Distribution and morphological changes of the Golgi apparatus during Drosophila spermatogenesis

In spermatogenesis, the Golgi apparatus is important for the formation of the acrosome, which is a sperm‐specific organelle essential for fertilization. Comprehensive examinations of the spatiotemporal distribution and morphological characterizations of the Golgi in various cells during spermatogenesis are necessary for functional analyses and mutant screenings in the model eukaryote Drosophila. Here, we examined the distribution and morphology of the Golgi during Drosophila spermatogenesis with immunofluorescence and electron microscopy. In pre‐meiotic germ cells, the Golgi apparatuses were distributed evenly in the cytoplasm. In contrast, they were located exclusively in two regions near the poles during the meiotic metaphase, where they were segregated prior to the chromosomes. In cells in anaphase to telophase, the Golgi were predominantly left behind in the equatorial region between the separating daughter nuclei. After completion of meiosis, the dispersed Golgi were assembled at the apical side of the spermatid nucleus to form the acrosome. Further investigation of the Golgi distribution in β2‐tubulin mutants showed aberrant and uneven distributions of the Golgi among sister cells in the meiotic spermatocytes and in the post‐meiotic spermatids. At the ultrastructural level, the Golgi apparatus in pre‐meiotic spermatocytes comprised a pair of stacks. The two stacks were situated adjacent to each other, as if they had duplicated before entering into meiotic division. These results highlight the dynamic nature of the Golgi during spermatogenesis and provide a framework for analyzing the correlations between the dynamics of the Golgi and its function in sperm development.     

Sperm ultrastructure of the spider crab Maja brachydactyla (Decapoda: Brachyura)

This study describes the morphology of the sperm cell of Maja brachydactyla, with emphasis on localizing actin and tubulin. The spermatozoon of M. brachydactyla is similar in appearance and organization to other brachyuran spermatozoa. The spermatozoon is a globular cell composed of a central acrosome, which is surrounded by a thin layer of cytoplasm and a cup‐shaped nucleus with four radiating lateral arms. The acrosome is a subspheroidal vesicle composed of three concentric zones surrounded by a capsule. The acrosome is apically covered by an operculum. The perforatorium penetrates the center of the acrosome and has granular material partially composed of actin. The cytoplasm contains one centriole in the subacrosomal region. A cytoplasmic ring encircles the acrosome in the subapical region of the cell and contains the structures‐organelles complex (SO‐complex), which is composed of a membrane system, mitochondria with few cristae, and microtubules. In the nucleus, slightly condensed chromatin extends along the lateral arms, in which no microtubules have been observed. Chromatin fibers aggregate in certain areas and are often associated with the SO‐complex. During the acrosomal reaction, the acrosome could provide support for the penetration of the sperm nucleus, the SO‐complex could serve as an anchor point for chromatin, and the lateral arms could play an important role triggering the acrosomal reaction, while slightly decondensed chromatin may be necessary for the deformation of the nucleus. J. Morphol., 2010. © 2009 Wiley‐Liss, Inc.     

Ultrastructural investigations of testes and spermiogenesis in two species of halacarid mites (Halacaridae, Actinedida, Actinotrichida): Thalassarachna basteri from the Baltic Sea and Halacarellus thomasi from McMurdo Sound (Antarctica)

Testes and sperm cells of two species of halacarid mites, Thalassarachna basteri from the Baltic Sea and Halacarellus thomasi from McMurdo Sound (Antarctica), were investigated. Testes are paired structures, composed of a glandular and a germinal part. The testicular lumen is filled with a very complex secretion that contributes to sperm cell aggregates. Early spermatids of T. basteri display unusual chromatin condensation within the nucleus, but the formation of an acrosomal complex with a small acrosomal vesicle and a long acrosomal filament can be regarded as typical for the group. Tubular invaginations of the plasmalemma occur at the cell periphery. A deep, ring-like infold divides the cell into one part containing the chromatin body and another containing mainly the invaginations and the acrosomal complex. The mature sperm cell is ovoid, aflagellate and surrounded by a distinct secretion sheath. In H. thomasi only a limited number of spermiogenesis stages were observable. Chromatin condensation was rather similar and peripheral invaginations also occurred. However, no acrosomal complex was observed in the early stages. The division of the mature sperm cells into two halves was even more pronounced in H. thomasi, since one half of the cell contained masses of convoluted structures. The same half also contained a structure that remotely resembled an acrosomal complex. The observed differences between T. basteri and H. thomasi sperms support the placing of the two halacarids in separate genera.     

