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Orna Cohen-Fix, Ph.D.

Senior Investigator

Cell Cycle Regulation and Nuclear Structure Section, Laboratory of Cell and Molecular Biology


Building 8, Room 319
8 Center Drive
Bethesda, MD 20814


Research Topics

Research Goal

The ultimate goal of our research is to understand basic processes that contribute to nuclear morphology and to elucidate the relationship between nuclear structure and nuclear function.

Current Research

The main research focus of my lab is the relationship between nuclear structure and nuclear function.  Altered nuclear shape is observed in certain types of disease, such as cancer and during aging.  However, the relationship between changes to nuclear morphology and either disease state or aging is unknown.  Moreover, in many cell types, there is a constant ratio between nuclear volume and cell volume.  How this ratio is established and its importance to normal cell function is unknown.  Finally, there are many basic questions related to nuclear structure and function that remain to be answered.  For example, how does the nuclear envelope form at the end of mitosis?  What dictates the formation of a single nucleus that encompasses all chromosomes rather than multiple nuclei that contain a subset of chromosomes?  How does the nuclear envelope expand?  Since the nuclear envelope is continuous with the endoplasmic reticulum (ER), what role does the ER play in nuclear morphology?  How does the nuclear envelope contribute to the intra-nuclear organization of chromosome domains and how does nuclear morphology affect processes such as DNA replication, transcription, splicing, and repair of DNA damage?  Given the link between pathology and nuclear morphology, we expect that gaining insight into the proteins and processes that affect nuclear shape will lead to a better understanding of disease progression, diagnostics, prevention, and treatment.

In order to uncover proteins and processes that contribute to nuclear structure and integrity, we are conducting genetic screens in budding yeast and C. elegans for mutations or conditions that alter nuclear shape.  For example, we found that lipid biosynthesis plays an important role in maintaining nuclear shape in both yeast and in C. elegans (see Campbell et al. and Golden et al.).  Based on our studies, we proposed a model that links ER structure to nuclear shape (see Webster et al. and Webster et al.).  We also discovered that in yeast cells, which undergo closed mitosis (i.e., without nuclear envelope breakdown), a mitotic delay results in altered nuclear shape in a specific region of the nuclear envelope (see Witkin et al.).  This observation raises the possibility that at least in yeast, the nuclear envelope is not homogenous; rather, it has distinct domains that are capable of expanding.  Studies are underway to determine how the yeast nuclear envelope expands, what defines these nuclear envelope domains, and how various mutants that alter nuclear shape contribute to nuclear morphology and nuclear function.

We also conducted a systematic RNA interference screen in C. elegans to identify additional genes and pathways that contribute to nuclear shape and function.  We currently have a large number of genes that, when down-regulated, affect nuclear structure and these fall into various functional categories—some of which are quite surprising, such as RNA processing, ribosome biogenesis, and protein transport (see Joseph-Struss et al.).  We are currently investigating the mechanisms by which these genes affect nuclear organization and nuclear function.

The main research focus of my lab is the relationship between nuclear structure and nuclear function.  Altered nuclear shape is observed in certain types of diseases, such as cancer and during aging.  However, the relationship between changes to nuclear morphology and either disease state or aging is unknown.  We use budding yeast and C. elegans, two very powerful genetic systems, to identify genes that, when mutated, lead to abnormal nuclear shape.

We currently are looking at a large number of genes that affect nuclear structure, and these fall into many functional categories, some of which are quite surprising, such as RNA processing, ribosome biogenesis, and protein transport.  The next step is to understand how these genes affect nuclear shape and to determine whether nuclear processes, such as transcription, DNA replication, and DNA repair, are affected by the alteration to nuclear shape.​

Applying our Research

Alteration in nuclear shape and size is associated with cancer and aging. While we don’t know how nuclear shape is linked to disease, it is likely that changes in nuclear morphology contribute to disease progression. Therefore, if we understand the underlying mechanisms that lead to altered nuclear morphology and how they change cell behavior (for example, contribute to the ability of cancer cells to divide uncontrollably), then it may be possible to design new therapeutic and preventative strategies to combat disease.

Need for Further Study

This field is still in its infancy. Almost every area related to nuclear morphology needs further study.


  • Adjunct Professor, Johns Hopkins University, 2011–Present
  • Director, the NIH/Johns Hopkins University Graduate Partnership Program, NIH, 2008–present
  • Senior Investigator and Section Chief, NIDDK, NIH, 2005–Present
  • Tenure-Track Investigator, NIDDK, NIH, 1998–2005
  • Postdoctoral Fellow, The Carnegie Institution of Washington, 1994–1998
  • Ph.D., Weizmann Institute of Science, 1994
  • M.S., Weizmann Institute of Science, 1989
  • B.A., Tel-Aviv University, 1986

Selected Publications

  1. Rahman MM, Rosu S, Joseph-Strauss D, Cohen-Fix O. Down-regulation of tricarboxylic acid (TCA) cycle genes blocks progression through the first mitotic division in Caenorhabditis elegans embryos. Proc Natl Acad Sci U S A. 2014;111(7):2602-7.
  2. Witkin KL, Chong Y, Shao S, Webster MT, Lahiri S, Walters AD, Lee B, Koh JL, Prinz WA, Andrews BJ, Cohen-Fix O. The budding yeast nuclear envelope adjacent to the nucleolus serves as a membrane sink during mitotic delay. Curr Biol. 2012;22(12):1128-33.
  3. Walters AD, May CK, Dauster ES, Cinquin BP, Smith EA, Robellet X, D'Amours D, Larabell CA, Cohen-Fix O. The yeast polo kinase Cdc5 regulates the shape of the mitotic nucleus. Curr Biol. 2014;24(23):2861-7.
  4. Joseph-Strauss D, Gorjánácz M, Santarella-Mellwig R, Voronina E, Audhya A, Cohen-Fix O. Sm protein down-regulation leads to defects in nuclear pore complex disassembly and distribution in C. elegans embryos. Dev Biol. 2012;365(2):445-57.
  5. Webster MT, McCaffery JM, Cohen-Fix O. Vesicle trafficking maintains nuclear shape in Saccharomyces cerevisiae during membrane proliferation. J Cell Biol. 2010;191(6):1079-88.
This page was last updated on December 3rd, 2015