HMW-2, the Sertoli cell cytoplasmic dynein from rat testis, is a dimer composed of nearly identical subunits

Lis1 restricts the conformational changes in cytoplasmic dynein on microtubules

Cytoplasmic dynein is a microtubule-based motor protein that transports intracellular cargo and performs various functions during cell division. We previously reported that Lis1 suppressed dynein motility on microtubules in an idling state. Recently, a model showed that Lis1 prevents the ATPase domain of dynein from transmitting a detachment signal to its microtubule-binding domain. However, conformational information on dynein is limited. We used electron microscopy to investigate the conformation of dynein and nucleotide-induced conformational changes on microtubules. The conformation of dynein differed depending on the presence or absence of a nucleotide. In the presence of the nucleotide ADP-vanadate, dynein displayed an extended form on microtubules (extended form), whereas in the absence of a nucleotide, dynein lay along microtubules (compact form). This conformational change reflects chemomechanical coupling in dynein walking on microtubules. We also found that Lis1 fixed the conformation of dynein in the compact form regardless of the nucleotide condition. Removal of the Lis1 dimerization motif abolished Lis1-dependent fixation of dynein in the compact form. This suggests that the idling state of dynein on microtubules induced by Lis1 occurs through the Lis1-dependent arrest of dynein chemomechanical coupling.

The Drosophila cyst stem cell lineage: Partners behind the scenes?

In all animals, germline cells differentiate in intimate contact with somatic cells and interactions between germline and soma are particularly important for germline development and function. In the male gonad of Drosophila melanogaster, the developing germline cells are enclosed by somatic cyst cells. The cyst cells are derived from cyst stem cells (CySCs) of somatic origin and codifferentiate with the germline cells. The fast generation cycle and the genetic tractability of Drosophila has made the Drosophila testis an excellent model for studying both the roles of somatic cells in guiding germline development and the interdependence of two separate stem cell lineages. This review focuses on our current understanding of CySC specification, CySC self-renewing divisions, cyst cell differentiation, and soma-germline interactions. Many of the mechanisms guiding these processes in Drosophila testes are similarly essential for the development and function of tissues in other organisms, most importantly for gametogenesis in mammals.

Neurodegenerative mutation in cytoplasmic dynein alters its organization and dynein-dynactin and dynein-kinesin interactions

A single amino acid change, F580Y (Legs at odd angles (Loa), Dync1h1^Loa), in the highly conserved and overlapping homodimerization, intermediate chain, and light intermediate chain binding domain of the cytoplasmic dynein heavy chain can cause severe motor and sensory neuron loss in mice. The mechanism by which the Loa mutation impairs the neuron-specific functions of dynein is not understood. To elucidate the underlying molecular mechanisms of neurodegeneration arising from this mutation, we applied a cohort of biochemical methods combined with in vivo assays to systemically study the effects of the mutation on the assembly of dynein and its interaction with dynactin. We found that the Loa mutation in the heavy chain leads to increased affinity of this subunit of cytoplasmic dynein to light intermediate and a population of intermediate chains and a suppressed association of dynactin to dynein. These data suggest that the Loa mutation drives the assembly of cytoplasmic dynein toward a complex with lower affinity to dynactin and thus impairing transport of cargos that tether to the complex via dynactin. In addition, we detected up-regulation of kinesin light chain 1 (KLC1) and its increased association with dynein but reduced microtubule-associated KLC1 in the Loa samples. We provide a model describing how up-regulation of KLC1 and its interaction with cytoplasmic dynein in Loa could play a regulatory role in restoring the retrograde and anterograde transport in the Loa neurons.

Genetic analysis of the cytoplasmic dynein subunit families

Cytoplasmic dyneins, the principal microtubule minus-end-directed motor proteins of the cell, are involved in many essential cellular processes. The major form of this enzyme is a complex of at least six protein subunits, and in mammals all but one of the subunits are encoded by at least two genes. Here we review current knowledge concerning the subunits, their interactions, and their functional roles as derived from biochemical and genetic analyses. We also carried out extensive database searches to look for new genes and to clarify anomalies in the databases. Our analysis documents evolutionary relationships among the dynein subunits of mammals and other model organisms, and sheds new light on the role of this diverse group of proteins, highlighting the existence of two cytoplasmic dynein complexes with distinct cellular roles.

