Paracercomonas kinetid ultrastructure, origins of the body plan of Cercomonadida, and cytoskeleton evolution in Cercozoa

Serial section reconstruction shows that kinetid ultrastructure in two genetically divergent Paracercomonas (P. virgaria, P. metabolica) is basically similar, differing somewhat from clade A cercomonads. Paracercomonas (Paracercomonadidae fam. n.) have a posterior root (dp1) attached to the posterior centriole, unlike Cercomonadidae (here revised to include only Eocercomonas, Cercomonas, Filomonas gen. n., and Neocercomonas), which belong in clade A (new suborder Cercomonadina) with Cavernomonas (Cavernomonadidae fam. n.). Whether dp1 is serially homologous to anterior root da is unclear. The common ancestor of Cercomonadida probably had five microtubular roots, two fibrillar microtubule-nucleating centres generating microtubular cones, and striated connectors between obtusely angled centrioles. Our new data leave the question of holophyly versus polyphyly of Cercomonadida unresolved, but clarify cercozoan root diversity and homologies. Ventral root vp1 is throughout Cercozoa; vp2 might be restricted to the new superclass Ventrifilosa plus Sarcomonadea. Though cercozoan microtubular arrangements differ substantially from others within the kingdom Chromista, the microtubular root numbering system used for other chromists and Plantae is applicable to them; in doing this we found that the single anterior root of excavates (probably ancestral to Chromista, Plantae and unikonts) and Euglenozoa corresponds with R3 (not R4 as previously thought) of corticate eukaryotes (Chromista plus Plantae).     

New genera, species, and improved phylogeny of Glissomonadida (Cercozoa)

Glissomonadida is an important cercozoan order of predominantly biflagellate gliding bacterivores found largely in soil and freshwater. Their vast diversity is largely undescribed. We studied 23 mostly newly isolated strains by light microscopy and sequenced their 18S rDNA genes; nine represent new species. For two misidentified ATCC 'Heteromita triangularis' strains, we establish novel gliding genera and species: the sandonid Mollimonas lacrima, the only glissomonad forming anterior and posterior pseudopodia, and Dujardina stenomorpha, a strongly flattened member of the new family Dujardinidae. A new strain from Oxfordshire grassland soil is the first reliably identified isolate of the virtually uniflagellate, smooth-gliding glissomonad genus, AllantionSandon, 1924. Phylogenetic analysis and cytological features reveal Allantion to be a member of Allapsidae. Sandona limna and Bodomorpha prolixa from Lake Baikal and Sandona hexamutans from volcanic Costa Rican soil are described as new species. Fifteen glissomonad strains were from grassland beside Lake Baikal. We describe two as new species of Sandona (S. heptamutans and S. octamutans); the others included strains of Sandona and Allapsa species that have already been described; and three were new species of Sandona and Allapsa but these died before being described. We discuss the ecological and evolutionary significance of these new strains.     

Molecular phylogeny of Cercomonadidae and kinetid patterns of Cercomonas and Eocercomonas gen. nov. (Cercomonadida, Cercozoa)

Cercomonads are among the most abundant and widespread zooflagellates in soil and freshwater. We cultured 22 strains and report their complete 18S rRNA sequences and light microscopic morphology. Phylogenetic analysis of 51 Cercomonas rRNA genes shows in each previously identified major clade (A, B) two very robust, highly divergent, multi-species subclades (A1, A2; B1, B2). We studied kinetid ultrastructure of five clade A representatives by serial sections. All have two closely associated left ventral posterior microtubular roots, an anterior dorsal root, a microtubule-nucleating left anterior root, and a cone of microtubules passing to the nucleus. Anterior centrioles (=basal bodies, kinetosomes) of A1 have cartwheels; the posterior centriole does not, suggesting it is older, and implying flagellar transformation similar to other bikonts. Strain C-80 (subclade A2) differs greatly, having a dorsal posterior microtubule band, but lacking the A1-specific fibrillar striated root, nuclear extension to the centrioles, centriolar diaphragm, extrusomes; both mature centrioles lack cartwheels. For clade A2 we establish Eocercomonas gen. n., with type Eocercomonas ramosa sp. n., and for clade B1 Paracercomonas gen. n. (type Paracercomonas marina sp. n.). We establish Paracercomonas ekelundi sp. n. for culture SCCAP C1 and propose a Cercomonas longicauda neotype and Cercomonas (=Neocercomonas) jutlandica comb. n. and Paracercomonas (=Cercomonas) metabolica comb. n.     

