Reconstruction of oocytes by meiotic spindle transferring and increase in the number of patients' oocytes by transferring the first polar body to the donor oocyte cytoplasm

Introduction

Assisted reproductive technology (ART) has different ways of infertility treatment. Nowadays, in-vitro fertilization (IVF) is one of the most effective methods of treatment fertility and genetic problems. Though, several fertility problems remain hard-to-treat: mitochondrial DNA (mtDNA) abnormalities, poor ovarian response, embryo fragmentation and poor blastocyst development. It is also known that the fertility function decreases with advanced age. This factor makes the treatment of patients with genetic problems more complicated. For example, by age 40 an average healthy woman has only a 5% chance of getting pregnant per cycle, and by age 45, use of donor eggs is the only reasonable alternative. However, many couples want to have genetically related children. Therefore, using the meiotic spindle transfer or the first polar body transfer techniques, the child receives nuclear DNA of the mother that packaged as chromosomes. Mitochondrial DNA mutations can cause various diseases that are inherited by all offspring regardless of gender, because all mitochondria in the embryo originates from the oocyte cytoplasm., So, we use the oocyte cytoplasm from the donor eggs to receive a healthy offspring that biologically native to patients.

Methods and techniques

There are two oocyte reconstruction techniques:

Oocyte meiotic spindle transfer

And the 1st polar body transfer

The transfer of the maternal oocyte meiotic spindle applied in the cases when maternal oocyte contains mitochondria with defective DNA. Maternal oocyte meiotic spindle consists of the nuclear DNA material (chromosomes) That is why a maternal spindle is transferred to the enucleated donor oocyte cytoplasm. For the fusion of maternal meiotic spindle with a donor oocyte cytoplasm we add a little volume of inactivated Sendai virus solution. Such modified oocyte can be further fertilized with the father's or donor's sperm by ICSI. Thus, the reconstructed egg contains nuclear DNA from the mother and the healthy mitochondria from the oocyte donor.

The second way of the oocyte reconstruction is using the 1st polar body as a source of nuclear DNA of maternal origin First we prepare the donor oocyte by aspirating and discarding a donor oocyte meiotic spindle. Then after hatching of zone pellucida the 1st polar body aspirated from the maternal oocyte and with some volume of Sendai virus inserted the maternal polar body to a donor oocyte cytoplasm. As a result, we receive two good-quality oocytes with the maternal chromosomal set that provides kinship with the children and that oocytes are ready for the ICSI.

meiotic spindle transferring the first polar body

Conclusion

Reconstruction of oocytes by meiotic spindle transferring is an effective technique for those who have mitochondrial DNA abnormalities. Meiotic spindle transfer increases the chances of getting good-quality embryos and prevents the future child from receiving mitochondrial DNA abnormalities. This method is beneficial for patients who have a child with a mitochondrial disease. If the mitochondrial disease was inherited, there is a high chance that each child in the family will inherit a mitochondrial disease.

What is more, the first polar body transfer technique can also help to prevent the birth of children with mitochondrial disease. Mitochondria are essential for optimal oocyte quality, fertilization, and embryo development. And as you know, the oocyte quality can be a significant factor in determining the fertilization of oocytes and their development to high quality embryos, as well as for treating infertility. Transfer of the oocyte meiotic spindle to the donor oocyte cytoplasm is very useful for the oocyte quality improvement and the blastocysts morphological quality enhancement. And there is no direct harmful effect on euploidy of embryos obtained after oocyte cytoplasm donation.

The 1st polar body transfers may be beneficial to patients with a history of delayed embryo development and embryo fragmentation. Fragmentation is defined as the presence of anucleate structures derived from blastomere. Oocyte plays the most important role in fragmentation. Poor oocyte quality can lead to highly fragmented embryos. However, normal blastocysts without fragmentation can develop from reconstructed oocytes after the 1st polar body transfer technique.

Insufficient oocyte quantity and quality more frequently observed in patients with poor ovarian response (POR). Diminished ovarian reserve is a phenomenon often noted in women in their mid to late thirties, but it may occur in younger women as well. POR reduces pregnancy rates. When repeated IVF cycles on infertility treatment are unsuccessful, the only options that remain are full oocyte donation or application of techniques in oocytes reconstruction.

The presented techniques will allow avoiding the most of religious and ethical controversies connected to manipulation with embryos.

To sum up, these techniques are the only help for women who are facing infertility with unsuccessful IVF treatment experience and embryo development arrest caused by mitochondrial DNA abnormalities, poor ovarian reserve or embryo fragmentation.Using of oocyte reconstruction techniques are their chance to have healthy biologically native kids.