Dissociation of double-headed cytoplasmic dynein into single-headed species and its motile properties

Cytoplasmic dynein is a minus-end directed microtubule motor and plays important roles in the transport of various intracellular cargoes. Cytoplasmic dynein comprises two identical heavy chains and forms a dimer (double-headed dynein); the total molecular weight of the cytoplasmic dynein complex is about 1.5 million. The dynein motor domain is structurally very different from those of kinesin and myosin, and our understanding of the mechanisms of dynein energy transduction is limited mainly because of the difficulty in obtaining a sufficient quantity of purified and active cytoplasmic dynein. We purified cytoplasmic dynein, which was free from dynactin and other dynein-associated proteins. The purified cytoplasmic dynein was active in an in vitro motility assay. The controlled dialysis of the purified dynein against 4 M urea resulted in its complete dissociation into monomeric species (single-headed dynein). The separation of the dynein heads by the treatment was reversible. The MgATPase activities of the single-headed and reconstituted double-headed dynein were comparable to that of intact dynein. The double-headed dynein bundled microtubules in the absence of ATP; the single-headed dynein did not. The single-headed dynein produced in vitro microtubule-gliding motility at velocities very similar to those of double-headed dynein at various ATP concentrations. These results indicate that a single cytoplasmic dynein heavy chain is sufficient to produce robust microtubule motility. Application of the double- and single-headed dynein molecules in various assay systems will elucidate the mechanism of action of the cytoplasmic dynein.

2,5-hexanedione-induced testicular injury

Now in its third decade of mechanistic investigation, testicular injury caused by 2,5-hexanedione (2,5-HD) exposure is a well-studied model with a rich database. The development of this model reflects the larger changes that have moved biology from a branch of chemistry into the molecular age. Critically examined in this review is the proposed mechanism for 2,5-HD-induced testicular injury in which germ cell maturation is disrupted owing to alterations in Sertoli cell microtubule-mediated functions. The goal is to evaluate the technical and conceptual approaches used to assess 2,5-HD-induced testicular injury, to highlight unanswered questions, and to identify fruitful avenues of future research.

Functional diversity of axonemal dyneins as studied in Chlamydomonas mutants

Cilia and flagella of most organisms are equipped with two kinds of motor protein complex, the inner and outer dynein arms. The two arms were previously thought to be similar to each other, but recent studies using Chlamydomonas mutants indicate that they differ significantly in subunit structure and arrangement within the axoneme. For example, whereas the outer dynein arm exists as a single protein complex containing three heavy chains, the inner dynein arm comprises seven different subspecies each containing one or two discrete heavy chains. Furthermore, the two kinds of arms appear to differ in function also. Most strikingly, our studies suggest that inner-arm dynein, but not outer-arm dynein, is under the control of the central pair microtubules and radial spokes. The axoneme thus appears to be equipped with two rather distinct systems for beating: one involving inner-arm dyneins, the central pair and radial spokes, and the other involving outer-arm dynein alone.

The dynein heavy chain: structure, mechanics and evolution

The translocation of dynein along microtubules is the basis for a variety of essential cellular movements. Despite a general domain organization that is found in all the cytoskeletal motors, there are structural features of dynein that set it apart from the other motors. These include a track-binding site that is located at the tip of a long projection, and six nucleotide-binding modules that together form the globular head of dynein. These unique features suggest that dynein produces movement by a mechanism that is different from that used by the other motors.

Modulation of cytoplasmic dynein ATPase activity by the accessory subunits

The microtubule-based motor molecule cytoplasmic dynein has been proposed to be regulated by a variety of mechanisms, including phosphorylation and specific interaction with the organelle-associated complex, dynactin. In this study, we examined whether the intermediate chain subunits of cytoplasmic dynein are involved in modulation of ATP hydrolysis, and thereby affect motility. Treatment of testis cytoplasmic dynein under hypertonic salt conditions resulted in separation of the intermediate chains from the remainder of the dynein molecule, and led to a 4-fold enhancement of ATP hydrolysis. This result suggests that the accessory subunits act as negative regulators of dynein heavy chain activity. Comparison of ATPase activities of dyneins with differing intermediate chain isoforms showed significant differences in basal ATP hydrolysis rates, with testis dynein 7-fold more active than dynein from brain. Removal of the intermediate chain subunits led to an equalization of ATPase activity between brain and testis dyneins, suggesting that the accessory subunits are responsible for the observed differences in tissue activity. Finally, our preparative procedures have allowed for the identification and purification of a 1:1 complex of dynein with dynactin. As this interaction is presumed to be mediated by the dynein intermediate chain subunits, we now have defined experimental conditions for further exploration of dynein enzymatic and motility regulation.