褐菖■精细胞晚期的变化及精子结构研究

本文研究卵胎生硬骨鱼褐菖（Ｓｅｂａｓｔｉｓｃｕｓｍａｒｍｏｒａｔｕｓ）精细胞的成熟变化和精子结构。褐菖精细胞发育晚期已具有硬骨鱼类精子的结构雏形：细胞核的背面较平坦,腹面稍外鼓,呈弧面;染色质浓缩成团块状,核的腹侧和后端的染色质较致密;中心粒复合体由近端中心粒和基体组成,近端中心粒和基体排成“Ｌ”形;近端中心粒向细胞核的背侧伸出中心粒附属物,中心粒附属物由９条微管组成,９条微管围成一筒状结构,类似轴丝。在晚期精细胞形成精子的过程中,中心粒附属物和近端中心粒相继退缩以至消失不见,同时细胞核后端的形状也随着发生变化。中心粒附属物和近端中心粒的相继消失可以看作是成熟的最后标志。精子的中心粒复合体由基体及其上方的基体帽组成,袖套接于核的后端,其中约有３０～４０个线粒体;鞭毛从袖套腔中伸出,鞭毛的中心结构是轴丝;轴丝外方为细胞质形成的侧鳍,在鞭毛的近核段,轴丝两侧的侧鳍较宽且不对称。     

Sperm ultrastructure in the inseminating Macropsobrycon uruguayanae (Teleostei: Characidae: Cheirodontinae)

Macropsobrycon uruguayanae is a small, inseminating characid (tetra) of the tribe Compsurini. Although spermatozoa can be found within the ovarian cavity close to oocytes, the exact moment of fertilization has not yet been determined. Spermatozoa have moderately elongate nuclei with electron-dense chromatin. During spermiogenesis, nuclear rotation takes place. Elongate mitochondria with lamellar cristae are found posterior to the nucleus. Centrioles are parallel to one another with the proximal centriole slightly anterior to the longer distal one. The anterior tip of the proximal centriole is located within a shallow nuclear fossa. Electron-dense spurs are associated within the anterior and posterior ends of the distal centriole. Striated centriolar rootlets radiate both anteriorly and posteriorly from the distal centriole. Nine longitudinal accessory microtubules surround the axoneme in the proximal flagellum. The flagellum has a typical 9 + 2 axoneme with no intratubular differentiation. Atypical spermatozoa are also found in the testicular lumen. These cells resemble spermatozoa in most aspects, except that their nuclei are variable in shape, with the granular chromatin less electron-dense than that seen in spermatozoa. The origin and function of these cells could not be determined. The specializations seen in the spermatozoa are discussed as possible adaptations related to the habit of insemination.     

大黄鱼精子的超微结构

大黄鱼的精子由头产和尾部两部分组成。头部结构较为独特,其腹侧有一较大的细胞核,背部有中心粒复合体。头部的后端是袖套。细胞核的腹面稍向外突出背面则稍向内凹。细胞核中的染以质浓缩成致密的团块状。团块状的染色质之间分布着松散的纤维状染色质。植入窝位于细胞核的背部表面,由细胞核背面向内凹陷而成,呈一沟状,其走向与精子的长轴平行。     

黄颡鱼(Pseudobagrus fulvidraco)精子的超微结构

黄颡鱼精子由头部、中段和鞭毛(尾部)三部分组成。头部的主要结构是细胞核。核中浓缩了的染色质呈颗粒状。染色质中有核泡存在。核泡中有致密颗粒状物。植入窝里井状,从核后端往前深陷入核的中央。中段的中心粒复合体位于植入窝中,结构独特。近端中心粒和基体首尾相对,排在同一直线上。某些精子的近端中心粒的中央腔中能见到一、二个粗大的颗粒状物。基体的中央腔中有一对中央微管。近端中心粒和基体之间有中心粒间体将两者隔开。中段的袖套连接于细胞核之后,其中分布着线粒体和一些囊泡。近袖套内膜处的细胞质中有一层膜与袖套内膜平行。鞭毛细长,其起始端位于袖套腔中。鞭毛上长有两排侧鳍。侧鳍呈波纹状,分居轴丝两侧,大致与轴丝的两条中央微管同在一个平面上。侧鳍的基部有囊泡。     

