Mimicking Mother Nature in the Field of Human Reproduction?

Although humans have made significant progress in understanding reproductive events, nature still has more information to reveal. Towards the end of the 19th century, humans started studying reproductive processes such as gametogenesis, fertilization, and embryo development.[1] Since sperm and egg roles in fertilization were introduced in 1870 for the first time, reproductive biologists tried to emulate the natural reproductive processes despite the significant lack of knowledge regarding in vivo reproductive mechanisms. In the quest to mimic or overcome natural reproduction processes, numerous attempts have been made to produce embryos from non-germ cells.[2] [3] These trials ultimately culminated in the birth of Dolly the sheep[4] as a result of somatic cell nuclear transfer, starting a new era of cloning or asexual reproduction. Though not fully understood at the time (1959), the work of Chang[5] regarding the fertilization of rabbit ova in vitro, paved the way for the application of artificial reproductive techniques (ART) in humans. Ever since then, it has always been considered that the best evidence for these technologies to be accepted is that the progeny derived from ART are capable of reproducing naturally, especially those conceived by in vitro fertilization (IVF). Researchers have tried to ensure in vitro maturation of the spermatogonial stem cells transplanted in testes, separated into small pieces, and cultured on agarose, which migrated towards the basal membrane and settled on it, as in the in vivo process.[6] On the other hand, have reported that after ovary tissue cryopreservation and orthotopic transplantation result in a 76% spontaneous pregnancy live baby rate in 119 human females 13 out 119 of these patients need also in vitro maturation of the oocytes,[7] which allows to postulate that the cryopreservation of ovarian tissue could be a promising method to preserve fertility in humans. However, transformation of the experience and data obtained from animals to humans has been failing.