Dynein from serotonin-activated cilia and flagella: extraction characteristics and distinct sites for cAMP-dependent protein phosphorylation

Clam Genome and Transcriptomes Provide Insights into Molecular Basis of Morphological Novelties and Adaptations in Mollusks

Bivalve mollusks, comprising animals enclosed in two shell valves, are well-adapted to benthic life in many intertidal zones. Clams have evolved the buried lifestyle, which depends on their unique soft tissue structure and their wedge-shaped muscular foot and long extendible siphons. However, molecular mechanisms of adaptative phenotype evolution remain largely unknown. In the present study, we obtain the high-quality chromosome-level genome of Manila clam R. philippinarum, an economically important marine bivalve in many coastal areas. The genome is constructed by the Hi-C assisted assembly, which yields 19 chromosomes with a total of 1.17 Gb and BUSCO integrity of 92.23%. The de novo assembled genome has a contig N50 length of 307.7 kb and scaffold N50 of 59.5 Mb. Gene family expansion analysis reveals that a total of 24 single-copy gene families have undergone the significant expansion or contraction, including E3 ubiquitin ligase and dynein heavy chain. The significant expansion of transposable elements has been also identified, including long terminal repeats (LTR) and non-LTR retrotransposons. The comparative transcriptomics among different clam tissues reveals that extracellular matrix (ECM) receptors and neuroactive ligand receptors may play the important roles in tissue structural support and neurotransmission during their infaunal life. These findings of gene family expansion and tissue-specific expression may reflect the unique soft tissue structure of clams, suggesting the evolution of lineage-specific morphological novelties. The high-quality genome and transcriptome data of R. philippinarum will not only facilitate the genetic studies on clams but will also provide valuable information on morphological novelties in mollusks.

Investigation of the effect of serotonin-activated semen washing medium on sperm motility at the molecular level: a pilot study

In Assisted Reproductive Technologies (ART), efficient sperm preparation is vital for successful fertilization, with washing media enhancing the process. This pilot study examines the molecular-level impact of a new serotonin-containing sperm-washing medium (Prototype) on sperm motility and ROS metabolism, comparing it with commercially available media (Origio and Irvine). Semen samples from thirty-one individuals underwent preparation using the swim-up method post-semen analysis. Each sample was separately washed with the Prototype, Origio and Irvine mediums. ROS formation was determined through flow cytometric, and AT2R and PRDX2 protein levels, associated with sperm motility, were assessed via Western blot. Statistical evaluation compared the findings among the three outlined media. Significant differences were found among three washing media in terms of total and progressive motility. The Prototype medium showed the highest increase in both total (66%) and progressive motility (59%), while the control group exhibited the lowest increases (41% and 27.7%, respectively). Regarding ROS levels, the prototype (11.5%) and Origio (10.7%) groups demonstrated a notable decrease, contrasting with Irvine (25.8%). Molecular assessment revealed a significant elevation in AT2R protein levels in the prototype medium (59%), compared to other media. Additionally, an increase in PRDX2 protein levels was observed in the prototype medium, although this didn't reach statistical significance. Serotonin-activated washing media for sperm preparation can be a suitable choice for selecting high-quality sperm in ART. A broader molecular analysis with a larger sample size is required to explore the mechanisms and effectiveness of using a serotonin-containing sperm-washing medium in routine ART.

In vitro effects of the combination of serotonin, selenium, zinc, and vitamins D and E supplementation on human sperm motility and reactive oxygen species production

Infertility affects 15% of all couples worldwide and 50% of cases of infertility are solely due to male factors. A decrease in motility in the semen is considered one of the main factors that is directly related to infertility. The use of supplementation to improve the overall sperm quality has become increasingly popular worldwide. The purpose of this study was to evaluate whether sperm motility was affected by the combination of serotonin (5-HT), selenium (Se), zinc (Zn), and vitamins D, and E supplementation. Semen samples were incubated for 75 min at 37°C in medium containing varying concentrations of 5-HT, Se, Zn, vitamin D, and E. 5-HT (200 μM), Se (2 μg/ml), Zn (10 μg/ml), vitamin D (100 nM), and vitamin E (2 mmol) have also been shown to increase progressive sperm motility. Three different mixtures of supplements were also tested for their combined effects on sperm motility and reactive oxygen species (ROS) production. While the total motility in the control group was 71.96%, this was found to increase to 82.85% in the first mixture. In contrast the average ROS level was 8.97% in the control group and decreased to 4.23% in the first mixture. Inclusion of a supplement cocktail (5-HT, Se, Zn, vitamins D and E) in sperm processing and culture medium could create an overall improvement in sperm motility while decreasing ROS levels during the incubation period. These molecules may enhance the success of assisted reproduction techniques when present in sperm preparation medium.

Role of the Neuroendocrine System of Marine Bivalves in Their Response to Hypoxia

Mollusks comprise one of the largest phylum of marine invertebrates. With their great diversity of species, various degrees of mobility, and specific behavioral strategies, they haveoccupied marine, freshwater, and terrestrial habitats and play key roles in many ecosystems. This success is explained by their exceptional ability to tolerate a wide range of environmental stresses, such as hypoxia. Most marine bivalvemollusksare exposed to frequent short-term variations in oxygen levels in their marine or estuarine habitats. This stressfactor has caused them to develop a wide variety of adaptive strategies during their evolution, enabling to mobilize rapidly a set of behavioral, physiological, biochemical, and molecular defenses that re-establishing oxygen homeostasis. The neuroendocrine system and its related signaling systems play crucial roles in the regulation of various physiological and behavioral processes in mollusks and, hence, can affect hypoxiatolerance. Little effort has been made to identify the neurotransmitters and genes involved in oxygen homeostasis regulation, and the molecular basis of the differences in the regulatory mechanisms of hypoxia resistance in hypoxia-tolerant and hypoxia-sensitive bivalve species. Here, we summarize current knowledge about the involvement of the neuroendocrine system in the hypoxia stress response, and the possible contributions of various signaling molecules to this process. We thusprovide a basis for understanding the molecular mechanisms underlying hypoxic stress in bivalves, also making comparisons with data from related studies on other species.

