The detection of female cell activity in male sex chromosome chimeric Rideau Arcott sheep, using the Xist gene product as a marker

The detection of the SRY (Sex-determining region on the Y chromosome) gene is a popular method used for the identification of freemartins (XX/XY female chimeras). This method relies on the fact that the SRY gene is a Y chromosome specific gene and is thus normally only present in males therefore detecting its presence in a female indicates the presence of male cells (XY cells) within the female. This concept can be extrapolated to the male counterparts of freemartins with regards to the Xist gene. This gene is normally only widely expressed in females and can be used as a marker for identifying females. Therefore, detecting Xist gene expression in males (in tissues other than the testes, as the Xist gene is expressed exclusively in the testes of males) may indicate that these males contain transcriptionally competent female cells and thus necessarily labels them as sex-chromosome chimeras. In the present study four previously identified male sex chromosome chimeras were screened for the expression of the Xist gene using reverse transcription Polymerase Chain Reaction (PCR), and it was detected in three of the four chimeras. Xist expression was not detected in one of the chimeras because the proportion of female cells in its blood is significantly low and thus it is likely that the blood sample used in the study did not possess female cells. None-the-less it was concluded that the detection of Xist expression in male sex chromosome chimeras can be used as an indication of the presence and transcriptional competence of female cells within them