Nuclear Apex Research Articles

The perforatorium and postacrosomal sheath of rat spermatozoa share common developmental origins and protein constituents†.

The perinuclear theca (PT) is a cytosolic protein capsule that surrounds the nucleus of eutherian spermatozoa. Compositionally, it is divided into two regions: the subacrosomal layer (SAL) and the postacrosomal sheath (PAS). In falciform spermatozoa, a third region of the PT emerges that extends beyond the nuclear apex called the perforatorium. The formation of the SAL and PAS differs, with the former assembling early in spermiogenesis concomitant with acrosome formation, and the latter dependent on manchette descent during spermatid elongation. The perforatorium also forms during the elongation phase of spermiogenesis, suggesting that like the PAS, its assembly is facilitated by the manchette. The temporal similarity in biogenesis between the PAS and perforatorium led us to compare their molecular composition using cell fractionation and immunodetection techniques. Although the perforatorium is predominantly composed of its endemic protein FABP9/PERF15, immunolocalization indicates that it also shares proteins with the PAS. These include WBP2NL/PAWP, WBP2, GSTO2, and core histones, which have been implicated in early fertilization and zygotic events. The compositional homogeny between the PAS and perforatorium supports our observation that their development is linked. Immunocytochemistry indicates that both PAS and perforatorial biogenesis depend on the transport and deposition of cytosolic proteins by the microtubular manchette. Proteins translocated from the manchette pass ventrally along the spermatid head into the apical perforatorial space prior to PAS deposition in the wake of manchette descent. Our findings demonstrate that the perforatorium and PAS share a mechanism of developmental assembly and thereby contain common proteins that facilitate fertilization.

Ultrastructure of spermatophoral sperm in the freshwater gastropod Thiara amarula (Linnaeus, 1758) (Cerithioidea: Thiaridae): potential taxonomic features including eusperm nuclear content differentiation

The ultrastructure of spermatophoral sperm is investigated for the first time in a cerithioidean gastropod. Thiara amarula (Linnaeus, 1758), a widespread Indo-West Pacific species of the Thiaridae, produces uniaxonemal euspermatozoa and multiaxonemal paraspermatozoa. Euspermatozoa possess a laterally-flattened acrosomal vesicle (with eccentrically positioned invagination and subacrosomal material), a tubular, laterally-compressed nucleus, an elongate midpiece (with four, straight, equal-sized mitochondria each with parallel cristae), an elongate glycogen piece and an end piece. The eusperm nucleus exhibits or is associated with a number of unusual features including: (1) nuclear contents differentiated into two components (fibrous, highly electron-dense material, enclosing a pair of less-dense, finely granular tracts); (2) nuclear invagination with two elongate grooves aligned at 90 degrees to the axonemal central microtubules and parallel with the 1 and 5 axonemal doublets; (3) a periodically-banded rootiet associated with the centriolar complex near the nuclear apex; (4) an electron-dense structure attaching the nucleus to the axoneme at the nucleus-midpiece junction. Feature (1) has been reported elsewhere in Melanoides tuberculata (Thiaridae), but in no other examined gastropods (or other molluscs) and its purpose is unknown. Paraspermatozoa of T. amarula possess an elongate head region (up to 14 axonemes and large, irregular mitochondria enclosed by sheath of spherical, dense vesicles), a short 'glycogen' region and a posterior tuft of glycogen tails. The two sperm types do not form spermatozeugmata and observations suggest that neither type undergoes any noticeable structural change while inside the spermatophore. Sperm features suggest a close relationship between T. amurula and M. tuberculata and more broadly with other 'Group T cerithioidean families exhibiting four equal-sized eusperm mitochondria, including Potamididae, Modulidae, Scaliolidae, Melanopsidae, Semisulcospiridae and Pleuroceridae.

Spermatogenic ultrastructure in the anomalodesmatan bivalve Myochama anomioides (Mollusca: Myochamidae) – does the nucleus help position the ‘temporary’ acrosome?