Structural and molecular characterization of dynein in a gall-midge insect having motile sperm with only the outer arm

The dipteran Monarthropalpus flavus possesses a peculiar sperm axoneme, characterized by multiple rows of microtubular doublets linked by the outer dynein arms only, lacking any equivalent of the central pair/radial spoke complex. The structure of these dynein molecules was studied by electron microscopy (EM). Using the quick-freeze, deep-etch method of EM, they were found to be similar to outer dynein arms described previously. Two globular "heads," each subdivided by a cleft, are clearly discernible. "Stalks" extend from proximal head to contact the B-tubule of the adjacent doublet. Unlike the situation in vertebrate sperm, the stalks sometimes branch into two thinner strands that contact the B-tubule at different sites. Treatment of demembranated sperm cells with ATP and vanadate induces conformational changes in the dynein outer arms. These are interpreted as the result of rotation of the dynein head with respect to what is observed in axonemes in rigor condition (after ATP depletion). SDS-PAGE indicates that the high-molecular-weight complement of this molecule comprises a single heavy chain. Specific dynein heavy chain-related DNA sequences corresponding to the catalytic-phosphate binding region were amplified by RT-PCR. Only one axonemal dynein sequence was identified among all amplified fragments. Southern blot analysis performed on genomic DNA using this sequence as a probe identified two hybridizing genes, only one of which is able to encode a functional product. Thus, genetic analysis indicates that this axonemal outer arm dynein is a homodymer of a single heavy chain subunit. In vivo, spermatozoa of this species are stored in a rolled configuration in female spermatheca, where they move rapidly with a wave-like motion. This movement could not be reproduced in vitro, except when spermatozoa were constrained in a bent configuration by some mechanical impediment. We propose that, in the absence of both the central pair/radial spoke complex and the inner arms, a curvature-dependent activation acts to trigger motility in these spermatozoa.

Probing the nucleotide binding sites of axonemal dynein with the fluorescent nucleotide analogue 2'(3')-O-(-N-Methylanthraniloyl)-adenosine 5'-triphosphate

MantATP [2'(3')-O-(-N-methylanthraniloyl)-adenosine 5'-triphosphate] was employed as a fluorescence probe of the nucleotide-binding sites of dynein from sea urchin sperm flagella. MantATP binds specifically with enhanced fluorescence (approximately 2.2-fold), homogeneous lifetime (8.4 ns), and high anisotropy (r approximately 0.38) to dynein and can be displaced by ATP and ADP added to the medium. The association constants of mantATP complexed with dynein were determined from anisotropy titration data. Using a multiple stepwise equilibrium model, the average values of the first two association constants are K1 = 2.7 x 10(5) M-1 and K2 = 1.8 x 10(4) M-1. This value of K1 is 7-8 times higher than that found previously for unsubstituted ATP, whereas K2 is little changed [Mocz and Gibbons (1996) Biochemistry 35, 9204-9211]. The lower-affinity binding sites, K3 and K4, observed previously could not be studied with mantATP within the available protein concentrations. The alpha and beta heavy chain subfractions have binding parameters similar to those of intact dynein. Formation of the stable ternary complex of mantATP with dynein and monomeric vanadate is accompanied by only a moderate increase in the binding affinities. Oligomeric vanadate reduces the binding affinities by approximately 50%. Addition of TritonX-100, methanol, or various salts changes the binding affinities by up to 50%, suggesting that the microenvironment of the nucleotide-binding sites involves significant contributions from both polar and apolar interactions. The distinct affinities of the individual binding sites are consistent with a physiological role in regulating nucleotide binding.

