Previous our studies have shown that CD44, the principal receptor for hyaluronan, is present on cumulus cells during oocyte maturation. Although hyaluronan-CD44 interaction has been implicated in cumulus expansion and/or oocyte maturation, the full significance of CD44 remains unknown. The objective of the present study was to further investigate the role of CD44 in cumulus expansion and oocyte maturation in pigs. We demonstrate here in that CD44 has a key role in oocyte maturation but not in cumulus expansion. Previous studies have reported the physiological significance of cumulus expansion in oocyte maturation. However, our results suggest that cumulus expansion is a necessary condition for oocyte maturation, but that it is not sufficient on its own. Furthermore, western blot analysis demonstrated that the CD44 of the in vitro-matured cumulus-oocyte complexes (COCs) had a larger molecular weight and more terminal sialic acid, which has been proven to inhibit the hyaluronan-binding ability of the receptor, than the CD44 of the in vivo-matured COCs, indicating that the hyaluronan-CD44 interactions during in vitro maturation might be insufficient compared with those in vivo. The insufficient interactions of hyaluronan-CD44 during in vitro maturation may cause the inferior capacity of fertilization and development of oocytes matured in vitro.
"Expanded cumuli prevents the flow of certain meiosis inhibiting factors to the oocyte  . Moreover, HA itself acts as a signal molecule regulating oocyte maturation  . These changes result in the activation of key cell cycle kinases that are pivotal for oocyte maturation: M-Phase/Maturation Promoting Factor (MPF) and Mitogen-Activated Protein Kinase (MAPK)  . "
"Hyaluronan is a major component of the cumulus-oocyte complex (COCs) and is synthesised and secreted by granulosa cells under the stimulation of LH and FSH . The insufficient interactions of hyaluronan and its receptor CD44 during in vitro maturation may decrease the capacity of fertilization and development of oocytes matured in vitro . The resumption of meiosis in mares, pigs, and rats is associated with decreased levels of connexin 43 (Cx43) . "
[Show abstract][Hide abstract] ABSTRACT: The objective of the present study was to evaluate the effect of hyaluronan (HA) during IVM on meiotic maturation, embryonic development, and the quality of oocytes,
granulosa cells (GC), and obtained blastocysts. COCs were matured in vitro in control medium and medium with additional 0.035% or 0.07% of exogenous HA. The meiotic maturity
did not differ between the analysed groups. The best rate and the highest quality of obtained blastocysts were observed when 0.07% HA was used. A highly significant difference
(P < 0.001) was noted in the mean number of apoptotic nuclei per blastocyst and in the DCI between the 0.07% HA and the control blastocysts (P < 0.01). Our results suggest that
addition of 0.035% HA and 0.07% HA to oocyte maturation media does not affect oocyte nuclear maturation and DNA fragmentation. However, the addition of 0.07% HA during
IVM decreases the level of blastocysts DNA fragmentation. Finally, our results suggest that it may be risky to increase the HA concentration during IVM above 0.07% as we found
significantly higher Bax mRNA expression levels in GC cultured with 0.07% HA. The final concentration of HA being supplemented to oocyte maturation media is critical for the
success of the IVP procedure.
"This is coherent since immature oocytes should be in contact with surrounding granulose cells to allow nutrient passage and reach its proper development . This agrees with data previously reported for other mammalian species such as porcine (Yokoo et al., 2007), bovine (Furnus et al., 2003), mice (Fulop et al., 1997), and human (Campbell et al., 1995), who did not detect CD44 in immature oocytes. No studies have established the role of the HA-CD44 system in oocyte maturation. "
[Show abstract][Hide abstract] ABSTRACT: The CD44 family belongs to a larger group of hyaluronic acid-binding proteins and plays important roles in oocyte maturation, fertilization and preimplantational embryo development. We analyzed the CD44 receptor in sheep oocytes and embryos. Immature oocytes (N = 66) were obtained from a local abattoir; mature oocytes (N = 35) and embryos (N = 41) were obtained by laparotomy from adult hair ewes submitted to ovarian stimulation treatment. The CD44 mRNA was detected by hemi-nested PCR, after reverse transcription, while proteins were located by indirect immunofluorescence, using anti-human CD44 monoclonal antibody. Human lymphocytes and immature bovine oocytes were used as positive and negative controls, respectively. Assessment of the oocyte nuclear stages as well as classification of the embryonic development stage were made with Hoechst 33342 staining. Indirect immunofluorescence detected CD44 expression on the surface of mature oocytes and embryos; immature oocytes did not take up the stain. These findings were supported by the RT-PCR data, which showed no mRNA templates for CD44, even after two consecutive amplifications, in material from immature oocytes and cumulus cells. The CD44 amplicons were detected after a second hemi-nested PCR in mature oocytes and embryos. The finding of CD44 in mature oocytes and preimplantational embryos could reflect the expression profile of hyaluronic acid during terminal folliculogenesis and preimplantational embryo development in sheep.
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