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The single active X in human cells: evolutionary tinkering personified
1McKusick Nathans Institute of Genetic Medicine, The Johns Hopkins University, 459 Broadway Research Building, 733 N Broadway, Baltimore, MD 21205, USA. bmigeon@jhmi.edu
Mammals utilize X dosage compensation to equalize X chromosome expression between sexes. Evolutionary variations exist in this process, with the active X chromosome being randomly chosen early on.
Area of Science:
- Genetics
- Developmental Biology
- Evolutionary Biology
Background:
- Mammals equalize X chromosome expression between sexes through dosage compensation.
- Mechanisms of X chromosome inactivation vary across species due to evolutionary adaptations.
- Recent research highlights species-specific variations in X chromosome regulation.
Purpose of the Study:
- To provide an overview of evolutionary variations in X dosage compensation in human cells.
- To discuss the selection of the single active X chromosome.
- To propose a model for the initial events in X chromosome inactivation.
Main Methods:
- Review of existing literature on X dosage compensation.
- Comparative analysis of X inactivation mechanisms across mammalian species.
- Hypothesis generation based on current understanding of gene regulation.
Main Results:
- X dosage compensation mechanisms exhibit significant evolutionary diversity.
- The process involves the random selection of a single active X chromosome, not the inactivation of specific ones.
- Early events likely involve the random choice of the future active X, potentially via XIST locus repression.
Conclusions:
- Evolutionary variations in X dosage compensation do not impede the establishment of a single active X.
- The selection of the active X chromosome is a critical early event in the process.
- Repression of the XIST locus may be a key mechanism for initiating X chromosome choice.
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