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T H Howard

Publications and source records attributed to T H Howard.

At least 19 recordsLinked to original sources
PubMed2001

Hair-forming activity of human lymphocyte specific protein 1 requires cooperation between its caldesmon-like domains and the villin headpiece-like domains.

LSP1 is an F-actin binding with multiple F-actin binding domains. Overexpression of LSP1 in NAD 47/89 patient's neutrophils created hair-like projections on the patient's neutrophil cell surfaces and inhibited neutrophil cell motility and transfection of LSP1 in serial cell lines recreate the NAD 47/89 phenotype and produce branching hair-like surface projections. Although LSP1 contains hair-forming ability and LSP1 F-actin binding domains have been defined, the LSP1 domains responsible for its hair-forming activity, the relationship to the F-actin binding domains, and the required domain interactions, if any, for hair formation are not well understood. To define the hair-forming domains of LSP1, the relationship to the known F-actin binding domains, and binding domain interactions, LSP1 truncates, which include or exclude the different F-actin binding domains, were created by PCR. LSP1 mutants were created by site-directed mutagenesis to define the amino acids important for hair formation. Sf9 cells were infected with recombinant baculovirus expressing the cDNA of LSP1 truncates and mutants, and the morphology of infected Sf9 cells was documented by DIC optics. Results show that (1) the hair-forming activity of LSP1 is localized to the basic C-terminal half of the molecule, which contains all of the F-actin binding domains; (2) both the caldesmon-like domains and the villin headpiece-like domains are required for the hair-forming activity of LSP1; (3) basic amino acids in the villin headpiece regions are crucial for the hair-forming activity of LSP1 molecule. The results suggest cooperation between the caldesmon-like domains and the villin headpiece-like domains are required for the hair-forming activity of human LSP1 in cells.

Amino Acid Motifs↗
PubMed2000

Human lymphocyte-specific protein 1, the protein overexpressed in neutrophil actin dysfunction with 47-kDa and 89-kDa protein abnormalities (NAD 47/89), has multiple F-actin binding domains.

Human lymphocyte-specific protein 1 (LSP1) is an F-actin binding protein, which has an acidic N-terminal half and a basic C-terminal half. In the basic C-terminal half, there are amino acid sequences highly homologous to the actin-binding domains of two known F-actin binding proteins: caldesmon and the villin headpieces (CI, CII, VI, VII). However, the exact numbers and locations of the F-actin binding domains within LSP1 are not clearly defined. In this report, we utilized 125I-labeled F-actin ligand blotting and high-speed F-actin cosedimentation assays to analyze the F-actin binding properties of truncated LSP1 peptides and to define the F-actin binding domains. Results show that LSP1 has at least three and potentially a fourth F-actin binding domain. All F-actin binding domains are located in the basic C-terminal half and correspond to the caldesmon and villin headpiece homologous regions. LSP1 181-245 and LSP1 246-295, containing sequences homologous to caldesmon F-actin binding site I and II, respectively (CI, CII), binds F-actin; similarly, LSP1 306-339 can bind F-actin and contains two inseparable villin headpiece-like F-actin binding domains (VI, VII). Although LSP1 1-305, which does not contain VI and VII regions, retains F-actin binding activity, its binding affinity for F-actin is much weaker than that of full-length LSP1. Site-directed mutagenesis of the basic amino acids in the KRYK (VI) or KYEK (VII) sequences to acidic amino acids create mutants that bind F-actin with lower affinity than full-length wild-type LSP1. High KCl concentrations decrease full-length LSP1 binding to F-actin, suggesting the affinity between LSP1 and F-actin is mainly through electrostatic interaction.

Actins↗
PubMed2000

LSP1 modulates the locomotion of monocyte-differentiated U937 cells.

