Ultrastructural Imaging Analysis of the Zona Pellucida Surface in Bovine Oocytes

The aims of the present study were to: (i) evaluate the ultrastructural differences in the zona pellucida (ZP) surface between immature and mature bovine oocytes, and (ii) describe a new objective technique to measure the pores in the outer ZP. Intact cumulus-oocyte complexes (COCs) obtained from a local abattoir were immediately fixed (immature group) or submitted to in vitro maturation (IVM) at 38.5 °C for 24 h in a humidified atmosphere of 5% CO2 in air (mature group). Oocytes from both groups were morphologically evaluated via Scanning Electron Microscopy (SEM) and the images were processed in the Fiji/ImageJ software using a new objective methodology through the Trainable Weka Segmentation plugin. The average number of pores in ZP was greater (p 0.05) between groups. In conclusion, it has been shown that the number of pores highlighted the main ultrastructural change in the morphology of the ZP surface of bovine oocytes during the IVM process. We have described an objective method that can be used to evaluate ultrastructural modifications of the ZP surface during oocyte maturation and early embryo development.

Time-dependent effects of heat shock on the zona pellucida ultrastructure and in vitro developmental competence of bovine oocytes

The aim of this study was to determine the effects of different exposure lenght to heat shock (HS) during in vitro maturation (IVM) on zona pellucida (ZP) ultrastructure and developmental competence of bovine oocytes. Cumulus-oocyte complexes (COCs) were matured in vitro (IVM) at 38.5 °C for 24 h (control group, CG), or incubated at 41 °C (HS) for 6 h (HS-6h), 12 h (HS-12h), 18 h (HS-18h), and 22h (HS-22h) followed by incubation at 38.5 °C to complete a full 24-h period of maturation. After IVM, oocytes were subjected to scanning electron microscopy (SEM) or in vitro fertilization and culture until the blastocyst stage. For heat-shocked oocytes, with exception of those in the HS-6h group, SEM examinations revealed that ZP surfaces were rough and characterized by a presence of spongy network. Oocytes from the HS-22h group displayed an increase in the number of pores, as well as a higher proportion of oocytes with amorphous ZPs. The proportion of oocytes that reached metaphase II (MII) stage decreased in all HS groups, regardless of the duration of exposure to 41 °C. These results provide evidence that HS during IVM for 12-22 h reduces the developmental competence of bovine oocytes, increasing the percentage of oocytes with abnormal chromosomal organization, and reducing fertilization and blastocysts formation rate. The effects of HS were more pronounced for the 22-h exposure group. The damage induced by HS on oocyte function clearly increased upon exposure to elevated temperature.

Observations of follicle cell processes in a holocephalan

The presence of follicular cellular processes (FCP) that cross the zona pellucida, has been recorded in the ovarian follicles of Callorhinchus callorhynchus. This constitutes the first report describing the presence of these structures in a species of the Holocephali. Considering that FCPs have only previously been reported in the Selachii, these findings suggest that FCPs could have been lost by the Batoidea after their divergence, around 280 M B.P.

Fourier Transform Infrared Spectroscopic Analysis of the Intact Zona Pellucida of the Mammalian Egg: Changes in the Secondary Structure of Bovine Zona Pellucida Proteins During Fertilization

The zona pellucida is the acellular transparent envelope surrounding the mammalian oocyte. An analysis of the changes in the structures of zona pellucida proteins is essential for understanding the molecular mechanisms underlying the important physiological roles of the zona during fertilization and prelmplantatlon. The hardening of the zona caused by the structural changes during fertilization is generally accepted to be responsible for blocking polyspermy. In this study, we analyzed changes in the secondary structure of the zona during fertilization by Fourier transform infrared (FTIR) spectroscopy and transmission electron microscopy. The predominance of β-sheet structure in porcine ovarian egg zona proteins in water was ascertained using FTIR spectra. α-Helix structure was also present. The attenuated total reflection (ATR)-FTIR spectrum of intact, unsolubilized porcine zonae pellucidae from ovarian eggs Indicated that the zona proteins in the native zona pellucida also have β-structure as the main constituent. Attenuated total reflectlon-FTIR spectroscopy of intact bovine zona pellucida obtained from ovarian and fertilized eggs at the blastocyst stage revealed that the β-structure content Increased during fertilization. Furthermore, a reduction of the thickness of the zona during fertilization was observed using transmission electron microscopy. Therefore, the change in the zona architecture that causes hardening of the zona during fertilization is accompanied by changes in the secondary structure of the zona proteins.

Integrity of Narrow Epithelial Tubes in the C. elegans Excretory System Requires a Transient Luminal Matrix

Most epithelial cells secrete a glycoprotein-rich apical extracellular matrix that can have diverse but still poorly understood roles in development and physiology. Zona Pellucida (ZP) domain glycoproteins are common constituents of these matrices, and their loss in humans is associated with a number of diseases. Understanding of the functions, organization and regulation of apical matrices has been hampered by difficulties in imaging them both in vivo and ex vivo. We identified the PAN-Apple, mucin and ZP domain glycoprotein LET-653 as an early and transient apical matrix component that shapes developing epithelia in C. elegans. LET-653 has modest effects on shaping of the vulva and epidermis, but is essential to prevent lumen fragmentation in the very narrow, unicellular excretory duct tube. We were able to image the transient LET-653 matrix by both live confocal imaging and transmission electron microscopy. Structure/function and fluorescence recovery after photobleaching studies revealed that LET-653 exists in two separate luminal matrix pools, a loose fibrillar matrix in the central core of the lumen, to which it binds dynamically via its PAN domains, and an apical-membrane-associated matrix, to which it binds stably via its ZP domain. The PAN domains are both necessary and sufficient to confer a cyclic pattern of duct lumen localization that precedes each molt, while the ZP domain is required for lumen integrity. Ectopic expression of full-length LET-653, but not the PAN domains alone, could expand lumen diameter in the developing gut tube, where LET-653 is not normally expressed. Together, these data support a model in which the PAN domains regulate the ability of the LET-653 ZP domain to interact with other factors at the apical membrane, and this ZP domain interaction promotes expansion and maintenance of lumen diameter. These data identify a transient apical matrix component present prior to cuticle secretion in C. elegans, demonstrate critical roles for this matrix component in supporting lumen integrity within narrow bore tubes such as those found in the mammalian microvasculature, and reveal functional importance of the evolutionarily conserved ZP domain in this tube protecting activity.

Most organs in the body are made up of networks of tubes that transport fluids or gases. These tubes come in many different sizes and shapes, with some narrow capillaries being only one cell in diameter. As tubes develop and take their final shapes, they secrete various glycoproteins into their hollow interior or lumen. The functions of these luminal proteins are not well understood, but there is increasing evidence that they are important for lumen shaping and that their loss can contribute to diseases such as cardiovascular disease and chronic kidney disease. Through studies of the nematode C. elegans, we identified a luminal glycoprotein, LET-653, that is transiently expressed in multiple developing tube types but is particularly critical to maintain integrity of the narrowest, unicellular tubes. We identified protein domains that direct LET-653 to specific apical matrix compartments and mediate its oscillatory pattern of lumen localization. Furthermore, we showed that the LET-653 tube-protecting activity depends on a Zona Pellucida (ZP) domain similar to that found in the mammalian egg-coat and in many other luminal or sensory matrix proteins involved in human disease.