Translocation of microtubules caused by the alphabeta, beta and gamma outer arm dynein subparticles of Chlamydomonas

Three kinds of subparticles of Chlamydomonas outer-arm dynein containing the alphabeta, beta and gamma heavy chains were isolated and assayed for their activities to translocate microtubules in vitro. All of them had activities to form bundles of microtubules in solution in an ATP-dependent manner and, when adsorbed on an appropriate glass surface, translocated microtubules. The alphabeta subparticle readily translocated microtubules on a silicone-coated glass surface with a velocity of 4.6 micron/second at 1 mM ATP. The beta subparticle translocated microtubules after it had been preincubated with tubulin dimer and when the Brownian movement of microtubules was suppressed by addition of methylcellulose. The velocity was on average 0.7 micron/second. The gamma subparticle translocated microtubules after being preincubated with tubulin dimer and adsorbed onto a silicone-coated glass surface. The velocity was about 3.8 micron/second. The tubulin dimer appeared to facilitate in vitro motility by blocking the ATP-insensitive binding of dynein subparticles to microtubule. The alphabeta, beta and gamma subparticles were thus found to have different properties as motor proteins. In addition, these subparticles showed different dependencies upon the potassium acetate concentration. Hence the outer-arm dynein of Chlamydomonas is a complex of motor proteins with different properties.

Structural characterization of a dynein motor domain

Cytoplasmic dynein is a microtubule-based mechanochemical protein that plays an essential role in cell division, vesicle transport, and cytoplasmic membrane organization. As a molecular motor, dynein utilizes an ATP hydrolysis mechanism to bind and release microtubules and to undergo conformational changes that result in a net displacement towards the microtubule's minus end. To visualize structural features of this motor protein, we have begun to characterize the dynein head domain by electron microscopy and image processing. Transmission electron microscopy of negatively stained native dynein from Dictyostelium has been performed and images of the head domain have been aligned and analyzed with the software SPIDER. The resulting 2D averages show an oblong round shape composed of seven to eight globular domains or lobes that encircle a stain-filled area. A recombinant 380 kDa fragment of the dynein heavy chain encodes just the globular head domain; analysis of these particles reveals a high structural similarity with the native head domain. A prominent stalk can be seen in several projections of this fragment, suggesting a structure analogous to the B-link described for some axonemal dyneins. Single tilt pair images were used to compute low resolution 3D reconstructions of the dynein head domain. These show a flattened spheroidal shape of 13.5 nm in length with seven similar domains arranged in a ring. Slices through the reconstructions reveal a large central cavity. This is the first detailed description of the head domain structure for a dynein molecule. The presence of a central cavity and the outer globular features, along with its large size make dynein structurally distinct from either myosin or kinesin.

Evidence for four cytoplasmic dynein heavy chain isoforms in rat testis

Recent studies have revealed the expression of multiple putative cytoplasmic dynein heavy chain (DHC) genes in several organisms, with each gene encoding a separate protein isoform. This finding is consistent with the hypothesis that different isoforms do different things, as is the case for the axonemal dyneins. Furthermore, the large number of tasks ascribed to cytoplasmic dynein suggests that there may be additional isoforms not yet identified. Two of the mammalian cytoplasmic dynein heavy chains are DHC1a and DHC1b. DHC1a is conventional cytoplasmic dynein and is found in all organisms examined. DHC1b is expressed in organisms that have multiple dyneins, and has been implicated in the intracellular trafficking of molecules in unciliated and ciliated cells. In the present study, we examined the DHC1b protein from rat testis. Testis cytoplasmic dynein contains a large amount of dynein heavy chain reactive with an antibody raised against a peptide sequence of rat DHC1b. The testis anti-DHC1b immunoreactive protein is slightly smaller than testis DHC1a, as assessed by SDS-PAGE. In Northern blots, the DHC1b mRNA is smaller than the DHC1a mRNA. In sucrose gradients made in low ionic strength, DHC1a sedimented at approximately 20S, and the anti-1b immunoreactive heavy chains sedimented in a broad band centered at approximately 14S. The V1-photolysis reaction of individual sucrose gradient fractions revealed three distinct patterns of photolysis, suggesting that there are at least three separate 1b-like heavy chain isoforms in testis. Using a high-stringency Western blotting protocol, the anti-1b antibody and the anti-DHC2 antibody recognized the same heavy chain and specifically bound to one of the three 1b-like heavy chains. We conclude that rat testis contains three 1b-like dynein heavy chains, and one of these is the product of the DHC1b/DHC2 gene previously identified.

