Narrow Results

There has been continued substantial interest from both scientists and the public in the therapeutic and scientific potential of stem cells since the first isolation of human embryonic stem cells (hESC) in 1998.¹ Pluripotent hESCs derived from the inner cell mass of preimplantation embryos following fertilisation in vitro (IVF) have been well studied, and proposed not only as potentially useful in treating degenerative diseases, but invaluable clinically relevant alternatives to animal models for studying early development, and for identifying novel pharmaceuticals with high throughput drug screens in vitro.² In addition, due to ethical controversy surrounding the use of embryos in stem cell research, there has been a paradigm shift in some research groups who have reported alternative methods of obtaining embryonic stem-like cells without the use of embryos. Most recently there has been some enthusiasm for exploring the use of induced pluripotent stem cells (iPS) which may be able to be derived from somatic cells by manipulation of transcription factors.³ The derivation, culture and characterisation of hESC are currently a labour intensive and time consuming process. Emerging tissue engineering technology such as robotic control of culture will overcome such hurdles and facilitate the scale-up needed for clinical therapies.

The essence of fertilization is the mingling of female and male genomes to create a new individual with a genomic combination that never existed before. In the female germ cell, the plasma membrane becomes fusion-competent first, and then maturation of the cytoplasm and nucleus follows. This order of maturation is reversed in the male germ cell: the male germ cell completes first its nuclear maturation, then its cytoplasmic maturation; the plasma membrane becomes fusion-competent last. The nuclei of polar bodies can be used as substitutes for female pronuclei to produce live offspring. At least in the mouse, the nuclei of spermatocytes can participate in embryo development after completion of meiosis within the oocytes. The nuclei of deformed spermatozoa can participate in embryo development as long as they are genomically normal. By ICSI, men with defective Y chromosomes transmit their infertility to their sons, but not to their daughters. In the future, it may be possible for defective Y chromosomes in spermatozoa and prespermatozoal cells to be repaired or replaced by the normal Y chromosomes of other individuals. Cloning using adult somatic cells is an entirely new reproduction method. Its efficiency is rather low at present, regardless of the species and cell types tested. In the future, cloning may become as efficient as natural reproduction, but exclusive use of cloning would not benefit long-term survival of the species.