How to Repair the Oocyte and Zygote?

Abstract

Abstract. The supply of human oocytes is very limited. This restricts not only certain assisted reproduction procedures in IVF clinics where recipients wait for oocytes from donors, but also development of some promising approaches, like therapeutic nuclear transfer with subsequent derivation of patient compatible embryonic stem cells. Moreover, in some patients, collected oocytes exhibit certain specific defects, and logically, we can expect that after fertilization, the embryos arising from these defective oocytes may not develop or that their development might eventually be compromised. For this reason, an increased effort to determine how to repair oocytes is evident in the literature. In general, abnormalities (defects) can be detected in different oocyte components, the zona pellucida, cytoplasm, nucleus (chromosomes) and nucleolus. Whereas defects of a nuclear component are impossible (nuclear DNA) or very hard to repair (nucleolus), zona pellucida abnormalities and cytoplasm defects (for example, if containing mutated mitochondrial DNA, mtDNA) can be repaired in some cases with the help of micromanipulation schemes. In the present article, we will briefly outline the current methodological approaches that can be used to repair the oocyte or one-cell stage embryo. Oocytes and one-cell stage embryos are most commonly used in model animal experiments and are also considered to be the most convenient biological material for relevant therapies in humans. The reason for this is their large size (in mammals, typically about 100 μm) and the relative ease of access to this material. The important aspect is that if the oocyte or one-cell stage embryo is repaired, the resulting cell will be, in theory, normal. This will not be the case, if for example, two-cell stage embryos are manipulated. In this case, both blastomeres must be manipulated to obtain a normal embryo. Logically, this is more complicated from a technical point of view, and thus this approach is not used.The oocytes can be collected either as immature with a prominent nucleus containing one or more nucleoli (germinal vesicle, GV), maturing (with condensed chromosomes, metaphase I, anaphase I or telophase I) or mature (metaphase II). Oocytes are enclosed with a glycoprotein coat known as the zona pellucida. Here, we speculate that only so-called fully-grown oocytes can be used for manipulations because only these cells are able to undergo germinal vesicle breakdown (GVBD) and reach metaphase II (MII) stage. Less advanced oocytes (growing) do not normally undergo GVBD in culture, and if they do, they only reach the metaphase I (MI) stage [1]. Because, mature (metaphase II) oocytes are almost exclusively collected from ovaries in human assisted reproduction, one may expect that this stage would be most commonly used for manipulations. Moreover, use of these oocytes is also advantageous because they are fully developmentally competent due to maturation in their natural environment, follicles. It is well documented that developmental competence decreases ...

Ovarian Stem Cell Niche and Follicular Renewal in Mammals

“…In contrast, however, the oocytes in degenerating primordial follicles exhibit dense ZP2 expression throughout the nucleus and ooplasm (black asterisk, panel A). Nuclear and zona pellucida abnormalities and cytoplasmic defects were reported in altered oocytes (Fulka et al, 2009).…”

Strategies to improve embryo implantation to supraphysiological rates

“…Indeed, a recent study by Wells et al , 16 with improved media technology, has identified that over 40% of blastocysts are still chromosomally abnormal, and that, contrary to previous findings, most monosomies can reach the blastocyst stage 16–20 . Moreover, other important factors, such as mitochondrial RNA activity and the bottleneck female origin of mitochondrial transmission, are involved in oocyte competence and could be involved in the aging process, directly influencing the meiotic and mitotic process 5–7 …”

“…[16][17][18][19][20] Moreover, other important factors, such as mitochondrial RNA activity and the bottleneck female origin of mitochondrial transmission, are involved in oocyte competence and could be involved in the aging process, directly influencing the meiotic and mitotic process. [5][6][7] Embryo-endometrial interactions The endometrial role has been evaluated by investigating the contributions of inflammatory factors: adhesion molecules such as integrins, 21 pinopodes, 22 leukemia inhibiting factor (LIF), 23 proteomics, 24,25 metabolomics, 26 and, recently, by studies into the regulatory effect of preimplantation factor (PIF). 27,28 Emerging from this evidence is that endometrial modifications by the embryo, and between the many players involved with the embryo, have a guiding role.…”

“…[1][2][3][4] It is possible, although only in theory, that animal species undergo an evolutionary process that goes from reduced fertility to a possible extinction, due to some regulatory cytoplasm modifications that until now we were unable to modify. [5][6][7]…”

Sperm selection for assisted reproduction by prior hyaluronan binding: the HABSelect RCT

“…These and other data suggest that sperm with poor DNA quality persist in washed sperm preparations from fertile and infertile men [8][9][10][11][12][13] and unlike IVF, where there is a natural selection by the egg, ICSI could be particularly vulnerable to a poor choice of sperm. We and others have reported that sperm DNA fragmentation is a risk factor for miscarriage in ICSI treatment 14,15 and this may result from an oocyte-mediated DNA repair process [16][17][18][19] that provides adequate support from fertilisation to clinical pregnancy (CP) (hence the lack of an association between DNA fragmentation and CP in ICSI compared with IVF), but may be inadequate to sustain it beyond CP with resulting pregnancy loss. By eliminating abnormal sperm from the sample preparation for ICSI, success rates could theoretically be improved.…”