Ultrastructural study of spermatogenesis in the free-living marine nematode <Emphasis Type="Italic">Paracyatholaimus pugettensis</Emphasis> Weiser et Hopper, 1967 (Chromadorida: Cyatholaimidae)

Spermatogenesis and the morphology of mature sperm in the free-living chromadorid Paracyatholaimus pugettensis from the Sea of Japan were studied using transmission electron microscopy. In spermatocytes fibrous bodies (FBs) appear; in spermatids, the synthetic apparatus is located in the residual body, whereas the main cell body (MCB) houses the nucleus, mitochondria, and FBs. The nucleus of the spermatid consists of a loose fibrous chromatin that is not surrounded by a nuclear envelope; centrioles lie in the perinuclear cytoplasm. The plasma membrane of the spermatid MCB forms numerous filopodia. Immature spermatozoa from the proximal part of the testis are polygonal cells with a central nucleus. The latter is surrounded by mitochondria and FBs with poorly defined boundaries. The immature spermatozoa bear lamellipodia all along their surface. Mature spermatozoa are polarized cells with an anterior pseudopodium, which is filled with filaments that make up the cytoskeleton; the MCB houses a nucleus that is surrounded by mitochondria and osmiphilic bodies. In many ultrastructural characteristics, the spermatozoa of P. Pugettensis are similar to those of most nematode species studied so far (i.e., they are ameboid, have no acrosome, axoneme, or nuclear envelope). On the other hand, as in other chromadorids, no aberrant membrane organelles were observed during spermatogenesis of P. Pugettensis.Original Russian Text Copyright © 2004 by Biologiya Morya, Zograf, Yushin.     

Ultrastructure of the testes and spermatogenesis in the mite Anystis baccarum

The epithelial lining of testes in Anystis baccarum is glandular and produces a secretory product necessary to form spermatophores. The main stages of spermatogenesis occur in the lumen of the testis in groups of synchronously developing sister cells. Spermatogonia and late spermatids are encircled by glandular cells. Reorganization of developing spermatids is typical of the trombidiform mites and includes formation of the acrosomal complex, cytoplasm elimination, disappearance of the nuclear envelope and formation of invaginations of plasmalemma. The chromatin material condensation is not followed by the entire chromatin body formation. In mature spermatoza, dense chromatin strands (80b nm in diameter) lie along the cell in the peripheral layer of the cytoplasm. Mature spermatozoa lack axonema or any protrusions. A layer of microtubules, visible underneath the outer membrane, may serve for sperm movement in the female genital duct. The acrosomal complex consists of acromal granule, acrosomal filament and subacrosomal substance. This, as well as two aggregates of typical mitochondria, looks plesiomorphic.     

Ultrastructural aspects of spermatogenesis in Calyptogena pacifica Dall 1891 (Vesicomyidae; Bivalvia)

The process of spermatogenesis and spermatozoon morphology was characterized from a deep‐sea bivalve, Calyptogena pacifica (Vesicomyidae, Pliocardiinae), a member of the superfamily Glossoidea, using light and electron microscopy. Spermatogenesis in C. pacifica is generally similar to that in shallow‐water bivalves but, the development of spermatogenic cells in this species has also some distinguishing features. First proacrosomal vesicles are observed in early spermatocytes I. Although, early appearance of proacrosomal vesicles is well known for bivalves, in C. pacifica, these vesicles are associated with electron‐dense material, which is located outside the limiting membrane of the proacrosomal vesicles and disappears in late spermatids. Another feature of spermatogenesis in C. pacifica is the localization of the axoneme and flagellum development. Early spermatogenic cells lack typical flagellum, while in spermatogonia, spermatocytes, and early spermatids, the axoneme is observed in the cytoplasm. In late spermatids, the axoneme is located along the nucleus, and the flagellum is oriented anteriorly. During sperm maturation, the bent flagellum is transformed into the typical posteriorly oriented tail. Spermatozoa of C. pacifica are of ect‐aqua sperm type with a bullet‐like head of about 5.8 μm in length and 1.8 μm in width, consisting of a well‐developed dome‐shaped acrosomal complex, an elongated barrel‐shaped nucleus filled with granular chromatin, and a midpiece with mainly four rounded mitochondria. A comparative analysis has shown a number of common traits in C. pacifica and Neotrapezium sublaevigatum.     

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

Spermatogenic 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.     

Do pygidial secretions of dung beetles have the potential to repel urban pest ants?

Various organisms emit malodorous secretions against competitors, and the potential use of these secretions in pest management should be investigated. For example, some ant species feed on similar resources as dung beetles, which might have led to counter chemical defences in dung beetles. We tested whether pygidial secretions of the dung beetle Canthon smaragdulus (Fabricius) (Coleoptera: Scarabaeidae, Scarabaeinae) alter the locomotor behaviour of the exotic urban pest ant Tapinoma melanocephalum (Fabricius) (Hymenoptera: Formicidae), specifically whether these secretions repel those ants. We also tested whether the disturbance in the locomotor behaviour of T. melanocephalum increases with the amount of pygidial secretion. We found that individual T. melanocephalum displayed changes in their locomotor behaviour when exposed to pygidial secretions of coupled dung beetles, single males, and single females. Additionally, the pygidial secretions from male and female dung beetles could repel ants. The change in the locomotor behaviour of T. melanocephalum increased with the amount of pygidial secretion. Our results suggest that the pygidial secretions of dung beetles have potential as a biological repellent of T. melanocephalum. Hence, pygidial secretions from dung beetles may be used in the future for the development of urban pest management strategies.     