Ultrastructural markers of quality are impaired in human metaphase II aged oocytes: a comparison between reproductive and in vitro aging

PURPOSE

Childbearing delay contributes to the increase of subfertile couples that require assisted reproductive technology (ART). Subfertility relates with reproductive aging (RA). In vitro aging (IvA) (due to extended culture) may also impair oocyte competence. Aims of this study were to evaluate and compare the oocyte ultrastructure after RA and IvA.

METHODS

Cumulus-oocyte complexes (COCs) (n = 68), with metaphase II oocyte and expanded cumulus, from consenting patients (<35 years old and ≥35 years old, n = 36), were selected by phase contrast microscopy and fixed at pick up, or after 24 h culture. COCs (n = 44) were studied by light and qualitative/morphometric transmission electron microscopy. Two-way ANOVA, with age and culture as grouping factors, was applied for statistical analysis (p < 0.05). Metaphase II cumulus-free oocytes (n = 24) were selected for confocal microscopy observations.

RESULTS

Significant decrease of mitochondria-smooth endoplasmic reticulum aggregates, increase of mitochondria-vesicle complexes size and amount, decrease of cortical granules and microvilli, and alterations of the spindle structure characterized both RA and IvA oocytes. These changes were significantly more evident in the RA oocytes submitted to IvA. RA oocytes also showed changes of the zona pellucida and occurrence of vacuoles after culture. Cumuli appeared re-compacted after culture, irrespective of the age of the patients.

CONCLUSIONS

These data demonstrated that aging is related to decay of oocyte ultrastructural quality, and that oocytes from elder women are more sensitive to prolonged culture (IvA) than the oocytes from younger women. These morphological results should be considered when applying ART in aged patients, rescue ICSI, or artificial oocyte activation.

[Oocyte quality as a predictive marker for assessment of IVF/ICSI procedure outcome]

The technology of in vitro fertilization consists mainly of pick up, selection and insemination of oocytes, embryo culture and their transfer into recipient's womb. Before any further manipulation of oocytes their quality has to be accurately evaluated as it has direct impact on the monospermic fertilization, early development, establishment and maintenance of pregnancy. Criteria applied for oocyte quality assessment are subdivided into morphological, cellular and molecular. Morphological ones include the structure of oocyte: cumulus-oocyte complex, cytoplasm, firstpolarbody, perivitelline space, zona pellucida, and meiotic spindle. Morphological alterations may be related to the particular patient and the treatment cycle characteristics, to affect most or all oocytes in the cohort. The aim of the resent review is by summarizing available data from literature to investigate if non-invasive observation of any morphological feature or group of features of MII phase human oocytes has strong predictive value for further development and the in vitro procedure outcome.

Ultrastructural interactions and genotoxicity assay of cerium dioxide nanoparticles on mouse oocytes

Cerium dioxide nanoparticles (C(e)O₂ ENPs) are on the priority list of nanomaterials requiring evaluation. We performed in vitro assays on mature mouse oocytes incubated with C(e)O₂ ENPs to study (1) physicochemical biotransformation of ENPs in culture medium; (2) ultrastructural interactions with follicular cells and oocytes using Transmission Electron Microscopy (TEM); (3) genotoxicity of C(e)O₂ ENPs on follicular cells and oocytes using a comet assay. DNA damage was quantified as Olive Tail Moment. We show that ENPs aggregated, but their crystal structure remained stable in culture medium. TEM showed endocytosis of C(e)O₂ ENP aggregates in follicular cells. In oocytes, C(e)O₂ ENP aggregates were only observed around the zona pellucida (ZP). The comet assay revealed significant DNA damage in follicular cells. In oocytes, the comet assay showed a dose-related increase in DNA damage and a significant increase only at the highest concentrations. DNA damage decreased significantly both in follicular cells and in oocytes when an anti-oxidant agent was added in the culture medium. We hypothesise that at low concentrations of C(e)O₂ ENPs oocytes could be protected against indirect oxidative stress due to a double defence system composed of follicular cells and ZP.

Cadmium impairment of reproduction in the female wall lizard Podarcis sicula

The exposure to environmental toxicants such cadmium (Cd) is an important research area in wildlife protection. In this study, the effect of Cd oral administration on the ovarian structure and function and on reproductive performance of the Italian wall lizard Podarcis sicula was studied. In vivo, adult female lizards were randomly assigned to three groups. Cd was given with food in single dose and in multiple doses 3 days/week for 4 weeks at dose of 1.0 μg/g body weight. Following euthanasia, the ovaries were removed and analyzed for morpho-functional changes. Results demonstrated that Cd increases prefollicular germ cells number; the evaluation of the number of follicles detects significantly higher number of atretic growing follicles, whereas primary follicles remain unchanged with respect to controls. After Cd treatments, follicles are deformed by the presence of large protrusions and a general dysregulation in the follicle organization is observed. The zona pellucida is also affected. Cd causes alteration in sugar metabolism and in metallothionein gene expression. Finally, Cd administration significantly reduces clutch size and dramatically increases embryo mortality. In conclusion, data here described show that Cd induces morpho-functional alterations in lizard follicles and indicates that these are responsible for a significant impairment of oogenesis. The effects of the dose are time independent, persisting essentially unchanged regardless of single or multiple administration, so it can be concluded that even occasional, sublethal Cd contamination may significantly impair reproductive performance in these animals.

Effects of partial or complete laser-assisted hatching on the hatching of mouse blastocysts and their cell numbers

BACKGROUND

It is still debatable whether a full-thickness assisted hatching (AH) is better than the partial zona thinning. In this research, we used a mouse model to study the effect of partial and complete laser-AH on the rate of completely hatched blastocyst and their cell numbers.

METHODS

In experiment 1, mouse morulae had 0, 1, 2 or 3 full-thickness openings of 10 microns created in the zona pellucida with an infrared laser beam. In the second experiment, 0, 1 and 2 openings of 20 microns were studied. In the third experiment, a full-thickness opening of 20 microns or quarter-thinning of the zonal circumference to a depth of 90% was compared with non-AH controls.

RESULTS

No difference in blastocyst formation was found in laser-treated groups and in the controls. In experiment 1, the rate of completely hatched blastocysts was significantly lower than the controls. In experiment 2 when the size of the opening was increased, blastocysts completely hatched at a significantly higher rate than that in the controls. In experiment 3, the rate of completely hatched blastocysts was the highest in the full-thickness group. Cell numbers in completely hatched blastocysts from both AH groups were significantly fewer than those in the controls.

CONCLUSIONS

Full-thickness opening resulted in a higher rate of completely hatched blastocysts than quarter zonal-thinning and controls, but the cell numbers were significantly decreased.

