Intracytoplasmic Morphological Abnormalities in Human Oocytes

The ultrastructural nature of human oocytes' cytoplasmic abnormalities and the role of cytoskeleton dysfunction

OBJECTIVE

To investigate the structural bases of human oocytes' cytoplasmic abnormalities and the causative mechanism of their emergence. Knowledge of an abnormal oocyte's intracellular organization is vital to establishing reliable criteria for clinical evaluation of oocyte morphology.

DESIGN

Laboratory-based study on experimental material provided by a private assisted reproduction clinic.

SETTING

University laboratory and imaging center.

PATIENTS

A total of 105 women undergoing hormonal stimulation for in vitro fertilization (IVF) donated their spare oocytes for this study.

INTERVENTIONS

Transmission electron microscopy (TEM) was used to analyze the fine morphology of 22 dysmorphic IVF oocytes exhibiting different types of cytoplasmic irregularities, namely, refractile bodies; centrally located cytoplasmic granularity (CLCG); smooth endoplasmic reticulum (SER) disc; and vacuoles. A total of 133 immature oocytes were exposed to cytoskeleton-targeting compounds or matured in control conditions, and their morphology was examined using fluorescent and electron microscopy.

MAIN OUTCOME MEASURES

The ultrastructural morphology of dysmorphic oocytes was analyzed. Drug-treated oocytes had their maturation efficiency, chromosome-microtubule configurations, and fine intracellular morphology examined.

RESULTS

TEM revealed ultrastructural characteristics of common oocyte aberrations and indicated that excessive organelle clustering was the underlying cause of 2 of the studied morphotypes. Inhibition experiments showed that disruption of actin, not microtubules, allows for inordinate aggregation of subcellular structures, resembling the ultrastructural pattern seen in morphologically abnormal oocytes retrieved in IVF cycles. These results imply that actin serves as a regulator of organelle distribution during human oocyte maturation.

CONCLUSION

The ultrastructural analogy between dysmorphic oocytes and oocytes, in which actin network integrity was perturbed, suggests that dysfunction of the actin cytoskeleton might be implicated in generating common cytoplasmic aberrations. Knowledge of human oocytes' inner workings and the origin of morphological abnormalities is a step forward to a more objective oocyte quality assessment in IVF practice.

Laser Microtomography for IVF Oocyte of Human

For in vitro fertilization technology, the quality of oocytes has a direct impact on the egg fertilization and developmental competence of early embryo. The morphological criteria are used for the estimation of oocyte quality before its fertilization in vitro. To date, only one method is known to determine the maturity of oocyte. This is the routine observation with a light microscope. The aim of this article was to adapt the noninvasive quantitative laser scanning microtomography (QLSM) for the investigation of morphological features of a human oocyte in vitro. This approach was used to accumulate the Z-stack gallery of optical sections of IVF oocyte. The layer-by-layer acquisition allows the fine cytoplasmic structure imaging. Applying the QLSM Z-stack of optical sections, the cellular volume was calculated with quantitative 3D reconstruction of a human oocyte. The volume value and intracellular structure were used as novel criteria to assess the oocyte state after the stress evoked by cryopreservation procedure.

Noninvasive Laser Microtomography of a Human Isolated Oocyte

Using a non-invasive approach, quantitative laser scanning microtomography (QLSM), the morphology of human oocyte was studied layer-by-layer. Then, the cell volume was computed based on 3D reconstruction of a stack of optical sections obtained by QLSM. The integrity of oocyte membrane after cryopreservation was assessed by measuring the changes in oocyte volume in response to hypotonic shock.

DYSMORPHISMS OF OOCYTES IN ART PROCEDURES. LITERATURE REVIEW

Currentliterature review presents the analysis of results of studies of morphological qualities and anomalies (dysmorphisms) of human oocytes in the field of assisted reproductive technologies. The variety of intracytoplasmic anomalies encountered in the clinical practice of in vitro fertilization, their effect on fertilization, cleavage, implantation frequency, clinical pregnancy rate were described. Moreover, the morphological characteristics of oocyte could be considered to use as biomarkers in predicting the quality of embryos and blastocysts, and further implantation potential.

Clinical outcomes of MII oocytes with refractile bodies in patients undergoing ICSI and single frozen embryo transfer

PURPOSE

This study aimed to analyze whether the presence of refractile bodies (RFs) negatively affects fertilization, embryo development, and/or implantation rates following intracytoplasmic sperm injection (ICSI).

METHODS

This retrospective embryo cohort study involved a total of 272 patients undergoing ICSI treatment of blastocyst cryopreservation.

RESULTS

In the study, no significant differences were found regarding 2PN formation rates between RF(+) (76.5%) and RF(-) oocytes (77.2%). However, the blastocyst formation rate on Day 5 in RF(+) oocytes was 45.8%, which was significantly lower than that of 52.2% in RF(-) oocytes (aOR 0.74, 95% CI 0.59-0.93, P = .011). Implantation rates were also significantly lower in RF(+) oocytes (24.2%) as compared to RF(-) oocytes (42.2%) (aOR 0.46, 95% CI 0.26-0.78, P = .005). Furthermore, the implantation rate of RF(+) oocytes (28.6%), when high-quality blastocysts were transferred, was significantly lower than that of RF(-) oocytes (46.1%) (aOR 0.50, 95% CI 0.25-0.96, P = .043).

CONCLUSION

Our results suggest that oocytes with the presence of RFs have a lower potential for blastocyst development. Even when they develop into high-quality blastocysts, the chances of implantation are reduced.

Synchrony of the first division as an index of the blastocyst formation rate during embryonic development

Purpose

To devise an uninvasive selection system for human embryos with high developmental potential after a single oocyte retrieval cycle by comparing the in vitro and in vivo effectiveness of first division synchrony against subsequent embryonic developmental stages.

Methods

The effects of using assisted reproductive technology on 948 embryos that were produced in 137 cycles were examined by dividing the embryos into “early cleavage” (first division within 25.90 hours) and “late cleavage” (first division at or after 25.90 hours) groups and comparing the blastocysts and good‐quality blastocyst formation rates between the two groups. These two groups were each divided further into “high synchrony” (first division synchrony within 3.96 hours) and “low synchrony” (first division synchrony at or after 3.96 hours) groups. The blastocysts, good‐quality blastocyst formation rates, and pregnancy rates were compared among these four groups.

Results

Both the blastocysts and good‐quality blastocyst formation rates were significantly higher in the early‐cleavage groups than in the late‐cleavage groups. The blastocyst formation rate of the latter was also significantly increased in the high‐synchrony, compared with the low‐synchrony, group.

Conclusion

First division synchrony in a single oocyte retrieval cycle could be a useful assessment of the blastocyst formation rate that enables the selection of viable embryos at an early stage of culture.

Relevance and Methodology for the Morphological Analysis of Oocyte Quality in IVF and ICSI

Oocytes collected from patients following ovarian stimulation exhibit varying qualities. The quality of oocytes has an effect on its subsequent fertilization, developmental competence post-fertilization and the viability of resultant embryos. The aim of this article was to review the morphological criteria devised for assessment of oocyte quality by ordinary light and polarized light microscopy before IVF or ICSI. The parameters employed in the evaluation of oocyte morphology include the appearance of: structure of the cumulus–oocyte complex, oocyte cytoplasm, perivitelline space, zona pellucida, polar body and meiotic spindle.