The Shape of Cilia

         

In her lab at Washington University in St. Louis, endocrinologist Jing Hughes studies a peculiar structure that sticks out of the surfaces of human pancreatic islet cells: the primary cilium. The cilia are antenna-like organelles that sense shifts in the extracellular environment and communicate these changes to the intracellular space.

Although scientists first identified primary cilia in human pancreatic islets 60 years ago and know that dysfunction of cilia affects the development and function of the pancreas, there are still many unanswered questions about their role and appearance.¹ “That, to me, was just screaming to be followed up on,” Hughes said. 

Hughes decided to begin by finding a way to visualize primary cilia on human islets. Over months, she and her collaborators optimized a protocol for peeling away the entire cell membrane to see the cytoskeletal components of the cilia. Then they applied this method to donated human pancreatic samples and used scanning electron microscopy to obtain a 3D view of cilia morphology.²

The resulting image reveals the richness of the surface of a pancreatic islet cell. Emerging from the microvilli-covered surface is a lone few microns-long primary cilium. Circular rings around its base form the transition zone of the cilium, from which nine parallel microtubules project into the extracellular space. About halfway through, the microtubules wind around each other, producing a directionality that was consistent across all cilia analyzed. Its effect on cilia function remains unclear, Hughes noted. 

By studying the structure of pancreatic cilia, Hughes hopes to understand their basic functions, which may help scientists determine how cilia defects can lead to disease. “It's a peculiar structure. It's long, it's awkward, it's vulnerable to a lot of mechanical stress, but certainly it has evolved to be that way to perfect a function that it serves,” Hughes said. “It really captured my imagination.”