We use techniques of quantitative cell and molecular biology
to investigate the orchestration of cell differentiation
and cell death. Our research paradigm is a remarkable unicellular
eukaryote, Naegleria gruberi, which can alternate
between walking amoebae and swimming flagellates. When reproducing
amoebae are transferred to a nutrient-free aqueous environment,
they undergo synchronous differentiation to streamlined
flagellates, a conversion completed within 100 minutes.
Amoebae walk using an actin-based motility system, which
becomes latent in the flagellates. The flagellates swim
using a tubulin-based motility system. The tubulin that
makes up the flagellar microtubules is synthesized as a
programmed event of differentiation. Thus the cells undergo
a yin-yang change in utilization of two fundamental eukaryotic
motility systems. Evidence that this differentiation is
regulated in part by changes in intracellular free calcium
ions led us to calmodulin, the conserved calcium-binding
protein that in all eukaryotes transduces the calcium signal
to diverse effector proteins. There are two calmodulins
in Naegleria flagellates, and they are neatly segregated
in the cells, with the major one (CaM-1) localized in the
flagella and the other (CaM-2) in the flagellate cell body.
During differentiation the mRNAs for the two calmodulins
increase in abundance and then rapidly decrease concurrently
with those for [[alpha]]-and ß-tubulins. We hope to
dissect signal transduction pathways from initiation of
differentiation through the regulation of transcription,
mRNA stability, and localization of proteins in flagella.
Two major current interests of our lab are derived from
this work. The first is the study of a calmodulin-related
protein, centrin. Centrin is a centriole-associated calcium-binding
protein that somehow participates in a unique type of contractility
which receives its energy from binding calcium ions rather
than from ATP hydrolysis. This little-understood contractility
is involved in movements within all eukaryotic cells, from
positioning centrioles for mitosis to the dramatic contraction
of the stalks of certain ciliates, such as Vorticella.
We are studying the nature of centrin and its associated
proteins in an effort to understand the structures it forms
and its involvement in motility.
A Naegleria agent induces in vertebrate cells a
unique mode of cell death called apoptosis. Apoptosis is
crucial in development and throughout life. The Naegleria
agent, a small protein, is not toxic to vertebrate cells
and does not affect their growth, but causes them to die
in a delayed fashion after the cells exit the cell cycle.
We wish to define this agent, to understand how it produces
delayed apoptosis, and then to explore possible therapeutic
uses.
Selected Publications
Fulton, C. (1993). Naegleria: A research partner
for cell and developmental biology. J. Euk. Microbiol.
40:520-532.
Fulton, C., Lai, E.Y. and Remillard. S.P. (1995). A flagellar
calmodulin gene of Naegleria, coexpressed during
differentiation with flagellar tubulin genes, shares DNA,
RNA, and encoded protein sequence elements. J. Biol.
Chem. 270:5839-48. [abstract]
Remillard SP, Lai EY, Levy YY, Fulton C. (1995). A calcineurin-B-encoding
gene expressed during differentiation of the amoeboflagellate
Naegleria gruberi contains two introns. Gene 154:39-45.
[abstract]
Levy, Y.Y., Lai, E.Y., Remillard, S.P., Heintzelman, M.B.
and Fulton, C. (1996). Centrin is a conserved protein that
forms diverse associations with centrioles and MTOCs in
Naegleria and other organisms. Cell Motil. Cytoskel.
33(4), 298-323. [abstract]
Levy YY, Lai EY, Remillard SP, Fulton C. (1998). Centrin
is synthesized and assembled into basal bodies during Naegleria
differentiation. Cell Motil Cytoskeleton. 40:249-60.
[abstract]
Fulton C, Lai EY. (1998) Stable intermediates and holdpoints
in the rapid differentiation of Naegleria. Exp Cell Res.
242:429-38. [abstract]
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