The zona pellucida porosity: three-dimensional reconstruction of four types of mouse oocyte zona pellucida using a dual beam microscope

In the last decade, the applicability of focus ion beam-field emission scanning electron microscopy (FIB-FESEM) in the biological field has begun to get relevance. Among the possibilities offered by FIB-FESEM, high-resolution three-dimensional (3D) reconstruction of biological structures is one of the most interesting. Using this tool, the 3D porosity of four different types of mouse oocyte zona pellucida (ZP) was analyzed. A surface analysis of the mouse oocyte ZP was first performed by SEM. Next, one oocyte per ZP type was selected, and an area of its ZP was completely milled, using the cut and view mode, in the FIB-FESEM. Through a 3D reconstruction of the milled area, a map of the distribution of the pores across the ZP was established and the number and volume of pores were quantified, thus enabling for the first time the study of the inner porosity of the mouse ZP. Differences in ZP porosity observed among the four types analyzed allowed us to outline a model to explain the changes that the ZP undergoes through immature, mature, predegenerative, and degenerative stages.

Whole-depth change in bovine zona pellucida biomechanics after fertilization: how relevant in hindering polyspermy?

Polyspermy is a common problem in bovine in vitro fertilization (IVF) and has a still unclear etiology. In this specie, after IVF, despite the lack of a biochemical post-fertilization hardening, the stiffness of the outer ZP layer is significantly increased. Therefore, polyspermy might be related to an incomplete or insufficient stiffening of the ZP. We obtained, by using atomic force spectroscopy in physiological conditions, a complete characterization of the biomechanical changes of the inner and outer ZP layers occurring during oocyte maturation/fertilization and correlated them to the ultrastructural changes observed by transmission electron microscopy using ruthenium red and saponin technique. In both the inner and outer ZP layers, stiffness decreased at maturation while, conversely, increased after fertilization. Contextually, at the nanoscale, during maturation both ZP layers displayed a fine filaments network whose length increased while thickness decreased. After fertilization, filaments partially recovered the immature features, appearing again shorter and thicker. Overall, the observed biomechanical modifications were substantiated by ultrastructural findings in the ZP filament mesh. In fertilized ZP, the calculated force necessary to displace ZP filaments resulted quite similar to that previously reported as generated by bovine sperm flagellum. Therefore, in bovine IVF biomechanical modifications of ZP appear ineffective in hindering sperm transit, highlighting the relevance of additional mechanisms operating in vivo.

Cell technology employing femtosecond laser pulses

Practical advantages of using femtosecond laser pulses for manipulations in cell surgery were demonstrated. The use of femtosecond laser pulses enables precision punching of the zona pellucida of the embryo without damaging its cells. With the help of femtosecond laser tweezers/scalpel, auxillary laser hatching was performed and a technique of optical biopsy of mammalian embryo was developed, which enabled non-contact sampling of embryonic material for preimplantation diagnostics. Our findings suggest that about 90% embryos retained the ability to develop at least to the blastula stage after this manipulation.

High doses of medroxyprogesterone as the cause of disappearance of adherence of the zona pellucida to an oocyte

The zona pellucida (ZP) is an external glycoprotein membrane of oocytes of mammals and embryos in the early stage of their development. ZP first appears in growing ovarian follicles as an extracellular substance between the oocyte and granular cells. The zona pellucid markedly affects the development and maturation of the oocyte. The morphology of the ZP-oocyte complex allows a more precise determination of the oocyte maturity. According to numerous experimental studies, ZP is essential for preimplantation embryonic development of humans and other mammals. It prevents dispersion of blastomeres and enhances their mutual interactions. ZP is a dynamic structure responsible for the provision of nutrients to early forms of oocytes in mammals. The aim of the present study was untrastructural evaluation of the ZP-oocyte contact during inhibited ovulation. Female white rats (Wistar strain) received a suspension of medroxyprogesterone acetate (MPA) in incremental intramuscular bolus doses of 3.7 mg (therapeutic dose), 7.4 mg and 11.1 mg. The animals were decapitated 5 days after the administration of MPA. Ovarian sections were evaluated under a transmission electron microscope (TEM) Zeiss EM 900. Morphometric analysis of ZP was conducted using the cell imaging system by Olympus. In females exposed to therapeutic doses of MPA, ZP showed the structure of granular-fibrous reticulum of a medium electron density with single cytoplasmic processes originating from the surrounding structures. The oocyte cell membrane generated single, delicate processes directed toward ZP. Microvilli of the oocyte were short and thin. In the group receiving 7.4 mg of MPA, ZP had the structure of a delicate, loose granular-fibrous reticulum, and the oocyte cell membrane generated single microvilli directed toward ZP. In both those groups, the close ZP-oocyte contact was observed. Otherwise, in the group exposed to the highest MPA doses (11.1 mg), thicker and more numerous oocyte microvilli were found, which did not penetrate ZP matrix. They were dense, irregularly separated contour, forming a barrier between ZP and oocyte. The present findings are likely to suggest that MPA has inhibiting effects on the synthesis of binding proteins and causes the loss of the oocyte contact with ZP.

[Ultrastructure of unfertilized human oocytes and undivided human zygoytes]

OBJECTIVE

To study the ultrastructure of unfertilized human oocytes and undivided human zygoytes.

METHODS

Unfertilized human oocytes and undivided human zygoytes were collected during in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI), and then observed under transmission electron microscope (TEM) after fixation, dehydration, embedding, and ultrashing.

RESULTS

The unfertilized oocytes from conventional IVF showed (1) normal zona pellucida (ZP) but without cortical granules (CG) beneath oolemma, condensed sperm nuclei, and disappearance of mitochondria and smooth endoplasmic reticulum (SER), (2) abnormal dense in ZP, lack of other organelles [SER tubuli (SER-T),SER vesicles (SER-V)] besides CG and mitochondria, and intact acrosome that penetrated the ZP. The unfertilized oocytes from ICSI showed (1) normal cortex containing one row of dense cortical granules beneath oolemma, SER-T and SER-V associated with mitochondria, some injected spermatozoon with lost nuclear envelope, and some decondensed chromatin, (2) little or scattered cortical granules, which dispersed beneath oolemma, scarce mitochondria and SER-T or isolated mitochondria. The undivided zygotes showed cortical granules contents free in the perivitelline space, little mitochondria, some second lysosomes filled with droplets, and large clumps of annulate lamellae (AL).

CONCLUSION

Appearance of organelles in abnormal position is related to oocytes cytoplasmic maturation, which leads to failure in fertilization. Absence of aerosome reaction and abnormal dense of zona pellucida are associated with failed fertilization in conventional IVF. Absence of oocyte activation is associated with failed fertilization in ICSI. The presence of lipofuscin body and abnormal assembly of annulate lamellae are associated with fertilization arrest at the pronuclear stage of human zygotic development.

In situ mechanical characterization of mouse oocytes using a cell holding device

This paper presents a cellular force measurement technique that allows for mechanical characterization of mouse oocytes during microinjection (i.e., in situ) without requiring a separate characterization process. The technique employs an elastic cell holding device and a sub-pixel computer vision tracking algorithm to resolve cellular forces in real time with a nanonewton force measurement resolution (2 nN at 30 Hz). Mechanical properties (i.e., stiffness) of both healthy and defective mouse oocytes are characterized. The experimental results suggest that the in situ obtained force-deformation data are useful for distinguishing healthy mouse oocytes from those with aging-induced cellular defects, promising an approach for oocyte quality assessment during microinjection. Biomembrane and cytoskeleton structures of the healthy and defective oocytes are also investigated in an attempt to correlate the measured subtle mechanical difference to cellular structure changes.