AbstractSpermatogenic ultrastructure in the marine bivalve mollusc Myochama anomioides (Myochamidae) is described and contrasted with other bivalves, especially other euheterodonts. Small (0.1 μm diameter), primary proacrosomal vesicles produced in spermatocytes give rise to much larger (0.4 μm diameter) secondary proacrosomal vesicles in early spermatids, which in turn form the dished‐shaped, definitive acrosomal vesicle (diameter 1.0 μm) of later spermatids. The acrosomal vesicle acquires a deposit of subacrosomal material and comes to lie close to or in contact with the plasma membrane. The acrosomal complex (acrosomal vesicle + subacrosomal material) initially positions itself at the apex of the condensing, fibrous nucleus (the so‐called temporary acrosome position), but subsequently begins to move posteriorly. The condensing nucleus becomes markedly folded so that its apex is posteriorly orientated towards the migrating acrosomal complex and the midpiece (mitochondria and centrioles). The close spatial relationship of nuclear apex to acrosomal complex during this folding strongly suggests that acrosomal migration in M. anomioides is assisted, at least in part, by movement of the late spermatid nucleus. Similar nuclear folding has previously been demonstrated in an early stage of fertilization in another anomalodesmatan (Laternula limicola) raising the possibility that one event might be a reversal of the other.

Ultrastructure of spermatozoa in Orthalicidae (Mollusca, Gastropoda, Stylommatophora) and its systematic implications

Sperm morphology of orthalicid gastropods Clessinia pagoda, Spixia tucumanensis, Plagiodontes daedaleus (Odontostominae) and Drymaeus hygrohylaeus, D. poecilus, Bostryx stelzneri (Bulimulinae) are examined and described for the first time using transmission electron microscopy. Spermatozoa show the general characteristic of Pulmonata: an acrosomal vesicle, sperm nucleus helical, mitochondrial derivative forming a continuous sheath with paracrystalline material and coarse fibers associated with axonemal doublets. Features in the acrosomal complex and shape of the nucleus distinguish orthalicid sperms from other stylommatophoran. The acrosomal pedestal is traversed by fine striations in all species examined except in S. tucumanensis. The structure and thickness of the perinuclear sheath with a single or double layer of electron-dense material ensheathing the nuclear apex is characteristic of the group. The presence of a subnuclear ring in Drymaeus, Bostryx and Clessinia species is also reported. A data matrix of eleven species per 34 characters (16 sperm plus 18 anatomical and shell characters) from orthalicids plus other stylommatophoran and systellommatophoran representative species was constructed. Three cladistic analyses (sperm-based, anatomical-based and a combined sperm + anatomical-based) were performed to test the phylogenetic potential of sperm ultrastructure in orthalicid systematics and understand how sperm characters affect the topology and resolution of the obtained trees. Stylommatophora resulted in a monophyletic clade in the sperm-based and in the combined-character analysis. Orthalicidae is monophyletic only in the combined-character cladogram. Within Orthalicidae, Odontostominae is recovered as a monophyletic clade in all analyses, while Bulimulinae is paraphyletic in all trees except in the combined phylogeny. The present study and cladistic analyses performed support the hypothesis that characters on sperm ultrastructure are informative for stylommatophoran systematic and phylogenetic approaches, providing synapomorphies at familiar, subfamiliar and generic level.

Choanocyte ultrastructure in Halisarca dujardini (Demospongiae, Halisarcida)