Phase partition analysis of nucleotide binding to axonemal dynein

The binding of nucleoside triphosphates and related ligands to dynein ATPase from sea urchin sperm flagella has been studied by equilibrium partition analysis in an aqueous biphasic system containing dextran and poly(ethylene glycol). The stoichiometry of binding and the corresponding stepwise binding constants are obtained from direct binding isotherms fitted to the primary data. The results suggest that dynein possesses four different binding sites for nucleoside triphosphates per mole of heavy chain. The stepwise binding constants for MgATP range from approximately 10(4) M-1 to approximately 10(5) M-1. The isolated alpha and beta heavy chains have binding parameters similar to intact dynein. The amount of ADP bound normally is approximately 75% that of ATP, both for the intact dynein and for the separated heavy chains, although full saturation is achieved at high nucleotide concentrations. In the presence of the ATPase inhibitor vanadate, ADP binds with affinities similar to those of ATP, with binding constants close to those of ATP in the absence of vanadate. No appreciable binding of AMP or EDTA/ATP is observed. The substitution of Ca2+ or Fe3+ for Mg2+ does not significantly alter the amount of ATP bound; however, CaATP is bound with a somewhat lower affinity. Scatchard and Hill plots of the binding data and the calculated site-binding constants suggest that ATP and ADP bind in a weakly cooperative manner. These results suggest that the multiple binding of nucleotide to dynein heavy chains occurs at physiological concentrations, putatively at the four binding sites predicted earlier on the basis of their amino acid sequences. The data are consistent with a model in which, in addition to a single catalytic site, nucleotide binding occurs at additional noncatalytic sites that represent an as yet unknown functional aspect of dynein.

A novel cytoplasmic dynein heavy chain: expression of DHC1b in mammalian ciliated epithelial cells

Organisms that have cilia or flagella express over a dozen dynein heavy chain genes. Of these heavy chain genes, most appear to encode axonemal dyneins, one encodes conventional cytoplasmic dynein (MAP1C or DHC1a), and one, here referred to as DHC1b, encodes an unclassified heavy chain. Previous analysis of sea urchin DHC1b (Gibbons et al. (1994) Mol. Biol. Cell 5, 57–70) indicated that this isoform is either an axonemal dynein with an unusual protein sequence or a cytoplasmic dynein whose expression increases during ciliogenesis. In the present study, we examined the expression of DHC1b in rat tissues. The DHC1b gene is expressed in all tissues examined, including unciliated liver and heart cells. In contrast, rat axonemal dyneins are only expressed in tissues that produce cilia or flagella. In cultured rat tracheal epithelial (RTE) cells, DHC1b is expressed in undifferentiated cells and increases in expression during ciliogenesis. In contrast, the expression of conventional cytoplasmic dynein, DHC1a, does not change during RTE differentiation and axonemal dynein is not expressed until after differentiation commences. In order to examine the expression of DHC1b protein, we produced an isoform-specific antibody to a synthetic peptide derived from the rat DHC1b sequence. The antibody demonstrated that DHC1b is a relatively minor component of partially purified cytoplasmic dynein. Indirect immunofluorescence microscopy revealed that DHC1b is not detected in cilia and remains in the cytoplasm of ciliated RTE cells, often accumulating at the apical ends of the cells. These results suggest that DHC1b is a cytoplasmic dynein that may participate in intracellular trafficking in polarized cells.

Differential expression and phosphorylation of the 74-kDa intermediate chains of cytoplasmic dynein in cultured neurons and glia

The 74-kDa intermediate chains (IC74) of the cytoplasmic dynein complex are believed to be involved in the association of dynein with membranous organelles. While each dynein molecule is thought to have two or three IC74 subunits, at least six different IC74 protein isoforms were found in dynein from brain. Therefore we investigated the relationships of the brain cytoplasmic dynein IC74 isoforms and their association in the dynein complex at the cellular level. We found that cultured cortical neurons and glia express distinct IC74 isoforms. The IC74 isoform pattern observed in dynein from cortical neurons was generally similar to that found in dynein from adult brain, indicating that there are different populations of cytoplasmic dynein in neurons. Two IC74 isoforms were observed on two-dimensional gels of dynein from glia, while a single glial IC74 mRNA was detected. Metabolic labeling of glial dynein with 32P followed by treatment of the isolated dynein with phosphatase in vitro demonstrated that one of the glial IC74 isoforms is the product of the single glial IC74 mRNA and that the other is its phosphoisoform. A single mRNA product and its phosphoisoform are therefore sufficient for constitutive dynein function and regulation in glial cells.