To examine the effect of lymphocyte specific protein 1 (LSP1) on phagocytic cell motility, stable transfection of LSP1-null U937 cell line with an episomal expression vector carrying the LSP1 complementary DNA created lines expressing varied LSP1 levels. Mock transfectants without LSP1 (U937(-)) and cell lines with LSP1 levels similar to those of monocytes (U937(+)) or 4-fold those of monocytes (U937(+)) express LSP1 as indicated and express other actin-binding proteins at normal levels before or after monocytic induction (MI) with dibutyryl cyclic adenosine monophosphate. The cell lines were compared for rate of growth and cell division and, after monocytic differentiation, were video-tracked to measure locomotion as distance moved in 2 hours and examined for morphologic changes. Rates of cell division and growth were similar for different U937 cell lines at all LSP1 levels. In contrast, mean rate of locomotion (micrometers moved in 2 hours) was slower in MI-U937( +) (7.78 + 1.11 microm, n = 3) and MI-U937(-) (23.89 + 2.78 microm, n = 3) than in MI-U937(+) cells (50.77 + 4.11 microm, n = 3). Compared with MI-U937(-), the locomotive histogram (n = 150 cells) of MI-U937(+) or MI-U937( +) cells shows all cells move respectively faster or slower as an entire cell population. In LSP1(+) U937 phagocytes, high LSP1 levels inhibit some (locomotion) but not all (cytokinesis) cell motile behaviors and cause the formation of surface projections. In contrast, normal LSP1 levels in U937 phagocytes enhance some (locomotion) but not all (cytokinesis) cellular motile behaviors and have no effect on cell morphology. Therefore, LSP1 level has a unique biphasic effect on cellular locomotion. The data suggest LSP1 is an important regulator of phagocyte locomotion.

Cell Differentiation↗
PubMed1998

Lymphocyte-specific protein 1 expression in eukaryotic cells reproduces the morphologic and motile abnormality of NAD 47/89 neutrophils.

Despite its name, the actin-binding protein lymphocyte-specific protein1 (LSP1) is found in all hematopoetic cells, and yet its role in cell function remains unclear. Recently, LSP1 was identified as the 47-kD protein overexpressed in the polymorphonuclear neutrophils of patients with a rare neutrophil disorder, neutrophil actin dysfunction with abnormalities of 47-kD and 89-kD proteins (NAD 47/89). These neutrophils are immotile, defective in actin polymerization in response to agonists, and display distinctive, fine, "hairlike" F-actin-rich projections on their cell surfaces. We now show that overexpression of LSP1 produces F-actin bundles that are likely responsible for the morphologic and motile abnormalities characteristic of the NAD 47/89 phenotype. Coincident with LSP1 overexpression, cells from each of several different eukaryotic lines, including a highly motile human melanoma line, develop hairlike surface projections that branch distinctively and contain F-actin and LSP1. The hairlike projections are supported at their core by thick actin bundles, composed of actin filaments of mixed polarity, which periodically anastomose to generate a branching structure. The motility of the melanoma cells is inhibited even at low levels of LSP1 expression. Therefore, these studies show that overexpression of LSP1 alone can recreate the morphologic and motile defects seen in NAD 47/89 and suggest that LSP1 is distinct from other known actin binding proteins in its effect on F-actin network structure.

Calcium-Binding Proteins↗
PubMed1998

Erythrocytapheresis limits iron accumulation in chronically transfused sickle cell patients.

Cerebrovascular accidents (CVA) as a complication of sickle cell disease occur most frequently in childhood. Life-long transfusion prevents recurrent stroke, but inevitably leads to iron overload. Although effective chelation exists, many patients are not compliant. Erythrocytapheresis, an automated method of red blood cell exchange, was evaluated as an alternative to control transfusion-related iron load. Eleven patients with sickle cell anemia and a history of stroke were converted from simple transfusion to pheresis. Total time on pheresis for the group averaged 19 months (range 4-36 months). No significant complications occurred with a mean pre-pheresis hemoglobin S (Hb S) level of 44%. Blood utilization increased by an average of 50%. The effect of pheresis on serum ferritin depended on the patient's pre-pheresis ferritin level and chelation regimen. Ferritin levels remained stable for chelated patients with ferritin levels > or = 5,000 ng/ml, but decreased in a chelated patient with a pre-pheresis ferritin level of 4,000 ng/ml. For non-chelated patients with significant pre-pheresis iron load, ferritin levels remained stable. No patient on chelation prior to pheresis was able to discontinue deferoxamine. However, one patient with pre-pheresis ferritin of 500 ng/ml maintained serum ferritin levels < 200 ng/ml for 36 months of pheresis without chelation. Pheresis is more expensive than simple transfusion unless the cost of chelation and organ damage from iron overload are considered. Erythrocytapheresis is a safe method of controlling Hb S levels and limiting or preventing iron load in chronically transfused sickle cell patients.

Adolescent↗
PubMed1998

Leukocyte transfusion-associated granulocyte responses in a patient with X-linked hyper-IgM syndrome.

