I am a K99/R00 Pathway to Independence Awardee in the lab of Prof. John Marko at Northwestern University  in the Department of Molecular Biosciences. I also have a close collaboration with Prof. Robert Goldman at Northwestern’s Feinberg School of Medicine in the Department of Cell and Molecular Biology.

I came to Northwestern to build a solid foundation in nuclear mechanics research by combining training in physics and cell biology. Prof. John Marko is a biophysicist expert in physical properties of chromatin and Prof. Robert Goldman is a renowned cell biologist in the field of nuclear lamins and intermediate filaments. My training has allowed me to develop a novel micromanipulation approach to isolate and measure the force response of a single mammalian nucleus from a living cell. Using this technique, I distinguished the role of chromatin from lamins in nuclear mechanics, providing the new observation of a two-regime force response dictated by chromatin for short strains and lamin A at long strains via strain stiffening (Stephens et al., MBoC 2017). This mechanical contribution of chromatin also has an affect on nuclear shape/morphology as decreased/increased chromatin-based nuclear mechanics induces/rescues nuclear blebbing, respectively, independent of lamin levels (Stephens et al., MBoC 2018). This work revealing novel findings of the separate roles of chromatin and lamins in nuclear mechanics and the critical contribution of my complementary force measurement technique is summarized in a recent mini-review (Stephens et al., Nucleus 2017).

My interdisciplinary research with physicists has resulted in a new physical model of nuclear mechanics that recapitulate experimental mechanics and reveal novel buckling characteristics of the modeled biopolymeric lamin shell, which are inhibited by chromatin filling the interior (Banigan, Stephens, et al., Biophysical J 2017). Furthermore, work with materials scientists in the Backman lab at Northwestern has revealed novel spatial and temporal correlations in chromatin structure, which is still under preparation for publication.

My graduate studies with Prof. Kerry Bloom, a prominent yeast geneticist and cell biologist at UNC Chapel Hill, provided training in cell biology, genetics, imaging, and physical measurements. I used in vivo fluorescent imaging of chromatin and chromatin proteins and genetic manipulations to deduce the spring-like properties and structure of centromere chromatin in metaphase (Stephens et al., JCB 2011).  I led collaborations with physicists, mathematicians, engineers and computer scientists which resulted in a mathematical force model of yeast metaphase (Stephens et al., JCB 2013 A) and a structural model of the distribution of the chromatin, cohesin, and condensin surrounding the centromere (Stephens et al., MBoC 2013). Further work revealed that cohesin and condensin coordinate stretching and motion of individual pericentromeres (Stephens et al., JCB 2013 B) and sumoylation determines the transition from arm cohesion to the pericentromere spring (Stephens et al., Cell Cycle 2015).

Beyond this work, I was a middle author on six other publications while a graduate student in the Bloom lab, which are displayed on the Publications page.