Importance of the Microtubule Cytoskeleton in Oocyte Competence

This study will assess if there are microtubule cytoplasmic features specifically associated with oocyte vitrification.

Study Overview

• Status: Completed
• Conditions: ART
• Intervention / Treatment: Device: Vitrification and thawing

Detailed Description

Successful fertilization is heavily dependent upon inherent qualities of the oocytes, and thus reliant upon the fidelity of oocyte maturation. Reduced oocyte developmental competence is one of the main reasons for the decreased potential of in-vitro-produced embryos. Approximately 8,6% to 15% of all infertility patients produce at least one meiotically incompetent oocyte. There are also extreme cases of women which generate oocytes with complete or predominant failure to complete meiosis. These oocytes arrest and do not complete meiosis in response to exogenous final maturation and ovulation triggering. The incidence of this is unknown, and given the complexity of the processes involved in oocyte maturation, it has been difficult to define the key events or morphological features underlying oocyte competence.

An increasing amount of evidence in the past years has suggested that the microtubule (MT) cytoskeleton may have an important role in providing the oocyte with competence potential. Oocyte maturation involves major rearrangements of the MT cytoskeleton. It is well known the importance of forming a proper microtubule meiotic spindle for chromosome segregation upon meiosis. Moreover, MTs seem to be important for the redistribution of different organelles upon maturation. However, the exact functional significance of this reorganization and how MTs influence competence through the repositioning of these organelles is largely unknown.

The main MT organizing center in eukaryotic cells is the centrosome. Indeed, centrosomes are essential for the formation of the mitotic MT bipolar spindle. Interestingly, in the vast majority of female eggs these structures are eliminated, and the meiotic spindle does not contain centrosomes. A recent study in the lab organism Drosophila melanogaster (fruit fly), showed that interrupting this elimination, forcing the maintenance of centrosomes up to meiosis, led to female infertility. Both meiosis and the first nuclear divisions upon fertilization showed abnormal MT spindles with abnormal chromosome congression. This shows that proper spaciotemporal MT organization is likely to have important implications on oocyte competence.

The long-term goal of this research group is to analyze the MT cytoskeleton of oocytes from women which, upon assisted reproductive technologies, generate a high percentage of arrested embryos. In order to do this, the MT features of already-available surplus and unused oocytes which are vitrified and available for research purposes will be compared. These oocytes were donated from cycles in which a low (<20% the fertilized embryos) and high (>20% the fertilized embryos) incidence of arrested embryos was seen. Previous studies have posited that oocyte vitrification and warming may expose the oocyte to a variety of physical and chemical processes which may impact on their structural and genomic integrity. Therefore, this initial feasibility pilot study will investigate potential structural consequences for the oocytes of the vitrification procedure used in house.

Thus, it will be assess whether the Cryotop® - Open System induces specific MT features which may be absent in fresh oocytes. In case that both fresh and vitrified oocytes (derived from the same patient - sibling oocytes study) show a similar MT cytoskeleton organization, a collection of cryopreserved oocytes donated for research purposes will be used in the planned future studies of this research group.

• Study Type: Observational
• Enrollment (Actual): 6

Contacts and Locations

Study Locations

• Portugal
  • Lisboa, Portugal
    • Instituto Valenciano de Infertilidade

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 18 years to 34 years (ADULT)
• Accepts Healthy Volunteers: Yes
• Genders Eligible for Study: Female

• Sampling Method: Non-Probability Sample

Study Population

Healthy women who have consented to a cycle of fresh oocyte donation and who have a total antral-follicle count (AFC) above 20 at the onset of ovarian stimulation.

Description

Inclusion Criteria:

• Informed consent form dated and signed.
• Already consented to perform oocyte donation.
• Age ≥18 and <35 years old.
• AFC ≥20.
• BMI ≥18.5 Kg/m2 and <30 Kg/m2.
• Two ovaries present.
• No current pregnancy-wish.

Exclusion Criteria:

• Simultaneous participation in another clinical study or participation in another clinical study before inclusion in the present study that could affect its objectives.
• Previous history of poor ovarian response (<4 oocytes retrieved) with a maximal dose of ovarian stimulation (≥300 IU/day).
• Use of hormone contraceptives in the month preceding eventual inclusion.
• Presence of a medical condition which is known to affect ART outcome (e.g. thyroid dysfunction).
• Active female smoking.
• Ongoing pregnancy.
• Current use of anti-depressants, anti-psychotics, steroids, antiepileptics or chemotherapy.
• Known allergy or hypersensitivity to any of the study non-IMP.

Study Plan

How is the study designed?

Number of groups / cohorts

2

Cohorts and Interventions

Group / Cohort	Intervention / Treatment
Fresh oocytes; Sibling oocytes not subjected to vitrification prior to assessment
Vitrified-thawed oocytes; Sibling oocytes subjected to vitrification using the Cryotop® - Open System and thawing prior to assessment	Device: Vitrification and thawing; Vitrification using the Cryotop® - Open System followed by thawing

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Ocurrence of diferent features in the microtubule cytoskeleton	Both fresh and vitrified-warmed oocytes will be analysed in respect to: spindle morphology; chromosome congression at the metáfase plate; presence of microtubule aggregates and presence of pericentriolar material aggregates.	From October 2020 up to December 2020

Collaborators and Investigators

• Sponsor: Instituto Valenciano de Infertilidade de Lisboa
• Investigators: Principal Investigator: Sofia Nunes, PhD, Instituto Valenciano de Infertilidade de Lisboa

Study record dates

Study Major Dates

• Study Start (ACTUAL): October 9, 2020
• Primary Completion (ACTUAL): October 12, 2021
• Study Completion (ACTUAL): October 12, 2021

Study Registration Dates

• First Submitted: September 8, 2020
• First Submitted That Met QC Criteria: September 8, 2020
• First Posted (ACTUAL): September 14, 2020

Study Record Updates

• Last Update Posted (ACTUAL): August 4, 2022
• Last Update Submitted That Met QC Criteria: August 3, 2022
• Last Verified: August 1, 2022

More Information

Terms related to this study

• Keywords: Oocyte vitrification; Oocyte competence; Cryobiology; Microtubule cytoskeleton
• Other Study ID Numbers: 1907-LIS-072-AP

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No