Effect of Air Exposure-Induced Hypoxia on Neurotransmitters and Neurotransmission Enzymes in Ganglia of the Scallop Azumapecten farreri

The nervous system expresses neuromolecules that play a crucial role in regulating physiological processes. Neuromolecule synthesis can be regulated by oxygen-dependent enzymes. Bivalves are a convenient model for studying air exposure-induced hypoxia. Here, we studied the effects of hypoxia on the expression and dynamics of neurotransmitters, and on neurotransmitter enzyme distribution, in the central nervous system (CNS) of the scallop Azumapecten farreri. We analyzed the expression of the neurotransmitters FMRFamide and serotonin (5-HT) and the choline acetyltransferase (CHAT) and universal NO-synthase (uNOS) enzymes during air exposure-induced hypoxia. We found that, in early-stage hypoxia, total serotonin content decreased in some CNS regions but increased in others. CHAT-lir cell numbers increased in all ganglia after hypoxia; CHAT probably appears de novo in accessory ganglia. Short-term hypoxia caused increased uNOS-lir cell numbers, while long-term exposure led to a reduction in their number. Thus, hypoxia weakly influences the number of FMRFamide-lir neurons in the visceral ganglion and does not affect peptide expression in the pedal ganglion. Ultimately, we found that the localization and level of synthesis of neuromolecules, and the numbers of cells expressing these molecules, vary in the scallop CNS during hypoxia exposure. This indicates their possible involvement in hypoxia resistance mechanisms.

Indolaminergic System in Adult Rat Testes: Evidence for a Local Serotonin System

Serotonin (5-HT) is member of a family of indolamine molecules that participate in a wide variety of biological processes. Despite its important role in the regulation of local blood systems, little is known about the physiological function of 5-HT in reproductive organs, its functional implications, and its role in the reproduction of mammals. In the present work, we evaluated the localization and distribution of 5-HT (using histochemical analysis of indolamines) and different components of the serotoninergic system in rat testes. We detected local synthesis and degradation through immunofluorescence and western blot analyses against the TPH1, MAO_A, 5-HT_T, and VMAT1 serotonin transporters. We also identified the localization and distribution of the 5-HT_1B, 5-HT_2A, and 5-HT_3A receptors. RT-PCR results showed the presence of the Tph1, Maoa, Slc6a4, and Htr3a genes in testes and in the brain stem (Tph1 was used as a negative control). High-performance liquid chromatography was used to determine the presence of 5-HT and the activity of tryptophan hydroxylase in testes homogenates in vitro. Our observations suggest that TPH1 activity and local 5-HT synthesis befall in rat testes. We propose that 5-HT could participate in the regulation of testosterone synthesis and in the spermatogenesis process via local serotoninergic system. However, more studies are needed before concluding that rat testes, or those of other mammals, contain an active form of tryptophan hydroxylase and produce 5-HT.

Spermatozoa motility in bivalves: Signaling, flagellar beating behavior, and energetics

Though bivalve mollusks are keystone species and major species groups in aquaculture production worldwide, gamete biology is still largely unknown. This review aims to provide a synthesis of current knowledge in the field of sperm biology, including spermatozoa motility, flagellar beating, and energy metabolism; and to illustrate cellular signaling controlling spermatozoa motility initiation in bivalves. Serotonin (5-HT) induces hyper-motility in spermatozoa via a 5-HT receptor, suggesting a serotoninergic system in the male reproductive tract that might regulate sperm physiology. Acidic pH and high concentration of K⁺ are inhibitory factors of spermatozoa motility in the testis. Motility is initiated at spawning by a Na⁺-dependent alkalization of intracellular pH mediated by a Na⁺/H⁺ exchanger. Increase of 5-HT in the testis and decrease of extracellular K⁺ when sperm is released in seawater induce hyperpolarization of spermatozoa membrane potential mediated by K⁺ efflux and associated with an increase in intracellular Ca²⁺ via opening of voltage-dependent Ca²⁺ channels under alkaline conditions. These events activate dynein ATPases and Ca²⁺/calmodulin-dependent proteins resulting in flagellar beating. It may be possible that 5-HT is also involved in intracellular cAMP rise controlling cAMP-dependent protein kinase phosphorylation in the flagellum. Once motility is triggered, flagellum beats in asymmetric wave pattern leading to circular trajectories of spermatozoa. Three different flagellar wave characteristics are reported, including "full", "twitching", and "declining" propagation of wave, which are described and illustrated in the present review. Mitochondrial respiration, ATP content, and metabolic pathways producing ATP in bivalve spermatozoa are discussed. Energy metabolism of Pacific oyster spermatozoa differs from previously studied marine species since oxidative phosphorylation synthetizes a stable level of ATP throughout 24-h motility period and the end of movement is not explained by a low intracellular ATP content, revealing different strategy to improve oocyte fertilization success. Finally, our review highlights physiological mechanisms that require further researches and points out some advantages of bivalve spermatozoa to extend knowledge on mechanisms of motility.

Phosphorylation of axonemal 21 kDa and 26 kDa proteins modulates activation of sperm motility in the ascidian, Ciona intestinalis

Protein phosphorylation is highly coupled with sperm motility activation in several animal species. The micro-tubule based flagellar motor protein, dynein, is a candidate for a phosphoprotein related to sperm activation in many animal species (Morisawa & Hayashi, 1985; Hayashi et al., 1987; Dey & Brokaw, 1991; Stephens & Prior, 1992; Inaba et al., 1998, 1999). Sperm motility of the ascidians Ciona intestinalis and C. savignyi is activated by a factor derived from unfertilised eggs named sperm activating and attracting factor (SAAF). SAAF elevates the intracellular cyclic AMP (cAMP) level by a mechanism dependent on membrane hyperpolarisation and extracellular Ca2+ (Yoshida et al., 1994; Izumi et al., 1999). Experiments using demembranated Ciona sperm showed that cAMP is required prior to ATP for the activation of axonemal movement (Opreska & Brokaw, 1983; Morisawa et al., 1984; Brokaw, 1985; Dey & Brokaw, 1991; Chaudhry et al., 1995) and that many sperm flagellar proteins including dynein light chain are phosphorylated during incubation of demembranated sperm with ATP and cAMP (Dey & Brokaw, 1991). However, there is no evidence of which proteins are phosphorylated during the SAAF-dependent activation of Ciona sperm motility.