Spermatozoa ultrastructure in Sciaenidae and Polynemidae (Teleostei:Perciformes) with some consideration on Percoidei spermatozoa ultrastructure

Spermatozoa ultrastructure was studied in five marines (Paralonchurus brasiliensis, Larimus breviceps, Cynoscion striatus, Micropogonias furnieri, Menticirrhus americanus, Umbrina coroides, Stellifer rastrifer), and one freshwater (Plagioscion squamosissimus) species of Sciaenidae and one species of Polynemidae (Polydactylus virginicus). The investigation revealed that, in all species, spermatozoa display a round head, a nucleus containing highly condensed, filamentous chromatin clusters, no acrosome, a short midpiece with a short cytoplasmic channel, and a flagellum showing the classic axoneme structure (9+2) and short irregular lateral fins. In Sciaenidae, the spermatozoa are type II, the flagellar axis is parallel to the nucleus, the lateral nuclear fossa is double arched, the centriolar complex is outside the nuclear fossa, the proximal centriole is anterior and perpendicular to the distal centriole, and no more than ten spherical (marine species) or elongate (freshwater species) mitochondria are observed. Polynemidae spermatozoa are of the intermediate type with the flagellar axis eccentric to the hemi-arc-shaped nucleus, and exhibit no nuclear fossa, the centriolar complex close to the upper nuclear end, the proximal centriole lateral and oblique to the distal centriole, and one large ring-shaped mitocondrion. The data available show that no characteristic is exclusively found in the spermatozoa of members of the Sciaenidae family when compared to other Percoidei with type II spermatozoa. However, three characteristics were exclusively found in Polynemidae: (1) the hemi-arched nucleus; the positioning of the centrioles; and (2) the ring-shaped mitocondrion. The interrelationships between Sciaenidae and Polynemidae as well as between these two families and other Percoidei are herein discussed.     

Spermiogenesis in Polyplacophora,with special reference to acrosome formation (Mollusca)

Summary The present study examines spermiogenesis, and in particular the formation of the acrosome, in ten species of chitons belonging to four families. This study emphasizes the formation of the acrosome but brings to light several other structures that have received little or no mention in previous studies. The process of spermiogenesis is essentially similar in each species, although Chaetopleura exhibits some significant differences. In early spermiogenesis the Golgi body secretes numerous small pro-acrosomal vesicles that gradually migrate into the apical cytoplasm. The chromatin condenses from granules into fibres which become twisted within the nucleus. A small bundle of chromatin fibres projects from the main nuclear mass into the anterior filament; this coincides with the appearance of a developing manchette of microtubules around the nucleus that originates from the two centrioles. Radiating from the distal centriole is the centriolar satellite complex, which is attached to the plasma membrane by the annulus. The distal centriole produces the flagellum posteriorly and it exits eccentrically through a ring of folded membrane that houses the annulus. Extending from the annulus on one side of the flagellum, in all but one species, is a dense fibrous body that has not been previously reported. The proximal centriole lies perpendicular to the end of the distal centriole and is attached to it by fibro-granular material. Pro-acrosomal vesicles migrate anteriorly through the cytoplasm and move into the anterior filament to one side of the expanding nucleus. Eventually these vesicles migrate all the way to the tip of the sperm, where they fuse to form one of two granules in the acrosome. In mature sperm the nucleus is bullet-shaped with a long anterior filament and contains dense chromatin with occasional lacunae. The mitochondria vary in both number and position in the mature sperm of different species. Both centrioles are housed eccentrically in a posterior indentation of the nucleus, where the membranes are modified. The elongate flagellum tapers to a long filamentous end-piece that roughly corresponds to the anterior filament and may be important in sperm locomotion for hydrodynamic reasons. An acrosome is present in all ten species and stained positively for acid phosphatase in three species that were tested.     

