Interaction of flagellar inner arm dynein isolated from sea urchin sperm with microtubules in the presence of ATP

We have isolated C/A dynein, which is considered to be a component of inner arms, from flagellar axonemes of sea urchin sperm (E. Yokota, I. Mabuchi, J. Cell Sci. 107, 345-351 (1994). C/A dynein binds to and bundles the microtubules in the absence of ATP. In contrast to outer arm 21S dynein, C/A dynein is not released from the microtubules in the presence of ATP (E. Yokota, I. Mabuchi, J. Cell Sci. 107, 353-361 (1994)). We further investigated the interaction of C/A dynein with microtubules in the presence of ATP. The turbidity at 350 nm of a mixture of C/A dynein and microtubules increased by the addition of ATP. Both the initial rate and final extent of the turbidity increase were dependent on C/A dynein or ATP concentration and were inhibited by vanadate. ATP hydrolysis by C/A dynein was linear during the time course of the turbidity increase. Negative staining electron microscopy revealed that microtubular bundles which formed in the presence of C/A dynein became thicker and longer after addition of ATP. Furthermore, sliding movements of microtubule(s) in the individual bundles were observed in the presence of ATP. This mode of interaction of C/A dynein with microtubules was distinct from that of flagellar or ciliary dyneins reported so far. These results suggest that C/A dynein, as a component of inner arms, may play a distinct role in the flagellar movement of sea urchin sperm.

A single Drosophila melanogaster myosin light chain kinase gene produces multiple isoforms whose activities are differently regulated

BACKGROUND

Myosin light chain kinase (MLCK) specifically phosphorylates the myosin regulatory light chain in a calcium/calmodulin (Ca2+/CaM)-dependent manner in animal cells. The roles of MLCK are not fully understood, particularly in nonmuscle cells. Therefore, we cloned and characterized a Drosophila MLCK gene as the first step in a genetic analysis of this process.

RESULTS

Four transcripts are produced from this gene. These transcripts encode at least three isoforms (isoform-I, -II and -III), which share a kinase domain, a fibronectin type III motif and an immunoglobulin C2 motif. However, regulatory regions differ between isoform-I/II and -III due to the alternative splicing of the exon encoding a CaM-binding domain. As a result, isoform-I and -II are Ca2+/CaM-dependent forms, whereas isoform-III is a Ca2+/CaM-independent form. Northern blotting and in situ hybridization showed that the expressions of these isoforms are distinctly regulated in stage- and tissue-dependent manners. Isoform-I seems to be expressed ubiquitously, while isoform-III is expressed predominantly in muscle tissues. In contrast to these isoforms, isoform-II is specific to late pupa and adult.

CONCLUSION

In Drosophila, a single MLCK gene produces multiple isoforms whose regulatory regions and expression patterns are different. These differences suggest various cellular functions of MLCK in Drosophila.

Cell cycle-dependent phosphorylation of smooth muscle myosin light chain in sea urchin egg extracts

We studied enzymatic activities in sea urchin egg extracts that phosphorylate myosin regulatory light chain (MRLC) from chicken gizzard smooth muscle. The activity in the presence of EGTA showed cell cycle-dependent changes similar to that of histone H1 kinase, namely, it peaked shortly before cleavage, while that in the presence of Ca2+ ions did not show significant change during division cycle. Phosphopeptide mapping revealed that both the sites phosphorylatable by smooth muscle myosin light chain kinase (MLCK sites) and the sites phosphorylatable by protein kinase C (PKC sites) were phosphorylated in the presence or absence of Ca2+ ions. By analyses using an inhibitor of cdc2 kinase, butyrolactone-I, and ion exchange column chromatography, at least three kinases were detected as kinases that phosphorylate MRLC in vitro. These kinases phosphorylated distinct sites on MRLC. The first one, which phosphorylated the PKC sites, was identified as cdc2 kinase. The second one phosphorylated the MLCK sites in the absence of Ca2+ ions. The third one phosphorylated unknown sites. Possible implication of these activities in regulation of cytokinesis is discussed.