Branchial cilia and sperm flagella recruit distinct axonemal components

Eukaryotic cilia and flagella have highly conserved 9 + 2 structures. They are functionally diverged to play cell-type-specific roles even in a multicellular organism. Although their structural components are therefore believed to be common, few studies have investigated the molecular diversity of the protein components of the cilia and flagella in a single organism. Here we carried out a proteomic analysis and compared protein components between branchial cilia and sperm flagella in a marine invertebrate chordate, Ciona intestinalis. Distinct feature of protein recruitment in branchial cilia and sperm flagella has been clarified; (1) Isoforms of α- and β-tubulins as well as those of actins are distinctly used in branchial cilia or sperm flagella. (2) Structural components, such as dynein docking complex, tektins and an outer dense fiber protein, are used differently by the cilia and flagella. (3) Sperm flagella are specialized for the cAMP- and Ca2+-dependent regulation of outer arm dynein and for energy metabolism by glycolytic enzymes. Our present study clearly demonstrates that flagellar or ciliary proteins are properly recruited according to their function and stability, despite their apparent structural resemblance and conservation.

Soluble adenylyl cyclase in health and disease

The second messenger cAMP is integral for many physiological processes. Soluble adenylyl cyclase (sAC) was recently identified as a widely expressed intracellular source of cAMP in mammalian cells. sAC is evolutionary, structurally, and biochemically distinct from the G-protein-responsive transmembranous adenylyl cyclases (tmAC). The structure of the catalytic unit of sAC is similar to tmAC, but sAC does not contain transmembranous domains, allowing localizations independent of the membranous compartment. sAC activity is stimulated by HCO(3)(-), Ca²⁺ and is sensitive to physiologically relevant ATP fluctuations. sAC functions as a physiological sensor for carbon dioxide and bicarbonate, and therefore indirectly for pH. Here we review the physiological role of sAC in different human tissues with a major focus on the lung. This article is part of a Special Issue entitled: The role of soluble adenylyl cyclase in health and disease, guest edited by J. Buck and L.R. Levin.

Evidence of 5-HT components in human sperm: implications for protein tyrosine phosphorylation and the physiology of motility

Serotonin (5-hydroxytryptamine; C(10)H(12)N(2)O (5-HT)) is produced in the CNS and in some cells of peripheral tissues. In the mammalian male reproductive system, both 5-HT and tryptophan hydroxylase (TPH) have been described in Leydig cells of the testis and in principal cells of the caput epididymis. In capacitated hamster sperm, it has been shown that 5-HT promotes the acrosomal reaction. The aim of this work was to explore the existence of components of the serotoninergic system and their relevance in human sperm physiology. We used both immunocytochemistry and western blot to detect serotoninergic markers such as 5-HT, TPH1, MAO(A), 5-HT(1B), 5-HT(3), and 5HT(T); HPLC for TPH enzymatic activity; Computer Assisted Semen Analysis assays to measure sperm motility parameters and pharmacological approaches to show the effect of 5-HT in sperm motility and tyrosine phosphorylation was assessed by western blot. We found the presence of serotoninergic markers (5-HT, TPH1, MAO(A), 5-HT(1B), 5-HT(2A), 5-HT(3), 5-HT(T), and TPH enzymatic activity) in human sperm. In addition, we observed a significant increase in tyrosine phosphorylation and changes in sperm motility after 5-HT treatment. In conclusion, our data demonstrate the existence of components of a serotoninergic system in human sperm and support the notion for a functional role of 5-HT in mammalian sperm physiology, which can be modulated pharmacologically.

Aquaporin inhibition changes protein phosphorylation pattern following sperm motility activation in fish

Our previous studies demonstrated that osmolality is the key signal in sperm motility activation in Sparus aurata spermatozoa. In particular, we have proposed that the hyper-osmotic shock triggers water efflux from spermatozoa via aquaporins. This water efflux determines the cell volume reduction and, in turn, the rise in the intracellular concentration of ions. This increase could lead to the activation of adenylyl cyclase and of the cAMP-signaling pathway, causing the phosphorylation of sperm proteins and then the initiation of sperm motility. This study confirms the important role of sea bream AQPs (Aqp1a and Aqp10b) in the beginning of sperm motility. In fact, when these proteins are inhibited by HgCl(2), the phosphorylation of some proteins (174 kDa protein of head; 147, 97 and 33 kDa proteins of flagella), following the hyper-osmotic shock, was inhibited (totally or partially). However, our results also suggest that more than one transduction pathways could be activated when sea bream spermatozoa were ejaculated in seawater, since numerous proteins showed an HgCl(2)(AQPs)-independent phosphorylation state after motility activation. The role played by each different signal transduction pathways need to be clarified.

Cyclic AMP signaling in bivalve molluscs: an overview

The cyclic AMP (cAMP)-dependent signaling accounts for the control of cellular cascades involved in many physiological functions, and a wealth of information is available on the cAMP system that operates in mammalian cells. Nevertheless, cAMP has a central role also in nonmammalian vertebrates and invertebrates. The present review aims at examining the information available on bivalve molluscs, from the first studies carried out in the early 1980s to the last progresses made in the present days. The major focus is on the structural and operational characteristics of the main actors of the signaling pathway, i.e., adenylyl cyclase, G proteins, and protein kinase A, and on the role played by the cyclic nucleotide on smooth muscle, heart, gills, gonads, and metabolism regulation. Moreover, recent evidence regarding the cAMP system as a target of environmental stress factors are discussed. It will become clear that cAMP does play a wide and important role in bivalve physiology. Several issues have been sufficiently clarified, although investigated only in a few model species. However, further fundamental aspects remain unknown, mainly regarding molecular features and interactions with other signaling pathways, thus requiring further elucidation.

Purification of dyneins from sperm flagella

Metazoan spermatozoa, especially those from marine invertebrates and fish, are excellent sources for isolating axonemal dyneins because of their cellular homogeneity and the large amounts that can be collected. Sperm flagella can be easily isolated by homogenization and subsequent centrifugation. Axonemes are obtained by demembranation of flagella with the nonionic detergent Triton X-100. The outer arm dyneins have been most widely studied because they are specifically extracted by a high-salt solution and can be isolated as a relatively pure fraction of ~20S two-headed dynein by sucrose density gradient centrifugation. Only a few reports have described the isolation of inner arm dyneins from sperm and the protocol has room for improvement. Sperm show clear changes in motility at fertilization, which are exerted through the regulation of axonemal dyneins by protein phosphorylation and Ca(2+) binding. Therefore dyneins from sperm flagella are an excellent biochemically tractable source for studying the regulation of axonemal dyneins. Here we describe protocols used for purification of flagellar dyneins from sperm of tunicates, sea urchins, and fish. The techniques described here could be applied to other species with appropriate modifications.