Understanding poriferan choanocyte ultrastructure is crucial if we are to unravel the steps of a putative evolutionary transition between choanoflagellate protists and early metazoans. Surprisingly, some aspects of choanocyte cytology still remain little investigated. This study of choanocyte ultrastructure in the halisarcid demosponge Halisarca dujardini revealed a combination of minor and major distinctive traits, some of them unknown in Porifera so far. Most significant features were 1) an asymmetrical periflagellar sleeve, 2) a battery of specialized intercellular junctions at the lateral cell surface complemented with an array of lateral interdigitations between adjacent choanocytes that provides a particular sealing system of the choanoderm, and 3) a unique, unexpectedly complex, basal apparatus. The basal apparatus consists of a basal body provided with a small basal foot and an intricate transverse skeleton of microtubules. An accessory centriole, which is not perpendicular to the basal body, is about 45 degrees . In addition, a system of short striated rootlets (periodicity = 50-60 nm) arises from the proximal edge of the basal body and runs longitudinally to contact the nuclear apex. This is the first flagellar rootlet system ever found in a choanocyte. The accessory centriole, the rootlet system, and the nuclear apex are all encircled by a large Golgi apparatus, adding another distinctive feature to the choanocyte cytology. The set of distinct features discovered in the choanocyte of H. dujardini indicates that the ultrastructure of the poriferan choanocyte may vary substantially between sponge groups. It is necessary to improve understanding of such variation, as the cytological features of choanocytes are often coded as characters both for formulation of hypotheses on the origin of animals and inference of phylogenetic relationships at the base of the metazoan tree.

Sperm ultrastructure in Glauconome plankta and its relevance to the affinities of the Glauconomidae (Bivalvia: Heterodonta)

Summary Using transmission electron microscopy, sperm morphology was investigated for the first time in a representative of the heterodont bivalve family Glauconomidae. Spermatozoa of Glauconome plankta (Iredale, 1936) consist of a head region (acrosomal complex + nucleus), short midpiece and a flagellum. The membrane-bound acrosomal vesicle is attenuate-conical (length 1.1 ± 0.08 μm) with a moderately deep basal invagination extending for most of the vesicle's length. Contents of the vesicle are differentiated into a highly electron-dense basal ring (cylindrical) sheathed by less dense material that also occupies the anterior two-thirds of the vesicle. Finely granular subacrosomal material fills the vesicle invagination and forms a layer between the nuclear apex and the vesicle, but no axial rod is discernible. The nucleus is rodshaped and straight, 4.4 ± 0.2 μm long and tapers slightly towards the apex. Nuclear contents are highly electron-dense, with the exception of occasional, electron-lucent lacunae. The midpiece consists of a pair of triplet-microtubular centrioles surrounded by four, approximately spherical mitochondria. Highly electron-dense granules of putative glycogen were observed between the mitochondria and around the distal centriole. The distal centriole is anchored to the plasma membrane via satellite fibres and is continuous with the flagellum (the latter 46 ± 3.0 μm long and exhibiting a conventional 9+2 axoneme). Comparison of sperm results does not suggest any especially close relationship between Glauconomidae (as exemplified by G. plankta) and other member families of the superfamily Veneroidea. Elsewhere within the Heterodonta no close relationship with the Corbiculoidea, Myoidea, Mactroidea, Tellinoidea or the Crassatelloidea is indicated by sperm morphology. Most promising seems a possible connection with Arctica (Arcticidae, Arcticoidea), which shows similar acrosomal and nuclear features. Supporting morphological and molecular evidence for this relationship is inconclusive but suggests further study.

Fine structural study of the spermatogenic cycle in Pitar rudis and Chamelea gallina (Mollusca, Bivalvia, Veneridae)

A comparative ultrastructural study of spermatogenesis was performed in the bivalve molluscs Pitar rudis and Chamelea gallina (Veneridae) from Turkey. Sertoli cells appeared to be rich in glycogen, lipid droplets and germ-cell phagolysosomes. Premeiotic cells exhibited nuage and a flagellum, with the Golgi complex and the rough endoplasmic reticulum originating proacrosomal vesicles during the pachytene stage. In round spermatids, the acrosomal vesicle migrated linked to the plasma membrane. In P. rudis, the acrosomal vesicle base formed a thin expansion that attached to the nuclear apex and was associated with development of the perforatorium. The cap-shaped acrosomal vesicle then differentiated into external and internal regions, and also into a small apical light region, although some cells exhibited an apical extension of the external component. On the contrary, two lateroapical light pouches developed in C. gallina. During spermiogenesis, chromatin became fibrillar and then condensed while the nucleus turned conical shaped in P. rudis or slightly curved in C. gallina. In P. rudis, the midpiece contained glycogen and four mitochondria, although five mitochondria were sometimes observed, whereas in C. gallina the midpiece contained four mitochondria. Comparison with other members of Veneroida shows a common ectaquasperm type, but novel findings in acrosome biogenesis.