Isolation and sequencing of two cDNA clones encoding Rho proteins from the fission yeast Schizosaccharomyces pombe

The rho genes encode a group of low-molecular-weight GTP-binding proteins that show about 30% identity in the amino-acid sequence to the ras gene product. Two cDNA clones, both of which are similar to the rho genes, were isolated from a cDNA library of the fission yeast Schizosaccharomyces pombe, using the human rhoA cDNA as a probe. These genes were called rho1+ and rho2+. The encoded Rho1 protein showed 72.7% identity to the budding yeast RHO1 and 66.8% to human RhoA, and the encoded Rho2 protein showed 53.2% identity to the budding yeast RHO2 and RhoA.

Cleavage furrow: timing of emergence of contractile ring actin filaments and establishment of the contractile ring by filament bundling in sea urchin eggs

Cleavage furrow formation at the first cell division of sea urchin and sand dollar eggs was investigated in detail by fluorescence staining of actin filaments with rhodamine-phalloidin of either whole eggs or isolated egg cortices. Cortical actin filaments were clustered at anaphase and then the clusters became fibrillar at the end of anaphase. The timing when the contractile ring actin filaments appear was precisely determined in the course of mitosis: accumulation of the contractile ring actin filaments at the equatorial cell cortex is first noticed at the beginning of telophase (shortly before furrow formation), when the chromosomal vesicles are fusing with each other. The accumulated actin filaments were not well organized at the early stage but were organized into parallel bundles as the furrowing progressed. The bundles were finally fused into a tightly packed filament belt. Wheat germ agglutinin (WGA)-binding sites were distributed on the surface of the egg in a manner similar to the actin filaments after anaphase. The WGA-binding sites became accumulated in the contractile ring together with the contractile ring actin filaments, indicating an intimate relationship between these sites and actin filament-anchoring sites on the plasma membrane. Myosin also appeared in the contractile ring together with the actin filaments. The ‘cleavage stimulus’, a signal hypothesized by Rappaport (reviewed by R. Rappaport (1986) Int. Rev. Cytol. 105, 245–281) was suggested to induce aggregation or bundling of the actin filaments in the cortical layer.

C/A dynein isolated from sea urchin sperm flagellar axonemes. Enzymatic properties and interaction with microtubules

C/A dynein is a novel dynein isolated from sea urchin sperm flagellar axonemes. It is composed of C and A heavy chains and some additional lower molecular mass polypeptide chains. The characterization of ATPase activity and the interaction of this dynein with microtubules polymerized from calf brain tubulin were investigated in this study. The ATPase activity of C/A dynein (0.3-0.4 mumol Pi/min per mg) was about one half that of outer arm 21 S dynein (0.6-0.8 mumol Pi/min per mg) at 25 degrees C. Vanadate inhibited the ATPase activity with a half-maximal inhibition at 1 microM. C/A dynein absorbed to the glass surface was able to translocate the microtubules towards its plus end. The velocity of the microtubule movement in the presence of 1 mM ATP was 4.0 to 4.5 microns/s at 22 degrees C. C/A dynein binds to and bundles the microtubules even in the presence of ATP. Cross-bridges were found between adjacent microtubules in the bundle with an axial periodicity of about 24 nm. The ATPase activity of C/A dynein was enhanced up to several-fold by the microtubules at concentration as low as 1 mg/ml. On the other hand, 21 S dynein bound to the microtubules with 24 nm axial periodicity only in the absence of ATP. Its ATPase activity was not activated by the microtubules. From these results, it is concluded that the manner of interaction with microtubules of C/A dynein is different from that of the outer arm dynein.

C/A dynein isolated from sea urchin sperm flagellar axonemes. Enzymatic properties and interaction with microtubules

