"VIRGIN-BIRTH" embryos have given rise to human embryonic stem cells capable of differentiating into neurons. The embryos were produced by parthenogenesis, a form of asexual reproduction in which eggs can develop into embryos without being fertilised by sperm. The technique could lead to a source of embryonic stem (ES) cells that could be used therapeutically without having to destroy a viable embryo.
Human eggs have two sets of chromosomes until fertilisation, when the second set is usually expelled. If this expulsion is blocked but the egg is accidentally or experimentally activated as if it had been fertilised, a parthenote is formed (see Diagram).
Because some of the genes needed for development are only activated in chromosomes from the sperm, human parthenotes never develop past a few days. This means that stem cells taken from them should bypass ethical objections of harvesting them from embryos with the potential to form human lives, say Fulvio Gandolfi and Tiziana Brevini of the University of Milan, Italy.
The researchers created human parthenotes that divided and formed immature embryos called blastocysts, from which ES cells could be derived. Another group's attempt to create stable lines of ES cells this way stalled at this stage because the cells died after a few days (New Scientist, 26 April 2003, p 17). "We were more lucky," says Brevini. Different conditions led to cells that could be cultured and the cell line was still dividing two years later. The cells display most of the molecular markers associated with pluripotency - the ability to differentiate into any cell type in the body. The researchers have shown that the ES cells can form precursors to all of the body's major cell layers, and differentiate into mature neurons.
"This is the first example I have seen of this in humans, and it is potentially very exciting," says Alan Trounson, an expert in the field of stem cell research at Monash University in Clayton, Australia. "It could be a source of embryonic stem cells that's not embryonic in the conventional sense."
However, he cautioned that more work is needed to prove that they are ES cells, since they do not display all the characteristics expected.
The results were presented at a meeting of the European Society for Human Reproduction and Embryology in Prague, Czech Republic, last week.
From issue 2558 of New Scientist magazine, 01 July 2006, page 19