Microtubule-independent phospholipid stimulation of cytoplasmic dynein ATPase activity

In this study we report that phospholipid vesicles activate ATP hydrolysis by cytoplasmic dynein but not kinesin, consistent with reported differences in the organelle/vesicle binding of these motor proteins. Dynein activation by phospholipids was comparable with that seen in the presence of microtubules but was not sensitive to moderate salt concentrations and was independent of the net charge of the phospholipid, suggesting that the means of interaction between dynein and the lipid vesicle was not strictly ionic in nature. Based on this result, previous data that show that the interaction between dynein and vesicles is not ATP sensitive, and the concentration dependence observed for lipid activation of cytoplasmic dynein, it is likely that the binding interaction between dynein and liposomes is a stable one. In contrast to a previous report, microtubules increased the hydrolysis rate of all naturally occurring nucleotides tested, whereas only ATPase activity was stimulated by phospholipids. As ATP is the physiologically relevant substrate and is the only nucleotide to promote motility, the activation of only the ATPase by phospholipids may represent a means of discriminating between coupled and uncoupled nucleotide hydrolysis in vitro.

Multi-dynein hypothesis

Axonemal dyneins and cytoplasmic dynein have evolved separate strategies to perform their tasks. The multi-dynein hypothesis accurately describes the highly specialized axonemal isoforms; each isoform is encoded by a separate gene, is located in a precise place, produces specific forces which contribute to the overall generation of propagated bending, and is not functionally interchangeable with other isoforms. In contrast, cytoplasmic dynein, although carrying many different cargoes, appears to be one isoform. An intriguing question is to determine whether there are additional cytoplasmic dyneins, heretofore uncharacterized, which, like their axonemal counterparts, are customized to perform specific tasks.

Dynein family of motor proteins: present status and future questions

Analysis of sequence relationships in dynein heavy chains shows that dynein motor proteins comprise a single homologous family with three main branches, cytoplasmic dynein, axonemal dynein, and a third branch represented by DYH1B that lies between the other two. In all branches of the family the dynein heavy chain has four copies of the P-loop motif for a nucleotide-binding site spaced approximately 300 residues apart in its midregion, with the amino acid sequence GPAGTGKT in the P-loop of the hydrolytic ATP-binding site. Cytoplasmic dyneins appear more primitive in that the heavy chain usually occurs as a homodimer, with traces of the early evolution of its four P-loop motifs by gene duplication being recognizable. In the axonemal subfamily the heavy chain occurs as heterodimers or heterotrimers encoded by multiple genes, and their non-hydrolytic P-loop motifs are much more divergent with little trace of their origin by gene duplication. The DYH1B subfamily is more closely related to the cytoplasmic dyneins in sequence, but appears related to axonemal dyneins in function since it becomes upregulated during reciliation and has not been found in organisms, such as yeast and Dictyostelium, that are totally without cilia or flagella.

A cytoplasmic dynein motor in Drosophila: identification and localization during embryogenesis

We have characterized a cytoplasmic dynein motor isoform that is present in extracts of Drosophila embryos. A prominent high molecular weight (HMW) polypeptide (> 400 kDa) is enriched in microtubules prepared from nucleotide-depleted embryonic extracts. Based on its ATP-sensitive microtubule binding activity, 20 S sedimentation coefficient, sensitivity to UV-vanadate and nucleotide specificity, the HMW polypeptide resembles cytoplasmic dyneins prepared from other organisms. The Drosophila cytoplasmic dynein acts as a minus-end motor that promotes microtubule translocation in vitro. A polyclonal antibody raised against the dynein heavy chain polypeptide was used to localize the dynein antigen in whole-mount preparations of embryos by immunofluorescence microscopy. These studies show that the dynein motor is associated with microtubules throughout embryogenesis, including mitotic spindle microtubules and microtubules of the embryonic nervous system.