Laboratory evaluation in oocyte cryopreservation suggests retrieved oocytes are comparable whether frozen for medical indications, deferred reproduction or oocyte donation

PURPOSE

to compare pre-cryo data from oocyte cryopreservation (OC) cycles performed for malignancy (MED) vs. elective deferment of reproduction (DR) or oocyte donation (OD).

METHODS

all patients were ≤40 y and underwent standard ovarian stimulation and retrieval. Prior to OC, meiotic spindle (MS) and zona pellucida (ZP) retardance was measured using digital polarized light microscopy (DPLM).

RESULTS

of 130 OC cycles, 49 were for MED, 73 for DR, and 8 for OD. Cycles completed for MED had an average of 9 ±1 spindle-positive oocytes with a mean MS retardance of 1.2  ± 02 nm and ZP retardance of 2.1 ± .06 nm, which was clinically comparable to the other groups.

CONCLUSIONS

women with malignancy can achieve adequate ovarian response and similar oocyte parameters to those of women undergoing fertility preservation for non-cancer indications. Such information, coupled with the ability to noninvasively study oocyte dynamics, may improve the counseling of cancer patients seeking fertility preservation.

Deleterious effects of nicotine on the ultrastructure of oocytes: role of gamma-tocotrienol

BACKGROUND

Previous studies have shown that nicotine enhances oxidative DNA damage and leads to increased lipid peroxidation, which affects embryo development. The present study investigated the effect of daily supplementation of gamma-tocotrienol on oocytes of nicotine-treated mice.

MATERIAL/METHODS

Immature female mice (18-25 g) were divided into three groups. For 30 days, group A (control group) received saline (0.2 ml/day s.c.), group B nicotine (5 mg/kg/day s.c. in saline), and group C nicotine with gamma-tocotrienol (60 mg/kg/day p.o.). The animals were superovulated following these schedules.

RESULTS

Scanning electron microscopy (SEM) showed that the nicotine-treated oocytes appeared nonspherical with rough surface and the zona pellucida (zp) was torn and became irregular. Supplementation with gamma-tocotrienol in the nicotine-treated mice retained the spherical shape of the oocytes with intact zp; however, the surfaces of the oocytes remained irregular and rough. Transmission electron microscopy (TEM) following chronic nicotine treatment showed loosening of the boundary and tearing of the zp. The perivitelline space was also widened. The cytoplasm of the oocytes retained abundant rough endoplasmic reticulum (rER) with numerous vesicles. Mitochondria were highly dense, with no cristae. The administration of gamma-tocotrienol partially reduced the detrimental effects of nicotine by retaining the smooth boundary of the zp with the tight perivitelline space. There was less rER with no visible vesicle and a lower amount of dense mitochondrial matrix.

CONCLUSIONS

This study documented that chronic nicotine treatment adversely affects the ultrastructure of oocytes, while gamma-tocotrienol treatment at least minimizes the nicotine-induced damage to oocytes.

Imaging the zona pellucida of canine and feline oocytes using scanning electron microscopy

Ultrastructure of the zona pellucida (ZP) of canine and feline oocytes has not been fully investigated. The objective of the study was to evaluate the potential use of the low vacuum scanning electron microscope (LVSEM) with oocytes. This required development of a method to prepare canine and feline cumulus-oocyte complexes (COCs) for LVSEM to provide ultrastructural information on the ZP. COCs were collected from ovaries, and cumulus cells were either partially or completely removed to reveal the ZP. COCs and zona-intact oocytes were fixed at 4 degrees C for 1 h in 2.5% glutaraldehyde in 0.1 M sodium cacodylate buffer, pH 7.4 and subsequently viewed wet or further processed by critical point drying, and viewed uncoated or sputter coated with gold. Although the spongy surface of the ZP was visible at low vacuum in uncoated oocytes, coated oocytes had more details at high vacuum. The ZP surface of canine and feline oocytes contained numerous various-sized, spherical or elliptical pores that narrowed centripetally splitting into several smaller, deep pores. The round to oblong cumulus cells tightly surrounded the ZP. Each corona radiata cumulus cell tapered into a thin projection that entered the ZP. Our detailed techniques will enable future studies connecting ultrastructural and molecular aspects of oocyte maturation and development in mammals.

Zona pellucida components are present in human fetal ovary before follicle formation

The zona pellucida is a glycoprotein matrix surrounding oocytes and early-stage embryos in mammals. To elucidate the roles of the zona pellucida glycoproteins ZP1 and ZP3 and their key regulatory factor FIGLA in human ovarian development and folliculogenesis, their expression and localization was studied in human fetal and adult ovaries. FIGLA mRNA and ZP3 mRNA/protein were localized mainly in the oocytes, and during fetal development their maximal expression was observed around the 20th week, the time of follicle formation. The expression of ZP1 mRNA was low both in fetal and adult ovaries. Present findings demonstrate that ZP3 and FIGLA transcripts are expressed in the oocytes from early ovarian development. The function of ZP proteins during early fetal life is not clear, but the simultaneous expression of FIGLA and ZP3 suggests, that they may have a role in the development of primordial follicle before zona pellucida formation.

Changes to the meiotic spindle and zona pellucida of mature mouse oocytes following different cryopreservation methods

This study is to investigate the change of morphology of the meiotic spindle and the extent of zona hardening relating to the morphological survival and developmental competence of thawed oocytes. Four- to 8-week-old female mice (C57BL/6) primed with an intraperitoneal injection of pregnant mare's serum gonadotropin and human chorionic gonadotropin. Cryopreserved oocytes using two protocols: vitrificaton using ethylene glycol (EG) and slow freezing using propanediol (PROH). The freezing oocytes were thawed and were fertilized and subsequently cultured in vitro. Spindle/chromosome imagery, dissolution of zona pellucida, and post-thawing survival and development were comparable between two groups. The vitrification cryopreservation method proved to be better than the slow-freezing protocol when comparing the frequency of normal-shaped spindle development post-thawing. The difference in the time required for the dissolution of the zona pellucida under treatment of pronase that was determined to exist between the two cryopreservation methods was statistically significant (P<0.005). The survival rate of post-thawed mature oocytes was significantly greater for the vitrification group than it was for the slow-freezing cryopreservation group (P=0.005). The vitrification cryopreservation of mature murine oocytes would appear to be more satisfactory than the slow controlled-rate freezing method as regards the post-thawing oocyte survival and also the incidence of the normal spindle apparatus in the ooplasm.

Chemical zona pellucida thinning with acidified Tyrode's solution: comparison between partial and circumferential techniques

PURPOSE

To compare effectiveness of two different chemical zona thinning techniques.

METHOD

We studied 163 patients who had experienced IVF or ICSI failures in two or more cycles. Patients were assigned to one of three groups: zona intact (n=72), partial thinning (n=59), or circumferential thinning (n=73). Before transfer, the zonae pellucidae of embryos were thinned partially or circumferentially using acidified Tyrode's solution.

