Embryo splitting

Attempts for Generation of Embryonic Stem Cells from Human Embryos Following In Vitro Embryo Twinning

In vitro embryo twinning can be used to increase the number of the human embryos available for production of human embryonic stem cell (hESC) lines. The aim of this study was to generate hESCs following the production of the twin embryos by in vitro embryo splitting procedures. In total 21 chromosomally abnormal (three pronuclei) embryos underwent in vitro embryo twinning and were allowed to develop to the blastocyst stage. As a result, 42 twin embryos were obtained, of which 24 developed to blastocyst stage. Using micromanipulation technique, the zona-free blastocysts were recovered and plated onto mitotically inactivated Yazd human foreskin fibroblast (Batch18; YhFF#18) feeder layers in microdrops. After 3 to 5 days of blastocyst culture onto human foreskin fibroblast feeder layers, the hESC-like outgrowths were passaged onto new feeders in microdrops. The initial outgrowths of hESC-like cells were generated, and cells were proliferated, passaged, and some of them expressed hESC and trophoblastic markers; however, no cell lines were established. This might be due to the low cell number and poor quality of inner cell mass within these twin blastocysts. In vitro embryo twinning by increasing the number of the human embryos could be useful in the future for the generation of new pluripotent stem cell lines. However, the challenge remains to optimize the methods.

Cleavage-stage embryo micromanipulation in the clinical setting

Embryo micromanipulation was developed after introduction of microinjection to overcome infertility. Embryo micromanipulation may be performed at any embryo stage from pronuclear to blastocyst. The technique started out as basic and turned out to be increasingly more complex. Embryo micromanipulation at the cleavage-stage includes a wide range of techniques, from opening the zona pellucida in order to improve the chance of implantation, to removing detrimental components from the embryo to enhance embryo development or blastomeres for preimplantation genetic diagnosis and embryo splitting. Evaluating the impact(s) of different micromanipulation techniques on epigenetics of the embryo and considering quality control during these techniques are important issues in this regard. This review aims to discuss the micromanipulation of cleavage-stage embryos in clinical assisted reproductive technology (ART).

ABBREVIATIONS

ART: assisted reproductive technology; ICSI: intracytoplasmic sperm injection; IVF: in vitro fertilization; PGD: preimplantation genetic diagnosis; PZD: partial zona dissection; ZP: zona pellucida; SUZI: subzonal insemination; PVS: perivitelline space; AH: assisted hatching; LAH: laserassisted hatching; ZT: zona thinning; UV: ultraviolet; IR: infrared; PCR: polymerase chain reaction; FISH: fluorescent in situ hybridization; NGS: next generation sequencing; QC: quality control; QA: quality assurance.