C/A dynein is a novel dynein isolated from sea urchin sperm flagellar axonemes. It is composed of C and A heavy chains and some additional lower molecular mass polypeptide chains. The characterization of ATPase activity and the interaction of this dynein with microtubules polymerized from calf brain tubulin were investigated in this study. The ATPase activity of C/A dynein (0.3-0.4 mumol Pi/min per mg) was about one half that of outer arm 21 S dynein (0.6-0.8 mumol Pi/min per mg) at 25 degrees C. Vanadate inhibited the ATPase activity with a half-maximal inhibition at 1 microM. C/A dynein absorbed to the glass surface was able to translocate the microtubules towards its plus end. The velocity of the microtubule movement in the presence of 1 mM ATP was 4.0 to 4.5 microns/s at 22 degrees C. C/A dynein binds to and bundles the microtubules even in the presence of ATP. Cross-bridges were found between adjacent microtubules in the bundle with an axial periodicity of about 24 nm. The ATPase activity of C/A dynein was enhanced up to several-fold by the microtubules at concentration as low as 1 mg/ml. On the other hand, 21 S dynein bound to the microtubules with 24 nm axial periodicity only in the absence of ATP. Its ATPase activity was not activated by the microtubules. From these results, it is concluded that the manner of interaction with microtubules of C/A dynein is different from that of the outer arm dynein.

Isolation and characterization of a novel dynein that contains C and A heavy chains from sea urchin sperm flagellar axonemes

A novel dynein (C/A dynein), which is composed of C and A heavy chains, two intermediate chains and several light chains, was isolated from sea urchin sperm flagella. The C/A dynein was released by the treatment with 0.7 M NaCl plus 5 mM ATP from the axonemes depleted of outer arm 21 S dynein. Sedimentation coefficient of this dynein was estimated by sucrose density gradient centrifugation to be 22–23 S. The C/A dynein particle appeared to be composed of three distinct domains; two globular head domains and one rod domain as seen by negative staining electron microscopy. The mobility of ‘A’ heavy chain of C/A dynein on SDS-gel electrophoresis was similar to that of A heavy chains (A alpha and A beta) of 21 S dynein. However, UV-cleavage patterns of C and A heavy chains of C/A dynein were different from those of A heavy chains of 21 S dynein. Furthermore, an antiserum raised against A heavy chain of C/A dynein did not crossreact with A heavy chains of 21 S dynein. Under the conditions in which the C/A dynein was released, some of inner arms were removed concomitantly from axonemes as observed by electron microscopy. These results suggested that C/A dynein is a component of the inner arms.

A rho-like protein is involved in the organisation of the contractile ring in dividing sand dollar eggs

Sand dollar eggs were microinjected with botulinum C3 exoenzyme, an ADP-ribosyltransferase from Clostridium botulinum that specifically ADP-ribosylates and inactivates rho proteins. C3 exoenzyme microinjected during nuclear division interfered with subsequent cleavage furrow formation. No actin filaments were detected in the equatorial cortical layer of these eggs by rhodamine-phalloidin staining. When microinjected into furrowing eggs, C3 exoenzyme rapidly disrupted the contractile ring actin filaments and caused regression of the cleavage furrows. C3 exoenzyme had no apparent effect on nuclear division, however, and multinucleated embryos developed from the microinjected eggs. By contrast, C3 exoenzyme did not affect the organisation of cortical actin filaments immediately after fertilisation. Only one protein (molecular weight 22,000) was ADP-ribosylated by C3 exoenzyme in the isolated cleavage furrow. This protein co-migrated with ADP-ribosylated rhoA derived from human platelets when analysed by two-dimensional gel electrophoresis. These results strongly suggest that a rho-like, small GTP-binding protein is selectively involved in the organisation and maintenance of the contractile ring.

45K actin filament-severing protein from sea urchin eggs: interaction with phosphatidylinositol-4,5-bisphosphate

An actin filament-severing activity of 45K protein isolated from sea urchin eggs was abolished when this protein was incubated with phosphatidylinositol-4,5-bisphosphate (PIP2). This effect was specific to PIP2 since phosphatidylinositol, phosphatidylinositol-4-monophosphate, inositol-1,4,5-trisphosphate, and phosphatidylserine did not show such an effect at the same concentration. Digestion of PIP2 with phospholipase C eliminated the effect. On the other hand, PIP2 did not affect either the formation of 45K protein-actin complex or actin filament-capping activity of the complex. Possible implication of the binding of PIP2 to 45K protein in cytoskeleton formation after fertilization of sea urchin eggs is discussed.