Molecular mechanisms determining sperm motility initiation in two sparids (Sparus aurata and Lithognathus mormyrus)

Molecular mechanisms involved in sperm motility initiation in two sparids (Sparus aurata and Lithognathus mormyrus) have been studied. Our comparative study demonstrates that osmolality is the key signal in sperm motility activation in both species, whereas K(+) and Ca(2+) do not have any role. The straight-line velocity that resulted, however, was significantly different when measured in sperm activated with non-ionic and/or calcium-free solutions with respect to that measured in seawater-activated sperm. In both species, motility initiation depends on cAMP-dependent protein phosphorylation. The phosphorylation/dephosphorylation patterns that resulted in gilthead and striped sea bream were quite different. In gilthead sea bream, the phosphorylated proteins have molecular weights of 174, 147, 138, 70, and 9-15 kDa, whereas the dephosphorylated proteins have molecular weights of 76, 57, and 33 kDa. In striped sea bream, phosphorylation after sperm motility activation occurred on proteins of 174, 147, 103, 96, 61, 57, and 28 kDa, whereas only one protein of 70 kDa resulted from dephosphorylation. Matrix-assisted laser desorption ionization-time of flight analyses allowed identification of the following proteins: In gilthead sea bream, the 9-15 kDa proteins that were phosphorylated after motility activation include an A-kinase anchor protein (AKAP), an acetyl-coenzyme A synthetase, and a protein phosphatase inhibitor, and in striped sea bream, 103- and 61-kDa proteins that were phosphorylated after motility activation were identified as a phosphatase (myotubularin-related protein 1) and a kinase (DYRK3), respectively.

Molecular basis of sperm flagellar axonemes: structural and evolutionary aspects

The axonemes serve as motile machineries in sperm flagella. Although atypical axonemal structures are observed in some cases, 9 + 2 microtubule structure of the axoneme is predominant in many organisms. Several structures are bound to these microtubules and comprise a highly organized protein network. Extensive proteomic analysis of the axonemes has led to find several repeats, domains, and motifs in axonemal proteins. Molecular comparison of subunit composition of axonemal substructures between the ascidian Ciona intestinalis and the green algae Chlamydomonas reinhardtti leads to an intriguing molecular aspect concerning the evolution of intracellular functional complex: The architecture of the axonemes has been well conserved through evolution, but the molecular structure of each axonemal component is not always conserved. In light of domain structure in the axonemal proteins, substructures like outer arm dynein and radial spoke contain a set of domain structures, although some domain-containing subunits are different between these two organisms. Thus, conservation of protein domains within a substructure seems to take precedence over that of each protein ("module-dominant conservation"), which may ultimately result in morphological and functional conservation of the axonemes through evolution.

Serotonin stimulates [Ca2+]i elevation in ciliary ectodermal cells of echinoplutei through a serotonin receptor cell network in the blastocoel

A full-length serotonin receptor mRNA from the 5Hthpr gene was sequenced from larvae of the sea urchin, Hemicentrotus pulcherrimus.The DNA sequence was most similar to 5HT-1A of the sea urchin Strongylocentrotus purpuratus found by The Sea Urchin Genome Project,and the protein sequence predicted the presence of seven transmembrane domains. Immunohistochemistry with anti-5HThpr antibodies indicated that the protein was expressed on blastocoelar cells that comprised the major blastocoelar network (serotonin receptor cell network). These network cells inserted their processes into the ectoderm in various regions, including the ciliary band region. Serotonin injected into the blastocoel stimulated a transient elevation of cytoplasmic Ca2+ concentration([Ca2+]i) in the ectoderm, as detected by Oregon-Green dextran, injected earlier in development. The calcium transient propagated as a wave at about 175 μm s–1, but was not detectable in the serotonin receptor-positive cell network. In larvae treated with p-chlorophenylalanine, a potent and irreversible serotonin synthesis inhibitor, serotonin application did not stimulate[Ca2+]i, the serotonin receptor cell network did not develop properly, and the swimming behavior of the larvae was abnormal. However, formation of a different nervous system comprising synaptotagmin-possessed neurites was not affected by p-chlorophenylalanine treatment. These results imply that serotonin secreted from the apical ganglion into the blastocoel stimulates the elevation of [Ca2+]i in the larval ectodermal cells through the serotonin receptor cell network.

A mixture of environmental contaminants increases cAMP-dependent protein kinase in Spisula embryos

Using the surf clam embryo, we investigated the effects of the combination of bromoform, chloroform, and tetrachloroethylene, three pollutants found in high concentrations in the municipal water supply in Brick, New Jersey. Exposure produced an increase in an isoform of the regulatory subunit (RII) of cAMP-dependent protein kinase, demonstrated by confocal microscopy and western blotting. Embryos showed an increase in RII where the primordial gill and ciliated velar epithelium are innervated. This increase correlated with increased ciliary activity, indicating a corresponding rise in the catalytic subunit. Treatment resulted in decreased threonine phosphorylation of actin. There was no effect on neurotransmitters or receptors of the serotonergic-dopaminergic nervous system. These effects occurred only with the ternary mixture. No significant effect was seen with individual or paired components. This is the first report showing that bromoform, chloroform, and tetrachloroethylene act synergistically to alter a key regulator of neuronal development.

The control of ciliary beat frequency

Ciliary movement is powered by axonemal dynein. This article considers how a signal transduction cascade initiated at the cell membrane may activate outer dynein arms to change the velocity of microtubule sliding and the swimming speed of ciliated cells. For Paramecium, a critical event in the cascade is the cAMP-dependent phosphorylation of a 29 kDa polypeptide that is associated with the outer dynein arm.

Characterization of a cAMP-dependent protein kinase catalytic subunit from rainbow trout spermatozoa

The cyclic AMP-dependent phosphorylation of proteins is essential for the initiation of sperm motility in salmonid fishes. This study isolated cDNA for the catalytic subunit of a cAMP-dependent protein kinase (PKA-C) from rainbow trout testis. The deduced amino acid sequence shows 75-80% identity to sequences previously reported in other organisms. However, the N-terminal regions of PKA-C from the testis as well as ovary in the trout appear slightly shorter than those from other tissues, suggesting that small PKA-C might be specific to germ cells. An immunofluorescence study using polyclonal antibody against trout testis PKA-C shows that it localizes along sperm flagellum. Furthermore, immunoelectron microscopy revealed that PKA-C is anchored to the outer arm dynein of flagellar axonemes. These results suggest that PKA-C is involved in regulating the flagellar motility of sperm via phosphorylation of a subunit of the outer arm dynein.