Spermatozoal ultrastructure of spiny oysters (Spondylidae, Bivalvia) including a comparison with other bivalves

Summary Sperm infrastructure in three representative species of the marine bivalve family Spondylidae (“spiny or thorny oysters”) is examined and compared with available data on other bivalves, especially other families of the subclass Pteriomorphia. Spondylid spermatozoa are of the externally fertilizing aquasperm type (ect-aquasperm). The acrosomal vesicle is conical with a deep basal invagination extending almost the full length of the vesicle. Vesicle contents are divisible into an inner, highly electron-dense anterior layer and a less dense posterior layer. The anterior layer is folded back on itself posteriorly and exhibits radiating plates (best developed peripherally). The vesicle rests on, and is partially embedded in, an extensive granular deposit of subacrosomal material at the nuclear apex. This deposit extends partly into acrosomal vesicle invagination and also fills a broad depression in the anterior of the nucleus. No pre-formed axial rod (perforatorium) is present. The nucleus is round-pyriform and its contents coarsely fibrogranular. At the base of the nucleus, four broad depressions partially accommodate the midpiece mitochondria. The midpiece consists the four spherical mitochondria and the proximal and distal centrioles. The centrioles are arranged at approximately 90° to each other, and each consists of nine, angularly-oriented, microtubular triplets embedded in a granular matrix. A short, periodically banded rootlet connects the proximal centriole to the nuclear fossa, whereas the distal centriole, which forms the basal body to the flagellar axoneme, is anchored to the plasma membrane by nine terminally forked satellite fibres. Extensive deposits of putative glycogen rosettes surround the centrioles and mitochondria. The flagellum consists of a 9+2 axoneme sheathed by the plasma membrane. Spondylid spermatozoa strongly resemble those of the Pectinidae, further confirming the traditional view (based on comparative anatomy and shell morphology) of a close relationship between the Spondylidae and the Pectinidae. Differences in acrosomal shape and dimensions were noted between the three species examined, indicating potential taxonomic utility for comparative sperm ultrastructure within the Spondylidae.

Relevance of sperm ultrastructure to the classification of giant clams (Mollusca, Cardioidea, Cardiidae, Tridacninae)

Abstract Examination of sperm ultrastructure in six out of eight of the living species of giant clams (‘Tridacnidae’) supports reduction in status of the Tridacnidae to a subfamily of the Cardiidae (Tridacninae), as suggested by recent cladistic analyses based on shell, anatomical and molecular characters. Tridacninae spermatozoa are all of the aquasperm type, featuring, in anterior-posterior sequence: a conical acrosomal vesicle, an oblong to rod-shaped nucleus, a short midpiece region (proximal and distal centrioles surrounded by four round mitochondria); and a flagellum (9 + 2 pattern axoneme). Substantial differences occur between species with respect to the shape and length of the nucleus, and in the spatial reationship between the acrosomal complex and the nuclear apex. Although the two extant genera can be distinguished on sperm features — Tridacna , nuclear peg associated with acrosome, centriolar connective absent; Hippopus , nuclear peg absent, connective present — no defining feature of the Tridacninae can be detected. Within Tridacna , the species T. (Chametrachea) maxima and T. (C.) crocea are distinguished from other species of the genus by a much finer nuclear peg and a considerably smaller acrosome. In contrast, and against expectation, T. (C.) squamosa shows acrosomal and nuclear dimensions very close to those obtained for T. (Tridacna) gigas . Recently proposed phylogenies and classificatory changes for ‘tridacnids’ are discussed in the light of available sperm data.

