# Barbara Panning
**Barbara Panning** (born 1963) is a Swiss-born molecular biologist and professor of [Biochemistry](https://www.edgepedia.org/biochemistry) and [Biophysics](https://www.edgepedia.org/biophysics) at the [University of California, San Francisco](https://www.edgepedia.org/university-of-california-san-francisco) (UCSF), known for her work on Xist RNA and X chromosome inactivation and on chromatin regulation in embryonic stem cells.[1](https://digital.sciencehistory.org/works/5z7vjlx) • [2](https://profiles.ucsf.edu/barbara.panning) She moved to Toronto as a young child and trained in Canada before her postdoctoral work at the Whitehead Institute and MIT.[1](https://digital.sciencehistory.org/works/5z7vjlx)
| Key facts | Detail |
|---|---|
| Field | Molecular biology: epigenetics, X chromosome inactivation, stem cell chromatin |
| Position | Professor, Biochemistry and Biophysics, UCSF School of Medicine (since 2012)[1](https://digital.sciencehistory.org/works/5z7vjlx) • [2](https://profiles.ucsf.edu/barbara.panning) |
| Training | BSc 1986 and PhD 1994, McMaster University (advisor James Smiley)[1](https://digital.sciencehistory.org/works/5z7vjlx) |
| Postdoctoral work | Whitehead Institute with Rudolf Jaenisch, 1994–1997; MIT with Philip Sharp, 1997–1999[1](https://digital.sciencehistory.org/works/5z7vjlx) |
| Signature work | "An RNAi Screen of Chromatin Proteins Identifies Tip60-p400 as a Regulator of Embryonic Stem Cell Identity", *Cell*, 2008[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC4308735/) |
| Best-known early result | X chromosome inactivation is mediated by Xist RNA stabilization, *Cell*, 1997[4](https://pubmed.ncbi.nlm.nih.gov/9298902/) |
| Funding | NIH R01 awards from 2001 through 2024; Pew Scholar in the Biomedical Sciences, 2002–2006[2](https://profiles.ucsf.edu/barbara.panning) • [1](https://digital.sciencehistory.org/works/5z7vjlx) |
## Education and career
Panning attended [McMaster University](https://www.edgepedia.org/mcmaster-university), majoring in biology and anthropology, and earned a BSc in biology in 1986. Her senior project involved work on [Roberts syndrome](https://www.edgepedia.org/roberts-syndrome). She stayed at McMaster for her PhD in Medical Sciences, completed in 1994 under James Smiley, studying how herpes virus and adenovirus regulatory proteins affect host gene expression; according to her dissertation, *Control of Cellular Gene Expression by Viral Regulatory Proteins*, herpes simplex virus type 1 and adenovirus type 5 modulate expression of host globin genes and Alu repetitive sequences.[1](https://digital.sciencehistory.org/works/5z7vjlx) • [5](http://hdl.handle.net/11375/6425)
She then moved into developmental genetics as a postdoctoral fellow in [Rudolf Jaenisch](https://www.edgepedia.org/rudolf-jaenisch)'s laboratory at the Whitehead Institute for Biomedical Research from 1994 to 1997, where she began work on X inactivation. She completed her postdoctoral training in Philip Sharp's laboratory at MIT's Center for Cancer Research from 1997 to 1999, in biochemistry.[1](https://digital.sciencehistory.org/works/5z7vjlx) She held Canadian Medical Research Council fellowships from 1994 to 1999.[1](https://digital.sciencehistory.org/works/5z7vjlx)
At UCSF she joined the Department of Biochemistry and Biophysics as an assistant professor in 1999, was promoted to associate professor in 2008, and has been professor since 2012.[1](https://digital.sciencehistory.org/works/5z7vjlx) • [2](https://profiles.ucsf.edu/barbara.panning)
## Xist RNA and X chromosome inactivation
In mammals, dosage compensation is achieved by transcriptional inactivation of one [X chromosome](https://www.edgepedia.org/x-chromosome) in female cells: any number of X chromosomes greater than one is silenced, and only one remains active. The Xist RNA plays critical roles in the choice of which X chromosome stays active and in the initial spread and establishment of silencing on the inactive X.[6](https://www.annualreviews.org/content/journals/10.1146/annurev.genet.36.042902.092433)
Panning's 1997 *Cell* paper established a stabilization mechanism. It showed that Xist is expressed at high levels only from the inactive X chromosome, and that differentiating female cells increase Xist expression from the inactive X prior to silencing, supporting a mechanism of X inactivation mediated by Xist RNA stabilization.[4](https://pubmed.ncbi.nlm.nih.gov/9298902/) A parallel 1997 study by another group, "Stabilization of Xist RNA Mediates Initiation of X Chromosome Inactivation" (*Cell* 91(1):99–107), reached the stabilization conclusion independently the same year.[7](https://pmc.ncbi.nlm.nih.gov/articles/PMC6936258/) According to a review in PMC, the mouse Xist transcript had been characterized in 1992 as a 15 kb inactive X-specific transcript with no conserved open reading frame, and in 1996 XIST RNA was shown to coat or "paint" the inactive X chromosome.[7](https://pmc.ncbi.nlm.nih.gov/articles/PMC6936258/)
Panning later framed the field's questions in two reviews: a 2002 Annual Review of Genetics article on Xist RNA and the mechanism of X chromosome inactivation, and a 2008 Journal of Biology review, "X-chromosome inactivation: the molecular basis of silencing", on which she was corresponding author.[6](https://www.annualreviews.org/content/journals/10.1146/annurev.genet.36.042902.092433) • [8](https://pubmed.ncbi.nlm.nih.gov/18983701/)
