Last Friday, Professor Winfield Sale from Emory University described his recent research on cell motility at the weekly Biology Department seminar.
Sale uses the biflagellate algae Chlamydomonas to study the basis for motion in cilia and flagella. Both cilia and flagella exhibit a characteristic “nine-plus-two” arrangement of microtubules, with nine on the periphery and two at the core of a circular structure known as the axoneme. The action of dynein motor proteins in the nine outer microtubules is what enables motion in cilia and flagella.
Sale focused largely on his recent research regarding the regulation of waveform in flagella motion. His research has shown that phosphorylation of axoneme components may have a complementary role to calcium in the stimulation of flagella motion. A series of mutants with a paralyzed flagella phenotype capable of extension through dynein sliding, but not bending, helped to clarify the effect of axoneme phosphorylation on flagella bending. Sale observed that the addition of a kinase inhibitor resulted in restored flagella motion. This led Sale to predict that phosphatases might be present in the central pair and radial spokes to counteract the phosphorylation of the axoneme in wild type flagella. Investigation of specific mutants revealed two phosphatases located in two different places in the axoneme: the catalytic subunit of type-1 protein phosphatase in the central pair and the A and C subunits of type 2A protein phosphatase in the outer ring.
Sale’s lab makes use of isolated flagella to study axoneme function. Flagella are separated from their cells using treatment and differential centrifugation, and MgATP is used to restore movement in in vitro flagella preparations. The Sale lab is currently using this technique to study phosphatases and kinases in the Chlamydomonas model, in hopes of better identifying the way in which flagella are anchored to the cell the impact of their subunit assembly on axoneme enzyme function.
Sale’s cilia and flagella research also has strong implications for the field of medicine. Right-left asymmetry defects in mammals are often strongly linked to malfunctions in genes associated with the assembly and functioning of cilia Such defects lead to highly unusual “isomeric” orientations of the liver, stomach and spleen, normally arranged from right to left within the body. Cardiac function is impaired in these intermediate arrangements of organs, but complete inversion does not result in symptoms. Cilia are present in an embryonic node thought to be responsible for defining left-right orientation during development, but the mechanism by which this node affects the process is yet unknown.
Further Information
Website for the Sale Lab at Clemson, with a list of publications: http://cellbio.emory.edu/lab/sale/