Fertilization in the sea

Chemical communication between sperm and egg is a key factor mediating sexual reproduction. Dissolved signal molecules that cause sperm to orient and accelerate towards an egg could play pivotal roles in fertilization success,but such compounds are largely undescribed. This investigation considered the behavioral responses of red abalone (Haliotis rufescens) sperm to soluble factors released into sea water by conspecific eggs. Sperm in proximity to individual live eggs swam significantly faster and oriented towards the egg surface. Bioassay-guided fractionation was employed to isolate the chemoattractant, yielding a single pure, fully active compound after reversed-phase and size-exclusion high-performance liquid chromatography. Chemical characterization by nuclear magnetic resonance spectroscopy indicated that the free amino acid L-tryptophan was the natural sperm attractant in H. rufescens.

Eggs released L-tryptophan at concentrations that triggered both activation and chemotaxis in sperm, exhibiting significant activity at levels as low as 10-8 mol l-1. The D-isomer of tryptophan was inactive,showing that the sperm response was stereospecific. Serotonin, a potent neuromodulator and tryptophan metabolite, had no effect on sperm swim speeds or on orientation. In experimental treatments involving an elevated, uniform concentration of tryptophan (10-7 mol l-1) or the addition of tryptophanase, an enzyme that selectively digests tryptophan,sperm failed to navigate towards live eggs. A natural gradient of L-tryptophan was therefore necessary and sufficient to promote recruitment of sperm to the surface of eggs in red abalone.

Differential localization of protein kinase A type II isozymes in the Golgi-centrosomal area

Selectivity in the action of cAMP may be mediated by compartmentalized pools of cyclic AMP-dependent protein kinase (PKA). PKA type II is directed to different subcellular loci by interaction of the type II regulatory subunits (RIIalpha, RIIbeta) with A-kinase anchoring proteins. In order to separately investigate the subcellular localization of PKA type II isozymes, monospecific antibodies to human RIIalpha and RIIbeta subunits of PKA were developed. We demonstrate that centrosomes bind both RIIalpha and RIIbeta. Centrosomes were the preferred intracellular anchoring site for RIIbeta. However, centrosomal localization of RIIbeta was observed only in some highly differentiated cells such as keratinocytes, granulosa cells, and macrophages and in all neoplastic cell lines examined. Centrosomal localization of RIIbeta was not observed in normal undifferentiated cells such as fibroblasts, myoblasts, and T and B cells. In contrast, RIIalpha was abundant in the Golgi area and in the trans-Golgi network (TGN). Furthermore, although RIIalpha appeared to colocalize with microtubules in the Golgi/TGN, extractions with nonionic detergent demonstrated that RIIalpha was mainly membrane-associated. In addition, alterations of microtubule dynamics with Nocodazole or Taxol affected the distribution of the detergent-extractable pool of RIIalpha, indicating that RIIalpha may localize with microtubule-associated vesicles. Thus, RIIalpha and RIIbeta clearly localize differently in the Golgi-centrosomal region. This indicates specific roles for PKA isozymes containing either RIIalpha or RIIbeta.

Tctex2-related outer arm dynein light chain is phosphorylated at activation of sperm motility

When the motility of sperm is activated, only one light chain of flagellar outer arm dynein is phosphorylated in many organisms. We show here that the light chain to be phosphorylated was shown to be light chain 2 (LC2) in rainbow trout and chum salmon sperm and LC1 in sea urchin sperm. Molecular analyses of the phosphorylated light chains from sperm flagella of the salmonid fishes and sea urchin revealed that the light chains are homologs of the mouse t complex-encoded protein Tctex2, which is one of the putative t complex distorters. These results suggest that mouse Tctex2 might also be a light chain of flagellar outer arm dynein and that the abortive phosphorylation of Tctex2/outer arm dynein light chain might be related to the less progressive movement of sperm.

Electrophoretic resolution of tubulin and tektin subunits by differential interaction with long-chain alkyl sulfates

Tubulin dimers, formed from globular alpha and beta subunits, and the tektins, three equimolar alpha-helical proteins that form filaments, mutually associate to form the junctional regions of doublet and triplet microtubules. When evaluated by SDS-PAGE, the apparent molecular weights of these proteins can deviate substantially from their sequence molecular weights in a manner sensitive to both the source of SDS and the species of origin. The electrophoretic mobility of sperm tail flagellar tubulins and tektins from an echinoderm and a mollusc were studied systematically using detergent-free stacking and resolving gels with a running buffer containing pure sodium dodecyl sulfate augmented with fixed amounts of C10, C14, C16, or C18 alkyl sulfates. Although having no systematic effect on molecular weight standards, the presence of alkyl sulfates of increasing chain length progressively exaggerated the separation of tubulin subunits, similarly facilitated the separation of two normally comigrating tektins, yet minimally influenced the relative migration of adequately separated tektins. This phenomenon is most likely due to preferential binding of longer chain alkyl sulfates by specific hydrophobic regions of these otherwise similar proteins. The use of binary mixtures of pure alkyl sulfates, required in the running buffer alone, may prove useful for reproducibly separating other proteins that characteristically bind SDS anomalously.

Regulation of ciliary beat frequency by both PKA and PKG in bovine airway epithelial cells

Ciliary beating is required for the maintenance of lung mucociliary transport. We investigated the role of cyclic nucleotide-dependent protein kinases in stimulating ciliary beat frequency (CBF) in bovine bronchial epithelial cells (BBECs). cAMP-dependent protein kinase (PKA) activity and cGMP-dependent protein kinase (PKG) activity were distinguished after DEAE-Sephacel chromatography of BBEC extracts. cAMP levels and PKA activity are increased in BBECs stimulated with 0.01-1 mM isoproterenol, with a corresponding increase in CBF. cGMP levels and PKG activity are increased in BBECs stimulated with 0.1-10 microM sodium nitroprusside, with a corresponding increase in CBF. Direct protein kinase-activating analogs of cAMP and cGMP (dibutyryl cAMP and 8-bromo-cGMP, respectively) also activate their specific kinases and stimulate CBF. Preincubation of BBECs with inhibitors of PKA or PKG [KT-5720 or Rp-8-(p-chlorophenylthio)-guanosine 3',5'-cyclic monophosphothioate] results in the inhibition of specific kinase activity as well as in the inhibition of CBF. These studies suggest that the activation of either PKA or PKG can lead to the stimulation of CBF in bovine airway epithelium.

