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Dysmorphic patterns are associated with cytoskeletal alterations in human oocytes

Dysmorphic patterns are associated with cytoskeletal alterations in human oocytes AbstractSTUDY QUESTIONAre specific morphological anomalies in human mature oocytes, as revealed by transmitted light microscopy, associated with intrinsic damage to the meiotic spindle and actin cytoskeleton?SUMMARY ANSWERAggregates of smooth endoplasmic reticulum (SER) and domains of centrally localized granular cytoplasm (GC) reflect intrinsic damage to the oocyte cytoskeleton, namely alterations in spindle size, chromosome misalignment and cortical actin disorganization.WHAT IS KNOWN ALREADYIn preparation for ICSI, oocytes are often selected for use in treatment by morphological criteria, but the rationale and implications of this practice are controversial. Very little information is available on the relationship between oocyte morphology and intrinsic cellular characteristics, such as the actin cytoskeleton, meiotic spindle and chromosome alignment.STUDY DESIGN, SIZE, DURATIONA total of 170 metaphase II (MII) oocytes were donated by consenting IVF patients and analysed; 62 were classified as morphologically normal (control), 54 had SER clusters and 54 had centrally localized GC.PARTICIPANTS/MATERIALS, SETTING, METHODSSupernumerary oocytes were fixed within 3 h from recovery and stained for tubulin, chromatin and actin. Spindles were analysed for 1D and 2D characteristics by high-performance confocal microscopy. Chromosomes were classified as scattered or aligned and the conformation and intensity of cortical actin was evaluated.MAIN RESULTS AND THE ROLE OF CHANCEIn comparison with control oocytes, both SER and GC oocytes showed greater spindle length (P = 0.033 and 0.003, respectively) and GC oocytes also showed greater spindle width (P= 0.049) and area (P= 0.036). Control and SER oocytes had statistically comparable rates of chromosome displacement from the metaphase plate, unlike GC oocytes where chromosome displacement occurred at higher rate (P = 0.013). In situations where a complete Z-stack was reconstructed from a polar angle, chromosome disposition was classified as being normal when two sets of concentric arrays were visible. Based on these parameters, the proportions of oocytes with normal chromosomal arrangement or partial/total disarrangement was not statistically different between control and SER oocytes. Conversely, in GC oocytes, chromosome disarrangement was higher (P = 0.002). All control oocytes displayed a continuous meshwork of suboolemmal actin, which appeared as an uninterrupted ring in thin optical sections. In contrast, in SER and  GC groups, integrity of suboolemmal actin was observed in only 66.7 and 42.9% of oocytes, respectively (P = 0.0001).LARGE SCALE DATAN/A.LIMITATIONS REASON FOR CAUTIONOnly two of several known oocyte dysmorphisms were investigated, while oocyte quality was assessed only by cytoskeletal criteria.WIDER IMPLICATIONS OF THE FINDINGSThis study represents a significant step toward a more objective assessment of oocyte morphology, offering information that can assist embryologists to make a more aware and rationally founded decision on whether, and with what possible implications, oocytes with certain dysmorphic characters should be used for treatment or discarded. More generally, it also demonstrates that morphometric parameters of the cytoskeleton and chromosome organization can be used as biomarkers of oocyte quality.STUDY FUNDING AND COMPETING INTEREST(S)This study was funded by Biogenesi Reproductive Medicine Centre (Monza, Italy). All authors declare no conflict of interests. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Human Reproduction Oxford University Press

Dysmorphic patterns are associated with cytoskeletal alterations in human oocytes

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Publisher
Oxford University Press
Copyright
© The Author 2017. Published by Oxford University Press on behalf of the European Society of Human Reproduction and Embryology. All rights reserved. For Permissions, please email: [email protected]
ISSN
0268-1161
eISSN
1460-2350
DOI
10.1093/humrep/dex041
pmid
28333241
Publisher site
See Article on Publisher Site

Abstract

AbstractSTUDY QUESTIONAre specific morphological anomalies in human mature oocytes, as revealed by transmitted light microscopy, associated with intrinsic damage to the meiotic spindle and actin cytoskeleton?SUMMARY ANSWERAggregates of smooth endoplasmic reticulum (SER) and domains of centrally localized granular cytoplasm (GC) reflect intrinsic damage to the oocyte cytoskeleton, namely alterations in spindle size, chromosome misalignment and cortical actin disorganization.WHAT IS KNOWN ALREADYIn preparation for ICSI, oocytes are often selected for use in treatment by morphological criteria, but the rationale and implications of this practice are controversial. Very little information is available on the relationship between oocyte morphology and intrinsic cellular characteristics, such as the actin cytoskeleton, meiotic spindle and chromosome alignment.STUDY DESIGN, SIZE, DURATIONA total of 170 metaphase II (MII) oocytes were donated by consenting IVF patients and analysed; 62 were classified as morphologically normal (control), 54 had SER clusters and 54 had centrally localized GC.PARTICIPANTS/MATERIALS, SETTING, METHODSSupernumerary oocytes were fixed within 3 h from recovery and stained for tubulin, chromatin and actin. Spindles were analysed for 1D and 2D characteristics by high-performance confocal microscopy. Chromosomes were classified as scattered or aligned and the conformation and intensity of cortical actin was evaluated.MAIN RESULTS AND THE ROLE OF CHANCEIn comparison with control oocytes, both SER and GC oocytes showed greater spindle length (P = 0.033 and 0.003, respectively) and GC oocytes also showed greater spindle width (P= 0.049) and area (P= 0.036). Control and SER oocytes had statistically comparable rates of chromosome displacement from the metaphase plate, unlike GC oocytes where chromosome displacement occurred at higher rate (P = 0.013). In situations where a complete Z-stack was reconstructed from a polar angle, chromosome disposition was classified as being normal when two sets of concentric arrays were visible. Based on these parameters, the proportions of oocytes with normal chromosomal arrangement or partial/total disarrangement was not statistically different between control and SER oocytes. Conversely, in GC oocytes, chromosome disarrangement was higher (P = 0.002). All control oocytes displayed a continuous meshwork of suboolemmal actin, which appeared as an uninterrupted ring in thin optical sections. In contrast, in SER and  GC groups, integrity of suboolemmal actin was observed in only 66.7 and 42.9% of oocytes, respectively (P = 0.0001).LARGE SCALE DATAN/A.LIMITATIONS REASON FOR CAUTIONOnly two of several known oocyte dysmorphisms were investigated, while oocyte quality was assessed only by cytoskeletal criteria.WIDER IMPLICATIONS OF THE FINDINGSThis study represents a significant step toward a more objective assessment of oocyte morphology, offering information that can assist embryologists to make a more aware and rationally founded decision on whether, and with what possible implications, oocytes with certain dysmorphic characters should be used for treatment or discarded. More generally, it also demonstrates that morphometric parameters of the cytoskeleton and chromosome organization can be used as biomarkers of oocyte quality.STUDY FUNDING AND COMPETING INTEREST(S)This study was funded by Biogenesi Reproductive Medicine Centre (Monza, Italy). All authors declare no conflict of interests.

Journal

Human Reproduction – Oxford University Press

Published: Apr 1, 2017

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