The project aims to define the germ cell niche in the fetal testis during the critical stage of development from gonocyte to prespermatogonium, a period during which the precursor (CIS) cells for TGCC are believed to arise. These studies, using fetal rat and human testis tissue, will primarily involve a xenografting approach that I have developed for investigating the fetal testis. Genetic manipulation of somatic cell genes, in which mutation has been postulated to result in aberrant germ cell development or testicular cancer, will be investigated using Lentiviral transfection and/or antagonists of specific pathways and testicular re-aggregation after xenografting. Re-aggregation experiments will also investigate the effect of introducing gonocytes into a pre-spermatogonial niche and vice versa, whilst transplantation of gonocytes (proposed precursor for CIS) or CIS cells into a postnatal niche will also be investigated. Analysis will involve morphological assessment, and state of the art confocal immunohistochemistry in which 3-4 proteins (including gonocyte and/or prespermatogonial markers) are visualised simultaneously to assess differentiation, proliferation and apoptosis in relation to the adjacent niche. Key goals are to characterise the fetal germ cell niche differences between gonocytes and prespermatogonia and how this can be perturbed to generate a model for origins of TGCC.