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Functional Topography of the Fully Grown Human Oocyte

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ABSTRACT

In vivo maturation (IVM) of human oocytes is a technique used to increase the number of usable oocytes for in vitro fertilization (IVF) and represents a necessity for women with different ovarian pathologies. During IVM the oocytes progress from the germinal vesicle stage (GV) through the metaphase II and during this journey both nuclear and cytoplasmic rearrangements must be obtained to increase the probability to get viable and healthy zygotes/embryos after IVF. As the successful clinical outcomes of this technique are a reality, we wanted to investigate the causes behind oocytes maturation arrest. For obvious ethical reasons, we were able to analyze only few human immature oocytes discarded and donated to research by transmission electron microscopy showing that, as in the mouse, they have different chromatin and cytoplasmic organizations both essential for further embryo development.

No MeSH data available.


A-D) Representative images of semi-thin sections of discarded human NSN oocyte; asterisk refers to heterochromatin blocks; LD, lipid droplets. E-H) Representative images of semi-thin sections of discarded human SN oocyte; arrows point to thin glycocalix distributed at the cellular surface.
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fig002: A-D) Representative images of semi-thin sections of discarded human NSN oocyte; asterisk refers to heterochromatin blocks; LD, lipid droplets. E-H) Representative images of semi-thin sections of discarded human SN oocyte; arrows point to thin glycocalix distributed at the cellular surface.

Mentions: Semi-thin sections from single oocytes (two peripheral, two tangential to the nuclear envelope and one equatorial) allowed us to describe the following differences among the oocytes. In particular: i) In NSN oocytes, the most significant aspect is the copious presence of vacuoli, likely lipid droplets (LD; as described later), mainly distributed in close proximity of the nucleus. Very few cytoplasmic organelles, mainly small mitochondria, appearing strongly stained, are detectable at the perinuclear level while their number increase at the cell periphery. Nucleoli are very well recognizable thanks to their strong basophyly; chromatin appears finely dispersed and just very few heterochromatin blocks are distinguishable (Figure 2 A-D, asterisk). ii) Instead, in SN oocytes very few vacuoli are scattered through all the cytoplasm and the organelles are uniformly distributed throughout the whole cytoplasmic area. Nucleoli are very well recognizable, as in the NSN oocytes, thanks to their strong basophyly; chromatin appears finely dispersed without any detectable heterochromatin blocks. A thin glycocalix is also easily detectable tightly tied to microvilli, which are uniformly distributed at the cellular surface (Figure 2 EH, arrows).


Functional Topography of the Fully Grown Human Oocyte
A-D) Representative images of semi-thin sections of discarded human NSN oocyte; asterisk refers to heterochromatin blocks; LD, lipid droplets. E-H) Representative images of semi-thin sections of discarded human SN oocyte; arrows point to thin glycocalix distributed at the cellular surface.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5304266&req=5

fig002: A-D) Representative images of semi-thin sections of discarded human NSN oocyte; asterisk refers to heterochromatin blocks; LD, lipid droplets. E-H) Representative images of semi-thin sections of discarded human SN oocyte; arrows point to thin glycocalix distributed at the cellular surface.
Mentions: Semi-thin sections from single oocytes (two peripheral, two tangential to the nuclear envelope and one equatorial) allowed us to describe the following differences among the oocytes. In particular: i) In NSN oocytes, the most significant aspect is the copious presence of vacuoli, likely lipid droplets (LD; as described later), mainly distributed in close proximity of the nucleus. Very few cytoplasmic organelles, mainly small mitochondria, appearing strongly stained, are detectable at the perinuclear level while their number increase at the cell periphery. Nucleoli are very well recognizable thanks to their strong basophyly; chromatin appears finely dispersed and just very few heterochromatin blocks are distinguishable (Figure 2 A-D, asterisk). ii) Instead, in SN oocytes very few vacuoli are scattered through all the cytoplasm and the organelles are uniformly distributed throughout the whole cytoplasmic area. Nucleoli are very well recognizable, as in the NSN oocytes, thanks to their strong basophyly; chromatin appears finely dispersed without any detectable heterochromatin blocks. A thin glycocalix is also easily detectable tightly tied to microvilli, which are uniformly distributed at the cellular surface (Figure 2 EH, arrows).

View Article: PubMed Central - PubMed

ABSTRACT

In vivo maturation (IVM) of human oocytes is a technique used to increase the number of usable oocytes for in vitro fertilization (IVF) and represents a necessity for women with different ovarian pathologies. During IVM the oocytes progress from the germinal vesicle stage (GV) through the metaphase II and during this journey both nuclear and cytoplasmic rearrangements must be obtained to increase the probability to get viable and healthy zygotes/embryos after IVF. As the successful clinical outcomes of this technique are a reality, we wanted to investigate the causes behind oocytes maturation arrest. For obvious ethical reasons, we were able to analyze only few human immature oocytes discarded and donated to research by transmission electron microscopy showing that, as in the mouse, they have different chromatin and cytoplasmic organizations both essential for further embryo development.

No MeSH data available.