Human cumulus cell sensitivity to vitrification, an ultrastructural study

Abstract

SummaryCumulus cells (CCs) play an important role in the regulation of female gamete development, meiotic maturation, oocyte-sperm interaction, capacitation and acrosome reaction. However, their role in maintaining oocyte competence after vitrification is unclear as controversial data on their protecting action against oocyte cryoinjuries are available. Here we described the effects of vitrification on the ultrastructure of human CCs collected from women undergoing assisted reproductive technologies (ARTs). In total, 50 patches of CCs, sampled from high-quality human cumulus-oocyte complexes, were randomly allocated into two groups after patient informed consent: 1, fresh CCs (controls, n = 25); 2, vitrified CCs (n = 25). Samples were then prepared and observed by transmission electron microscopy. In fresh CCs, in which small cell clusters were visible, cell membranes were joined by focal gap junctions. Microvilli were rare and short. Nuclei, mitochondria, smooth endoplasmic reticulum (SER), Golgi apparatus and lipid droplets appeared well preserved; vacuoles were scarce. After vitrification, we observed two populations of CCs: light CCs, with a smooth appearance and few short microvilli; and dark CCs, with numerous and long microvilli. In both, most of the organelles appeared similar to those of fresh CCs. Lipid droplets were denser and more numerous, with respect to fresh CCs. They were mainly located in the peri-nuclear and sub-plasmalemmal regions. Numerous packed electron-negative vacuoles were visible. The vitrification procedure did not cause alterations in the fine structure of major organelles, except for an increased amount of lipid droplets and vacuoles. This specific sensitivity of human CCs to vitrification should be considered during ARTs.

The Effect of L-Carnitine Additive During In Vitro Maturation on the Vitrification of Pig Oocytes

“…The same result is obtained in the vitrification of bovine cumulus/oocyte complexes (COCs) (Zhou et al, 2010). It is supposed that retained CCs create a sort of natural, protective shield around the oocyte against physicochemical insults due to the cryopreservation procedure and might reduce the cryodamage to the oocyte (Taghizabet et al, 2018).…”

“…CCs can contact the oocyte directly via functional gap junctions through the surrounding ZP (Buccione et al, 1990). It plays an important role in the regulation of female gamete development, meiotic maturation, oocyte/sperm interaction, capacitation, and acrosome reaction (Taghizabet et al, 2018). Compared with human oocytes that removed CCs before freezing, human oocytes that retained CCs had a higher survival rate, cleavage rate, and high-quality embryo rate ( Jin et al, 2012).…”

“…In addition, the status of oocytes was another main factor responsible for the success of vitrification. First, retained CCs around oocytes during vitrification could reduce the cryodamage of oocytes (Taghizabet et al, 2018), and might compromise the functional coupling between oocytes and CCs (Luciano et al, 2009). However, vitrification induced the death of CCs invariably at the periphery of the cumulus layers, without compromising gap junction function or the ability of the oocytes to complete nuclear maturation (Tharasanit et al, 2009).…”

Morphological reproductive characteristics of testes and fertilization capacity of cryopreserved sperm after the Fukushima accident in raccoon (Procyon lotor)

“…Ultrathin sections (60–80 nm) were cut with a diamond knife, mounted on copper grids, and contrasted with Urany Less and lead citrate (SIC, Rome, Italy). Sections were examined and photographed using Philips TE CM100 electron microscopes operating at 80 kV (Belli et al., 2019; Taghizabet et al., 2018).…”

Repeated hyperstimulation affects the ultrastructure of mouse fallopian tube epithelium

“…We evaluated the following parameters for the qualitative assessment of the ultrastructural preservation of mouse oviducts: general features; morphology of the tunica mucosa , muscularis and serosa ; membrane integrity of the cells; morphology of the nucleus, chromatin, and nuclear envelope; type and quality of organelles and inclusions; configuration of mitochondria; type of granules, vesicles and vacuoles; intercellular projections; microvillus pattern and presence or extent of cilia [ 32 , 33 , 34 , 35 , 36 ].…”