A central focus of developmental biology is understanding how cells are organized into tissues and organs. One type of organization is planar cell polarity (PCP), the biological process through which a cell develops a specific orientation or direction within the plane of an epithelium (Figure 1). Disruption of PCP leads to improper development of multiple tissues. For example, in vertebrates this manifests in disorganization of auditory hair cells1, fluid buildup in the brain due to disrupted cilia2, and misoriented cell division leading to cysts in the kidney3. While every organism relies on functional PCP, it is a very difficult process to study in humans, and thus much research - including our own - has been focused on Drosophila melanogaster (the fruit fly). In Drosophila, PCP is readily visible in the orientation of wing hairs (Figure 1B).
Our broad research question:
How do cells develop planar cell polarity?
Figure 1. Examples of Planar Cell Polarity in the stereocilia of the vertebrate auditory cells of the inner ear (A) and in the hairs of the fruit fly wing (B). The far right images shows the PCP of individual cells that extend stereocilia or hairs. (Figure adapted from references 4-9.)
Some aspects of PCP, regulated by the frizzled signaling pathway, have been well studied and findings have been extended from flies into vertebrates3. More recent research has revealed an additional cell signaling pathway dependent upon the cell junction proteins Gliotactin and Coracle4. This pathway controls “local” PCP, and wings with reduced Gliotactin have crisscrossed hairs (in contrast to the parallel hairs in normal wings)4. However, beyond the requirement for Gliotactin and Coracle, little is understood about this novel pathway. Identifying additional proteins in this pathway would allow us to fit together one more piece in the puzzle of PCP. This is the goal of our ongoing, multi-year research project.
Our narrow research questions:
What additional proteins work with Gliotactin and Coracle to regulate PCP?
How do these proteins regulate PCP?
Figure 2. A 3-D rendering of the Drosophila wing acquired from the confocal fluorescence microscope. Using fluorescent antibodies, we labeled specific proteins in order to observe protein localization during the course of the wing hair development. This particular sample shows the developing hairs (red) jutting out from above and below the wing. Blue labels the cell nuclei, while green highlights Discs large, a component of the septate junction.
In order to explore these questions, our lab utilizes a combination of genetic, developmental biology, cell biology, molecular biology, and microscopy techniques. Much of our research relies on the confocal fluorescence microscope, a laser-equipped microscope that enables us to build 3D representations of fluorescently-labeled normal and mutant tissues (Figure 2).
We present updates on our ongoing research through oral and poster presentations on campus (i.e. our annual Celebration of Scholarship event) and off campus at regional conferences.
(1) Lu X, Sipe CW. Developmental regulation of planar cell polarity and hair-bundle morphogenesis in auditory hair cells: lessons from human and mouse genetics. Wiley Interdiscip Rev Dev Biol 5:85-101 (2016).
(2) Ohata S, Alvarez-Buylla A. Planar Organization of Multiciliated Ependymal (E1) Cells in the Brain Ventricular Epithelium. Trends Neurosci 39:543-51 (2016)
(3) Simons M, Mlodzik M. Planar cell polarity signaling: from fly development to human disease. Annu Rev Genet. 42:517-40 (2008).
(4) Venema D, Zeev-Ben-Mordehai T, Auld VJ. Transient apical polarization of Gliotactin and Coracle is required for parallel alignment of wing hairs in Drosophila. Dev Bio 275:301-14 (2004).
(5) Cho, A. Biophysics. What's shakin' in the ear? Science 288: 1954 – 1955 (2000).
(6) Steel, Karen et al. (www.kcl.ac.uk/ioppn/depts/wolfson/about/people/staff/steelkaren.aspx)
(7) Axelrod, JD. Basal bodies, kinocilia and planar cell polarity. Nat Genet. 40:10-1 (2008).
(8) Vladar EK, Axelrod JD. Dishevelled links basal body docking and orientation in ciliated epithelial cells. Trends Cell Biol. 18:517-20 (2008).
(9) Devenport D. The cell biology of planar cell polarity. J Cell Biol. 207:171-9 (2014).