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5 Reversing Polarity

Author: Dale Kaiser1
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Affiliations: 1: Departments of Biochemistry and Developmental Biology, Stanford University Medical School, Stanford, CA 94305
Content Type: Monograph
Publication Year: 2008
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Abstract:

Colonies of on the surface of agar spread outward, and genetic studies of motility began with the isolation of mutants having abnormal spreading patterns. Motile strains can produce slime from either end and simply switch the producing end when they reverse. Bipolar slime secretion suggested that by trying to move in both directions simultaneously, cells were unable to make progress in either. A movie of single cells reversing, made by Lars Jelsbak, shows that cells simply stop momentarily before moving off in the opposite direction. How C-signaling gives rise to two different reversal patterns is explained by the signal transduction circuit. Rosa Yu isolated and characterized many new null-motility mutants and from the mutant phenotypes was able to draw two general conclusions about A-motility. First, all of her mutant strains that retained some A-motility, including mglB mutants, produced slime only at one end of each cell. The second conclusion was that mglA and all other “nonmotile” mutants that she had detected were secreting slime from both ends. The author suggests that the rapid reversals of mglA mutants are not due to signals from the reversal generator but are a statistical consequence of active slime secretion from both ends. For example, pilA, which encodes the pilin monomer, is one of the most highly transcribed genes in . The mechanism of gliding reversal that is proposed in this chapter explains how Mgl is shared by two engines that have no protein molecules in common.

Citation: Kaiser D. 2008. 5 Reversing Polarity, p 93-102. In Whitworth D (ed), Myxobacteria. ASM Press, Washington, DC. doi: 10.1128/9781555815677.ch5

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5 Reversing Myxococcus xanthus Polarity
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Citation: Kaiser D. 2008. 5 Reversing Polarity, p 93-102. In Whitworth D (ed), Myxobacteria. ASM Press, Washington, DC. doi: 10.1128/9781555815677.ch5
/content/10.1128/9781555815677.ch05.ch05fig01
Figure 1
Polarized slime secretion. (A) Wild type; (B) mutant; (C) mutant. Photographs from Yu and Kaiser, 2007.
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Figure 1

Polarized slime secretion. (A) Wild type; (B) mutant; (C) mutant. Photographs from Yu and Kaiser, 2007.

Citation: Kaiser D. 2008. 5 Reversing Polarity, p 93-102. In Whitworth D (ed), Myxobacteria. ASM Press, Washington, DC. doi: 10.1128/9781555815677.ch5
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Figure 2
(A) Rate of swarm expansion versus initial cell density for the AS strain DK1622. Points are shown for six independent experiments. The best-fitting smooth curve has the following form: rate = 0.1 + 1.48 (1- ). Reproduced from Kaiser and Crosby, 1983. (B) Rate of swarm expansion versus initial cell density for three AS strains (closed symbols) and two AS strains (open symbols). Points are shown for six independent experiments. The smooth curve for the AS has the following form: rate = 0.47 (1 - ). The smooth curve for the AS has the following form: rate = 0.1 + 0.52 (1 - ).
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Figure 2

(A) Rate of swarm expansion versus initial cell density for the AS strain DK1622. Points are shown for six independent experiments. The best-fitting smooth curve has the following form: rate = 0.1 + 1.48 (1- ). Reproduced from Kaiser and Crosby, 1983. (B) Rate of swarm expansion versus initial cell density for three AS strains (closed symbols) and two AS strains (open symbols). Points are shown for six independent experiments. The smooth curve for the AS has the following form: rate = 0.47 (1 - ). The smooth curve for the AS has the following form: rate = 0.1 + 0.52 (1 - ).

Citation: Kaiser D. 2008. 5 Reversing Polarity, p 93-102. In Whitworth D (ed), Myxobacteria. ASM Press, Washington, DC. doi: 10.1128/9781555815677.ch5
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Figure 3
The frizzy signaling pathway for vegetative cells. When FrzCD is methylated, it triggers the phosphorylation of FrzE. FrzE~P signals a reversal of polarity.
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Figure 3

The frizzy signaling pathway for vegetative cells. When FrzCD is methylated, it triggers the phosphorylation of FrzE. FrzE~P signals a reversal of polarity.