Calyculin A induces contractile ring-like apparatus formation and condensation of chromosomes in unfertilized sea urchin eggs

Calyculin A, a protein phosphatase inhibitor, induced cleavage-like morphological change in unfertilized sea urchin eggs. A contractile ring-like apparatus containing both filamentous actin and myosin was formed in the cleavage furrow. Wheat germ agglutinin receptors were also found in the same region. The eggs did not develop further after constriction of the ring. No aster-like microtubular structure was found in the calyculin A-treated eggs. The cleavage was not inhibited by the antimicrotubule drug griseofulvin. Calyculin A also increased histone H1 kinase activity and induced chromosome condensation. These changes also occurred in the presence of emetine (an inhibitor of protein synthesis) and aphidicolin (an inhibitor of DNA synthesis). It is suggested that calyculin A induced these changes in the sea urchin eggs by inhibiting the activity of protein phosphatase 1.

Homologous recombination at c-fyn locus of mouse embryonic stem cells with use of diphtheria toxin A-fragment gene in negative selection

In attempting to produce a mutant mouse with embryonic stem cells, the critical step is the efficient isolation of homologous recombinants; the frequency of the homologous recombination is usually low and the potency of the cells to differentiate into germ cells is unstable in culture. Here, we report an efficacious method for such isolation in which the diphtheria toxin A-fragment gene is used to negatively select nonhomologous recombinants. In contrast to the use of the herpes simplex virus thymidine kinase gene, the selection can be made singly by the neomycin analog G418 without using a drug such as ganciclovir, a nucleoside analog. At the c-fyn locus, the diphtheria-toxin negative selection enriched the recombinants about 10-fold, and half of the cells integrating with the neomycin phosphotransferase gene were homologous recombinants.

Primary structure of profilins from two species of Echinoidea and Physarum polycephalum

Profilin is a small G-actin-binding protein, the amino acid sequence of which was previously reported for calf, human, Acanthamoeba and yeast. Here the amino acid sequences of three profilins obtained from eggs of two species of Echinoidea, Clypeaster japonicus (order, Clypeasteroida) and Anthocidaris crassispina (order, Echinoida), and plasmodium of Physarum polycephalum were determined. Two echinoid profilins were composed of 139 amino acid residues, N-termini were acylated and the molecular mass was calculated to be 14.6 kDa, slightly larger than that of 13 kDa estimated by SDS/PAGE [Mabuchi, I. & Hosoya, H. (1982) Biomed. Res. 3, 465-476]. On the other hand, Physarum profilin was composed of 124 amino acid residues, the N-terminus was acylated, and the calculated molecular mass was 13132 Da. The sequences of C. japonicus and A. crassispina profilins were homologous (84% identical). However, the similarity of these profilins with those form other organisms was low. The sequence of Physarum profilin was homologous with Acanthamoeba profilin isoforms (51% identical) and with yeast profilin (42% identical), but not with other profilins. The relatively conservative sequence of profilins from yeast, Physarum, Acanthamoeba, echinoid eggs and mammalian cells was found in the N-terminal region, which was suggested to be a common actin-binding region. The C-terminal region was also conserved, although to a lesser extent than the N-terminal region.

The cAMP-dependent protein kinase in sea urchin sperm tails: association of the enzyme with the flagellar axonemes

When sea urchin spermatozoa were treated with a Triton X-100 solution, cAMP-dependent protein kinase (cA-kinase) activity was extracted. Further extraction with Triton X-100 of axonemes isolated from the Triton-extracted sperm again released a considerable amount of the cA-kinase activity. The activity which remained after extraction three times with Triton X-100 was released by treatment with a low salt solution. These activities found in the various extracts were likely to be due to the same cA-kinase, which was a mammalian type II-like enzyme. The cA-kinase activity that remained in the axonemes after the first Triton X-100 extraction may be involved in the regulation of flagellar movement in the Triton-extracted sperm.

End-label fingerprintings show that an N-terminal segment of depactin participates in interaction with actin

A 1:1 complex of actin and depactin, an actin-depolymerizing protein isolated from starfish oocytes [Mabuchi, I. (1983) J. Cell Biol. 97, 1612-1621], was cross-linked with 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide (EDC) to introduce covalent bonds at their contact site. Locations of cross-linking sites were identified along the depactin sequence by the end-label fingerprinting, which employed site-directed antibodies against the N- and C-termini of depactin as end labels. Mappings with these end labels have revealed that the N-terminal segment of depactin (residues 1-20) contains sites in contact with the N- and C-terminal segments of actin, both of which participate in interaction with depactin [Sutoh, K., & Mabuchi, I. (1986) Biochemistry 25, 6186-6192].