X-linked hyper-IgM syndrome (XHIM) is a severe congenital immunodeficiency caused by mutations in CD154 (CD40 ligand, gp39), the T cell ligand for CD40 on B cells. Chronic or cyclic neutropenia is a frequent complicating feature that heightens susceptibility to severe infections. We describe a patient with a variant of XHIM who produced elevated levels of serum IgA as well as IgM and suffered from chronic severe neutropenia. Eight of ten leukocyte transfusions with cells from a maternal aunt, performed because of mucosal infections, resulted in similar episodes of endogenous granulocyte production. Transfection studies with the mutant CD154 protein indicate that the protein is expressed at the cell surface and forms an aberrant trimer that does not interact with CD40. The data suggest that allogeneic cells from the patient's aunt, probably activated T cells bearing functional CD154, may interact with CD40+ recipient cells to produce maturation of myeloid precursors in the bone marrow.

Adolescent↗
PubMed1995

The actin-binding protein, lymphocyte-specific protein 1, is expressed in human leukocytes and human myeloid and lymphoid cell lines.

Lymphocyte-specific protein 1 (LSP1) was originally reported as a lymphocyte-specific actin-binding protein using murine LSP1 probes. Subsequently, we identified LSP1 in polymorphonuclear neutrophils (PMN) and showed that it is the overexpressed 47-kDa protein in neutrophil actin dysfunction with 47- and 89-kDa abnormalities. This suggests that regulation of LSP1 expression in myeloid cells may be a functionally important event. LSP1 expression in human leukocytes, lymphoid cell lines, and myeloid cell lines (PLB985, HL60, and U937), uninduced (U) or induced to granulocytic (GI) or monocytic (MI) differentiation, was analyzed by Northern blot and immunoblot. By immunoblot, LSP1 is strongly expressed in PMN, less expressed in lymphocytes and monocytes (30-40% and 55-65% of the PMN level, respectively). By immunoblot and Northern blot, LSP1 is minimally expressed in U-PLB985 and U-HL60 (< 10% of the PMN level) and is weakly expressed in the B lymphoid cell line Daudi, but is not expressed in the pro-B, pre-B, T lymphoid cell lines tested, U-U937 or MI-U937. LSP1 mRNA and protein are up-regulated in GI-PLB985, GI-HL60, and MI-HL60. In HL60, LSP1 mRNA and protein increase in parallel to a maximum of eightfold the basal level on days 5 to 6 of granulocytic differentiation and four- to fivefold the basal level on day 3 of monocytic differentiation. The results show that LSP1 is expressed in all human leukocytes, and its expression is up-regulated during granulocytic and monocytic differentiation of myeloid cells in vitro. Since its overexpression is implicated in the functional pathogenesis of a novel human neutrophil motile dysfunction and microfilamentous cytoskeletal abnormality (NAD 47/89), finding LSP1 in all human leukocytes suggests that it plays a role in regulating microfilamentous cytoskeleton structure and motile function in all leukocytes. Since the protein is not lymphocyte specific and is an F-actin binding protein, and its isoforms are expressed in stromal and embryonic mesenchymal cells, we propose that the protein's name be changed to leufactin, as an abbreviated form of leukocyte F-actin binding protein.

Actins↗
PubMed1995

Dynamics of triton-insoluble and triton-soluble F-actin pools in calcium-activated human polymorphonuclear leukocytes: evidence for regulation by gelsolin.

Gelsolin, a Ca++ activated, 90 kd actin binding protein, can regulate actin polymerization in polymorphonuclear leukocytes (PMNs) via severing of filaments to dissolve gels or by capping of filament ends to limit polymerization. In Triton-lysed PMNs, 30% of gelsolin is bound to the Triton-soluble F-actin (TSF) pool and none is bound to the Triton-insoluble F-actin (TIF) pool. Calcium-activated PMNs exhibit concurrent temporal and quantitative TIF growth and TSF and total F-actin loss. To determine if gelsolin plays a role in regulating TSF pool size, we monitored gelsolin-actin interactions and TIF, TSF and G-actin content at 5 second intervals in PMNs activated with the calcium ionophore, ionomycin. Actin pools were measured by NBDphallacidin binding and by gel scans and expressed relative to basal; gelsolin-actin interactions were measured as change in the amount of EGTA-resistant gelsolin:actin (G:A) complexes and by immunoblot quantification of gelsolin in actin pools. In basal PMNs, 33% of PMN gelsolin is bound in 1:1 EGTA-resistant G:A complexes and TSF and TIF retain 30% and 0% of PMN gelsolin, respectively. By 20 seconds after ionomycin addition, TSF decreases, TIF increases and a fraction of gelsolin repartitions from the TSF to the TIF pool. At maximum change (60 seconds), total F-actin (TIF + TSF) and TSF decrease and TIF increases by 25%; gelsolin is bound to both TSF and TIF (35% of total gelsolin in each pool), and 1:1 EGTA-resistant G:A complexes increase from 33% to 70%. No changes occur in cells activated by ionomycin in the absence of Ca++. The data show Ca++ activated TIF growth and TSF loss are temporally and quantitatively associated with an increase in the percent of gelsolin bound to actin and the translocation of gelsolin from TSF to TIF. This is unique, since no other PMN activator is known to repartition gelsolin into TIF actin. Further, the Ca++ activated initial increase in TIF concurrent with a fall in TSF without a change in total F-actin or G-actin content suggest that TIF grows initially only by TSF annealing/cross-linking to TIF. Gelsolin may regulate these events.

