Understanding the mechanism and genetics of male human infertility linked to chromosome segregation defects and meiotic arrest

Background

Infertility affects approximately one in six people during their lifetime and carries a substantial psychological and social burden.¹ Male factors contribute to around half of infertility cases, but many affected men remain without a molecular diagnosis. In men with azoospermia, defined as the absence of spermatozoa in the ejaculate, identifying the underlying genetic defect can have direct implications for counselling. For some established genetic causes of spermatogenic arrest, sperm retrieval is highly unlikely to succeed. A diagnosis supported by sufficient clinical evidence can therefore help avoid unsuccessful surgical procedures and inform counselling about inheritance and reproductive options.²

Sperm production requires accurate chromosome segregation during both the mitotic expansion of spermatogonia and the subsequent meiotic divisions. Kinetochores, spindle components and motor proteins coordinate these processes, but the contribution of variants in many of their encoding genes to human infertility remains poorly understood. We hypothesise that rare variants in this machinery disrupt protein function and chromosome segregation, leading to impaired spermatogenesis or meiotic arrest. The project will identify candidate genetic causes and establish how selected variants affect molecular function and cell division.

We have exome and genome data from a unique cohort of 800 men with non-obstructive azoospermia or oligozoospermia, including approximately 303 parent-offspring trios. The student will screen these data for rare variants in cell division genes, assessing sequencing quality, population frequency, predicted consequence and inheritance. Trio analyses will identify de novo variants and assess recessive inheritance, including whether two variants in the same gene were inherited from different parents. Genetic findings will be integrated with semen parameters, endocrine findings and testicular histology, to identify genotype-phenotype correlations and distinguish different patterns of spermatogenic failure.

Variant prioritisation will combine this evidence with in silico predictions, structural modelling and gene-based burden analyses. We have access to data from our collaborators within the International Male Infertility Genetics Consortium as well as other partners to look for replication and enrichment of predicted pathogenic mutations in cases vs controls (~10k cases, ~10k controls).enabling burden analyses while accounting for ancestry and sequencing differences. Structural modelling will guide hypotheses about altered protein stability, interactions or activity. A small number of candidates with strong genetic support and experimentally tractable functions will be selected for detailed investigation.

The experimental work will compare wild-type and variant proteins using complementary biochemical and cell-based approaches. Depending on the candidate, assays will measure protein expression, folding and stability, interactions with known binding partners, or motor activity. In cultured somatic cells, fluorescence microscopy and live-cell imaging will assess protein localisation, spindle organisation, chromosome alignment and segregation, and progression through cell division. Appropriate expression controls and, where feasible, rescue experiments will help determine whether the observed defects are attributable to the variant.

The most promising candidates will subsequently be investigated in spermatogonial stem-cell models to assess effects on germ-cell proliferation and survival. These experiments will test whether defects observed in somatic cells are also present in a germ-cell context. Since spermatogonial stem cells are premeiotic, links to meiotic arrest will be assessed through patient testicular phenotypes and, where feasible, models supporting meiotic differentiation.

By integrating human genetics with functional investigations, the project aims to identify causes of male infertility and explain how defects in conserved cell division machinery impair spermatogenesis. The resulting evidence will support improved variant interpretation and genotype-informed counselling, with clinical predictions requiring independent validation. The student will gain training in genomic analysis, clinical phenotyping, structural modelling, biochemistry and quantitative imaging through the complementary expertise of the supervisory team.

References: 

1. World Health Organization. 1 in 6 people globally affected by infertility: WHO. Published 4 April 2023. Available online.

2. Riera-Escamilla A, Arafa MM, Farnetani G, et al. Genetic determinants of testicular sperm extraction outcomes: insights from a large multicentre study of men with non-obstructive azoospermia. Human Reproduction Open. 2025;2025(3):hoaf049. doi:10.1093/hropen/hoaf049