The amino acid sequence, immunofluorescence and microinjection studies on the 15 kDa calcium-binding protein from sea urchin egg

The 15 kDa protein is the most abundant low molecular weight Ca2+-binding protein, different from calmodulin, in eggs of sea urchin, Hemicentrotus pulcherrimus. The data from the amino acid sequence demonstrated that the 15 kDa protein belonged to the troponin C superfamily. Based on immunofluorescent and immunomicroscopic observations, we showed that the 15 kDa protein localized in the nuclei of fertilized eggs and mitotic apparatus of dividing eggs. Microinjection of the antibody against 15 kDa protein into sea urchin blastomeres resulted in the arresting of cell division. These results suggest that the 15 kDa protein plays an important role in mitosis of sea urchin egg.

Cleavage furrow isolated from newt eggs: contraction, organization of the actin filaments, and protein components of the furrow

The cleavage-furrow region was isolated surgically from newt eggs at the early stage of the first cleavage. The isolated furrow contracted in the presence of ATP at a Ca2+ concentration of 10 or 100 nM, although the speed was less than that of the furrow in vivo. Cytochalasin B, cytochalasin D, phalloidin, p-chloromercuribenzoate, and N-ethyl-maleimide interfered with the contraction, but colchicine did not. The furrow contained bundles of actin filaments of opposite polarities oriented parallel to the long axis of the furrow; these bundles may be the main component of the contractile arc. From electron microscopic observation of thin sections of the furrow, it was suggested that the actin bundles of the contractile arc were organized from preexisting cortical filaments that were connected to the plasma membrane by granular materials at their barbed ends. Contractile-arc actin filaments were revealed to be crosslinked by thin strands by the rapid freezing/deep etching-replication technique. Two-dimensional polyacrylamide gel electrophoresis showed that several proteins found in the furrow cortex are absent from the cortical layer before the cleavage furrow is formed.

A novel actin filament-capping protein from sea urchin eggs: a 20,000-molecular-weight protein-actin complex

A novel protein factor which reduced the low-shear viscosity of rabbit skeletal muscle actin was purified from a 0.6 M KCl-extract of an insoluble fraction of sea urchin eggs by ammonium sulfate fractionation, gel filtration column chromatography, DNase I column chromatography, and hydroxylapatite column chromatography. This protein factor was shown to be a one-to-one complex of a 20,000-molecular-weight protein and egg actin. This protein complex accelerated the initial rate of actin polymerization, but reduced the steady-state viscosity of F-actin. It inhibited at substoichiometric amounts the elongation of actin filaments on sonicated F-actin fragments and depolymerization of F-actin induced by dilution. In addition, it increased the critical concentration of actin for polymerization. All these effects of this protein complex on actin could be explained by the "capping the barbed end" of the actin filament by the complex. The 20,000-molecular-weight protein which was separated from actin also possessed the barbed end-capping activities, but differed from the complex in that it did not accelerate the polymerization of actin.

Localization and possible function of 20 kDa actin-modulating protein (actolinkin) in the sea urchin egg

We have previously described a novel actin-capping protein, a 20,000-molecular weight protein (20K protein)-actin complex (20K-A) isolated from sea urchin eggs. In the present study, the localization and possible function of this 20K protein were investigated. The 20K protein was localized in the sea urchin egg cortex. Its distribution in the cortex as revealed by immunofluorescence microscopy did not change during or after fertilization up to the first mitosis, but it was concentrated to some extent in the cleavage furrow region. Exogenously added actin polymerized on the cortex isolated from unfertilized egg; however, actin did not polymerize on the cortex extracted with 0.6 M KCl, that is, the cell membrane, which lost the 20K protein. The cell membrane preincubated with 20K-A restored the activity to grow actin filaments. When decorated with myosin subfragment 1, almost all the actin filaments showed the arrowhead configuration pointing away from the membrane, indicating that they were connected to the membrane at their barbed ends. These results strongly suggest that the 20K protein connects actin filaments to the plasma membrane of sea urchin eggs. Because of this property we call this protein "actolinkin".