The ultrastructural organization of the mature spermatozoon of Luidia clathrata (Say) (Echinodermata: Asteroidea)

The sperm of Luidia clathrata are morphologically typical of asteroid sperm. The head is spherical and contains the nucleus and acrosomal complex. The nucleus has an anterior indentation in which rests the acrosomal complex. There is no evidence of a centriolar fossa along the posterior border of the nucleus. The acrosome is a cup-shaped structure containing a less electron dense central region. The periacrosomal material is homogeneous in nature, and the subacrosomal specialization of the periacrosomal materials appear as bands of varying electron density. The middle piece is an annular band of mitochondria which surrounds the proximal and distal centrioles. The centrioles exhibit the typical nine triplet arrangement. Both the centrioles and the axoneme project to one side of the middle piece region. Associated with the distal centriole is an elaborate pericentriolar process.     

Components and development of the centriolar complex during and beyond spermiogenesis in a passeridan bird, the Masked weaver (Ploceus velatus)

The fate of the proximal centriole in passeridan birds is an area of controversy and relative lack of knowledge in avian spermatogenesis and spermatology. This study examines, for the first time, spatiotemporal changes in the centriolar complex in various phases of spermiogenesis in a passerine bird, the Masked weaver (Ploceus velatus). It also describes the configuration of the centriolar complex and the relationship between it and the granular body in both intra- and extra-testicular spermatozoa. It is shown that the proximal centriole is retained and attaches, at its free end, to the granular body of spermatids in every step of spermiogenesis, as well as in mature intra-testicular and post-testicular spermatozoa, including those in the lumen of the seminal glomus. As the centriolar complex, along with its attached granular body, approaches the nucleus in the early spermatid, the proximal centriole articulates with the distal centriole at an acute angle of about 45°, and thereafter, both centrioles, still maintaining this conformation, implant, by means of their articulating proximal ends, at the implantation fossa of the nucleus. In the mature spermatid and spermatozoon, the granular body winds itself helically around the centriolar complex in the neck/midpiece region of the cell, and, thus, becomes the granular helix. The significance of this observation must await future studies, including possible phylogenetic re-evaluation and classification of birds.     

Spatial relationships between the anterior centriole and the mitotic center during interphase in the amoebae of the myxomycete Physarum polycephalum

Amoebae of the Myxomycete Physarum polycephalum in the interphase state typically contain only one proflagellar apparatus in which the anterior kinetosome (anterior centriole) is attached to the microtubule organizing center 1 (mtoc 1). We built strains possessing more than one mtoc 1 and a variable number of anterior centrioles to allow the appearance of new structures. In 8% of the amoebae of these strains, the 1:1 attachment between the anterior centriole and the mtoc 1 is not always respected. In nine cases studied using tridimensional reconstructions from ultrastructural thin sections, the pattern of attachment was more complex. A mtoc 1 could be linked to several anterior centrioles, and/or reciprocally an anterior centriole could be linked to several mtoc 1. In one case, an anterior centriole was not linked to a mtoc 1 and in three cases, a single centriole exhibited anterior and posterior characteristics. These observations suggest that (1) each pair of centrioles constitutes a morphological and physiological entity that is distinct from the mitotic center (mtoc 1); (2) the attachment of the anterior centriole to the mtoc 1 occurs at the end of each mitosis; (3) there is an inductory process during the morphogenesis of the link between the anterior centriole and the mtoc 1; (4) the anterior characteristics of a centriole can be present in the absence of the link with the mtoc 1; (5) the anterior and posterior characteristics of a centriole are not exclusive of each other, ruling out the existence of a lineage corresponding to the anterior centriole and a lineage corresponding to the posterior centriole; and (6) the differences between anterior and posterior centrioles result from a maturation process.     

Ultrastructure of the spermatogenesis of the cockle Anadara granosa L. (Bivalvia: Arcidae)

In this paper spermatogenesis and sperm ultrastructure of the cockle Anadara granosa are studied using transmission electron microscopy. The spermatocyte presents electron-dense vesicles and the arising axoneme that begins to form the flagellum. During spermatid differentiation, proacrosomal vesicles appear to migrate towards the presumptive anterior pole of the nucleus; eventually these vesicles become acrosome. The spermatozoon of Anadara granosa is of the primitive type. The acrosome, situated at the apex of the nucleus, is cap-shaped and deeply invaginated at the inner side. The spherical nucleus of the spermatozoon contains dense granular chromatin and shows invagination at the posterior poles. The centriole shows the classic nine triplets of microtubules. The middle piece consists of the centriolar complex surrounded by five giant mitochondria. It is shown that the ultrastructure of spermatozoa and spermiogenesis of Anadara granosa reveals a number of features that are common among bivalves. Received: 29 September 1998 / Received in revised form: 20 May 1999 / Accepted: 14 June 1999     

