How are the micron-scale functions of organelles determined by the assembly of nanometer-scale proteins? We study this question in the context of the mammalian centrosome-cilium complex.
Centrosomes and cilia are micron-scale, highly-conserved organelles involved in many essential cellular processes, including cell division, signaling, and motility. These organelles are critical in development, and defects in the centrosome-cilium complex are associated with a wide range of disease states, including cancer and a group of syndromes known as ciliopathies. Our overall aim is to understand how centrosomes and cilia are formed and regulated to enable these important cellular functions. We use molecular, cellular, and biochemical approaches and our questions integrate scales from tissues to proteins.
Main areas of research
Centrosome function and regulation
How do centrosomes get to the right location to build cilia? In mouse olfactory sensory neurons, centrosomes must travel up to 100 um to reach the apical surface for cilia formation. Once they arrive, they template the formation of dozens of cilia for chemosensation. Using expansion microscopy, live imaging, and a novel explant system, we found that centrioles migrate slowly and non-processively in large groups, and migration is dependent on microtubule dynamics. We are now interested in further exploring the roles of centrioles and cilia in olfactory sensory neurons.
Centrosome and cilium structure
Centrosomes are composed of two barrel-shaped microtubule structures, known as centrioles, surrounded by pericentriolar material that nucleates microtubules. In almost all organisms, centrioles have a conserved, unique structure, consisting of triplet microtubules arranged with nine-fold symmetry. Within a single centrosome, the older centriole harbors distal and subdistal appendages that allow for cilium formation and microtubule anchoring. How do the hundreds of proteins that make up these incredibly complex organelles interact with each other to create functional structures?
Centrosomal and ciliary proteins
Among the proteins of the centrosome-cilium complex, we are particularly interested in studying the roles of the tubulin superfamily. Of the six members of this superfamily, three are known to form structural components of the centrosome-cilium complex:
Alpha- and beta-tubulin create the barrel wall of centrioles and form the microtubules that emanate from the pericentriolar material.
Gamma-tubulin is required for nucleating microtubules as well as one of the microtubules within the triplet.
In addition to these well-known tubulins, three additional family members are involved in centriole structure and function: delta-tubulin, epsilon-tubulin, and zeta-tubulin.
What are the roles of delta-, epsilon-, and zeta-tubulin? Using CRISPR/Cas9 gene editing in mammalian cells, we found that cells lacking delta-tubulin or epsilon-tubulin lack triplet microtubules, similar to mutations in these genes in other organisms including Chlamydomonas, Tetrahymena, and Paramecium. We are now interested in identifying the molecular mechanisms by which these proteins act.