Stephen DiNardo, Ph.D.

faculty photo
Professor of Cell and Developmental Biology
Department: Cell and Developmental Biology
Graduate Group Affiliations

Contact information
421 Curie Boulevard
Philadelphia, PA 19104-6058
Office: 215-898-1367
Fax: 215-898-9871
Columbia University, 1977.
Ph.D. (Biochemistry/Molecular Biology)
Dept. of Biochemistry, SUNY at Stony Brook, Laboratory of Rolf Sternglanz, 1983.
Permanent link

Description of Research Expertise

Research Interests

1 Niche - Stem Cell Interactions
2 Epithelial Morphogenesis

Key words: Stem Cells, Niche, Epithelial Morphogenesis, Cell Polarity

Description of Research

1.Niche - Stem Cell Interactions

Stem cells hold the key to the continual renewal of many of our tissues. In addition, the manipulation of these cells holds much promise for regenerative medicine. Unfortunately, there are severe limitations in our knowledge of the regulation of stem cells and that compromises our understanding of normal tissue renewal, and restrains their clinical utility. To uncover the general principles of stem cell regulation, we study adult stem cells within their natural environment, the niche, by using Drosophila spermatogenesis as a model system. This allows us to apply both genetic and genome-scale molecular approaches to uncover novel factors governing niche-stem cell interactions. Our work has revealed aspects of stem cell self-renewal, differentiation, proliferation and stem cell aging. Given the deep conservation of developmental mechanisms across species, we are confidant that concepts revealed by our studies in the fruitfly will apply to some mammalian stem cell – niche interactions.

Among the strengths of this system is the fact that we have molecular markers and techniques to unambiguously identify the niche cells, as well the two stem cell lineages that maintain this tissue. The micrograph shows the tip of a testis (left) where the central cluster of cells (blue-green) comprise the niche (called a “hub”); the germline stem cells (GSCs) map to the first tier of (red) cells surrounding the niche, and these GSCs are intermingled with somatic stem cells (green), which express high levels of a stem cell factor that we first identified, called Zfh-1. Another advantage to studying this system is that we can culture the testis and live-image the production of new stem cells (come see some gorgeous movies made by Kari!).

Given that the niche is such a critical component regulating stem cell behavior, we also study how its cells are first specified, and how they assemble to form a functional niche. The right-hand micrograph shows a gonad with newly specified niche cells, marked by a cell surface protein (green). Again, combining genetics with lineage tracing and live-imaging we have uncovered several circuits necessary to specify these cells, and are studying how the individual cells migrate directionally and coalesce together, undergoing a mesenchymal-to-epithelial transition to form the niche.

2. Epithelial Morphogenesis

Developmental Biology has had great success in uncovering the hierarchies that govern the patterning of embryos, tissues and organs. However, there has been less success in understanding how sheets of cells respond to pattern organizing signals, and actually execute the instructed pattern. Thus, we study how signaling pathways direct the cytoskeletal and membrane biology of responding cells. To attack this, we study three cell biological outputs of developmental signals in the fruitfly embryonic epidermis. The middle panel of the image tryptich below shows (roughly) three columns of cell outlines (red); note how strikingly these cells are stacked - one right on top of another, with very straight up-down edges. There are three important characteristics of this cell packing arrangement: 1 -- it is FAR from equilibrium; normally cells are hexagonal packed, and in fact, these very cells were hexagonal packed just a scant few hours ago; 2 -- they achieved this alignment by remodeling cell-cell interfaces; 3 -- the cells are planar polarized: note that the f-actin based protrusions (green, left panel; & merge, right panel) that emerge from each of their surfaces are always located at the right-hand edge of each cell.

Output 1: Remodeling cell-cell interfaces
This is a common, but little understood event that drives epithelial morphogenesis, and, thus, is fundamental to constructing proper tissue form. Within an epithelium, how do specific cell-cell interfaces become singled out for remodeling, while other interfaces remain untouched? Importantly, how is that information communicated across the sheet of cells to coordinate tissue morphogenesis?

Output 2: Shaping actin-based, apical protrusions
Such protrusions are found in brush border microvilli, sensory bristles, and hair cell stereocilia. Thus, making these protrusions properly and organizing their pattern across an epithelium is central to proper tissue function.