Actins↗
PubMed1994

Giant actin inclusions in hematopoietic cells associated with transfusion-dependent anemia and grey skin discoloration.

We evaluated a 13-month-old boy with cytoplasmic inclusions in hematopoietic cells, transfusion-dependent anemia, splenomegaly, and striking grey skin discoloration. Bright blue inclusions, 1 to 5 microns in diameter, were observed, primarily in the cytoplasm, of 30% to 40% of myeloid cells and in occasional monocytes, megakaryocytes, and lymphocytes on Wright Giemsa-stained bone marrow and blood smears. They occasionally involved the nucleus. The inclusions lacked lysosomes, polysaccharides, or lipids. Ultrastructurally, they lacked limiting membranes and consisted of tightly packed microfilaments averaging 7 nm in diameter, consistent with the size of actin monofilaments. On light microscopy, the inclusions stained with a monoclonal antibody to muscle-specific actin. Inclusion-positive cells contained increased F-actin content and were defective in chemotactic factor-activated actin polymerization; inclusion-negative cells polymerized actin normally. Neutrophil and platelet numbers and functional studies were mildly abnormal. Anemia and skin discoloration resolved spontaneously after 18 months, but the giant inclusions have persisted to the present. We conclude that this child has a previously unreported constellation of clinical and laboratory findings comprising severe anemia, intermittent neutropenia and thrombocytopenia, abnormal neutrophil migration and platelet aggregation, giant inclusions of actin in hematopoietic cells, and grey skin discoloration.

Actins↗
PubMed1994

Role of tropomyosin, alpha-actinin, and actin binding protein 280 in stabilizing Triton insoluble F-actin in basal and chemotactic factor activated neutrophils.

F-actin is a major component of the neutrophil (PMN) cytoskeleton. In basal PMNs, F-actin exists in two structurally and functionally distinct pools: Triton insoluble F-actin (TIF)--cold insensitive, not depolymerizable by dilution, and distributed in pseudopods and submembranous locations; and Triton soluble F-actin (TSF)--unstable in cold, diffusely distributed, and gelsolin enriched. The element(s) conferring these unique properties to the Triton insoluble F-actin pool are unknown, but logically include distinct actin regulatory proteins. To study the morphologic and functional determinants of the Triton insoluble F-actin pool, the distribution and quantity of three candidate regulatory proteins, alpha-actinin, tropomyosin (TM), and actin binding protein (ABP-280), were compared in F-actin (Triton insoluble and Triton soluble) and G-actin pools isolated from basal and chemotactic factor activated human PMNs in suspension, using immunoblots and ionic extraction. F-actin content was measured by NBDphallacidin binding and gel scans. The results show that: (1) alpha-actinin, actin binding protein 280, and tropomyosin are localized to TIF and excluded from TSF; (2) TM, alpha-actinin, and ABP 280 are required to stabilize fractions of Triton insoluble F-actin in PMNs; and (3) chemotactic factor activation results in release of a fraction of TM from the Triton insoluble F-actin pool in temporal association with F-actin polymerization in the Triton insoluble F-actin pool. Shifts in ABP 280 or alpha-actinin do not occur. The results suggest that TM, alpha-actinin, and ABP 280 provide structure to TIF and that TM release from TIF is involved in chemotactic factor induced actin polymerization in PMNs.

Actinin↗
PubMed1994

A clinically applicable technique to study cytoskeletal dynamics in normal and abnormal polymorphonuclear leukocytes isolated from small volume blood samples.

