"Male Development of Chromosomally Female Mice Transgenic for Sry gene" (1991), by Peter Koopman, et al.

Early 1990s research conducted by Peter Koopman, John Nigel Vivian, Peter Goodfellow, and Robin Lovell-Badge, showed that chromosomally female (XX) mice embryos can develop as male with the addition of a genetic fragment from the Y chromosome of male mice. The genetic fragment contained a segment of the mouse [4] Sry gene, which is analogous to the human SRY gene. The researchers sought to identify Sry gene as the gene that produced the testis determining factor protein (Tdf protein in mice or TDF protein in humans [5] ), which initiates the formation of testis. Koopman's team published their results in 1991 in "Male Development of Chromosomally Female Mice Transgenic for Sry gene. " Their results showed that Sry gene partly determines the sex of an embryo and is the only gene on the Y chromosome necessary for initiation of male development in mice. The researchers conducted the Sry gene experiment on mice at the Laboratory of Eukaryotic Molecular Genetics, MRC National Institute for Medical Research in London, England, in conjunction with the Human Molecular Genetics Laboratory, Imperial Cancer Research Fund also in London. Koopman and his colleagues had previously worked to identify the gene or genes [6] present on the Y chromosome that partly determine the sex of embryos. Their work had led them to identify a region of the Y chromosome containing the Sry gene as a candidate for primary sex determination [7] due to the gene's high degree of similarity among several mammalian species. Additional support for the claim that Sry genes [6] were the primary sex determining gene came from researchers Ralf Jäger, Philippe Berta, and their early 1990s colleagues. The researchers independently published findings from genetic testing of genetically male (XY) humans [5] who developed as females due to either a change in the open reading frame of the gene (frameshift mutation), or a deletion of the region on the Y chromosome containing the of the mouse [4] Sry gene and the human SRY gene were interchangeable across species. One of the researchers, Gubbay, had previously shown the two genes [6] to be similar, despite the differences of twenty-three of their seventy-nine total amino acids. Koopman and colleagues produced two lines of mice offspring containing the human SRY gene. No transgenic XX females developed as males nor displayed any evidence of altered sexual reproductive tracts. A third line of offspring produced only a single XX transgenic female that again developed normally as a female. The team concluded that the integration of the human SRY gene could not create a sex reversal in genetically female mice, either because it was unable to be transcribed into a protein or it produced non-functional proteins within mice, resulting in normal development in transgenic mice. "Male Development of Chromosomally Female Mice Transgenic for Sry gene"; reports the conclusions of Koopman and colleagues that a fourteen kilobase fragment containing Sry gene can initiate testicular formation, and thus sex determination [7] in mice. The data showed that the genetic fragment contained both the entire Sry gene and all of the regulatory elements required for its expression in the embryo. The results also suggested that scientists could further analyze genes [6] used in sex determination [7] through the gradual elimination of sequences from the original fragment to determine the function of each sequence. The experiment identified Sry gene as a sex determining gene in mice.