Stereological study of organelle distribution in human oocytes at metaphase I

Abstract

Summary We have previously presented a stereological analysis of organelle distribution in human prophase I oocytes. In the present study, using a similar stereological approach, we quantified the distribution of organelles in human metaphase I (MI) oocytes also retrieved after ovarian stimulation. Five MI oocytes were processed for transmission electron microscopy and a classical manual stereological technique based on point-counting with an adequate stereological grid was used. Kruskal–Wallis and Mann–Whitney U-tests with Bonferroni correction were used to compare the means of relative volumes (Vv) occupied by organelles. In all oocyte regions, the most abundant organelles were mitochondria and smooth endoplasmic reticulum (SER) elements. No significant differences were observed in Vv of mitochondria, dictyosomes, lysosomes, or SER small and medium vesicles, tubular aggregates and tubules. Significant differences were observed in other organelle distributions: cortical vesicles presented a higher Vv (P = 0.004) in the cortex than in the subcortex (0.96% vs 0.1%) or inner cytoplasm (0.96% vs 0.1%), vesicles with dense granular contents had a higher Vv (P = 0.005) in the cortex than in the subcortex (0.1% vs 0%), and SER large vesicles exhibited a higher Vv (P = 0.011) in the inner cytoplasm than in the subcortex (0.2% vs 0%). Future stereological analysis of metaphase II oocytes and a combined quantitative data of mature and immature oocytes, will enable a better understanding of oocyte organelle distribution during in vivo maturation. Combined with molecular approaches, this may help improve stimulation protocols and in vitro maturation methods.

High-Resolution 3D Reconstruction of Human Oocytes Using Focused Ion Beam Scanning Electron Microscopy

“…The quantitative analysis of the 3D image data indicated that, in our samples of maturing human oocytes, mitochondrion occupies approximately 4.26% cytoplasm volume (Figure 2J). This result derived from densely recorded 3D datasets provide a more accurate estimate than the previous TEM stereological studies using 2D image data (Pires-Luís et al, 2016;Coelho et al, 2020).…”

High-resolution 3D reconstruction of human oocytes using FIB-SEM

“…The quantitative analysis of the 3D image data indicated that, in our samples of MI and MII oocytes, mitochondrion occupies approximately 4.26 % cytoplasm volume (Figure 2J). This result provides a more accurate estimate than previous 2D stereological studies [7,8].…”