The role of chromosome segregation and nuclear organisation in human subfertility.

Spermatogenesis is central to successful sexual reproduction, producing large numbers of haploid motile male gametes. Throughout this process, a series of equational and reductional chromosome segregation precedes radical repackaging of the haploid genome. Faithful chromosome segregation is thus crucial, as is an ordered spatio-temporal 'dance' of packing a large amount of chromatin into a very small space. Ergo, when the process goes wrong, this is associated with an improper chromosome number, nuclear position and/or chromatin damage in the sperm head. Generally, screening for overall DNA damage is relatively commonplace in clinics, but aneuploidy assessment is less so and nuclear organisation studies form the basis of academic research. Several studies have focussed on the role of chromosome segregation, nuclear organisation and analysis of sperm morphometry in human subfertility observing significant alterations in some cases, especially of the sex chromosomes. Importantly, sperm DNA damage has been associated with infertility and both extrinsic (e.g. lifestyle) and intrinsic (e.g. reactive oxygen species levels) factors, and while some DNA-strand breaks are repaired, unexpected breaks can cause differential chromatin packaging and further breakage. A 'healthy' sperm nucleus (with the right number of chromosomes, nuclear organisation and minimal DNA damage) is thus an essential part of reproduction. The purpose of this review is to summarise state of the art in the fields of sperm aneuploidy assessment, nuclear organisation and DNA damage studies.

The production of pig preimplantation embryos in vitro: Current progress and future prospects.

Human assisted reproductive technology procedures are routinely performed in clinics globally, and some of these approaches are now common in other mammals such as cattle. This is currently not the case in pigs. Given that the global population is expected to increase by over two billion people between now and 2050, the demand for meat will also undoubtedly increase. With this in mind, a more sustainable way to produce livestock; increasing productivity and implementing methods that will lead to faster genetic selection, is imperative. The establishment of routine and production scale pig embryo in vitro production could be a solution to this problem. Producers would be able to increase the overall number of offspring born, animal transportation would be more straightforward and in vitro produced embryos could be produced from the gametes of selected elite. Here we review the most recent developments in pig embryology, outline the current barriers and key challenges that exist, and outline research priorities to surmount these difficulties.