Topic: Dosage Compensation According to the syllabus of this course, development can be viewed as an "integral" of molecular and cell biological events. Dosage compensation is a gene regulatory strategy to compensate the difference in the dosage of sex chromosome-linked genes, so that similar amounts of gene products can be produced despite the two-fold difference in gene dosage. In mammals, this is achieved by X-chromosome inactivation (XCI): a developmental phenomenon by which one of the two X chromosomes in female is silenced in early development. A specific locus on X-chromosome called X-inactivation center (Xic) is responsible for XCI. In particular, a gene encoding a non-coding RNA, Xist, play a crucial role in the chromosome-wide silencing of the X chromosome. In addition, an antisense transcript originating from Xic called Tsix/Xite is involved in the suppression of Xist transcription. Before reading this paper, please try to imagine how many processes XCI is composed of. In this class, we will take up one process: "counting" the number of X chromosomes. The authors tested a hypothesis that in order to count the number of X chromosomes, X chromosomes within a cell must recognize each other. Indeed, they found that two X chromosomes are temporally connected through Xic at the beginning of XCI. They further examined the involvement of Xic in the interaction by conducting loss- and gain-of-function analyses of Xic. This paper succeeded in connecting one process, namely "counting", with a cell biological event, "chromosome dynamics". At the same time, the model they proposed also provided us with new questions. We hope you can join the discussion on their achievements.
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