Multicolour interphase cytogenetics in human sperm and embryos: Chromosome copy number and the relevance of nuclear address

Interphase cytogenetics by fluorescent in situ hybridisation (FISH) involves the study of chromosome copy number and nuclear organisation in non-dividing nuclei. It has found particular utility in studies of sperm and IVF embryos but would benefit further from multi-target strategies to detect numerous loci in the same nucleus. The purpose of this thesis was to develop such strategies then apply them to study the relationship between aneuploidy, nuclear organisation, male infertility and human preimplantation embryogenesis. Specifically:

• To ask whether novel inorganic nanomaterials Quantum Dots (QDs) could be used for FISH in the place of organic fluorochromes. Results suggest that, in their current form, QDs are sub-optimal for FISH despite some successful experiments.

• To develop alternative approaches using fast hybridising oligonucleotide probes labelled with organic fluorochromes to assess chromosome copy number and nuclear organisation for each human chromosome on the same nucleus. A 24 chromosome FISH method was successfully developed in a four layer sequential experiment and applied to sperm and embryos.

• To use the above approach to test the hypothesis that severely infertile oligoasthenoteratozoospermic (OAT) males display altered nuclear organisation (manifested as different nuclear address of specific loci) compared to their normal counterparts. Results suggested the presence of a “chromocentre” in both fertile and infertile men, with slight alterations of this strict organisation in some OAT males.

• To use the above approach to assess the level of aneuploidy in “spare” human preimplantation embryos following PGS. Results suggested very high levels of abnormality mostly associated with mosaicism, further calling into question the efficacy of FISH for PGS.

• To test the hypothesis that altered nuclear organisation in human preimplantation embryos is related to increased aneuploidy. Differences between two groups, one with multiple abnormalities, the other with relatively few were apparent providing data on nuclear organisation in individual blastomeres and whole embryos.

Insight into the relationship between chromosome abnormalities and nuclear organisation in sperm and embryos is provided. Applications of the methodology involve sperm aneuploidy screening, “follow-up” of embryos, but probably not PGS.