Unique Checkpoints During the First Cell Cycle of Fertilization After Intracytoplasmic Sperm Injection in Rhesus Monkeys

Intracytoplasmic sperm injection has begun an era of considerable improvements in treating male infertility. Despite its success, questions remain about the dangers of transmitting traits responsible for male infertility, sex and autosomal chromosome aberrations1 and possible mental, physical and reproductive abnormalities2,3. We report here the first births of rhesus monkeys produced by intracytoplasmic sperm injection at rates greater or equal to those reported by clinics. Essential assumptions about this process are flawed, as shown by results with the preclinical, nonhuman primate model and with clinically discarded specimens. Dynamic imaging demonstrated the variable position of the second meiotic spindle in relation to the first polar body; consequently, microinjection targeting is imprecise and potentially lethal. Intracytoplasmic sperm injection resulted in abnormal sperm decondensation, with the unusual retention of vesicle-associated membrane protein and the perinuclear theca, and the exclusion of the nuclear mitotic apparatus from the decondensing sperm nuclear apex. Male pronuclear remodeling in the injected oocytes was required before replication of either parental genome, indicating a unique G1-to-S transition checkpoint during zygotic interphase (the first cell cycle). These irregularities indicate that the intracytoplasmic sperm injection itself might lead to the observed increased chromosome anomalies4,5.

Unique checkpoints during the first cell cycle of fertilization after intracytoplasmic sperm injection in rhesus monkeys.

Intracytoplasmic sperm injection has begun an era of considerable improvements in treating male infertility. Despite its success, questions remain about the dangers of transmitting traits responsible for male infertility, sex and autosomal chromosome aberrations and possible mental, physical and reproductive abnormalities. We report here the first births of rhesus monkeys produced by intracytoplasmic sperm injection at rates greater or equal to those reported by clinics. Essential assumptions about this process are flawed, as shown by results with the preclinical, nonhuman primate model and with clinically discarded specimens. Dynamic imaging demonstrated the variable position of the second meiotic spindle in relation to the first polar body; consequently, microinjection targeting is imprecise and potentially lethal. Intracytoplasmic sperm injection resulted in abnormal sperm decondensation, with the unusual retention of vesicle-associated membrane protein and the perinuclear theca, and the exclusion of the nuclear mitotic apparatus from the decondensing sperm nuclear apex. Male pronuclear remodeling in the injected oocytes was required before replication of either parental genome, indicating a unique G1-to-S transition checkpoint during zygotic interphase (the first cell cycle). These irregularities indicate that the intracytoplasmic sperm injection itself might lead to the observed increased chromosome anomalies.

Quantitative assessment of normal and potentially premalignant epithelium at different levels of human colorectal crypts.

The present study uses morphometric techniques to assess whether altered differentiation patterns exist in PPM which might reflect its premalignant status. Samples were obtained from resected malignant lesions of large bowels of 10 Chinese patients. Normal (N) samples were biopsied from the margins of each resected large bowel. Potentially premalignant (PPM) mucosae were obtained from within 2 cm of the margins of the malignant lesions. Tissues were processed for histological examination and using strict criteria, colorectal crypts were divided into basal (B), intermediate (I) and surface (S) segments. Interactive digitisation of sections from each group was used to generate the following morphometric parameters in each segment: nuclear profile circularity indices (NSF and NCI); nuclear numerical density (NA and NV); the degree of deviation of the major nuclear axis in relation to the epithelial-connective junction (AGDMAX); cell height (CH); the distance between nuclear apex to cell apex (DNACA); the distance between cell base to nuclear apex (DCBNA); stratification index (SI)--the ratio of DCBNA and CH; and the volume density of mucous vacuoles in the reference epithelium (VVMV,EP). In comparisons of different segments within groups, the nuclei at the S segment of N and PPM crypts were more irregular and less circular in shape than nuclei from other segments. There was a shift of nuclear profile shape (NSF and NCI) from circular to ellipsiodal between B and S segments. In comparisons of similar segments between groups, no significant nuclear shape changes were detected in nuclei of PPM crypts when compared with nuclei in similar segments of N crypts and the pattern of nuclear shape alterations resembled those of normal crypts. In comparisons of different segments within groups of N and PPM crypts, AGDMAX, DNACA, DCBNA, CH and SI parameters demonstrated that epithelial cells at the I segments have more centrally positioned nuclei with the tallest epithelial height when compared with epithelial cells in other segments of both crypts. In B segments, nuclear NA and NV were almost double those of other segments in both N and PPM crypts, with marked reductions in these parameters between B and I segments. VVMV,EP was significantly highest in the I segment and significantly lowest in the S segment of both groups. Both N and PPM crypts showed similar trends in VVMV,EP within the crypt segments but when comparing similar segments between both crypts, a significant difference was detected only between S segments. The alterations of nuclear shape and packing densities, orientation and mucous content in N crypts were similarly expressed in PPM crypts and distinct differences in numerical density (NV) and stratification index existed in crypts between these two groups when comparing similar segments. All values in PPM were consistently lower when compared with N crypts. These preliminary observations may represent a subtly altered state of cellular differentiation in PPM which may be a reflection of early preneoplastic transformation.

