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smlA fruiting bodies |
wild-type fruiting bodies |
countin fruiting bodies |
When wild-type Dictyostelium cells starve, they aggregate into
groups of roughly 2X104 cells. However when the smlA
gene is repressed by antisense transformation or homologous recombination,
the starved cells form large numbers of small aggregates. smlA
mRNA is expressed in vegetative and early developing cells. Immunofluorescence
and staining of Western blots of cell fractions indicated that SmlA is
a 35-kD cytosolic protein present in all vegetative and developing cells
and is absent from smlA cells. The absence of SmlA did not
affect the growth, motility, differentiation, or developmental speed of
cells. We found that the smlA phenotype is due to these
cells oversecreting a factor, which we called Counting Factor (CF), that
regulates group size.
We purified CF and found that it is a complex of polypeptides which is
secreted by developing wild-type cells. One of the polypeptides
is countin, a 40-KD hydrophilic protein. In transformants with a
disrupted countin gene, there is no detectable secretion of counting
factor and the aggregation streams do not break up, resulting in the formation
of huge fruiting bodies. We are currently working on characterizing
additional members of the CF polypeptide complex, and the CF signal transduction
pathway.
Key Papers
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Two
components of a secreted cell-number counting factor bind to cells
and have opposing effects on cAMP signal transduction in Dictyostelium.
Brock, D.A.,
Ehrenman, K., Ammann, R., Tang, Y., and Gomer, R.H. J.
Biol. Chem. In press.
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CF45-1,
a secreted protein which participates in group size regulation in
Dictyostelium. Brock, D.A., Hatton, R.D., Giurgiutiu,
D-V, Scott, B., Jang, W., Ammann, R., and Gomer, R.H.Eukaryotic
Cell 2003 2, 788-797.
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The
different components of a multisubunit cell number-counting factor
have both unique and overlapping functions.
Brock, D.A., Hatton, R.D., Giurgiutiu, D-V, Scott, B., Ammann, R.,
and Gomer, R.H Development 2003 129, 3657-3668
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A
Dictyostelium mutant with defective aggregate size determination.
Brock DA, Buczynski G, Spann TP, Wood SA, Cardelli J, Gomer RH.
Development 1996 122:2569-78
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A
cell-counting factor regulating structure size in Dictyostelium.
Brock DA, Gomer RH. Genes & Development 1999
13:1960-9.
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Just
the right size: cell counting in Dictyostelium.
Brown JM, Firtel RA.
Trends Genet. 2000 16:191-3. (A review of the above paper).
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A
Precise Group Size in Dictyostelium Is Generated by a Cell-Counting
Factor Modulating Cell-Cell Adhesion. Roisin-Bouffay C,
Jang W, Caprette DR, Gomer RH. Molecular Cell. 2000
6:953-959.
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Mutagenesis
and gene identification in Dictyostelium by shotgun antisense.
Spann TP, Brock DA, Lindsey DF, Wood SA, Gomer RH. Proc
Natl Acad Sci U S A 1996 93:5003-7
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Gene
identification by shotgun antisense. Gomer RH. Methods
1999 18:311-5
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Not
being the wrong size.
Gomer RH. Nature Reviews 2001 2, 48-54
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A
cell number-counting factor regulates the cytoskeleton and cell
motility in Dictyostelium. Tang, L., Gao, T., McCollum,
C., Jang, W., Vicker, M.G., Ammann, R.R., and Gomer, R.H.
Proc. Natl. Acad. Sci. USA. 99, 1371-1376
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Cells respond to and bind countin, a component of a multisubunit
cell-number counting factor. Gao, T., Ehrenman, K., Tang,
L., Leippe, M., Brock, D.A., and Gomer, R.H J. Biol. Chem.
2002 277, 32596-32605
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