RESULTS

Implantation rates were 8.9% in the intact zona group, 17.6% in the partial thinning group, and 11.9% in the circumferential thinning group: respective clinical pregnancy rates were 16.7% (12/72), 32.2% (19/59), and 27.4% (20/73). Both rates were significantly higher in the partial thinning group than the intact zona group. For circumferential thinning versus zona intact groups, differences fell short of significance.

CONCLUSIONS

Following embryo transfer failure, partial thinning would be recommended over circumferential thinning for successful assisted hatching.

Blastocyst Axis Is Specified Independently of Early Cell Lineage But Aligns with the ZP Shape

The mechanisms controlling the establishment of the embryonic-abembryonic (E-Ab) axis of the mammalian blastocyst are controversial. We used in vitro time-lapse imaging and in vivo lineage labeling to provide evidence that the E-Ab axis of the mouse blastocyst is generated independently of early cell lineage. Rather, both the boundary between two-cell blastomeres and the E-Ab axis of the blastocyst align relative to the ellipsoidal shape of the zona pellucida (ZP), an extraembryonic structure. Lack of correlation between cell lineage and the E-Ab axis can be explained by the rotation of the embryo within the ZP.

Meiotic spindle and zona pellucida characteristics as predictors of embryonic development: a preliminary study using PolScope imaging

This study assesses meiotic spindle and zona pellucida characteristics using the PolScope, and analyses their relationship to embryonic development potential. A total of 205 matured oocytes retrieved from 25 patients undergoing ovarian stimulation were imaged for meiotic spindle and zona pellucida characteristics using the PolScope. After intracytoplasmic sperm injection, the oocytes were cultured and assessed for progression to blastocysts. Meiotic spindles were visualized in 78.0% of oocytes. Significantly more oocytes with visible spindles fertilized and progressed to blastocysts compared with oocytes without visible spindles. Oocytes with spindle retardance of >3 nm showed a greater progression to blastocysts compared with those with a retardance of 2-3 nm or <2 nm. More blastocysts were obtained from oocytes with spindle lengths of >12 nm than from oocytes with spindle lengths 10-12 nm or <10 nm. A difference in progression to blastocyst was observed in oocytes with a zona inner layer retardance of >3 nm compared with oocytes with retardance of 2-3 nm or <2 nm. Oocytes with an inner layer zona of 10-12 nm thickness showed better progression compared with those with a thickness of 8-10 nm or <8 nm. Quantitative measurement of length and retardance of the meiotic spindle and zona pellucida has a positive predictive value in relation to embryonic development.

Tritrichomonas foetus damages bovine oocytes in vitro

Tritrichomonas foetus is an extracellular parasite of the urogenital tract in cattle. It causes infertility and abortion, but there is no documented information on the susceptibility of bovine oocytes to the parasite, except by one article that claimed no effects of T. foetus on oocytes or embryos. The aim of the present study was to study the effects provoked by T. foetus when in interaction with bovine oocytes. Oocytes were obtained from cow ovaries and divided into two groups: (1) one group contained cumulus cells, whereas (2) a second group was denuded from these cells. Light microscopy, video microscopy and scanning electron microscopy (SEM) revealed that exposure of oocytes to T. foetus caused rapid adhesion of the trichomonads to cumulus cells and to the zona pellucida (ZP). Motile parasites were observed for 12 h. The ZP was completely damaged, and the parasites were able to infiltrate beneath the ZP and reached the oocytes directly when the oocytes were denuded of the cumulus cells. Both the oocytes and the cumulus cells exhibited morphological characteristics compatible with apoptosis after interaction with T. foetus, such as chromatin condensation, the presence of several cytoplasmic vacuoles, with intact cellular membranes and organelles. The results from this study demonstrate that when a large number of T. foetus interacts with oocytes in vitro damage and apoptosis are provoked in the cow's reproductive cells. The behavior of this parasite as one of the causes of cattle infertility is discussed.

Stereo-electron microscopy of the ovarian follicles of cat and mouse

Three dimensional structure of developing ovarian follicles in the cat and the mouse were examined to clarify the cellular and the extra cellular components during follicular maturation by scanning electron microscopy. Epithelial cells of the membrana granulosa (MG) and the cumulus oophorus (CO) show variable morphology, which depends on the location of the cells in the follicle. In the small antral follicle, there is no morphological difference between the surface structure of the MG and the CO lining cells. In the large antral follicle, however, the lumenal lining cells of the MG change their spherical shape to a rather flattened one showing numerous pseudopodial processes creeping over the surrounding lumenal cells. The CO cells remain rounded with fine cytoplasmic protrusions on their outer surfaces which seem to make a network. The outer surface view of the zona appears as composed of labyrinthine canals with relatively large pores of various sizes, however, the inner surface is rather compact with a number of small pores.

The zona pellucida of the koala (Phascolarctos cinereus): its morphogenesis and thickness

In this study the ultrastructural organization of the koala oocyte and the thickness of the surrounding extracellular coat, the zona pellucida, has been determined to ascertain whether there is coevolution of the morphology of the female gamete with that of the highly divergent male gamete that is found in this marsupial species. Ovaries from several adult koalas were obtained and prepared for transmission electron microscopy. Oocytes in large tertiary follicles were somewhat smaller than those of most other marsupials, although their ultrastructural organization appeared similar and included many yolk vesicles. The zona pellucida surrounding the oocytes in tertiary follicles was approximately 8 microm thick and thus is of similar thickness to that of some eutherian mammals but at least twice as thick as that of most marsupial species so far studied. The results indicate that the koala oocyte is unusually small for a marsupial species whereas the zona pellucida is, by contrast, much thicker. How this relates to sperm-egg interaction at the time of fertilization has yet to be determined.

Laser-assisted hatching of cryopreserved-thawed embryos by thinning one quarter of the zona

Laser-assisted hatching is little documented in the literature regarding its efficacy in cryopreserved-thawed (CT) embryo transfer cycles. The aim of the present study was to evaluate in a randomized manner the efficacy of thinning one quarter of the zona pellucida of CT embryos to a depth of 50-80% of the original thickness, via laser treatment (the qLZT-AH procedure), in improving implantation and pregnancy rates. Two populations were studied: population I, patients who had all their supernumerary embryos cryopreserved, regardless of their morphology, and population II, patients at risk of ovarian hyperstimulation syndrome who had all their embryos cryopreserved. Artificial and natural protocols were used for the embryo transfers. A total of 350 laser-thinned CT embryos were compared with 352 intact zona embryos. No difference in implantation or pregnancy rate was found after using qLZT-AH in either population. These findings suggest that qLZT-AH should not be routinely performed in cryopreserved embryo programmes.

