Xist’s Other Functions
Xist was first studied in the 1990s, and most research has centered on its primary role in X-chromosome inactivation. A research group led by Kathrin Plath, PhD, at the University of California, Los Angeles, has been occupied for years with untangling exactly how Xist does what it does. “It’s a very clever RNA, right? It can silence the whole chromosome,” Dr. Plath said in an interview.
Dr. Kathrin Plath
In 2021, Dr. Plath and her colleagues established in detail how Xist executes silencing, setting down pairs of molecules in specific spots along the chromosome and building huge protein clouds around them. “We worked on learning where Xist binds and what proteins it binds, drilling down to understand how these proteins and the RNA are coming together.”
Dr. Plath has long suspected that Xist has other functions besides X inactivation, and she and her colleagues are starting to identify them. Early this year they published the surprising finding that Xist can regulate gene expression in autosomes, or non–sex-linked chromosomes, “which it might well also do in cancer cells and lymphocytes,” Dr. Plath said. “And now there is this new evidence of an autoimmune function,” she said. “It’s a super exciting time.”
The different hypotheses surrounding Xist’s role in sex-biased autoimmunity aren’t mutually exclusive, Dr. Plath said. “There’s a tremendous enrichment of proteins occurring” during X inactivation, she said, supporting the Stanford team’s hypothesis that proteins are triggering autoimmunity. As for the Johns Hopkins researchers’ understanding that Xist RNA itself is the trigger, “I’m totally open to that,” she said. “Why can’t it be an autoantigen?”
The other model in the field, Dr. Plath noted, is the one proposed by Dr. Anguera — “that there’s [gene] escape from X-inactivation — that females have more escape expression, and that Xist is more dispersed in the lymphocytes [of patients with lupus]. In fact, Xist becoming a little dispersed might make it a better antigen. So I do think everything is possible.”
The plethora of new findings related to autoimmunity has caused Dr. Plath to consider redirecting her lab’s focus toward more translational work, “because we are obviously good at studying Xist.” Among the mysteries Dr. Plath would like to solve is how some genes manage to escape the Xist cloud.
What is needed, she said, is collaboration. “Everyone will come up with different ideas. So I think it’s good to have more people look at things together. Then the field will achieve a breakthrough treatment.”