The Transcription Pattern Of Xist In The Development Of Mouse Preimplantation Embryo

Dosage compensation in female mammals is achieved by inactivating the transcription of one of the X chromosome. During this process, a series of modification appeared on the Xi, which led to the formation of stable heterochromatin that can be inherited steadily in cell duplication. Xist is an important gene wich is located in the Xic(X chromosome inactivation center) region and is closely related to the X chromosome inactivation. The gene silences the Xi chromosome by spreading along the Xi and inhibits most of its gene transcription..Due to the important role it played in the inactivation process, Xist is gradually becoming a hot spot.. Our research was mainly focused on the transcription pattern of Xist in preimplantation mouse embryos.. We employed the RT-PCR method to investigate whether Xist is transcribed in some of the developing stages of mouse. First, different mouse tissues which have been proved to transcribe Xist and Sry simultaneously were used to establish the appropriate conditions for Xist and Sry RT-PCR. When the annealing tempreture of 55℃ has been determined, the nestled RT-PCR method was used to analyze the transcription pattern of Xist. Using the Hprt gene as a positive control, our result suggested that both the testis tissue and the male embryos from which Sry transcription can be detected failed to yield any positive results of Xist. Female embryos at the pronucleus stage and 2-cell failed to produce any positive result of Sry and Xist too. While since the 4-cells period, Xist is constantly transcribed until blastocyst stages. We also successfully amplified Sry from pronucleus stage embryos, which prove that embryo can be sexed by Sry PCR method using one cell instead of the minimal detectable cell amount of 4 cells proved by others. Therefore, we can conclude that the earlist Xist transcription appeared at 4-cell stages in mouse. By establishing the transcription pattern of the preimplantion embryos, This experiment not only helped to explain some of the X chromosome inactivation phenomena, but also furnished the researcher who were dedicated to the research of reprogramming of somatic cloning and preimplantation development with useful materials and references.