Shape change and motility of polymorphonuclear leukocytes (PMNs) are essential for host defense and require dynamic reorganizations of microfilamentous cytoskeleton by reversible polymerization of G-actin into filaments (F-actin). Although clinical disorders of actin polymerization are rare, recently described simple methodologies for assaying actin dynamics in PMNs make the technique readily applicable to clinical studies. To develop a clinically useful F-actin assay, the authors investigated the optimal preparation conditions for PMN isolation that resulted in the least in vitro cytoskeletal activation and evaluated the variability in actin dynamics in acutely and chronically infected patients. Basal and chemotactic factor-activated PMN F-actin content was measured by a previously described flow cytometric technique in fixed, permeabilized, NBDphallacidin-stained PMNs isolated by centrifugation in Percoll or Ficoll-Hypaque density gradients or by countercurrent elutriation. F-actin content is expressed as mean fluorescent channel or relative fluorescence intensity. Basal F-actin in PMNs prepared from countercurrent elutriation (mean fluorescent channel = 79.0 +/- 4.5, n = 6) or by Ficoll Hypaque (82.0 +/- 3.5, n = 4) was significantly higher than endotoxin free, Percoll purified PMNs, whether purified in bulk (56.1 +/- 7.9, n = 8) or by the small volume modification applicable to clinical studies (53.3 +/- 8.7, n = 15). Basal Ficoll Hypaque purified PMNs have evidence of shape change, whereas endotoxin free, Percoll purified PMNs are smooth and round and represent the most basal cell equivalent in F-actin content to a circulating PMN.(ABSTRACT TRUNCATED AT 250 WORDS)

Actins↗
PubMed1994

Actin polymerization and leukocyte function.

The coordinated remodeling of the filamentous actin-based microfilamentous cytoskeleton via regulated polymerization and depolymerization of globular and filamentous actin is required for polymorphonuclear leukocyte motile functions including locomotion, shape change, phagocytosis, and adhesion. Significant new observations on the structure and function of distinct filamentous actin pools in polymorphonuclear leukocytes, the mechanisms of chemotactic peptide-mediated actin polymerization, the role of filamentous actin in polymorphonuclear shape change in suspension and on a surface, the identification and characterization of rare patients with polymorphonuclear motile defects and actin dysfunctions, and regulation of actin reorganizations by actin regulatory proteins, the phosphorylation or dephosphorylation states of proteins, and the second messengers--the phosphoinositides--were reported in the past year. These observations form the basis for an improved understanding of the cellular and molecular role of actin assembly in polymorphonuclear function and are the subject of this review.

Actins↗
PubMed1993

Mechanisms for actin reorganization in chemotactic factor-activated polymorphonuclear leukocytes.

Cytoskeletal structure in polymorphonuclear leukocytes (PMNs) is thought to reflect a simple equilibrium between two actin pools (globular [G]- and filamentous [F] actin). Recent description of two distinct F-actin pools in PMNs (Triton-insoluble [stable] and Triton-soluble [labile] F-actin pools) (Watts and Howard, Cell Motil Cytoskeleton, 21:25, 1992) suggest a tripartite equilibrium between these F-actin pools and G-actin and multiple possible mechanisms for polymerization. To study the contribution of each actin pool to actin dynamics in PMNs, changes in actin content of the Triton-soluble and -insoluble F-actin pools and G-actin in chemotactic factor (CTF)-activated PMNs were measured by NBDphallacidin binding and by gel scans of Triton-lysed PMNs. From 0 to 30 seconds after CTF activation, PMNs rapidly increase total (Triton-soluble + Triton-insoluble) F-actin content (maximum = 1.7- +/- 0.10-fold basal at 30 seconds). Concurrent measures of the actin content of individual actin pools (Triton-soluble and -insoluble F-actin and G-actin) show that at all times (0 to 30 seconds) only the Triton-insoluble F-actin pool grows (maximum = 2.81- +/- 0.73-fold basal at 30 seconds), whereas both the Triton-soluble and G-actin pools simultaneously decrease (50% decrease at 30 seconds). Concurrent growth of one F-actin pool (Triton-insoluble) and loss of another F-actin pool (Triton-soluble) emphasize the functional uniqueness of the F-actin pools and can occur only if the Triton-soluble F-actin anneals or cross-links filament-to-filament with the Triton-insoluble fraction or if the Triton-insoluble F-actin pool first depolymerizes to monomer, which is then added to the Triton-insoluble pool. Because from 0 to 30 seconds after FMLP activation G-actin never increases, but, like the Triton-soluble F-actin progressively decreases, the results suggest that F-actin growth results from simultaneous new filament growth by monomer addition to the Triton-insoluble F-actin and cytoskeletal remodelling by Triton-soluble F-actin annealing or cross-linking to Triton-insoluble F-actin. These findings offer important new insights into the mechanism(s) of actin polymerization in CTF-activated human PMNs.