Proteasomes regulate the motility of salmonid fish sperm through modulation of cAMP-dependent phosphorylation of an outer arm dynein light chain

Proteasomes are involved in ATP-dependent regulation of sperm motility in salmonid fish. We have demonstrated here by immunoelectron microscopy that proteasomes are located at the structure of the chum salmon sperm flagellum that attaches at the base of the outer arm dynein and extends toward the plasma membrane. Furthermore, substrates and inhibitors of proteasome inhibit the cAMP-dependent phosphorylation of a 22 kDa axonemal protein in chum salmon sperm. The 22 kDa phosphoprotein was solubilized by treatment of the axoneme with a high salt solution and subsequent sucrose density gradient centrifugation of the extract revealed that it cosedimented with 19 S outer arm dynein, indicating that it is a dynein light chain. These results suggest that proteasomes modulate the activity of outer arm dynein by regulating cAMP-dependent phosphorylation of the 22 kDa dynein light chain.

A model for flagellar motility

Experimental investigation has provided a wealth of structural, biochemical, and physiological information regarding the motile mechanism of eukaryotic flagella/cilia. This chapter surveys the available literature, selectively focusing on three major objectives. First, it attempts to identify those conserved structural components essential to providing motile function in eukaryotic axonemes. Second, it examines the relationship between these structural elements to determine the interactions that are vital to the mechanism of flagellar/ciliary beating. Third, the vital principles of these interactions are incorporated into a tractable theoretical model, referred to as the Geometric Clutch, and this hypothetical scheme is examined to assess its compatibility with experimental observations.

Molecular identification of a Schistosoma mansoni tegumental protein with similarity to cytoplasmic dynein light chains

The tegument of Schistosoma mansoni contains a number of proteins that presumably function in its maintenance and/or repair against damage incurred from host-mediated humoral immune responses. Here, we show that the schistosome antigen identified by monoclonal antibody 709A2/2 is a cytoplasmic dynein light chain. Dynein light chains are components of dynein, an enzyme complex involved in various aspects of microtubule-based motility. Monoclonal antibody 709A2/2 recognizes two polypeptides, one of 8.9 kDa and a second of 7.6 kDa, as determined by SDS-polyacrylamide gel electrophoresis. We find that expression of S. mansoni dynein light chain is developmentally regulated and localized to the tegument in the schistosomula, lung stage worms, and adult worms, but is not present in the cercariae or ciliated miracidia. By Northern blot analysis of adult worm RNA, S. mansoni dynein light chain is encoded by a single message of approximately 600 base pairs. A cDNA encoding this polypeptide contains an open reading frame of 89 amino acids with a deduced molecular mass of 10.4 kDa. Coprecipitation of an apparent 18.4-kDa antigen with S. mansoni dynein light chain by monoclonal antibody 709A2/2 illustrates that this molecule has an affinity for other proteins. Such interactions may play a role in S. mansoni dynein light chain participation in organelle trafficking in S. mansoni.

From oocyte to neuron: do neurotransmitters function in the same way throughout development?

1. Classical neurotransmitters (such as acetylcholine, biogenic amines, and GABA) are functionally active throughout ontogenesis. 2. Based on accumulated evidence, reviewed herein, we present an hypothetical scheme describing developmental changes in this functional activity, from the stage of maturing oocytes through neuronal differentiation. This scheme reflects not only the spatio-temporal sequence of these changes, but also the genesis of neurotransmitter functions, from "protosynapses" in oocytes and cleaving embryos to the development of functional neuronal synapses. 3. Thus, it appears that neurotransmitters participate in various forms of intra- and intercellular signalling throughout all stages of ontogenesis.

Brain cytoplasmic and flagellar outer arm dyneins share a highly conserved Mr 8,000 light chain

Sequence comparisons with the Mr 8,000 light chain from Chlamydomonas outer arm dynein revealed the presence of highly conserved homologues (up to 90% identity) in the expressed sequence tag data base (King, S. M. & Patel-King, R. S. (1995a) J. Biol. Chem. 270, 11445-11452). Several of these homologous sequences were derived from organisms and/or tissues that lack motile cilia/flagella, suggesting that these proteins may function in the cytoplasm. In Drosophila, lack of the homologous protein results in embryonic lethality (Dick, T., Ray, K., Salz, H. K. & Chia, W.(1996) Mol. Cell. Biol., 16, 1966-1977). Fractionation of mammalian brain homogenates reveals three distinct cytosolic pools of the homologous protein, one of which specifically copurifies with cytoplasmic dynein following both ATP-sensitive microtubule affinity/sucrose density gradient centrifugation and immunoprecipitation with a monoclonal antibody specific for the 74-kDa intermediate chain (IC74). Quantitative densitometry indicates that there is one copy of the Mr 8,000 polypeptide per IC74. Dual channel confocal immunofluorescent microscopy revealed that the Mr 8,000 protein is significantly colocalized with cytoplasmic dynein but not with kinesin in punctate structures (many of which are associated with microtubules) within mammalian oligodendrocytes. Thus, it appears that flagellar outer arm and brain cytoplasmic dyneins share a highly conserved light chain polypeptide that, at least in Drosophila, is essential for viability.

Two functional thioredoxins containg redox-senesitive vicinal dithiols from the Chlamydomonas outer dynein arm

We describe here the molecular cloning and analysis of the Mr 14,000 and 16,000 outer arm dynein light chains (DLCs) from Chlamydomonas flagella. Within the outer arm, the Mr 14,000 DLC apparently is associated with the intermediate chains at the base of the soluble dynein particle; the Mr 16,000 DLC interacts directly with the a dynein heavy chain. Sequence analysis indicates that both molecules are novel members of the thioredoxin superfamily and share approximately 30% sequence identity with thioredoxin from Penicillium. Both DLCs have a perfect copy of the thioredoxin active site (WCGPCK); the Mr 16,000 DLC also contains the canonical P-loop motif (AX4GKS). There is a single gene for both DLCs within Chlamydomonas and only single messages that were upregulated more than 10-fold upon deflagellation were observed on Northern blots. Both recombinant DLCs were specifically eluted from a phenylarsine oxide matrix with beta-mercaptoethanol indicating that they contain vicinal dithiols competent to undergo reversible oxidation/reduction. Furthermore, we demonstrate that outer (but not inner) arm dynein may he purified on the basis of its affinity for phenylarsine oxide suggesting that the predicted redox-sensitive vicinal dithiols exist within the native complex.