Citation: Kaiser D. 2008. 5 Reversing Polarity, p 93-102. In Whitworth D (ed), Myxobacteria. ASM Press, Washington, DC. doi: 10.1128/9781555815677.ch5
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Figure 4
C-signal transduction circuit. Early in development, reception of A-signal triggers FruA expression. When a cell receives C-signal by contact with another cell, FruA is phosphorylated. Double-headed open arrows are shorthand for a pair of reversed arrows as in Fig. 3 . Negative feedback, indicated by a minus sign (—) in the arrow from FrzE~P to the arrows between FrzCD and Me-FrzCD, causes the frizzy signaling circuit to oscillate. Phosphorylated FruA drives the oscillator, giving it a precise period. Also, when a cell receives C-signal, ActB is phosphorylated and the expression of is increased. This raises the number of C-signal molecules on the cell surface. The arrow from FrzE~P to inactivation of old engines could have more than one step.
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Figure 4

C-signal transduction circuit. Early in development, reception of A-signal triggers FruA expression. When a cell receives C-signal by contact with another cell, FruA is phosphorylated. Double-headed open arrows are shorthand for a pair of reversed arrows as in Fig. 3 . Negative feedback, indicated by a minus sign (—) in the arrow from FrzE~P to the arrows between FrzCD and Me-FrzCD, causes the frizzy signaling circuit to oscillate. Phosphorylated FruA drives the oscillator, giving it a precise period. Also, when a cell receives C-signal, ActB is phosphorylated and the expression of is increased. This raises the number of C-signal molecules on the cell surface. The arrow from FrzE~P to inactivation of old engines could have more than one step.

Citation: Kaiser D. 2008. 5 Reversing Polarity, p 93-102. In Whitworth D (ed), Myxobacteria. ASM Press, Washington, DC. doi: 10.1128/9781555815677.ch5
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Figure 5
Oscillation frequency of the Frizilator as a function of the level of FruA~P, the signaling strength, measured as the level of FrzCD methylation. Oscillation ceases above a critical level of signaling as described in the text. Modified from Igoshin et al., 2004.
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Figure 5

Oscillation frequency of the Frizilator as a function of the level of FruA~P, the signaling strength, measured as the level of FrzCD methylation. Oscillation ceases above a critical level of signaling as described in the text. Modified from Igoshin et al., 2004.

Citation: Kaiser D. 2008. 5 Reversing Polarity, p 93-102. In Whitworth D (ed), Myxobacteria. ASM Press, Washington, DC. doi: 10.1128/9781555815677.ch5
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Figure 6
Observed and predicted distribution of speeds of individual Δ cells. Black bars, observed data from Spormann and Kaiser, 1999. Gray bars, predicted as the difference in speed of two independent ends, each end distributed as observed for Δ in Spormann and Kaiser, 1999.
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Image of Figure 6
Figure 6

Observed and predicted distribution of speeds of individual Δ cells. Black bars, observed data from Spormann and Kaiser, 1999. Gray bars, predicted as the difference in speed of two independent ends, each end distributed as observed for Δ in Spormann and Kaiser, 1999.

Citation: Kaiser D. 2008. 5 Reversing Polarity, p 93-102. In Whitworth D (ed), Myxobacteria. ASM Press, Washington, DC. doi: 10.1128/9781555815677.ch5
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Figure 7
Growth produces two new polar engines that are always compatible with the polarity of the old ends.
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Image of Figure 7
Figure 7

Growth produces two new polar engines that are always compatible with the polarity of the old ends.

Citation: Kaiser D. 2008. 5 Reversing Polarity, p 93-102. In Whitworth D (ed), Myxobacteria. ASM Press, Washington, DC. doi: 10.1128/9781555815677.ch5
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