Actin Cytoskeleton↗
PubMed1992

Evidence for a gelsolin-rich, labile F-actin pool in human polymorphonuclear leukocytes.

Filamentous (F) actin is a major cytoskeletal element in polymorphonuclear leukocytes (PMNs) and other non-muscle cells. Exposure of PMNs to agonists causes polymerization of monomeric (G) actin to F-actin and activates motile responses. In vitro, all purified F-actin is identical. However, in vivo, the presence of multiple, diverse actin regulatory and binding proteins suggests that all F-actin within cells may not be identical. Typically, F-actin in cells is measured by either NBDphallacidin binding or as cytoskeletal associated actin in Triton-extracted cells. To determine whether the two measures of F-actin in PMNs, NBDphallacidin binding and cytoskeletal associated actin, are equivalent, a qualitative and quantitative comparison of the F-actin in basal, non-adherent endotoxin-free PMNs measured by both techniques was performed. F-actin as NBDphallacidin binding and cytoskeletal associated actin was measured in cells fixed with formaldehyde prior to cell lysis and fluorescent staining (PreFix), or in cells lysed with Triton prior to fixation (PostFix). By both techniques, F-actin in PreFix cells is higher than in PostFix cells (54.25 +/- 3.77 vs. 23.5 +/- 3.7 measured as mean fluorescent channel by NBDphallacidin binding and 70.3 +/- 3.5% vs. 47.2 +/- 3.6% of total cellular actin measured as cytoskeletal associated actin). These results show that in PMNs, Triton exposure releases a labile F-actin pool from basal cells while a stable F-actin pool is resistant to Triton exposure. Further characterizations of the distinct labile and stable F-actin pools utilizing NBDphallacidin binding, ultracentrifugation, and electron microscopy demonstrate the actin released with the labile pool is lost as filament. The subcellular localization of F-actin in the two pools is documented by fluorescent microscopy, while the distribution of the actin regulatory protein gelsolin is characterized by immunoblots with anti-gelsolin. Our studies show that at least two distinct F-actin pools coexist in endotoxin-free, basal PMNs in suspension: 1) a stable F-actin pool which is a minority of total cellular F-actin, Triton insoluble, resistant to depolymerization at 4 degrees C, gelsolin-poor, and localized to submembranous areas of the cell; and 2) a labile F-actin pool which is the majority of total cellular F-actin, Triton soluble, depolymerizes at 4 degrees C, is gelsolin-rich, and distributed diffusely throughout the cell. The results suggest that the two pools may subserve unique cytoskeletal functions within PMNs, and should be carefully considered in efforts to elucidate the mechanisms which regulate actin polymerization and depolymerization in non-muscle cells.

Actins↗
PubMed1992

Relationship of F-actin distribution to development of polar shape in human polymorphonuclear neutrophils.

Polymerization of actin has been associated with development of polar shape in human neutrophils (PMN). To examine the relation of filamentous actin (F-actin) distribution to shape change in PMN, we developed a method using computerized video image analysis and fluorescence microscopy to quantify distribution of F-actin in single cells. PMN were labeled with fluorescent probe NBD-phallicidin to measure filamentous actin and Texas red to assess cell thickness. We show that Texas red fluorescence is a reasonable measure of cell thickness and that correction of the NBD-phallicidin image for cell thickness using the Texas red image permits assessment of focal F-actin content. Parameters were derived that quantify total F-actin content, movement of F-actin away from the center of the cell, asymmetry of F-actin distribution, and change from round to polar shape. The sequence of change in F-actin distribution and its relation to development of polar shape in PMN was determined using these parameters. After stimulation with chemotactic peptide at 25 degrees C, F-actin polymerized first at the rim of the PMN. This was followed by development of asymmetry of F-actin distribution and change to polar shape. The dominant pseudopod developed first in the region of lower F-actin concentration followed later by polymerization of actin in the end of the developed pseudopod. Asymmetric F-actin distribution was detected in round PMN before development of polar shape. Based upon these data, asymmetric distribution of F-actin is coincident with and probably precedes development of polar shape in PMN stimulated in suspension by chemotactic peptide.

Actin Cytoskeleton↗