Amino acid sequence of starfish oocyte depactin

The amino acid sequence of starfish oocyte depactin was determined by aligning lysyl endopeptidase, Staphylococcus aureus V8 protease, and cyanongen bromide peptides. Starfish oocyte depactin is composed of 150 amino acid residues and the N terminus is free proline. The molecular weight is calculated to be 17,590, in good agreement with the value estimated by sodium dodecyl-polyacrylamide gel electrophoresis. Prediction of the secondary structure shows that depactin contains 64% alpha-helix. Comparison of depactin sequence with those of other proteins shows no significant similarity.

Accumulation of fluorescently labeled actin in the cortical layer in sea urchin eggs after fertilization

Actin from sea urchin eggs was fluorescently labeled with fluorescein isothiocyanate (FITC), N-(7-dimethylamino-4-methylcoumarinyl)-maleimide (DACM), or 5-iodoacetamidofluorescein (IAF) and microinjected into sea urchin eggs and oocytes. It distributed evenly in the cytoplasm of unfertilized eggs. Upon fertilization, actin accumulated first around the sperm binding site and, soon afterwards, in the fertilization cone. The accumulation propagated all over the cortex after a latent period of 10-20 sec. In the case of Clypeaster japonicus eggs, propagation of the accumulation coincided with a shape change in the egg, suggesting that the accumulated actin in the cortex generates forces. FITC-actin was incorporated into microvilli and retained in the cortex after cleavage. On the other hand, DACM- or IAF-actin was not incorporated into microvilli and was dispersed from the cortex by cleavage. These differences may be attributable to differences in the properties of the actins labeled at different sites. After photobleaching by laser light irradiation, FITC- or IAF-actin redistributed in the cortex of fertilized egg as quickly as it did before fertilization. When an unfertilized egg was injected with both actin and a calcium buffer (intracellular free Ca2+ concentration 9 microM), the actin accumulation was similar to that during fertilization but without the latent period. This suggests that the accumulation depended on the increase in the intracellular free Ca2+ concentration. When the unfertilized egg was injected with 0.2 M EGTA after injection of labeled actin and then inseminated, it accumulated only in the protrusion of cytoplasm where the sperm had entered, and fertilization was not completed. In immature oocytes, the accumulation was observed in the cortical region, including the huge protrusion of the cytoplasm where the sperm had entered. These results suggest that actin accumulation in the sperm binding site plays an important role in the sperm reception mechanism of the egg.

A 250K-molecular-weight actin-binding protein from actin-based gels formed in sea urchin egg cytoplasmic extract

The actin-based gel formed at 35 degrees C in the cytoplasmic extract from eggs of a sea urchin, Tripneustes gratilla, contains several high-molecular-weight proteins. Among them, the 250K-molecular-weight protein was isolated and characterized. This protein migrated slightly more slowly than filamin from chicken gizzard upon polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. It reacted only very weakly with antibodies against chicken gizzard filamin or against a high-molecular-weight actin-binding protein from Physarum plasmodia. It did not react with antibodies against chicken erythrocyte alpha-spectrin nor against the 220K protein from the same egg. A chemical crosslinking experiment revealed the presence of dimers in the purified 250K protein preparation. A rotary shadowed specimen of such a preparation showed wavy single-stranded molecules 120-170 nm long, having five to six globular domains, which may represent dimers. The appearance was different from that of spectrin or actin-binding protein from macrophage or chicken gizzard filamin. This protein increased the viscosity of F-actin solution. It bound to F-actin preferably at low KCl concentrations such as 20 mM. The binding ability was not influenced by pH between 6.0 and 7.5, although it was somewhat reduced above pH 8.0. The binding was insensitive to low Ca ion concentrations. Electron microscopy using the negative staining technique supported the idea that this protein crosslinks actin filaments. In addition, a second protein from egg gels, with a reported molecular weight of about 220K (Kane, R.E., J. Cell Biol. 66, 305-315 (1975)), comigrated with human erythrocyte alpha-spectrin on an SDS-gel and reacted with antibodies against chicken erythrocyte alpha-spectrin. This suggests that this protein is a sea urchin egg spectrin. The role of these proteins in the cytoskeleton formation in the sea urchin egg is discussed.