Equine zona protein synthesis and ZP structure during folliculogenesis, oocyte maturation, and embryogenesis

In the equine, the zona pellucida (ZP) is the major barrier to successful in vitro fertilization. Therefore the aim of our studies was to analyze species-specific features of the equine ZP in regard to structure and glycoprotein ZPB and ZPC expression sites during oocyte development and embryogenesis. The equine ZP revealed high immunological cross-reactivity to porcine ZPB and ZPC. In the ovary, the distribution of ZPB and ZPC was co-localized and correlated with the developmental stage of the follicle. ZPB and ZPC expression started in the oocyte of the late primordial and primary follicle. In the secondary follicle, both the oocyte and the cumulus cells contributed to ZPB and ZPC synthesis. After in vivo maturation the oocyte stopped ZPB and ZPC production whereas the cumulus cells continued synthesis. Contrary, in vitro matured (IVM) cumulus-oocyte-complexes (COCs) revealed a reverse expression pattern. This was correlated to alterations in the distribution, number, and size of pores in the ZP. In the zona, N-acetylglucosamine residues were co-localized with ZPC. The acellular glycoprotein capsule surrounding early equine embryos was negative for ZPB and ZPC. Our results imply that in the horse ZPB and ZPC glycoprotein expression is differentially regulated during folliculogenesis, oocyte maturation, and embryogenesis. Contrary to the bovine and porcine, zona protein synthesis during in vivo maturation is completely overtaken by the cumulus cells implying that in the horse these cells are crucial for zona integrity. During IVM, the cumulus cells lose their ability to synthesize glycoproteins leading to alterations in the zona structure.

Mechanism of sperm-zona pellucida penetration during mammalian fertilization: 26S proteasome as a candidate egg coat lysin

Despite years of research work, biologists remain divided over the issue of zona pellucida function during fertilization and the mode of sperm-ZP penetration. The present review examines the emerging evidence for the participation of ubiquitin-proteasome pathway in the process of sperm-ZP penetration generated in the last five years in species of mammals, ascidians and invertebrates. The 26S proteasome, a multi-subunit protease, selectively recognizes, and degrades, egg coat substrate proteins tagged by a covalent ligation of a small, multimeric protein, ubiquitin. Our in vitro work with pig gametes indicates that the sperm-borne 26S proteasomes selectively degrade an ubiquitinated ZP (glyco)protein during fertilization. We suggest that one or more of the ZP proteins are ubiquitinated, and proteasomes associated with the inner acrosomal membrane, are exposed as a result of acrosomal exocytosis. Sperm-ZP penetration may involve the ZP-deubiquitination, with several proteasomal subunits becoming phosphorylated. Polyubiquitin chain recognition activities associated with the sperm acrosomal proteasome could also contribute to anti-polyspermy control after sperm-egg fusion. Here, we bring together the relevant recent data on the mechanism of sperm-ZP penetration in mammals. Such observations could possibly lead to the development of novel non-hormonal contraceptives, improvement of infertility diagnostics and optimization of assisted reproduction.

Features that affect secretion and assembly of zona pellucida glycoproteins during mammalian oogenesis

For sperm to fertilize eggs, they must bind to and penetrate the zona pellucida (ZP) that surrounds the plasma membrane of all mammalian eggs. The ZP first appears during oocyte growth and increases in thickness as oocytes increase in diameter. The ZP is an extracellular matrix composed of long, crosslinked filaments. In mice, three glycoproteins, called mZP1-3, are synthesised and secreted by growing oocytes and assembled into a thick (-6.5 microm) extracellular coat over a 2-3 week period. Recently, we identified several regions of nascent ZP glycoproteins that affect their secretion and incorporation into the ZP (assembly) by growing oocytes. Among these are the ZP domain, the consensus furin cleavage site (CFCS) and the C-terminal propeptide (CTP) with its transmembrane domain (TMD), external hydrophobic patch (EHP), charged patch (CP), conserved cysteine (Cys) residue, and short cytoplasmic tail (CT). Particularly important is the ZP domain, a approximately 260 amino acid region with 8 conserved Cys residues that is common to a variety of extracellular proteins of diverse functions found in a wide range of multicellular eukaryotes. Our results show that the ZP domain functions as a polymerisation module and that its N-terminal half, including 4 conserved Cys residues, is largely responsible for this role. Additionally, two conserved hydrophobic sequences, one within the ZP domain (internal hydrophobic patch; IHP) and another within the CTP (EHP), apparently regulate polymerisation of nascent ZP glycoproteins. Collectively, our findings suggest a general mechanism for assembly of all ZP domain proteins based on coupling between proteolytic processing and polymerisation.

The axis of polarity of the mouse blastocyst is specified before blastulation and independently of the zona pellucida

BACKGROUND

Rather than being prepatterned, orientation of the embryonic-abembryonic (Em-Ab) axis of the mouse blastocyst has been claimed to depend on the conceptus being constrained by its zona pellucida (ZP) during blastulation. This hypothesis merited closer scrutiny, because it seemed at variance with observations on living conceptuses.

METHODS

Two-cell conceptuses with an oil drop injected into the lesser diameter (LD) of the ZP at the first cleavage plane were cultured until shortly before blastulation when the blastomere underlying the drop was labelled with carbocyanine dye. After removing the ZP, conceptuses were re-cultured to the blastocyst stage for recording the position along the axis of the centres of the patches of labelled cells.

RESULTS

These centres showed significant bias towards the equatorial (Eq) region of the axis compared with those resulting from labelling a blastomere at random, even following softening of the ZP at the 2-cell stage. This was also true if conceptuses were denuded at the 2-cell stage and the blastomere underlying an intact second polar body (PB) labelled in morulae.

CONCLUSIONS

These findings further support the view that the Em-Ab axis of the mouse blastocyst is normally prepatterned and provide no evidence of a role for the ZP in its specification.

Heterocomplex formation and cell-surface accumulation of hen's serum zona pellucida B1 (ZPB1)with ZPC expressed by a mammalian cell line (COS-7): a possible initiating step of egg-envelope matrix construction

The egg envelope, referred to as zona pellucida (ZP) in mammalian eggs, is a fibrous and noncollagenous extracellular matrix surrounding vertebrate eggs, and composed of three to four homologous glycoproteins with a common ZP domain. In birds, a liver-derived ZP glycoprotein (ZP1/ZPB1) is transported through the bloodstream to ovarian follicles and joins the egg-envelope matrix construction together with the other ZP glycoproteins, such as ZPC and ZPD/ZPX2, both secreted from follicular granulosa cells. We report here that, through its ZP domain, ZPB1 specifically associates with ZPC, which might lead to the construction of egg-envelope matrix. The ZPB1 in laying hen's serum specifically bound to ZPC, but not to ZPX2, separated by SDS-PAGE and blotted on a membrane. Hemagglutinin (HA)-tagged ZPC expressed in a mammalian cell line (COS-7) cells was processed and secreted as a mature-form into the culture medium. From the culture supernatant of ZPC-expressing transfectants cultured in the presence of ZPB1, both ZPB1 and ZPC were recovered as heterocomplexes by immunoprecipitation using either anti-HA or anti-ZPB1 antibody. Interestingly, a monoclonal antibody, 8E1, which immunoprecipitated free ZPB1, did not immunoprecipitate the ZPB1-ZPC heterocomplexes. An 8E1 epitope was mapped on a C-terminal region of the ZP domain in a ZPB1 molecule by identifying an 8E1-positive peptide using mass spectroscopy. Furthermore, by laser scanning confocal microscopy, ZPB1 and ZPC were observed to colocalize on the surface of ZPC-expressing transfectants cultured in the presence of ZPB1, whereas almost no ZPC was detected on the surface of the transfectants cultured in the absence of ZPB1. Taken together, these results suggest that ZPB1 transported into ovarian follicles encounters and associates with ZPC secreted from granulosa cells, resulting in the formation of heterocomplexes around an oocyte. In addition, it appears that such ZPB1-ZPC complexes accumulated on the oocyte surface act as a scaffold for subsequent matrix construction events including ZPX2 association.