Morphology and phylogeny of Sainouron acronematica sp. n. and the ultrastructural unity of Cercozoa

Sainouron are soil zooflagellates of obscure taxonomy. We studied the ultrastructure of S. acronematica sp. n. and sequenced its extremely divergent 18S rDNA and that of Cholamonas cyrtodiopsidis (here grouped as new family Sainouridae) to clarify their phylogeny. Ultrastructurally similar, they weakly group together, deeply within Monadofilosa. Sainouron has three cytoplasmic microtubules; all organelles specifically link to them or the nucleus. Mature centrioles have fibrous rhizoplasts. The posterior centriole bearing the motile cilium (with cortical filaments) has a transitional hub-lattice; a dense spiral fibre links its thicker rhizoplast and triplets; its ciliary root has two microtubules: mt1, underlying the plasma membrane, initiates at the spiral fibre; mt2, laterally attached to mt1 and nucleus, initiates in the amorphous centrosomal region. The anterior younger cilium, an immotile stub with submembrane skeleton as in Cholamonas, lacks axoneme, microtubular root, rhizoplasts and spiral fibre, but becomes the posterior one every cell cycle. The nuclear envelope donates coated vesicles directly to the Golgi, which makes kinetocyst-type extrusomes, concentrated at the cell anterior for extrusion into phagosomes. Ciliary transition region proximal hub-lattices (postulated to contain centrin) and distal nonagonal fibres are cercozoan synapomorphies, found with slight structural variation in all flagellate Cercozoa, but not in outgroups.     

Sperm morphology in five species of cicadettine cicadas (Hemiptera: Cicadomorpha: Cicadidae)

Mature spermatozoa from five species of cicadas of the subfamily Cicadettinae (Quintilia wealei, Melampsalta leucoptera, Stagira simplex, Xosopsaltria thunbergi and Monomatapa matoposa) were examined by light and electron microscopy. In each species sperm are elongate, aggregated into organized bundles with their heads embedded in a homogenous matrix to form spermatodesmata, and exhibit polymegaly. The head of the sperm consist of an anteriorly positioned conical acrosome that has a tubular substructure and a deep, posterior invagination that forms the subacrosomal space (eccentrically positioned anteriorly). The acrosome is flattened anteriorly; posteriorly it extends along either side of the nucleus as two tubular processes that gradually decrease in diameter. The filiform nucleus tapers anteriorly and intrudes into the subscrosomal space. Posteriorly the nucleus has a lateral invagination that houses material of the so-called centriolar adjunct. Posterior to the centriolar adjuct and the nucleus are two crystalline mitochondrial derivatives and a centriole, respectively, the latter giving rise to the axoneme, which has a 9 + 9 + 2 arrangement of microtubules. In these respects the sperm are similar to those of platypleurine cicadas. However, some features seem unique to cicadettines, including the structural organization of an enlarged centriolar adjunct and the dimensions of the tails. The enlarged centriolar adjunct has a lamella-like substructure and can be considered a synapomorphic character in the Cicadettinae. It is, therefore, potentially useful in the separation of this subfamily from the Cicadinae. In addition, the great length of the sperm nucleus of long-headed sperm in M. matoposa could be a synapomorphy of this genus and related taphurine and cicadettine species.     

The Origin of the Second Centriole in the Zygote of Drosophila melanogaster

Centrosomes are composed of two centrioles surrounded by pericentriolar material (PCM). However, the sperm and the oocyte modify or lose their centrosomes. Consequently, how the zygote establishes its first centrosome, and in particular, the origin of the second zygotic centriole, is uncertain. Drosophila melanogaster spermatids contain a single centriole called the Giant Centriole (GC) and a Proximal centriole-like (PCL) structure whose function is unknown. We found that, like the centriole, the PCL loses its protein markers at the end of spermiogenesis. After fertilization, the first two centrioles are observed via the recruitment of the zygotic PCM proteins and are seen in asterless mutant embryos that cannot form centrioles. The zygote’s centriolar proteins label only the daughter centrioles of the first two centrioles. These observations demonstrate that the PCL is the origin for the second centriole in the Drosophila zygote and that a paternal centriole precursor, without centriolar proteins, is transmitted to the egg during fertilization.     

