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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.

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A-D) Transmission electron microscopy images of discarded human NSN oocyte; asterisk refers to mitochondria with microvacuolized matrix and both external and internal membrane protrusion; arrow points to residual ghosts of mitochondrial lysis. E-H) Transmission electron microscopy images of discarded human SN oocyte. Asterisks refer to mitochondrial vacuolar protrusions; arrow in E points to Golgi apparatus and arrows in G refer to smooth/rough reticulum; cytoplasmic lattices are visible in H (arrows); insert in H shows a magnification of CPLs.
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fig003: A-D) Transmission electron microscopy images of discarded human NSN oocyte; asterisk refers to mitochondria with microvacuolized matrix and both external and internal membrane protrusion; arrow points to residual ghosts of mitochondrial lysis. E-H) Transmission electron microscopy images of discarded human SN oocyte. Asterisks refer to mitochondrial vacuolar protrusions; arrow in E points to Golgi apparatus and arrows in G refer to smooth/rough reticulum; cytoplasmic lattices are visible in H (arrows); insert in H shows a magnification of CPLs.

Mentions: Images obtained with transmission electron microscopy (TEM) showed: i) cytoplasm of human NSN oocytes is dispersed with an abundant amorphous component. Organelles are mainly represented by small roundish mitochondria with a low electron dense matrix and a low number of cristae mostly distributed at the periphery. Mitochondria with microvacuolized matrix and both external and internal membrane protrusion, similar to superficial blebs, are abundant. These structures are lacking of mitochondrial matrix (Figure 3A, asterisk). These features are associated with degenerative mitochondrial damage. Endoplasmic reticulum is rare. Some endoplasmic reticulum profiles with associated ribosomes and polyribosomes are rare too. Vacuolar structures are very abundant and their ultrastructure is variable (Figure 3 B-C). Likely, they are made by lipids, proteins and glycoproteins components related to cytoplasmic autolysis processes. Residual ghosts of mitochondrial lysis are also visible at higher magnification (40.000X, Figure 3D). These structures can be considered as secondary lysosomes which are performing active intracellular digestion of cytoplasmic components. No cytoplasmic lattices or structures similar to them have been seen. ii) cytoplasm of human SN oocytes is very well preserved, with a homogenous matrix with a normal medium-electron density. Mitochondrial vacuolization is rare, limited to some protrusions of the external mitochondrial membrane (Figure 3 E-F, asterisks). Golgi apparatus is very well represented with stacks of flattened cisternae (Figure 3E, black arrow). At higher magnification, profiles of smooth/rough endoplasmic reticulum (Figure 3G, black arrows) and cytoplasmic lattices (Figure 3H, black arrows) are visible.


Functional Topography of the Fully Grown Human Oocyte
A-D) Transmission electron microscopy images of discarded human NSN oocyte; asterisk refers to mitochondria with microvacuolized matrix and both external and internal membrane protrusion; arrow points to residual ghosts of mitochondrial lysis. E-H) Transmission electron microscopy images of discarded human SN oocyte. Asterisks refer to mitochondrial vacuolar protrusions; arrow in E points to Golgi apparatus and arrows in G refer to smooth/rough reticulum; cytoplasmic lattices are visible in H (arrows); insert in H shows a magnification of CPLs.
© Copyright Policy - open-access
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5304266&req=5

fig003: A-D) Transmission electron microscopy images of discarded human NSN oocyte; asterisk refers to mitochondria with microvacuolized matrix and both external and internal membrane protrusion; arrow points to residual ghosts of mitochondrial lysis. E-H) Transmission electron microscopy images of discarded human SN oocyte. Asterisks refer to mitochondrial vacuolar protrusions; arrow in E points to Golgi apparatus and arrows in G refer to smooth/rough reticulum; cytoplasmic lattices are visible in H (arrows); insert in H shows a magnification of CPLs.
Mentions: Images obtained with transmission electron microscopy (TEM) showed: i) cytoplasm of human NSN oocytes is dispersed with an abundant amorphous component. Organelles are mainly represented by small roundish mitochondria with a low electron dense matrix and a low number of cristae mostly distributed at the periphery. Mitochondria with microvacuolized matrix and both external and internal membrane protrusion, similar to superficial blebs, are abundant. These structures are lacking of mitochondrial matrix (Figure 3A, asterisk). These features are associated with degenerative mitochondrial damage. Endoplasmic reticulum is rare. Some endoplasmic reticulum profiles with associated ribosomes and polyribosomes are rare too. Vacuolar structures are very abundant and their ultrastructure is variable (Figure 3 B-C). Likely, they are made by lipids, proteins and glycoproteins components related to cytoplasmic autolysis processes. Residual ghosts of mitochondrial lysis are also visible at higher magnification (40.000X, Figure 3D). These structures can be considered as secondary lysosomes which are performing active intracellular digestion of cytoplasmic components. No cytoplasmic lattices or structures similar to them have been seen. ii) cytoplasm of human SN oocytes is very well preserved, with a homogenous matrix with a normal medium-electron density. Mitochondrial vacuolization is rare, limited to some protrusions of the external mitochondrial membrane (Figure 3 E-F, asterisks). Golgi apparatus is very well represented with stacks of flattened cisternae (Figure 3E, black arrow). At higher magnification, profiles of smooth/rough endoplasmic reticulum (Figure 3G, black arrows) and cytoplasmic lattices (Figure 3H, black arrows) are visible.

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.


Related in: MedlinePlus