## Representative work
Her 2008 *Cell* paper, "An RNAi Screen of Chromatin Proteins Identifies Tip60-p400 as a Regulator of Embryonic Stem Cell Identity" ([doi:10.1016/j.cell.2008.05.031 reported an [RNA interference](https://www.edgepedia.org/rna-interference) screen of more than 800 loci encoding chromatin proteins in mouse embryonic stem cells. Knockdown of 68 proteins produced diverse phenotypes, including seven subunits of the Tip60-p400 complex, a 17-protein histone acetyltransferase and nucleosome remodeling assembly. The screen showed that Tip60-p400 is necessary for the cellular memory that maintains embryonic stem cell identity: without it, embryonic stem cells turned into a cell type with features of a differentiated cell.[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC4308735/) • [9](https://www.ucsf.edu/news/2008/07/96614/genes-control-embryonic-stem-cell-fate-identified) • [10](https://www.nature.com/articles/stemcells.2008.109)
The paper also showed that p400 localization to promoters depends on the H3K4me3 chromatin mark, and that Tip60-p400 integrates signals from the pluripotency factor Nanog and H3K4me3 to regulate gene expression in embryonic stem cells.[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC4308735/) A Nature commentary on the work noted that the complex binds the regulatory regions of most genes, particularly H3K4me3-marked areas near genes that trigger differentiation and are repressed by polycomb factors.[10](https://www.nature.com/articles/stemcells.2008.109)
The published paper reports 68 chromatin proteins with diverse knockdown phenotypes. The two figures count different outcomes, and the paper's own number is the primary one.[9](https://www.ucsf.edu/news/2008/07/96614/genes-control-embryonic-stem-cell-fate-identified) • [3](https://pmc.ncbi.nlm.nih.gov/articles/PMC4308735/)
## The Panning laboratory and funding
Her laboratory works on mammalian stem cell epigenetics, X inactivation, and chromatin modifiers, including how the inactive X chromosome is organized before the onset of X inactivation.[11](https://grantome.com/grant/NIH/R01-GM100341-04) Her NIH R01 awards as principal investigator include R01GM063671 on Xist RNA and chromatin structure (2001–2006), R01GM085186 on Tip60-p400 (2009–2013), R01GM088506 on regulation of Xist RNA processing in embryonic stem cells (2010–2015), R01GM100341 on X chromosome organization before the onset of X inactivation (2012–2016, with a 2015 support year totaling $299,408), and R01GM128431, "OGT as a dosage sensor" (September 15, 2019 to June 30, 2024).[2](https://profiles.ucsf.edu/barbara.panning) • [11](https://grantome.com/grant/NIH/R01-GM100341-04) She was a Pew Scholar in the Biomedical Sciences from 2002 to 2006.[1](https://digital.sciencehistory.org/works/5z7vjlx)
## Recent activity
She remains active. Her ORCID record lists a July 2024 preprint, "The nuclear periphery confers repression on H3K9me2-marked genes and transposons to shape cell fate", and a March 5, 2025 *Science Advances* paper, "Aging activates escape of the silent X chromosome in the female mouse hippocampus", on which she is an author.[12](https://orcid.org/0000-0002-8301-1172)
## References
1. Oral history interview with Barbara Panning, Science History Institute. https://digital.sciencehistory.org/works/5z7vjlx
2. Barbara Panning, PhD, UCSF Profiles. https://profiles.ucsf.edu/barbara.panning
3. An RNAi Screen of Chromatin Proteins Identifies Tip60-p400 as a Regulator of Embryonic Stem Cell Identity, *Cell* (2008). https://pmc.ncbi.nlm.nih.gov/articles/PMC4308735/
4. X chromosome inactivation is mediated by Xist RNA stabilization, *Cell* (1997). https://pubmed.ncbi.nlm.nih.gov/9298902/
5. Control of Cellular Gene Expression by Viral Regulatory Proteins, McMaster University dissertation (1994). http://hdl.handle.net/11375/6425
6. Xist RNA and the Mechanism of X Chromosome Inactivation, Annual Review of Genetics (2002). https://www.annualreviews.org/content/journals/10.1146/annurev.genet.36.042902.092433
7. Localized accumulation of Xist RNA in X chromosome inactivation. https://pmc.ncbi.nlm.nih.gov/articles/PMC6936258/
8. X-chromosome inactivation: the molecular basis of silencing, Journal of Biology (2008). https://pubmed.ncbi.nlm.nih.gov/18983701/
9. Genes that control embryonic stem cell fate identified, UC San Francisco (2008). https://www.ucsf.edu/news/2008/07/96614/genes-control-embryonic-stem-cell-fate-identified
10. Packaging DNA for pluripotency, Nature Reports Stem Cells (2008). https://www.nature.com/articles/stemcells.2008.109
11. Investigation of X chromosome organization before the onset of X-inactivation, NIH grant record. https://grantome.com/grant/NIH/R01-GM100341-04
12. Barbara Panning, ORCID record. https://orcid.org/0000-0002-8301-1172
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*Topic: Encyclopedia › Life and health › Life and health scientists › Life scientists › Researchers in molecular and cell biology › Epigenetics and chromatin biology › DNA methylation and epigenetic inheritance*
*Initially written Sep 21, 2026 · Reviewed: Sep 25, 2026 · Edited: Sep 25, 2026; Oct 11, 2026; Oct 15, 2026 · Last review: Sep 25, 2026*
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