COMPARATIVE SPERM MORPHOLOGY OF THE PULMONATE LIMPETS TRIMUSCULUS COSTATUS, T. RETICULATUS (TRIMUSCULIDAE) AND BURNUPIA STENOCHORIAS AND ANCYLUS FLUVIATILIS (ANCYLIDAE)

Sperm infrastructure is described for the first time in representatives of the pulmonate 'limpet' families Trimusculidae (Trunusculus costatus, T. reticulatus: marine) and Ancylidae (Bumupia stenochorias, Ancylus fluviatilis: freshwater). All show characteristic heterobranch sperm features (a spheroidal acrosomal vesicle supported by an acrosomal pedestal; a helically keeled nucleus and a complex, very elongate midpiece featuring paracrystalline and matrix layers sheathing the axoneme, coarse fibers and one or more glycogen helices). Posterior to the midpiece, a glycogen piece (axoneme sheathed by glycogen granules) and annulus are also present in all species. Taxonomically useful differences in the shape and dimensions of the acrosome, nucleus and midpiece occur between the species. Results support the decision of recent workers to transfer the Trimusculidae from the Siphonarioidea to a separate superfamily Trimusculoidea (characteristic sperm features including: narrow acrosomal pedestal overlapping with nuclear apex; heavily keeled nucleus; midpiece with strongly projecting secondary and glycogen helices). The relationship of the Trimusculoidea to other pulmonates, as indicated by sperm ultrastructure, remains uncertain largely because comparative data for several important groups are unavailable. Spermatozoa of the two ancylids most closely resemble those of other investigated planorboideans and to a lesser extent, those of the Lymnaeoidea. However, differences between Bumupia stenochorias (unique(?) accessory structure on the acrosomal pedestal; glycogen wedges within the nuclear fossa; other features similar to planorbids) and Ancylus fluviatilis (all sperm features very similar to planorbids) suggests that these patelliform ancylids are not closely related.

Spermatozoan ultrastructure in the trigonioid bivalveNeotrigonia margaritacea Lamarck (Mollusca): Comparison with other bivalves, especially Trigonioida and Unionoida

Spermatozoa of the trigonioid bivalveNeotrigonia margaritacea (Lamarck) (Trigoniidae, Trigonioida) are examined ultrastructurally. A cluster of discoidal, proacrosomal vesicles (between 9 to 15 in number) constitutes the acrosomal complex at the nuclear apex. The nucleus is short (2.4–2.6 μm long, maximum diameter 2.2 μm), blunt-conical in shape, and exhibits irregular lacunae within its contents. Five or sometimes four round mitochondria are impressed into shallow depressions in the base of the nucleus as is a discrete centriolar fossa. The mitochondria surround two orthogonally arranged centrioles to form, collectively, the midpiece region. The distal centriole, anchored by nine satellite fibres to the plasma membrane, acts as a basal body to the sperm flagellum. The presence of numerous proacrosomal vesicles instead of a single, conical acrosomal vesicle setsNeotrigonia (and the Trigonioida) apart from other bivalves, with the exception of the Unionoida which are also known to exhibit this multivesicular condition. Spermatozoa ofN. margaritacea are very similar to those of the related speciesNeotrigonia bednalli (Verco) with the exception that the proacrosomal vesicles ofN. margaritacea are noticeably larger than those ofN. bednalli.

