Centriole Biogenesis and Stabilization for Centrosomes
In the Pearson Lab, we delve into several fascinating
aspects of centrioles and basal bodies as they perform roles in organizing
centrosomes and cilia. Centrosomes consist of a pair of centrioles surrounded
by a matrix of pericentriolar material that nucleates cytoplasmic microtubules.
During G0/G1 of the cell cycle, centrioles are commonly modified to serve as
basal bodies that organize cilia. These cilia (known as primary cilia), sense
their environment and transmit signals to the cell nucleus. Other cells produce
motile cilia that produce hydrodynamic force generating fluid flow. In the case
of motile cilia and the basal bodies that organize them, we capitalize on the
ciliated protist, Tetrahymena thermophila, to understand how centrioles and
basal bodies assemble, organize at the cell surface and resist mechanical
stress produced by ciliary beating.
Centriole and basal body biogenesis and stabilization
Centrioles and basal bodies must be assembled to resist
mechanical forces from either the mitotic spindle or ciliary motility. Using
Tetrahymena, we have identified molecules and structures that reinforce basal
bodies against the forces produced by ciliary undulations. Although the triplet
microtubules of the basal body are radially symmetrical, we find stabilizing
microtubule post-translational modifications are asymmetrically localized to
the side of the basal body that receives the most compressive force. We have
also identified proteins (both asymmetric andsymmetric around the basal body)
that promote resistance to ciliary mechanical force by facilitating linkages
between triplet microtubules. Remarkably, tubulin post-translational
modifications and stabilizing proteins can compensate for each other when one
stabilization pathway is lost. We are now studying what establishes the
asymmetric positioning of post-translational modifications and how the proteins
we have identified promote triplet microtubule linkages.
Basal body organization
In addition to basal bodies resisting ciliary forces, they
must also maintain their cellular position and orientation, and they must
efficiently transmit ciliary forces to the cell. This requires a dynamic
cortical cytoskeleton. Moreover, each individual basal body is polarized and
positioned with respect to the cell’s global geometry. Using quantitative live
cell microscopy, transmission electron microscopy (EM), EM tomography,
computational modeling, and genetics we are elucidating the mechanisms by which
the cortical cytoskeleton influences and maintains basal body positioning and
orientation in the face of large asymmetric forces produced by ciliary beating.
Controlling centriole number
We previously discovered that a short isoform of CEP135, a
protein that when full-length promotes centriole duplication and stabilization,
represses duplication. The short CEP135 isoform (CEP135mini) is a natural
dominant negative whose levels are tightly regulated through the cell cycle. We
hypothesize that the relative levels of full length and CEP135mini are
important for maintenance of the normal homeostasis of centriole number that is
altered in many cancer cells. Indeed, CEP135, but not CEP135mini, is
upregulated in cancer. Our current studies aim to understand the mechanisms of
RNA processing that control the relative levels of the CEP135 isoforms. Other
proteins involved in the control of centriole duplication and function are also
regulated by pre-mRNA processing and we are investigating RNA splicing factors
responsible for this control. Moreover, we are exploring the mechanism by which
CEP135mini represses centriole duplication.
Centrosome and cilia dysfunction in Down syndrome
Down syndrome is caused by an extra copy of chromosome 21.
Interestingly, there are clinical similarities between individuals with Down
syndrome and those with ciliopathies (a class of genetic diseases that affect
ciliary function), including cerebellar hypoplasia, craniofacial dysmorphology,
and cardiac septal defects. Consistent with this, we discovered that trisomy 21
cells from individuals with DS have primary cilia defects. The gene encoding
the major centrosome scaffolding protein, Pericentrin, is present on chromosome
21 and we find that elevated Pericentrin alone is sufficient to suppress cilia
formation and cilia-dependent signaling. We are now exploring how Pericentrin
levels affect cytoplasmic trafficking, primary cilia formation, ciliary
signaling and centrosome function during mitosis. These studies shed light both
on human disease and fundamental centrosomal processes.
Latest Publications in PubMed
Domenico F. Galati, Kelly D. Sullivan, Andrew T. Pham, Joaquin
M. Espinosa, and Chad G. Pearson (2018) Trisomy 21 represses cilia
formation and function. Dev. Cell. 46(5)641-650.
Brian A. Bayless, Domenico F. Galati, Anthony Junker,
Chelsea B. Backer, Jacek Gaertig, Chad G. Pearson. (2016) Asymmetrically
localized proteins stabilize basal bodies against ciliary beating forces. J.
Cell Biol. 215(4): 457-466.
Janet B. Meehl, Brian A. Bayless, Thomas H. Giddings Jr.,
Chad G. Pearson*, Mark Winey* (2016) Tetrahymena Poc1 ensures proper
inter-triplet microtubule linkages to maintain basal body integrity.
Domenico F. Galati, David S. Abuin, Gabriel Tauber, Andrew
Pham, and Chad G. Pearson. (2015) Automated image analysis reveals the
dynamic 3-dimensional organization of multi-ciliary arrays. Biol. Open.
Kristin D. Dahl, Divya Ganapathi Sankaran, Brian A. Bayless,
Mary E. Pinter, Thomas H. Giddings Jr., and Chad G. Pearson. (2015) A
short Cep135 splice isoform controls centriole duplication. Curr. Biol. 25(19)
Domenico Galati, Stephanie Bonney, Zev Kronenberg, Mark
Yandell, Nels Elde, Maria Jerka-Dziadosz, Joseph Frankel, and Chad G.
Pearson. (2014) DisAp-dependent striated fiber elongation is required to
organize ciliary arrays. J. Cell Biol. 207(6) 705-15.
Brian A. Bayless, Thomas H. Giddings Jr., Mark Winey, Chad
G. Pearson. (2012) Bld10/Cep135 stabilizes basal bodies to resist cilia
generated forces. Mol. Biol. Cell. 23(24):4820-4832.