Sperm structure of Mecoptera and Siphonaptera (Insecta) and the phylogenetic position of<Emphasis Type="Italic"> Boreus hyemalis</Emphasis>

Sperm ultrastructure has been studied in three species of the taxa Mecoptera and Siphonaptera. The spermatozoon of the scorpion fly Panorpa germanica shows an apical bilayered acrosome, a helicoidal nucleus, a centriolar region and a 9+2 flagellar axoneme helicoidally arranged around a long mitochondrial derivative. A second mitochondrial derivative is very short and present only in the centriolar region. A single accessory body is present and it is clearly formed as a prolongation of the centriole adjunct material. Two lateral lamellae run parallel to the nucleus. The snow fly Boreus hyemalis has a conventional sperm structure and shows a bilayered acrosome, a long nucleus, a centriolar region, two mitochondrial derivatives and two accessory bodies. The axoneme is of the 9+2 type and is flattened at the tail tip. Both P. germanica and B. hyemalis have two longitudinal extra-axonemal rods and have a glycocalyx consisting of longitudinal parallel ridges or filaments. The spermatozoon of the flea Ctenocephalides canis has a long apical bilayered acrosome, a nucleus, a centriolar region, a 9+2 axoneme wound around two unequally sized mitochondrial derivatives, and two triangular accessory bodies. In the posterior tail end the flagellar axoneme disorganises and a few microtubular doublets run helicoidally around the remnant mitochondrial derivative. The glycocalyx consists of fine transverse striations. In all three species, the posterior tail tip is characterised by a dense matrix embedding the disorganised axoneme. From this comparative analysis of the sperm structure it is concluded that Mecoptera, as traditionally defined, is monophyletic and that B. hyemalis is a member of Mecoptera rather than of Siphonaptera.     

C-NAP1 and rootletin restrain DNA damage-induced centriole splitting and facilitate ciliogenesis

Cilia are found on most human cells and exist as motile cilia or non-motile primary cilia. Primary cilia play sensory roles in transducing various extracellular signals, and defective ciliary functions are involved in a wide range of human diseases. Centrosomes are the principal microtubule-organizing centers of animal cells and contain two centrioles. We observed that DNA damage causes centriole splitting in non-transformed human cells, with isolated centrioles carrying the mother centriole markers CEP170 and ninein but not kizuna or cenexin. Loss of centriole cohesion through siRNA depletion of C-NAP1 or rootletin increased radiation-induced centriole splitting, with C-NAP1-depleted isolated centrioles losing mother markers. As the mother centriole forms the basal body in primary cilia, we tested whether centriole splitting affected ciliogenesis. While irradiated cells formed apparently normal primary cilia, most cilia arose from centriolar clusters, not from isolated centrioles. Furthermore, C-NAP1 or rootletin knockdown reduced primary cilium formation. Therefore, the centriole cohesion apparatus at the proximal end of centrioles may provide a target that can affect primary cilium formation as part of the DNA damage response.     

C-NAP1 and rootletin restrain DNA damage-induced centriole splitting and facilitate ciliogenesis

Cilia are found on most human cells and exist as motile cilia or non-motile primary cilia. Primary cilia play sensory roles in transducing various extracellular signals, and defective ciliary functions are involved in a wide range of human diseases. Centrosomes are the principal microtubule-organizing centers of animal cells and contain two centrioles. We observed that DNA damage causes centriole splitting in non-transformed human cells, with isolated centrioles carrying the mother centriole markers CEP170 and ninein but not kizuna or cenexin. Loss of centriole cohesion through siRNA depletion of C-NAP1 or rootletin increased radiation-induced centriole splitting, with C-NAP1-depleted isolated centrioles losing mother markers. As the mother centriole forms the basal body in primary cilia, we tested whether centriole splitting affected ciliogenesis. While irradiated cells formed apparently normal primary cilia, most cilia arose from centriolar clusters, not from isolated centrioles. Furthermore, C-NAP1 or rootletin knockdown reduced primary cilium formation. Therefore, the centriole cohesion apparatus at the proximal end of centrioles may provide a target that can affect primary cilium formation as part of the DNA damage response.