In the technique developed at Newcastle, stem cells with XY chromosomes (male) were developed into germline stem cells which were then prompted to complete meiosis - cell division with halving of the chromosome set. These were shown to produce fully mature sperm called In Vitro Derived sperm (IVD sperm).
In contrast, stem cells with XX chromosomes (female) were prompted to form early stage sperm, spermatagonia, but did not progress further. This demonstrates to researchers that the genes on a Y chromosome are essential for meiosis and for sperm maturation.
The IVD sperm can't be used for fertility treatment because it's prohibited by UK law but the research team also say fertilization of human eggs and implantation of embryos would hold no scientific merit for them; they just want to study the process as a model for research.
"While we can understand that some people may have concerns, this does not mean that humans can be produced 'in a dish' and we have no intention of doing this. This work is a way of investigating why some people are infertile and the reasons behind it. If we have a better understanding of what's going on it could lead to new ways of treating infertility," says professor Karim Nayernia of Newcastle University and the NorthEast England Stem Cell Institute (NESCI).
The Newcastle University team have developed a method for establishing early stage sperm from human embryonic stem cells in the laboratory. The embryonic stem cells were cultured in a new medium containing vitamin A derivative (retinoic acid), in a new technique established by the team. Based on this technique, the cells differentiated into germline stem cells.
These expressed a protein which was stained with a green fluorescent marker and they were separated out by FACSTM (Fluorescence-activated cell sorting) using a laser. After further differentiation, these in vitro derived germline stem cells expressed markers which are specific to primordial germ cells, spermatogonial stem cells, meiotic (spermatocytes) and post meiotic germ cells (spermatids and sperm).
These results indicated maturation of the primordial germ cells to haploid male gametes – called IVD sperm - characterized by containing half a chromosome set (23 chromosomes).