Paper of the Month: Toward a better understanding of cilia and flagella function
This month's featured paper is from the Daniel Carr lab, and is titled, "Loss of ASP but Not ROPN1 Reduces Mammalian Ciliary Motility." It was published in the journal Cytoskeleton. The research in this paper was conducted by scientists in the OHSU Department of Medicine, the Portland VA Medical Center, the University of Nebraska Medical Center, and at the University of North Carolina at Chapel Hill*
Primary ciliary dyskinesia (PCD) is a rare genetic disease characterized by abnormal ciliary motion and impaired mucociliary clearance.
In people with PCD, the tiny hair-like projections called cilia, which remove debris by constantly moving a protective mucus layer away from the lung, are abnormal or do not move. Thus, the mucus accumulates, causing blockage and infections.
In their study, scientists in the Daniel Carr lab, located at the Portland VA Medical Center, looked at cilia and sperm flagella (tail). The physical structure of the molecular motors responsible for the movement of both cilia and sperm flagella are very similar. The axoneme consists of nine microtubule doublets arrayed in a radially symmetric fashion around a central pair of microtubules. Ciliary beating occurs when dynein ATPases interact with adjacent microtubules and move the microtubules relative to each other.
Mary Stenzel-Poore, PhD
"The findings in this paper are an elegant example of the power of genetic mouse mutants to inform our understanding of complex biology."
Although scientists have a pretty good idea of how their molecular motors work, the signaling mechanism that controls the speed of the movement is still poorly understood. Dr. Carr's team wanted to learn more about these regulatory biochemical mechanisms so they could identify targets for treatment of cilia and sperm dysfunction.
Previous studies have shown that increasing the concentration of cAMP, a trigger that activates a signaling enzyme called Protein Kinase A (PKA), will increase the beat frequency of both cilia and flagella. "Because PKA is a very potent enzyme with a wide variety of functions, its location within the cell is highly regulated," said Daniel Carr, PhD, Research Professor, Department of Medicine, and Portland VA Medical Center. "To accomplish this localization, PKA binds to other cellular proteins referred to as A-Kinase Anchoring Proteins (AKAPs)." Several AKAPs have been identified in both cilia and flagella. PKA has a unique domain or latch that allows it to interact with all these cellular AKAPs.
Research in the Daniel Carr lab discovered that two other proteins, ASP and ROPN1, also contain this unique domain that allows them to bind to AKAPs. These proteins are highly concentrated in cilia and flagella. To test the hypothesis that these proteins are involved in the regulation of cilia and flagella movement, the team created three mutant mouse lines, one lacking ASP, one lacking ROPN1 and one lacking both ASP and ROPN1.
"By examining these mice, we discovered that mice lacking ASP have a significantly reduced ciliary beat frequency," said Dr. Carr. "Lack of ROPN1 had no effect on ciliary motility. In contrast, mice lacking ASP seemed to have normal sperm movement and fertility while mice lacking ROPN1 had reduced motility and fertility. In mice lacking both, the team discovered that the sperm were immotile and completely infertile.
Based on this data, the investigators conclude that ASP is a key regulator of cilia movement while ROPN1 is a primary regulator of sperm motility. "Thus, in spite of the great similarity of the structure of the axoneme in both cilia and flagella, our evidence suggests they each have a unique mechanism of regulation," said Dr. Carr.
Future studies to further define the mechanisms regulating the movement of cilia and flagella could translate into reduced respiratory infections or treatments for male factor infertility.
Read published paper in Cytoskeleton.
Pictured above: Daniel Carr, PhD, and Sarah Fiedler, BA
Cross section of an axoneme
A cross sectional diagram through a typical eukaryotic flagellum showing the 9+2 arrangement of microtubules
Image owned and created by Smartse. Use of image doesn't imply that author endorses article. Image taken from Google Images.
Sarah E. Fiedler, BA, (1, 2); Joseph H. Sisson, MD, (3); Todd A. Wyatt, PhD, (3); Jacqueline A. Pavlik, BS, (3); Todd M. Gambling, MPH, (4); Johnny L. Carson, PhD, (4, 5); Daniel W. Carr, PhD (1, 2)
- VA Medical Center, Portland, Oregon
- Department of Medicine, Oregon Health & Science University, Portland, Oregon
- Department of Internal Medicine, Pulmonary, Critical Care, Sleep & Allergy Division, Durham Research Center II, Nebraska
- Medical Center, University of Nebraska Medical Center, Omaha, Nebraska
- Center for Environmental Medicine, Asthma, and Lung Biology, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina
- Department of Pediatrics, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina
ABOUT THE PAPER OF THE MONTH
The School of Medicine newsletter spotlights a recently published faculty research paper in each issue. The goals are to highlight the great research happening at OHSU and to share this information across departments, institutes and disciplines. The monthly paper summary is selected by Associate Dean for Basic Science Mary Stenzel-Poore, PhD.
The findings in this paper, published in Cytoskeleton, are an elegant example of the power of genetic mouse mutants to inform our understanding of complex biology—in this case, the biology and signaling mechanisms involved in the movement of cilia and flagella that influence such vital processes as respiration and reproduction.
January's Published Papers
The entire list of OHSU papers published in January is here