Output 3: Planar Polarity
Planar Polarity is a fundamental property of all epithelia. And, while the proteins involved are conserved from fruitfly to us, it remains unclear just how these proteins define coordinates of a cell, and, importantly, how this information is choreographed across a field of cells.

Rotation Projects, 2012-2013
1. Niche - Stem Cell interaction projects:
Students will use genetic and genome-scale molecular techniques, combined with live-imaging, to identify factors that 1) first specify Niche cells, 2) specify the Stem cells nurtured by the niche, and 3) that regulate the balance between self-renewal and differentiation. Students can dive in to functional studies already ongoing in these areas. As work progresses, we envision collaborative opportunities for translational work, where students can explore whether our discoveries in Drosophila apply to mammalian spermatogenesis as well as other stem cell systems investigated here at Penn.

2. Epithelial Morphogenesis projects:
Students will ask how signaling pathways control tissue shape in the animal, rather than in the contrived environment of a cultured cell. They will investigate how cell biological responses are coordinated across the epithelium. This involves examining the cytoskeletal changes that occur during cell rearrangement in real-time, using live imaging with Spinning Disk Confocal Microscopy (come by and see some of Kynan's cool movies!). That approach is complemented by in vivo manipulation of target proteins of the key signaling pathways involved - proteins such as small GTPases, polarity proteins or adhesion and cytoskeletal components. In turn, those perturbations are coupled with high resolution imaging techniques to examine the changes at cell-cell interfaces, such as changes to cell bond tension by laser cutting or by FRET/FRAP, to map out how selective alterations of cyto-architecture affect tissue dynamics.

Selected Publications

Okegbe, Tishina C. DiNardo, Stephen.: The endoderm specifies the mesodermal niche for the germline in Drosophila via Delta-Notch signaling. Development 138(7): 1259-67, Apr 2011.

Donoughe, Seth. DiNardo, Stephen.: dachsous and frizzled contribute separately to planar polarity in the Drosophila ventral epidermis. Development 138(13): 2751-9, Jul 2011 Notes: Faculty of 1000 manuscript.

DiNardo, Stephen. Okegbe, Tishina. Wingert, Lindsey. Freilich, Sarah. Terry, Natalie.: lines and bowl affect the specification of cyst stem cells and niche cells in the Drosophila testis. Development 138(9): 1687-96, May 2011.

Leatherman, J. L., DiNardo, S.: Germline self-renewal requires cyst stem cells and stat regulates niche adhesion in Drosophila testes. Nat Cell Biol 12: 806–811, August 2010 Notes: COVER photo.

Dilks, S. A. and DiNardo, S. : Non-cell-autonomous control of denticle diversity in the Drosophila embryo. Development in press, April 2010.

Simone, R. and DiNardo, S. : Actomyosin contractility and Discs large contribute to junctional conversion in guiding cell alignment within the Drosophila embryonic epithelium. Development 137: 1385-94, April 2010 Notes: COVER photo.

Leatherman, J. L., DiNardo, S.: Zfh-1 controls somatic stem cell self-renewal in the Drosophila testis and nonautonomously influences germline stem cell self-renewal. Cell Stem Cell 3(1): 44-54, July 2008.

Walters, James W., Dilks, Stacie A., DiNardo, Stephen.: Planar polarization of the denticle field in the Drosophila embryo: roles for Myosin II (zipper) and fringe. Developmental Biology 297(2): 323-39, Sep 15 2006 Notes: with COVER.

Terry, Natalie A., Tulina, Natalia, Matunis, Erika, DiNardo, Stephen.: Novel regulators revealed by profiling Drosophila testis stem cells within their niche. Developmental Biology 294(1): 246-57, Jun 1 2006.

Wallenfang, Matthew R., Nayak, Renuka., DiNardo, Stephen.: Dynamics of the male germline stem cell population during aging of Drosophila melanogaster. Aging Cell 5(4): 297-304, Aug 2006 Notes: with COVER.

back to top
Last updated: 11/14/2012
The Trustees of the University of Pennsylvania