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Localized depolymerization of the major sperm protein cytoskeleton correlates with the forward movement of the cell body in the amoeboid movement of nematode sperm.

Italiano JE, Stewart M, Roberts TM - J. Cell Biol. (1999)

Bottom Line: At pH 6.35, the cytoskeleton pulled away from the leading edge and receded through the lamellipodium as its disassembly at the cell body continued.The cytoskeleton disassembled rapidly and completely in cells treated at pH 5.5, but reformed when the cells were washed with physiological buffer.These results indicate that cell body retraction is mediated by tension in the cytoskeleton, correlated with MSP depolymerization at the base of the lamellipodium.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Science, Florida State University, Tallahassee, Florida 32306, USA.

ABSTRACT
The major sperm protein (MSP)-based amoeboid motility of Ascaris suum sperm requires coordinated lamellipodial protrusion and cell body retraction. In these cells, protrusion and retraction are tightly coupled to the assembly and disassembly of the cytoskeleton at opposite ends of the lamellipodium. Although polymerization along the leading edge appears to drive protrusion, the behavior of sperm tethered to the substrate showed that an additional force is required to pull the cell body forward. To examine the mechanism of cell body movement, we used pH to uncouple cytoskeletal polymerization and depolymerization. In sperm treated with pH 6.75 buffer, protrusion of the leading edge slowed dramatically while both cytoskeletal disassembly at the base of the lamellipodium and cell body retraction continued. At pH 6.35, the cytoskeleton pulled away from the leading edge and receded through the lamellipodium as its disassembly at the cell body continued. The cytoskeleton disassembled rapidly and completely in cells treated at pH 5.5, but reformed when the cells were washed with physiological buffer. Cytoskeletal reassembly occurred at the lamellipodial margin and caused membrane protrusion, but the cell body did not move until the cytoskeleton was rebuilt and depolymerization resumed. These results indicate that cell body retraction is mediated by tension in the cytoskeleton, correlated with MSP depolymerization at the base of the lamellipodium.

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Escape of a tethered sperm. This sequence of images, taken 6 s apart, shows the locomotory behavior of a sperm as it breaks an abnormal attachment that has tethered the trailing margin of its cell body to the glass substrate. When the cell is tethered, force produced in the cytoskeleton causes the cell body to stretch, distorting its shape, but the shape of the lamellipodium is unaffected (a). When this abnormal attachment is broken (b) the cell body recoils to its normal hemispherical shape and the cell resumes locomotion (b–d). The lamellipodium maintained its shape throughout this process and, in fact, lengthened slightly as the cell crawled away. Bar, 10 μm.
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Figure 2: Escape of a tethered sperm. This sequence of images, taken 6 s apart, shows the locomotory behavior of a sperm as it breaks an abnormal attachment that has tethered the trailing margin of its cell body to the glass substrate. When the cell is tethered, force produced in the cytoskeleton causes the cell body to stretch, distorting its shape, but the shape of the lamellipodium is unaffected (a). When this abnormal attachment is broken (b) the cell body recoils to its normal hemispherical shape and the cell resumes locomotion (b–d). The lamellipodium maintained its shape throughout this process and, in fact, lengthened slightly as the cell crawled away. Bar, 10 μm.

Mentions: The behavior of crawling sperm that have become tethered to the glass substrate at their cell body (Fig. 2) indicated that lamellipodial extension is not sufficient for cell locomotion. In these cells, the lamellipodium continued to exert force against the cell body sufficient to distort its shape from hemispherical to elongate, but there was no stretching of the lamellipodium (Fig. 2). In tethered cells, the leading edge underwent cycles of extension and retraction with no net advance, and yet cytoskeletal flow continued. In some cells, the lamellipodium lost its attachment and the entire cell was pulled toward the tether site. Others, like the sperm shown in Fig. 2, broke the tether, after which the cell body recoiled toward the lamellipodium and regained its hemispherical shape as protrusion of the leading edge and locomotion resumed. By contrast, there was no shortening of the lamellipodium when the cell body recoiled. These observations show that the cell body does not follow passively behind the motile lamellipodium but, instead, that tension within the cytoskeleton pulls the cell body forward. Moreover, the force pulling against the cell body appears to be generated at the base of the lamellipodium. If that tension was produced at the leading edge by the force that drives protrusion, then the entire cell would stretch when tethered at the rear and recoil when the tether was broken.