Microtubules and microtubule motors: mechanisms of regulation

Microtubule-based motility is precisely regulated, and the targets of regulation may be the motor proteins, the microtubules, or both components of this intricately controlled system. Regulation of microtubule behavior can be mediated by cell cycle-dependent changes in centrosomal microtubule nucleating ability and by cell-specific, microtubule-associated proteins (MAPs). Changes in microtubule organization and dynamics have been correlated with changes in phosphorylation. Regulation of motor proteins may be required both to initiate movement and to dictate its direction. Axonemal and cytoplasmic dyneins as well as kinesin can be phosphorylated and this modification may affect the motor activities of these enzymes or their ability to interact with organelles. A more complete understanding of how motors can be modulated by phosphorylation, either of the motor proteins or of other associated substrates, will be necessary in order to understand how bidirectional transport is regulated.

Identification of a Ca(2+)-binding light chain within Chlamydomonas outer arm dynein

We describe here the molecular cloning of the M(r) 18,000 dynein light chain from the outer arm of Chlamydomonas flagella. In vivo, this molecule is directly associated with the gamma dynein heavy chain. Sequence analysis indicates that this light chain is a novel member of the calmodulin superfamily of Ca2+ binding regulatory proteins; this molecule is 42, 37 and 36% identical to calmodulin, centrin/caltractin and troponin C, respectively, and also shows significant similarity to myosin light chains. Although four helix-loop-helix elements are evident, only two conform precisely to the EF hand consensus and are therefore predicted to bind Ca2+ in vivo. In vitro Ca2+ binding studies indicate that this dynein light chain (expressed as a C-terminal fusion with maltose binding protein) has at least one functional Ca2+ binding site with an apparent affinity for Ca2+ of approximately 3 × 10(−5) M. Within the Chlamydomonas flagellum, the transition from an assymmetric to a symmetric waveform (which implies an alteration in dynein activity) is mediated by an increase in intraflagellar Ca2+ from 10(−6) to 10(−1) M; this transition is altered in mutants that lack the outer arm. The data presented here suggest that a Ca(2+)-dependent alteration in the interaction of this dynein light chain with the motor containing heavy chain may affect outer arm function during flagellar reversal.

The M(r) = 8,000 and 11,000 outer arm dynein light chains from Chlamydomonas flagella have cytoplasmic homologues

We report here the molecular cloning of the M(r) = 8,000 and 11,000 dynein light chains (DLCs) from the outer arm of Chlamydomonas flagella. These two molecules, which are associated with the intermediate chains at the base of the soluble dynein particle, have predicted masses of 10.3 and 13.8 kDa, respectively, and are 40% identical. Southern blot analysis indicates that one gene exists for each DLC in the Chlamydomonas genome and only a single message was observed for each on Northern blots. Secondary structure predictions suggest that both molecules contain a highly amphiphilic alpha helix that is presumably involved in protein-protein interactions. Several DLC homologues were identified in the GenBank databases. One, predicted from the genomic sequence of Caenorhabditis elegans, is 88.8% identical with the M(r) = 8,000 Chlamydomonas DLC. A second, from rice callus cDNA, is 47% identical with the same DLC. As neither nematodes nor higher plants have motile cilia or flagella at any stage of their life cycles, these DLC homologues presumably must function within the cytoplasm where they may represent previously unrecognized components of cytoplasmic dynein.

Outer arm dynein from Newt lung respiratory cilia: purification and polypeptide composition

Dyneins are multimeric ATPases that comprise the inner and outer arms of cilia and flagella. It previously has been shown that salt extraction of newt lung axonemes selectively removes > 95% of the outer arm dynein (OAD), and that the beat frequency of OAD-depleted axonemes cannot be activated as compared to controls [Hard et al., 1992: Cell Motil. Cytoskeleton 21:199-209]. Therefore, expression of the activated state appears to require the presence of outer dynein arms. The present study was undertaken to ascertain basic information on the structure and molecular composition of newt OAD. Populations of demembranated axonemes were extracted with 0.375 M salt. Each lung released approximately 1.4 x 10(7) axonemes during isolation, yielding approximately 120 ng of salt extractable OAD. Electron microscopy of negatively stained samples revealed that newt OAD consisted of two globular heads joined together by a Y-shaped stem, similar to sea urchin and trout sperm OAD. Each head appeared to be roughly spherical in shape, measuring approximately 17 nm in diameter. Electrophoretic analysis of whole axonemes revealed more than six dynein heavy chains when resolved in silver stained 0-8 M urea, 3-5% acrylamide gradients. Extracted OAD, either crude in high salt or purified by alloaffinity, was composed of two heavy chains. UV-induced (366 nm) photolytic cleavage at the V1 site, performed in the presence of Mg2+, vanadate, and ATP, produced four new polypeptides (M(r) 234, 232, 197, and 189 kD). Photolysis was supported by Mg2+ and Ca2+, but did not occur in the presence of Mn2+. The apparent M(r) of the dynein heavy chains was determined to lie between 430-420 kD. Eight discrete polypeptides (putative intermediate chains, IC1-IC8, M(r), 175-56 kD) copurified with the alpha- and beta-heavy chains by microtubule-alloaffinity. Based on its extraction characteristics, polypeptide composition in purified and crude samples, and structure, we conclude that this two-headed particle represents the entire newt respiratory outer arm dynein.

