Co-localisation of OCT4 and VASA in 16 week ovary and testes. Panel a, ovary, cells with intense immunopositive staining for OCT4 are found at the periphery of the organ (red nuclei), VASA was detected in the cytoplasm and was most intense in cells located in nests (N) closer to the centre of the ovary. An intermediate population of cells with low intensity nuclear staining for OCT4 and low intensity staining for VASA (arrowheads) was also present. Panel b, testis, OCT4 positive and VASA positive germ cells were found within the same seminiferous cords; germ cells with intense nuclear OCT4 expression (red nuclei) were VASA negative and those with intense cytoplasmic expression of VASA (e.g. arrowed in inset panel b) were OCT 4 negative. Two other populations of male germ cells were identified, a population with low intensity immunoexpression of OCT4 which also had low intensity staining for VASA (arrowheads) and cells with nuclear VASA expression (asterisks) which were typically found in pairs.