The dawn of the future: 30 years from the first biopsy of a human embryo. The detailed history of an ongoing revolution

Following early studies showing no adverse effects, cleavage stage biopsy by zona drilling using acid Tyrode’s solution, and removal of single blastomeres for preimplantation genetic testing (PGT) and identification of sex in couples at risk of X-linked disease, was performed by Handyside and colleagues in late 1989, and pregnancies reported in 1990. This method was later used for specific diagnosis of monogenic conditions, and a few years later also for chromosomal structural and/or numerical impairments, thereby establishing a valuable alternative option to prenatal diagnosis. This revolutionary approach in clinical embryology spread worldwide, and several other embryo biopsy strategies developed over three decades in a process that is still ongoing. The rationale of this narrative review is to outline the different biopsy approaches implemented across the years in the workflow of the IVF clinics that provided PGT: their establishment, the first clinical experiences, their downsides, evolution, improvement and standardization. The history ends with a glimpse of the future: minimally/non-invasive PGT and experimental embryo micromanipulation protocols. This grand theme review outlines a timeline of the evolution of embryo biopsy protocols, whose implementation is increasing worldwide together with the increasing application of PGT techniques in IVF. It represents a vade mecum especially for the past, present and upcoming operators and experts in this field to (re)live this history from its dawn to its most likely future.

Effects of ketamine/xylazine premedication on emulsified isoflurane general anaesthesia in swine undergoing embryo transplantation

Cardiorespiratory effects were assessed during ketamine/xylazine premedication followed by emulsified isoflurane anaesthesia in swine undergoing experimental embryo transplantation. Ketamine (10 mg/kg) and xylazine (3.5 mg/kg) were premedicated intravenously, followed by continuous administration of intravenous emulsified isoflurane (2.8 ml/kg/h). Cardiorespiratory parameters, including heart rate, respiratory rate, mean arterial blood pressure, arterial oxygen saturation, and rectal temperature, were recorded in sows undergoing surgical embryo transplantation. Ketamine/xylazine premedication resulted in anaesthetic induction and lateral recumbency within 1 minute without any adverse effects. The physiological changes observed after drug administration remained within biologically acceptable limits. In conclusion, the combination of ketamine/xylazine provided anaesthetic induction, muscle relaxation, and analgesia sufficient for emulsified isoflurane intravenous anaesthesia. There were no adverse events in the experimental animals. This finding supports the use of emulsified isoflurane following ketamine/xylazine premedication in pigs.

Cell number in relation to primary pattern formation in the embryo of Xenopus laevis

Results are presented which offer strong evidence that extensive alteration of the fates of embryonic Xenopus cells occurs independently of the schedule of cell division, after operations which lead to a doubling of the axial pattern of mesodermal differentiation in the gastrula. The experimental strategy was to make estimates of total mesodermal cell numbers and mitotic index in closely matched sets, each of three synchronous sibling embryos, fixed during the ten hours following the close of gastrulation. Within each set two embryos, an unoperated control and a sham-operated embryo whose own dorsal-lip (organizer) cells had been replaced with an equivalent graft, were developing normally. The third, experimental embryo had received an organizer implant to replace an equivalent number of cells from its ventral marginal zone, and was thus developing two axial mesodermal patterns of differentiation in relation to two dorsal midlines, the extra pattern embracing much host tissue. Mitotic index was also determined, in specific regions and throughout the mesoderm, in similar sets of embryos but at mid-gastrula stages. The conclusions are justified by the results of a control investigation which show that there is normally no difference in cell cycle time along the presumptive dorso-ventral mesodermal. dimension, during the interval between time of operations and the determination of patterni The lack of any enhancement of mesodermal cell number in late embryos with dual axia patterns, or intervening enhancement of mitotic index in younger operated embryos, thus suggests that new patterns may be determined in the Xenopus gastrula without generation of extra cells. The results are discussed in relation to recent ideas about pattern formation, and the concepts of morphallaxis and epimorphosis.