Sperm Ultrastructure of the Tropical Notaspidean Pleurehdera Haraldi with Evaluation of the Phylogenetic Position of the Genus

Sperm ultrastructure is described for Pleurehdera haraldi Er. & Ev. Marcus, 1970 and contrasted with data from previously investigated members of the Notaspidea. The acrosomal vesicle is small (length 0.13 pm, breadth 0.09 pm) and supported basally by a short (0.37 pm) pedestal which overlaps extensively with the tapered nuclear apex. Nuclei are approxi-mately 15 pm long and sometimes exhibit a single helical keel. Absence of the keel in many of the observed spermatozoa suggests possible dimorphism with regard to this feature. A short basal invagination of the nucleus forms the point of attachment for the centriolar derivative and axoneme/coarse fibre com-plex. A single glycogen-filled helix is present within the mitochondrial derivative of the midpiece. Distally, an annulus occurs at the junction of the elongate (at least 160 pm) midpiece and short (1.5 pm) glycogen piece. Axonemal microtubules persist to the posterior tip of the spermatozoon. Comparison with other Notaspidea confirms that Pleurehdera is closest to Berthella and Berthellina within the Pleurobranchinae (of the family Pleurobranchidae). Sperm morphology supports the unity of the pleurobranchine tribe Berth- ellini.

THE FLAGELLAR APPARATUS OF MALLOMONAS SPLENDENS (SYNUROPHYCEAE) AT INTERPHASE AND ITS DEVELOPMENT DURING THE CELL CYCLE1

ABSTRACTThe interphase configuration of the flagellar apparatus of Mallomonas splendens (G. S. West) Playfair displays several features that are novel in the Synurophyceae. One of the two basal bodies usually has no flagellum, and two fibrous bands connect the basal bodies. Surrounding the basal bodies is a distinctive, fibrous capsule which is continuous with a thick, fibrous band that constitutes the anterior portion of the rhizoplast. The remainder of the rhizoplast spreads over the nuclear apex as numerous, prominently striated straps. A single, three‐membered, mi‐crotubular root (R1) forms a loop at the cell anterior and then descends from the loop to abutt on the rhizoplast near the nuclear apex. The descending portion of R1 displays at least two orientations with respect to the basal bodies.Two new basal bodies appear before mitosis and bear the rudiments of new Ills. At preprophase these new roots are 2–3 μm long, and new rhizoplasts, which organize (nucleate?) microtubules of the incipient mitotic spindle, arise from the proximal end of the new basal bodies. The latter produce new fiagella as the parental flagellum shortens. Simultaneous to these developments is the disassembly of the parental rhizoplast and the descending portion of the parental RI. At metaphase the two pairs of basal bodies have separated so that each pair consists of a parental and a daughter basal body. The parental R1 loop is absent and the new R1s form semi‐loops around each pair of basal bodies. The rhizoplasts extend down either side of the nuclear material as the spindle becomes fully formed. The new loops are completed at mid‐cytokinesis. At the end of cytokinesis the roots elongate towards the nuclear apex, and each rhizoplast takes on the interphase appearance. Mitosis in M. splendens is compared to that in the Chrysophyceae.

Ultrastructure of spermiogenesis inVampyroteuthis infernalis Chun — a relict cephalopod mollusc

Spermiogenesis in the relict deep-sea cephalopodVampyroteuthis infernalis Chun is examined using transmission electron microscopy (TEM), and the results compared with available data on other cephalopods. Early spermatids ofVampyroteuthis exhibit an ovoid nucleus (with dense irregular patches), numerous mitochondria and a pair of triplet substructure centrioles (arranged parallel to each other). Subsequently, the following morphological changes take place: (1) nuclear contents condense into a fibrous reticulum, then into thick fibres; (2) the acrosomal vesicle (presumably Golgi-derived) positions itself in a shallow depression at the nuclear apex; (3) the flagellum forms from one of the two centrioles; (4) mitochondria cluster around the flagellum at the base of the nucleus; (5) a dense, fibrous plug forms within the basal invagination of the nucleus. Microtubules surround the acrosome and condensing nucleus of spermatids. The dense plug is of special systematic importance since it also occurs in spermatids and spermatozoa ofOctopus spp., but not in any investigated species of the Sepiida, Sepiolida or Teuthida. Late spermatids and mature spermatozoa ofVampyroteuthis strongly resemble developing spermatids ofOctopus, suggesting a close phylogenetic relationship betweenVampyroteuthis (and the Vampyromorpha) and octopods.