Dynein inner arm heavy chain identification in cAMP-activated flagella using class-specific polyclonal antibodies

While studying cAMP-dependent dynein alpha-heavy chain phosphorylation, we found previously [Stephens and Prior, 1992: J. Cell Sci. 103:999-1012] that high salt extraction of sperm flagella from the mussel Mytilus edulis or the clam Spisula solidissima removed most visible dynein arms, accompanied by an amount of Mg+2-ATPase that correlated with the mass of dynein alpha- and beta-heavy chains removed. However, although almost devoid of ATPase activity, such extracted axonemes retained one third of the heavy chain mass as two sets of electrophoretically-distinct, vanadate-cleavable, non-phosphorylated proteins. To explore the nature of these dynein-like proteins, antibodies to the alpha- and beta-heavy chains were blot affinity-purified from a rabbit antiserum raised against gradient-purified Spisula 18-20S flagellar outer arm dynein. Although able to recognize common epitopes of the opposite chain type, neither the alpha- nor the beta-heavy chain antibody recognized the tightly-bound proteins in either species, proving that they are immunologically distinct. While the beta-antibody recognized its heavy chain homolog in gill cilia, the alpha-antibody did not, demonstrating immunological distinction between flagellar and ciliary dynein alpha-heavy chains. Immunization of a mouse with nitrocellulose strips containing one of the two tightly-bound Spisula flagellar proteins produced an antiserum that cross-reacted with each tightly-bound protein in both species and also recognized alpha- and beta-heavy chains. The anti-molluscan serum cross-reacted strongly with sea urchin sperm flagellar dynein B-, C-, and D-bands, considered to be inner arm components, but not with sea urchin outer arm alpha- or beta-heavy chains. These data indicate that the electrophoretically and immunologically distinct, tightly-bound proteins of molluscan flagella are inner arm dynein heavy chains.

Regulation of dynein-driven microtubule sliding by an axonemal kinase and phosphatase in Chlamydomonas flagella

The following is a summary of physiological and pharmacological studies of the regulation of dynein-driven microtubule sliding in Chlamydomonas flagella. The experimental basis for the study is described, and data indicating that an axonemal cAMP-dependent protein kinase can regulate inner arm dynein activity are reviewed. In addition, preliminary data are summarized indicating that an axonemal type 1 phosphatase can also regulate dynein-drive microtubule sliding velocity. It is predicted that the protein kinase, phosphatase, and an inner dynein arm component form a regulatory complex in the axoneme.

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 model of flagellar and ciliary functioning which uses the forces transverse to the axoneme as the regulator of dynein activation

Ciliary and flagellar motion is driven by the dynein-tubulin interaction between adjacent doublets of the axoneme, and the resulting sliding displacements are converted into axonemal bends that are propagated. When the axoneme is bent in the normal beating plane, force develops across the axoneme in the plane of the bend. This transverse force (t-force) has maximal effect on the interdoublet spacing of outer doublets 2-4 on one side of the axoneme and doublets 7-9 on the opposite side. Episodes of sliding originates as the t-force brings these doublets into closer proximity (allowing dynein bridges to form) and are terminated when these doublets are separated from each other by the t-force. A second factor, the adhesive force of the dynein-tubulin attachments (bridges), also acts to pull neighboring doublets closer together. This force resists termination of a sliding episode once initiated, and acts locally to give the population of dynein bridges a type of excitability. In other words, as bridges form, the probability of nearby bridges attaching is increased by a positive feedback exerted through the interdoublet spacing. A conceptual working hypothesis explaining the behavior of cilia and flagella is proposed based on the above concepts. Additionally, the feasibility of this proposed mechanism is demonstrated using a computer simulation. The simulation uses a Monte Carlo-type algorithm for dynein attachment and adhesive force, together with a geometric evaluation of the t-force on the key microtubule pairs. This model successfully develops spontaneous oscillations from any starting configuration (including a straight position). It is compatible with the physical dimensions, mechanical properties and bridge forces measured in real cilia and flagella. In operation, it exhibits many of the observed actions of cilia and flagella, most notably wave propagation and the ability to produce both cilia-like and flagella-like waveforms.

Protein kinase C-dependent phosphorylation of a ciliary membrane protein and inhibition of ciliary beating

The present study examined whether protein kinase C phosphorylated a ciliary protein and whether this phosphorylation event was temporally correlated with a decrease in ciliary beat frequency. Activation of protein kinase C decreased ciliary beat frequency of sheep tracheal epithelium, an effect fully blockable by pretreatment of the tissue pieces with H-7, a protein kinase inhibitor. Using cilia removed from these epithelial surfaces and incubated in solutions containing stimulators of protein kinase C along with [gamma-32P]ATP or [gamma-35S]ATP, a single protein target of ciliary protein kinase C activity was identified. The protein is a polypeptide of molecular mass 37 kDa (p37) as estimated by SDS-polyacrylamide gel electrophoresis. Protein kinase C dependency of p37 phosphorylation was proven by showing that Calphostin C, a specific protein kinase C inhibitor, blocked label incorporation into p37 completely, and by demonstrating that purified protein kinase C phosphorylated p37. Inhibitors of cAMP-dependent kinase and calcium/calmodulin-dependent kinase did not change the phosphorylation of p37 in the presence of protein kinase C activators. p37 was recovered in a Triton X-100-extractable fraction of this ciliary preparation, suggesting that p37 is membrane associated. This hypothesis was further supported by the fact that p37 was present in a pellet representing reconstituted membranes. Thin-layer electrophoresis revealed that p37 was phosphorylated on serine and tyrosine residues, suggesting that the activation of protein kinase C also stimulated tyrosine kinase activity. p37 did not precipitate with annexin I or II antibodies. These results show that sheep tracheal cilia contain protein kinase C activity and that activated protein kinase C phosphorylates a membrane-associated ovine ciliary target, an effect temporally related to a protein kinase C-mediated decrease in ciliary beat frequency.

In vitro phosphorylation of ciliary dyneins by protein kinases from Paramecium

Paramecium dyneins were tested as substrates for phosphorylation by cAMP-dependent protein kinase, cGMP-dependent protein kinase, and two Ca(2+)-dependent protein kinases that were partially purified from Paramecium extracts. Only cAMP-dependent protein kinase caused significant phosphorylation. The major phosphorylated species was a 29 kDa protein that was present in both 22 S and 12 S dyneins; its phosphate-accepting activity peaked with 22 S dynein. In vitro phosphorylation was maximal at five minutes, then decreased. This decrease in phosphorylation was inhibited by the addition of vanadate or NaF. The 29 kDa protein was not phosphorylated by a heterologous cAMP-dependent protein kinase, the bovine catalytic subunit. Phosphorylation of dynein did not change its ATPase activity. In sucrose gradient fractions from the last step of dynein purification, phosphorylation by an endogenous kinase occurred. This phosphorylation could not be attributed to the small amounts of cAMP- and cGMP-dependent protein kinases known to be present, nor was it Ca(2+)-dependent. This previously uncharacterized ciliary protein kinase used casein as an in vitro substrate.