Description of Research Expertise

Research Interests

1 Niche Assembly & Stem Cell Control
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, self-renewal, differentiation, proliferation and stem cell aging. Most importantly, it allows for high-resolution, real-time imaging of the initial assembly of the niche, and of stem cell behavior. Given the deep conservation of mechanisms across species, we are confident that concepts revealed by our studies will apply to mammalian stem cell – niche interactions.





Among the strengths of this system are the 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 the somatic stem cell-specific factor 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 Gabby and Liz!).

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 to form the niche (come see some gorgeous movies made by Lauren, Kara and Bailey!).



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 patterning 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 cells in outline (red); these cells are striking in how they are stacked one right on top of another, with very straight up-down edges. There are three important characteristics of this cell 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.



We examine this tissue pattern to study three cell biological concepts:
1: Remodeling cell-cell interfaces
This is a conserved, 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?

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

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.


Lab Personnel
PhD Student
Bailey Warder
Gabriela Vida
Kara Nelson
S Fallacaro

Postdoctoral Scholars
Lauren Anllo



Research Assistants
Liz Botto
Tynan Gardner


Don't forget Steve, he's at the bench, too!

Rotation Projects, 2021-2022
1. Niche - Stem Cell interaction projects:
Students will use genetic and genome-scale molecular techniques, combined with live-imaging, to identify factors 1) that first specify Niche cells, 2) that organize those cells into a functioning niche, and 3) that regulate the balance between self-renewal and differentiation within the stem cells. Students can dive into functional studies already ongoing in these areas. Come by to see Lauren & Bailey's neat movies of a niche first being formed, as well as Gabby and Liz's beautiful movies of action at a stem cell niche!! As work progresses, we envision collaborative opportunities for work, where students can explore how the concepts we are revealing in this Drosophila system apply to other niche-stem cell systems investigated here at Penn.

2. Morphogenesis of a niche projects:
Students will ask how signaling pathways control the shape and behaviors of niche cells in the animal, rather than in the contrived environment of a cultured cell. They will investigate how cell biological responses are coordinated between niche and associated stem cell. 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 Bailiey'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

Ong Katy, Collier Camille, DiNardo Stephen: Multiple feedback mechanisms fine-tune Rho signaling to regulate morphogenetic outcomes. Journal of Cell Science 132(8), Apr 2019.

Lenhart Kari F, Capozzoli Benjamin, Warrick Gwen S D, DiNardo Stephen: Diminished Jak/STAT Signaling Causes Early-Onset Aging Defects in Stem Cell Cytokinesis. Current Biology : CB 29(2): 256-267.e3, Jan 2019.

*Anllo Lauren, *Plasschaert Lindsey W, *Sui Justin, DiNardo Stephen: Live imaging reveals hub cell assembly and compaction dynamics during morphogenesis of the Drosophila testis niche. Developmental Biology 446(1): 102-118, 02 2019 Notes: * Co-First Authors.

Ly Dan, Resch Erin, Ordiway George, DiNardo Stephen: Asymmetrically deployed actomyosin-based contractility generates a boundary between developing leg segments in Drosophila. Developmental biology 429(1): 165-176, 09 2017.

Kari F. Lenhart Stephen DiNardo: Somatic cell encystment promotes abscission in germline stem cells following a regulated block in cytokinesis. Developmental Cell 34(2): 192-205, July 2015.

Wingert L; DiNardo S. : Traffic jam functions in a branched pathway from Notch activation to niche cell fate. Development. Company of Biologists, 142(13): 2268-77, July 2015.

Lawlor Kynan T, Ly Daniel C, DiNardo Stephen: Drosophila Dachsous and Fat polarize actin-based protrusions over a restricted domain of the embryonic denticle field. Developmental biology 383(2): 285-94, Nov 2013.

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.

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.

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.

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Last updated: 10/13/2022
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