Localized depolymerization of the major sperm protein cytoskeleton correlates with the forward movement of the cell body in the amoeboid movement of nematode sperm.

Italiano JE, Stewart M, Roberts TM - J. Cell Biol. (1999)

Escape of a tethered sperm. This sequence of images, taken 6 s apart, shows the locomotory behavior of a sperm as it breaks an abnormal attachment that has tethered the trailing margin of its cell body to the glass substrate. When the cell is tethered, force produced in the cytoskeleton causes the cell body to stretch, distorting its shape, but the shape of the lamellipodium is unaffected (a). When this abnormal attachment is broken (b) the cell body recoils to its normal hemispherical shape and the cell resumes locomotion (b–d). The lamellipodium maintained its shape throughout this process and, in fact, lengthened slightly as the cell crawled away. Bar, 10 μm.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2169480&req=5

Figure 2: Escape of a tethered sperm. This sequence of images, taken 6 s apart, shows the locomotory behavior of a sperm as it breaks an abnormal attachment that has tethered the trailing margin of its cell body to the glass substrate. When the cell is tethered, force produced in the cytoskeleton causes the cell body to stretch, distorting its shape, but the shape of the lamellipodium is unaffected (a). When this abnormal attachment is broken (b) the cell body recoils to its normal hemispherical shape and the cell resumes locomotion (b–d). The lamellipodium maintained its shape throughout this process and, in fact, lengthened slightly as the cell crawled away. Bar, 10 μm.
Mentions: The behavior of crawling sperm that have become tethered to the glass substrate at their cell body (Fig. 2) indicated that lamellipodial extension is not sufficient for cell locomotion. In these cells, the lamellipodium continued to exert force against the cell body sufficient to distort its shape from hemispherical to elongate, but there was no stretching of the lamellipodium (Fig. 2). In tethered cells, the leading edge underwent cycles of extension and retraction with no net advance, and yet cytoskeletal flow continued. In some cells, the lamellipodium lost its attachment and the entire cell was pulled toward the tether site. Others, like the sperm shown in Fig. 2, broke the tether, after which the cell body recoiled toward the lamellipodium and regained its hemispherical shape as protrusion of the leading edge and locomotion resumed. By contrast, there was no shortening of the lamellipodium when the cell body recoiled. These observations show that the cell body does not follow passively behind the motile lamellipodium but, instead, that tension within the cytoskeleton pulls the cell body forward. Moreover, the force pulling against the cell body appears to be generated at the base of the lamellipodium. If that tension was produced at the leading edge by the force that drives protrusion, then the entire cell would stretch when tethered at the rear and recoil when the tether was broken.

Bottom Line: At pH 6.35, the cytoskeleton pulled away from the leading edge and receded through the lamellipodium as its disassembly at the cell body continued.The cytoskeleton disassembled rapidly and completely in cells treated at pH 5.5, but reformed when the cells were washed with physiological buffer.These results indicate that cell body retraction is mediated by tension in the cytoskeleton, correlated with MSP depolymerization at the base of the lamellipodium.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Science, Florida State University, Tallahassee, Florida 32306, USA.

ABSTRACT
The major sperm protein (MSP)-based amoeboid motility of Ascaris suum sperm requires coordinated lamellipodial protrusion and cell body retraction. In these cells, protrusion and retraction are tightly coupled to the assembly and disassembly of the cytoskeleton at opposite ends of the lamellipodium. Although polymerization along the leading edge appears to drive protrusion, the behavior of sperm tethered to the substrate showed that an additional force is required to pull the cell body forward. To examine the mechanism of cell body movement, we used pH to uncouple cytoskeletal polymerization and depolymerization. In sperm treated with pH 6.75 buffer, protrusion of the leading edge slowed dramatically while both cytoskeletal disassembly at the base of the lamellipodium and cell body retraction continued. At pH 6.35, the cytoskeleton pulled away from the leading edge and receded through the lamellipodium as its disassembly at the cell body continued. The cytoskeleton disassembled rapidly and completely in cells treated at pH 5.5, but reformed when the cells were washed with physiological buffer. Cytoskeletal reassembly occurred at the lamellipodial margin and caused membrane protrusion, but the cell body did not move until the cytoskeleton was rebuilt and depolymerization resumed. These results indicate that cell body retraction is mediated by tension in the cytoskeleton, correlated with MSP depolymerization at the base of the lamellipodium.

Show MeSH
Related in: MedlinePlus