The dynein genes of Paramecium tetraurelia. Sequences adjacent to the catalytic P-loop identify cytoplasmic and axonemal heavy chain isoforms

Paramecium tetraurelia is a unicellular organism that utilizes both axonemal and cytoplasmic dyneins. The highly conserved region containing the catalytic P-loop of the dynein heavy chain was amplified by RNA-directed polymerase chain reaction. Eight different P-loop-containing cDNA fragments were cloned. Southern hybridization analysis indicated that each fragment corresponds to a separate dynein gene and that there are at least 12 dynein heavy chain genes expressed in Paramecium. Seven of the eight cloned contain sequence motif A, which is found in axonemal dyneins, and one contains sequence motif B, which is found in the dyneins from cell types that do not have cilia or flagella. Two of the Paramecium dynein genes were further investigated: DHC-6 which contains motif A, and DHC-8 which contains motif B. Additional sequencing of the central portions of these genes showed that DHC-6 most closely matches sea urchin ciliary beta heavy chain and DHC-8 is similar to the cytoplasmic dynein from Dictyostelium. Deciliation of the cells resulted in a substantial increase in the steady state concentration of DHC-6 mRNA but only a small change in DHC-8 mRNA. Antisera were produced against synthetic peptides derived from sequence motifs A and B. Competitive solid-phase binding assays demonstrated that each antiserum was peptide-specific. In western blots, the antiserum to motif A reacted with both ciliary and cytoplasmic dyneins. In contrast, the antiserum to motif B reacted with the cytoplasmic dyneins of Paramecium and bovine brain but did not react with ciliary dynein.(ABSTRACT TRUNCATED AT 250 WORDS)

Association of cytoplasmic dynein with manchette microtubules and spermatid nuclear envelope during spermiogenesis in rats

During spermiogenesis, the shape of the spermatid nucleus, which is spherical, changes and it becomes the sperm head. A microtubular structure called a manchette is thought to be involved in this morphogenetic process. In this report, we demonstrate the localization of cytoplasmic dynein and manchette development by a double immunofluorescence technique using anti-bovine brain MAP 1C and anti-tubulin. Before step 6 of the Leblond and Clermont staging, the microtubules showed a fine reticular network, and the dynein staining was homogeneous. In step 6, the microtubular network was concentrated around the nucleus. The manchette developed in step 7 spermatids, and was fully formed, with a skirt-like appearance, covering the nuclear surface in step 8. Dynein fluorescence was associated with the microtubular manchette in steps 7–10. During these steps, the nucleus was protruded from the cytoplasm. In steps 11–13, the most active stages in nuclear shaping, the dynein was densely localized at the nuclear surface covered by the manchette. As the nucleus acquired a shape similar to the mature spermatozoon at step 14, the dynein fluorescence was localized only at the concave side of the nuclear caudal edge. The manchette became narrower and elongated. In step 15, the manchette extended into the elongated cytoplasm, diminishing during steps 16–18. The localization of the dynein was limited to the ventral aspect of the caudal head in these steps. There was little dynein fluorescence in mature spermatozoa. Immunoelectron microscopy showed positive reactions in the nuclear envelope and the inner region of the microtubular manchette. These observations suggest that cytoplasmic dynein, possibly bound to the nuclear envelope, and manchette microtubules are involved in the protrusion of the spermatid nucleus from the cytoplasm.

Molecular cloning of the retrograde transport motor cytoplasmic dynein (MAP 1C)

Overlapping cDNAs encoding the entire heavy chain of cytoplasmic dynein (MAP 1C) have been obtained. A 4644 amino acid polypeptide containing four ATP-binding consensus sequences is predicted. Homology with the sea urchin flagellar outer arm dynein beta heavy chain is observed within the C-terminal two-thirds of the protein. The N-terminal third of the two polypeptides shows no clear relationship, suggesting that this region of MAP 1C is responsible for its association with retrograde organelles and other functions. Northern blot analysis reveals a 16.5 kb band in brain and other tissues. Southern blot analysis is consistent with a single cytoplasmic dynein gene. Thus, in contrast with cilia and flagella, which contain numerous forms of dynein, our results are consistent with the existence of only a single cytoplasmic dynein heavy chain gene, which appears to produce only a single transcript.