| Three genes showed altered expression patterns in a differential screen performed by Mann et al, (1995), using parthenogenetic and fertilized blastocysts. The results of allelic expression assays performed on two of the genes, Cytochrome oxidase VIIc (CoxVIIc) and Pyruvate kinase M (PkM) are described here. Reciprocal crosses of two strains of mice that contained a polymorphism for each gene were made, and allele specific expression was assessed. CoxVIIc showed biallelic expression from blastocysts and adult tissues. An analysis of PkM revealed a slightly more complex situation likely resulting from the strains of mice used rather than genomic imprinting effects. Preferential expression from the maternal allele of PkM was revealed in early stages of development of heterozygous F1 embryos crossed in one direction. However, equal levels of expression from maternal and paternal alleles were evident in the F2 backcrossed embryos functioning as our reciprocal cross.; These results may be due to heterochronic differences in the expression pattern of PkM between the two strains of mice used, or alternatively may result from a genomic imprinting effect in one of the two strains of mice used. Nonetheless, although CoxVIIc and PkM showed altered expression patterns in parthenogenetic embryos, CoxVIIc and PkM do not appear to be imprinted as predicted.; A targeted null mutation in Protein Phosphatase 1cγ (Pp1cγ) in mice reveals that this gene is not imprinted in mice, but is required for spermatogenesis. Experiments described in this thesis attempted to identify the cell type(s) in mammalian testis that are defective in Pp1cγ−/− mutants. Chimera aggregations and germ cell transplants indicate a requirement for Pp1cγ in both germ cells and Sertoli cells. These results underscore the intimate relationship between germ cells and Sertoli cells in mammalian spermatogenesis.; Thus, although the genes analysed in this study all display altered levels of expression in parthenogenetic embryos, none appear to be imprinted in mouse development. Various speculations exist regarding why each of these genes was isolated in the differential hybridization screen exist; however, the most likely cause may pertain to the pathological state of parthenogenetic embryos. |