Screening oocytes by polar body biopsy

Preimplantation genetic aneuploidy screening performed by polar body biopsy has become a frequently used method, especially as in several countries only preconceptional genetic diagnosis is allowed. To penetrate the zona pellucida, mechanical, chemical and laser-assisted techniques have been introduced. In this paper, the advantages, disadvantages, efficacy and safety of these techniques are elucidated.

Recovery of human sperm motility and ability to interact with the human zona pellucida after more than 28 years of storage in liquid nitrogen

Six donor semen samples were evaluated after 28 years cryopreservation in liquid nitrogen. The results showed that the samples retained good postthaw motility recovery and normal levels of binding to the human zona pellucida and that four of the five samples tested also gave normal levels of zona-induced acrosome reaction. In conclusion, human sperm can survive very long-term storage, which is pertinent information for clinicians referring boys and young men for sperm banking before chemotherapy.

Tracking Down the ZP Domain: From the Mammalian Zona Pellucida to the Molluscan Vitelline Envelope

Oocytes from virtually all organisms are surrounded by at least one coat. This specialized extracellular matrix, called the zona pellucida (ZP) in mammals and the vitelline envelope (VE) in nonmammals, has a structural function and plays essential roles in oogenesis, fertilization, and early development. During the last 15 years, compelling evidence has accumulated that all ZP/VE subunits polymerize using a conserved sequence, the ZP domain, so that the basic structural features of egg coat matrices have been maintained through evolution. Moreover, ZP domains have been identified in many other polymeric extracellular proteins from eukaryotes. This review compares the ultrastructure and molecular composition of egg coats from mollusc to human, suggests a common mechanism for assembly of ZP/VE proteins, and discusses alternative models of how these could be arranged within filaments.

Do age and extended culture affect the architecture of the zona pellucida of human oocytes and embryos?

Advanced female age and extended in vitro culture have both been implicated in zona pellucida (ZP) hardening and thickening. This study aimed to determine the influence of (i) the woman's age and (ii) prolonged in vitro culture of embryos on ZP thickness and density using non-invasive polarized light (LC-PolScope) microscopy. ZP thickness and density (measured as retardance) were determined in oocytes, embryos and blastocysts in women undergoing intracytoplasmic sperm injection (ICSI) in two age groups (older, >38 years; younger, ≤38 years). A total of 193 oocytes from 29 patients were studied. The younger group contained 100 oocytes and the older group 93 oocytes. The ZP was significantly thicker in metaphase II oocytes in the older group compared with the younger group (mean ± SD: 24.1 ± 2.5 μm vs 23.1 ± 3.3 μm; p = 0.01) but ZP density was equal (2.8 ± 0.7 nm). By day 2 of culture, embryos from the two groups had similar ZP thickness (22.2 ± 2.2 μm vs 21.7 ± 1.6 μm; p = 0.28) and density (2.9 ± 0.7 nm vs 2.8 ± 0.8 nm; p = 0.57). For the embryos cultured to blastocyst (older: n = 20; younger: n = 18) ZP thickness was similar in the two groups (19.2 ± 2.7 μm vs 19.1 ± 5.0 μm; p = 0.8) but thinner than on day 2. The older group had significantly denser ZP than the younger group (4.2 ± 0.5 nm vs 3.3 ± 1.0 nm, p < 0.01). Blastocysts from both groups had significantly denser ZP than their corresponding day 2 embryos (older: 4.2 ± 0.5 nm vs 2.9 ± 0.7 nm, p < 0.001; younger: 3.3 ± 1.0 nm vs 2.8 ± 0.8 nm, p = 0.013). It is concluded that there is little relationship between ZP thickness and its density as measured by polarized light microscopy. While ZP thickness decreases with extended embryo culturing, the density of the ZP increases. ZP density increases in both age groups with extended culture and, interestingly, more in embryos from older compared with younger women.

Mitochondrial DNA deletion in granulosa and cumulus oophorus cells

The incidence of the 4,977-bp deletion in mitochondrial DNA (DeltamtDNA4977) in 73 pairs of granulosa and cumulus oophorus cells was studied with polymerase chain reaction (PCR), and was significantly higher in granulosa cells (GC) (67/73, 91%) than in cumulus oophorus cells (17/73, 23.3%), independent of the donors' age. In the cumulus oophorus cells, the oocyte morphology, the ooplasma diameter, and the proportion of oocytes fertilized normally were comparable between those with and without DeltamtDNA4977; whereas the oocyte diameter and the zona thickness were significantly higher in those with DeltamtDNA4977.

Effects of assisted hatching method and age on implantation rates of IVF and ICSI

The objective of this study was to investigate whether a change in assisted hatching (AH) technique from total to partial penetration of the zona pellucida improved the outcome of IVF and intracytoplasmic sperm injection cycles where AH was indicated. This was an observational study conducted from the beginning of January 2000 to the end of April 2005. Total AH was performed in 312 cycles, while partial AH was performed in 592 cycles. In women of all ages, implantation, clinical pregnancy and live birth rates were higher in the partial AH group than in the total AH group (12.6 versus 7.2%, P = 0.0001; 22.3 versus 15.7%, P = 0.02; 18.2 versus 12.5%, P = 0.03 respectively). The benefit of partial AH was most marked in women under 38 years old (i.e. the recurrent implantation failure group). The authors conclude that partial AH is associated with higher implantation and pregnancy rates than total AH, especially in women under 38 years old who suffer from recurrent implantation failure.

Bovine blastocyst diameter as a morphological tool to predict embryo cell counts, embryo sex, hatching ability and developmental characteristics after transfer to recipients

The aim of the present study was to explore whether the blastocyst diameter and the zona thickness at 168 h after fertilisation are useful parameters to predict quality and viability of bovine in-vitro-produced (IVP)-embryos. Although significant (P < 0.05), the blastocyst diameter at 168 h correlated only poorly with the total number of cells (R2 = 0.13) and with the number of trophectoderm (TE) cells (R2 = 0.17). Hatched blastocysts (n = 66) at 216 h had a significantly greater mean diameter at 168 h (194.8 ± 16.8 µm) compared with either blastocysts that had started but not finished hatching at 216 h (n = 26, 178.4 ± 16.7 µm) or failed to commence hatching (n = 136, 162.7 ± 12.9 µm). Transfer of 101 IVP blastocysts to synchronised recipients resulted in the birth of 38 calves (38%). There were significantly more bull calves born than cow calves (P < 0.05), but this was not correlated with blastocyst diameter or zona thickness at 168 h. There was also no correlation between the diameter of blastocysts or the zona thickness at 168 h and parameters of subsequent developmental characteristics, including rates of pregnancy, resorptions and abortions, pregnancy duration, delivery to term and birthweight. Overall, the present results indicate that the blastocyst diameter and the zona thickness at 168 h are good predictors for subsequent hatching ability in vitro, but not for the number of TE cells, inner cell mass cells or total cells and neither for subsequent developmental characteristics after transfer to recipients.