Ultrastructural and cytochemical study of spermatogenesis in Scrobicularia plana (Mollusca, Bivalvia).

The ultrastructure of the mature spermatozoa and spermatogenesis of the bivalve Scrobicularia plana are described. Support cells extend from the basal lamina to the lumen of the testis and are laterally connected to the germinal epithelium. Germ cells present intercellular bridges and flagella since the spermatogonial stage. While spermatogonia and spermatocytes appear connected to support cells by desmosome-like junctions, elongated spermatids are held at the acrosomal region by support cell finger-like processes. During spermiogenesis, the acrosomal vesicle differentiates from a golgian saccule and then migrates to the nuclear apex. A microtubular manchette arising from centrioles surrounds the acrosomal vesicle, the nucleus, and the mitochondria at the time these three organelles start their elongation, disappearing after that. The mature spermatozoon of S. plana lacks a distinct midpiece because the mitochondria extend from the region of the pericentriolar complex along the nucleus anteriorly for approximately 1.4 microns. The features of this bivalve type of modified spermatozoon are compared with those of other animal groups having similar modifications.

Spermiogenesis and spermatozoa in the relict bivalve genus Neotrigonia: relevance to trigonioid relationships, particularly Unionoidea

Spermiogenesis and spermatozoa in the relict trigonioid genus Neotrigonia are examined ultrastructurally. Mature Neotrigonia spp. spermatozoa exhibit the following features: (1) a blunt-conical nucleus; (2) an acrosomal complex composed of discoidal vesicles (9 to 15) arranged as a thin layer over the nuclear apex; (3) five (rarely four) spherical mitochondria positioned in depressions at the base of the nucleus; (4) proximal and distal centrioles (surrounded by the mitochondria); (5) a satellite complex anchoring the distal centriole and flagellum to the plasma membrane; and (6) a single flagellum. Spermatozoa of unionoids examined to date (Unionidae and Hyriidae only) exhibit similar features, including a nucleus with a blunt apex capped by a thin acrosomal complex (showing up to three vesicles). Among the Bivalvia, only Neotrigonia spp. and unionoid sperm possess an acrosomal complex composed of multiple vesicles. These data suggest that the Trigonioidea and Unionoidea are phylogenetically linked, but further work particularly on primitive unionoids is required to determine if this relationship is one of common ancestry or whether the Unionoidea have in fact been derived from the Trigonioidea.

Ultrastructural Analysis of Sperm Head Development inNerita polita(Mollusca: Archaeogastropoda) from the Jordan Gulf of Aqaba (Red Sea)

Summary In early spermatids of Nerita polita small proacrosomal vesicles are formed from a basally located Golgi body. Later, these vesicles fuse into one which invaginates to form a U-shaped structure, into which a cisterna of endoplasmic reticulum fits. The cavity of this vesicle is then lined with an electron dense material. The proacrosomal vesicle becomes tube-like, and starts migrating to the nuclear apex, while the Golgi body remains basal. The final acrosome shape is conical. The nucleus changes from a spherical body with granular material to a compact cylindrical structure enclosing an intranuclear canal. This canal is first plugged with a fibrillar mass, which eventually disintegrates and forms two interrupted double tubes on the nuclear canal interior. The two centrioles observed between Golgi body and nucleus in early spermiogenesis are present at the base of the intranuclear canal in late spermatids. In mature sperm, the centrioles and the axoneme penetrate deep into the intranuclear canal.