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Title: Paternal age effect mutations in germ cell development : pathological correlates in normal testis and testicular tumours
Author: Lim, Jasmine
ISNI:       0000 0004 2721 0470
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2011
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Pathogenic gain-of-function mutations associated with increased paternal age, albeit harmful to embryonic development, are paradoxically enriched in the normal testis. Evidence from previous studies indicates that these so-called paternal age-effect mutations confer a proliferative advantage to the spermatogonia in which they arise, leading to clonal expansion within the normal testis over time. Recently, spermatocytic seminoma (SS; a rare testicular germ cell tumour that occurs mainly in older men) has emerged as a key link between the processes of somatic and germline mutation (Goriely et al, Nat Genet. 41:1247-52, 2009), suggesting that the proposed clonal expansion events can in some cases lead to testicular tumourigenesis. In this thesis, I have used immunohistochemistry to seek evidence for putative clones of cells in the normal adult testis. To address this, a screening approach was developed using markers chosen from analysis of normal testicular tissues and SS. The ontogeny of OCT2 and SSX expression in human testis, from embryonic development to adulthood, identified distinct subpopulations of spermatogonia at different maturation stages. Together, these data reveal the potential of OCT2 as a novel marker of Adark spermatogonia (human reserve spermatogonial stem cells). In parallel with these observations, two distinct types of SS characterised by differential OCT2 and SSX immunoexpression were identified, providing new evidence for heterogeneity of this tumour. This work provided the backdrop to the detailed immunohistochemical study of normal adult testis by characterising in serial sections the expression of five spermatogonial markers, MAGEA4, SSX, FGFR3, OCT2 and SAGE1, and a proliferation marker, Ki67. Independent sections were screened with predetermined criteria set to identify unusual positively-stained cellular clusters within the seminiferous tubules. Several antigenic combinations previously described in SS were observed in a subset of these clones, suggesting differing genetic origins and a possible link with early events of testicular tumourigenesis. The size (minimum number of cells) of each clonal event was estimated and its correlation with the staining pattern of the molecular markers was investigated. In summary, the data presented in this thesis convincingly identify for the first time the previously hypothesised clonal events in the testis using immunohistochemical markers. My research will pave the way for future work involving genetic analysis of microdissected cells from these putative clones, aimed at identifying the underlying mutational events thought to be present.
Supervisor: Wilkie, Andrew O. M. Sponsor: Malaysian Ministry of Higher Education
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Clinical laboratory sciences ; Clinical genetics ; Pathology ; paternal age effect mutations ; normal testis ; testicular tumours