Cx37 and Cx43 localize to zona pellucida in mouse ovarian follicles

In the ovarian follicle, granulosa cells adjacent to the oocyte extend processes through the zona pellucida matrix, and these projections establish gap junctions both with the oocyte and with neighboring transzonal projections. The identity of connexins contributing to gap junctions between transzonal projections has not been extensively studied. Here, we examined the expression pattern of Cx37 and Cx43 in mouse zona pellucida using multiple connexin-specific antibodies. Immunofluorescence staining revealed abundant Cx37 and Cx43 puncta within the zona pellucida of both preantral and antral follicles. Cx37 persisted in the zona pellucida of mature follicles up to 5 h after an ovulatory stimulus whereas Cx43 was reduced in the zona pellucida by 3 h after an ovulatory stimulus. We suggest that in addition to its role in oocyte-granulosa cell communication, Cx37 could enable a distinct communication pathway between those granulosa cells that are in direct contact with the oocyte.

In-vitro developmental potential of individual mouse blastomeres cultured with and without zona pellucida: future implications for human assisted reproduction

This study was designed to compare the developmental potential of individual blastomeres derived from 2-, 4-, 6- and 8-cell mouse embryos cultured with and without zona pellucida (ZP). In the first series, one, three, five and seven blastomeres were biopsied from 2-, 4-, 6- and 8-cell embryos respectively, and inserted individually into empty ZP recipients, leaving the remaining blastomere within its original ZP. In the second series, the same protocol was used except that the biopsied blastomeres were cultured without ZP and compared with the remaining blastomere within its original ZP. For the first series, individual blastomeres derived from 2-, 4-, 6- and 8-cell embryos cultured with ZP showed blastocyst development of 82.4, 68.6, 44.4 and 23.1% respectively, with corresponding hatching rates of 70.6, 60.0, 25.9 and 7.7%. For the second series, individual blastomeres cultured without ZP progressed with blastocyst development of 73.3, 64.5, 35.7 and 22.7% respectively. Blastocyst multiplication was achieved most efficiently when using individual blastomeres from 4- and 6-cell embryos. This is the first report on comparative in-vitro propagation of single blastomeres derived from various cleavage stages in a mammalian species. Blastomere cloning with its multiple applications may be envisaged for human assisted reproductive technologies.

[The impact of cigarette smoking on oocytes and embryos quality during in vitro fertilization program]

The aim of the study was to investigate the influence of smoking on different parameters in woman treated by in vitro fertilization. Twenty-seven patients undergoing IVF were classified as smokers and 32 as non-smokers on the basis of medical history. Smokers had decreased number of retrieved oocytes compared with non-smokers (p < 0.05). Our study demonstrates that active cigarette smoking increases the zona pellucida thickness of oocytes and decreases a quality of oocytes. Cigarette smoking is associated with reduced number of embryo obtaining after classical in vitro fertilization in smokers compared to non-smokers, There was no significant difference in number embryos obtained after ICSI treatment in both groups. Women who smoked had also statistically significantly lower quality of embryos versus non-smokers patients. The clinical pregnancy rate per cycle in smokers was significantly lower.

Three-dimensional structure of the zona pellucida at ovulation

The mammalian zona pellucida (ZP) is an extracellular matrix surrounding oocytes and early embryos, which is critical for normal fertilization and preimplantation development. It is made up of three/four glycoproteins arranged in a delicate filamentous matrix. Scanning electron microscopy (SEM) studies have shown that ZP has a porous, net-like structure and/or nearly smooth and compact aspect. In this study, the fine 3-D structure of the human and mouse ZP is reviewed with the aim to integrate ultrastructural and molecular data, considering that the mouse is still used as a good model for human fertilization. By conventional SEM observations, numerous evidences support that the spongy ZP appearance well correlates with mature oocytes. When observed through more sophisticated techniques at high resolution SEM, ZP showed a delicate meshwork of thin interconnected filaments, in a regular alternating pattern of wide and tight meshes. In mature oocytes, the wide meshes correspond to "pores" of the "spongy" ZP, whereas the tight meshes correspond to the compact parts of the ZP surrounding the pores. In conclusion, the traditional "spongy" or "compact" appearance of the ZP at conventional SEM appears to be only the consequence of a prevalence of different arrangements of microfilament networks, according to the maturation stage of the oocyte, and in agreement with the modern supramolecular model of the ZP at the basis of egg-sperm recognition. Despite great differences in molecular characterization of ZP glycoproteins between human and mouse ZP, there are no differences in the 3-D organization of glycoproteic microfilaments in these species.

Structural, biochemical and functional aspects of sperm-oocyte interactions in pigs

Polyspermic fertilization is still a major issue in porcine IVF systems. New information is available to characterize the zona pellucida (ZP) at different developmental stages by scanning electron microscopy (SEM) and by confocal microscopy to show the distribution of ZP glycoproteins. SEM images indicated no differences between in vivo and in vitro matured oocytes; however a change in the surface structure between immature and matured oocytes, as well as between mature oocytes and preimplantation embryos was obvious. In addition, spermatozoa were more tightly fixed in the ZP of in vivo produced compared to the ZP of in vitro produced embryos. The ZP undergoes biochemical changes during maturation prior to fertilization. The acidity of the ZP increases during maturation as indicated by a shift of 1.3 pl units for ZPB/ZPC and 0.8 pl units for ZPA in 2D gel electrophoresis, which is based on increasing sulfation of the oligosaccharides during maturation. Mass spectrometry in combination with in-gel deglycosylation allowed the mapping of new glycosylation sites. Functionality of the ZP also depends on its maturation status. Induction of the acrosome reaction was delayed when capacitated spermatozoa were exposed to immature oocytes.

Surface ultrastructural alterations of bovine oocytes after parthenogenetic activation

Oocyte activation is a critical component of the current animal cloning scheme. This study was designed to examine surface characteristics of bovine oocytes by scanning electron microscopy (SEM) after activation by calcium ionophore A23187 (A23187) and electric pulse combined with cycloheximide (CHX) or 6-dimethylaminopurine (6-DMAP) treatments. In vitro matured (IVM) oocytes were activated then harvested at 0 to 19 hours after the onset of treatments for SEM processing. The zona pellucida (ZP) of untreated IVM oocytes exhibited an open mesh structure. The ZP surface showed little changes after A23187 alone, but dramatically changed to a less porous surface 3 hours after combined treatments with CHX or 6-DMAP. The vitelline membrane of IVM oocytes was covered with well-developed microvilli (MV). The MV became shorter (0.83 vs. 1.35 microm, p < 0.01) 8 hours after A23187 treatment alone. The vitelline membrane was altered in all oocytes examined 3 hours after incubation with A23187 plus CHX or 6-DMAP. A 1.5-fold increase in the diameter of MV in the CHX group and a higher incidence of large cytoplasmic protrusions (more than 1 microm width) in the 6-DMAP group were observed. After removal of inhibitors, the surface morphologies of the ZP and vitelline membrane were returned nearly to those of untreated IVM oocytes in both groups. The present study clearly showed that surface characteristics of the bovine oocyte were more profoundly changed by a combination of agents for parthenogenetic stimulation, and that the ultrastructural effects were reversible.