid-gestationof operated zygotes and2-cell embryos transferred directly tothe oviduct was significantly lower than that of sham-operatedor unoperated controls. However, the operation had no discernibleeffect on the development of 2-cel embryos that were culturedfor 2 days prior to transfer to the uterus, or on embryos composedof 8 or more cells transferred directly to the oviduct. Zonaslit zygotes and 2-cell embryos exhibited a significantly higherrate of anomalous development to the morula or blastocyst stagethan controls following short-term transfer to the adult orimmature oviduct. Such anomalies could not be attributed todamage of the embryos by leucocytes or bacteria entering throughthe wound in the zona. Rather, the typically non-spherical shapeof slit zonae, together with the fact that some were empty onrecovery, was consistent with operated embryos having been damagedby compression during passage through the oviduct. This suggeststhat, providing it is intact, the zona pellucida protects theearly embryo from contraction of the oviductual musculaturewhich is sufficient to lyse, arrest or extrude blastomeres priorto the formation of intercellular junctions. Hence, in experimentalmanipulations entailing damage to the zonae of early embryos,there may be a case for allowing them to form morulae in vitroprior to transfer, rather than returning them directly to theoviduct     

Using hyperosmolar stress to measure biologic and stress-activated protein kinase responses in preimplantation embryos

We used hyperosmolar stress to test blastocysts for their biologic and enzymatic responses to culture stress. Embryos mount dose- and time-dependent responses to hyperosmolar stress. Biological responses included slowed cavitation and cell accumulation and increased apoptosis at increasing doses. These responses were preceded by stress-activated protein kinase (SAPK) phosphorylation and nuclear translocation consistent with its causal role. For cavitation and new cell cycle initiation, 200 mM sorbitol caused stasis. Above 200 mM, sorbitol was ultimately lethal and below 200 mM, its embryos had milder effects. Phosphorylated SAPK was induced rapidly in embryos at 0.5 h in a dose-dependent manner from 0 to 600 mM sorbitol. Higher hyperosmolarity caused a biphasic peak of phosphorylated SAPK, but there was no return to baseline through 3 h. At 24 h, a dose-dependent response persisted that was linear from 0 to 200 mM sorbitol. Hyperosmolar stress rapidly induced, within 0.5 h, phosphorylated, nuclear c-Jun and decreased phosphorylated, nuclear c-Myc in a SAPK-dependent manner. The data suggest that SAPK is induced and functions on down-stream effector molecules in a temporal and quantitative manner consistent with its function in the embryonic homeostatic response to stress. The remarkable resistance of embryos to high concentrations of sorbitol suggests that part of its homeostatic response is different from that of somatic cells.     

Caspase cascade of Fas-mediated apoptosis in human normal endometrium and endometrial carcinoma cells

Human endometrial epithelial cells undergo apoptosis immediately before the menstrual period. Apoptotic signalling was analysed using human endometrial tissue and a human endometrial carcinoma cell line (HHUA). Activity levels of caspase-3, -8, and -9 were elevated in human endometrium during the late secretory phase and in HHUA cells incubated with an anti-Fas monoclonal antibody (mAb). Fas-mediated apoptosis of HHUA cells was blocked by prior exposure to inhibitors of caspase-9, -8 and -3. In HHUA cells treated with anti-Fas mAb, a release of cytochrome c was detected in the cytosolic fraction, in addition a full-length Bid was degraded. Full-length FLIP(L) (p55) was degraded during apoptosis, and p29 (regarded as the product of p55 cleavage) appeared instead of FLIP(L). In normal human endometrial tissue, Bid degradation was also observed in a cyclic manner with a peak during the early secretory phase of the menstrual cycle. Furthermore, the release of cytochrome c was seen in the early secretory phase. However, expression of FLIP(S) was only observed during the menstrual cycle in normal endometrial tissue. We concluded that the main apoptotic signalling in both normal human endometrial tissue and HHUA cells exposed to anti-Fas mAb is the mitochondrial pathway via Bid degradation. Although the function of FLIP is still unknown on normal endometrial tissue, it may be regulated by FLIP(L) expression on HHUA cells derived from human endometrial carcinoma.