Date of Award
x-chromosome, genetics, DNA, calico cats
To prevent abnormal development caused by expressing both X chromosomes, female mammals inactivate one of their X chromosomes using an epigenetic process called dosage compensation. This literature review examines how X chromosome inactivation (XCI) occurs during the formation and development of an embryo. This condensation of DNA is marked by histone tail modifications, DNA methylation, and the arrival of structural proteins resulting in extraordinarily stable heterochromatin. X-inactivation is regulated in cis by the X-inactivation center (Xic) that contains the Xist gene and its antisense gene, Tsix. On one X chromosome, Xist RNA is expressed and coats the center of the future inactive X chromosome. Xist RNA recruits epigenetic regulators, Polycomb Repressive Complexes PRC1 and PRC2 that catalyze H2AK119 ubiquitination and H3K27 trimethylation. These events lead to the X chromosome being condensed into a Barr body. The tightly packed DNA is silenced. X-inactivation is responsible for a calico cat’s beautiful color patches. The fur color gene is located on the X chromosome. Some cells inactivate the X carrying the black fur allele and others inactivate the X with the orange fur allele. The patches are formed from millions of cells expressing black fur and millions expressing orange fur, each patch growing from a single cell.
Weston, Serena, "X-inactivation and Epigenetics" (2019). Thinking Matters Symposium. 173.