Analysis of gemini pollen 3 mutant suggests a broad function of AUGMIN in microtubule organization during sexual reproduction in Arabidopsis

In flowering plants, male gametes arise via meiosis of diploid pollen mother cells followed by two rounds of mitotic division. Haploid microspores undergo polar nuclear migration and asymmetric division at pollen mitosis I to segregate the male germline, followed by division of the germ cell to generate a pair of sperm cells. We previously reported two gemini pollen (gem) mutants that produced twin‐celled pollen arising from polarity and cytokinesis defects at pollen mitosis I in Arabidopsis. Here, we report an independent mutant, gem3, with a similar division phenotype and severe genetic transmission defects through pollen. Cytological analyses revealed that gem3 disrupts cell division during male meiosis, at pollen mitosis I and during female gametophyte development. We show that gem3 is a hypomorphic allele (aug6‐1) of AUGMIN subunit 6, encoding a conserved component in the augmin complex, which mediates microtubule (MT)‐dependent MT nucleation in acentrosomal cells. We show that MT arrays are disturbed in gem3/aug6‐1 during male meiosis and pollen mitosis I using fluorescent MT‐markers. Our results demonstrate a broad role for the augmin complex in MT organization during sexual reproduction, and highlight gem3/aug6‐1 mutants as a valuable tool for the investigation of augmin‐dependent MT nucleation and dynamics in plant cells.     

A transmission electron microscopy investigation: the membrane complex in spermatogenesis of <Emphasis Type="Italic">Fenneropenaeus chinensis</Emphasis>

The transforming characteristics of the membrane complex in spermatogenesis of Fenneropenaeus chinensis have been studied by using transmission electron microscopy. Two types of membrane complex have been investigated based on their sources: one originating from nucleus and the other from cytoplasm. The first one, consisted of annular structures, monolayer membrane blebs, and double or multi-lamellar membrane vesicles, emerges in the primary spermatocyte, then diffuses with the nuclear membrane and finally enters the cytoplasm. This type of membrane complex seems to play an important role in the materials transfusion from nucleus to cytoplasm, and it mainly exists inside the primary spermatocyte with some inside the secondary spermatocyte. The latter, originated from cytoplasm, is formed during the anaphase of spermiogenesis. It also exists in mature sperm, locating at both sides of the nucleus under the acrosomal cap. This type of membrane complex mainly comprises rings of convoluted membrane pouches, together with mitochondria, annular lamina bodies, fragments of endoplasmic reticulum, nuclear membrane and some nuclear particles. It releases vesicles and particles into the acrosomal area during the formation of the perforatorium, suggesting a combined function of the endoplasmic reticulum, mitochondria and Golgi’s mechanism.     

Ultrastructure of sperm development and mature sperm morphology in three species of commensal bivalves (Mollusca: Galeommatoidea)

Ultrastructural features of the ovotestes, spermatogenesis, and the mature sperm are described for three galeommatid bivalves, Divariscintilla yoyo, Divariscintilla troglodytes, and Scintilla sp., from stomatopod burrows in eastern Florida. All three species yielded similar results except with respect to mature sperm dimensions. The ovotestis contains three types of somatic cells within the testicular portion: flattened myoepithelial cells defining the outer acinal wall; underlying pleomorphic follicle cells containing abundant glycogen deposits; and scattered, amoeboid cells containing lysosomal-like inclusions which are closely associated with developing sperm. Early spermatogenesis is typical of that reported from other bivalves. In contrast, the late stages of spermiogenesis involve the migration and gradual rotation of the acrosomal vesicle, resulting in a mature acrosome tilted about 70° from the long axis of the cell. The mature sperm possesses an elongated, slightly curved nucleus; a subterminal, concave acrosome with a nipple-like central projection; five spherical mitochondria and two centnoles in the middlepiece; and a long flagellum. The rotational asymmetry and the presence of perimitochondrial glycogen deposits in these sperm are unusual in the Bivalvia and may be associated with fertilization specializations and larval brooding common among galeommatoideans.     

Assembly of the fluorescent acrosomal matrix and its fate in fertilization in the water strider,Aquarius remigis

Animal sperm show remarkable diversity in both morphology and molecular composition. Here we provide the first report of intense intrinsic fluorescence in an animal sperm. The sperm from a semi‐aquatic insect, the water strider, Aquarius remigis, contains an intrinsically fluorescent molecule with properties consistent with those of flavin adenine dinucleotide (FAD), which appears first in the acrosomal vesicle of round spermatids and persists in the acrosome throughout spermiogenesis. Fluorescence recovery after photobleaching reveals that the fluorescent molecule exhibits unrestricted mobility in the acrosomal vesicle of round spermatids but is completely immobile in the acrosome of mature sperm. Fluorescence polarization microscopy shows a net alignment of the fluorescent molecules in the acrosome of the mature sperm but not in the acrosomal vesicle of round spermatids. These results suggest that acrosomal molecules are rearranged in the elongating acrosome and FAD is incorporated into the acrosomal matrix during its formation. Further, we followed the fate of the acrosomal matrix in fertilization utilizing the intrinsic fluorescence. The fluorescent acrosomal matrix was observed inside the fertilized egg and remained structurally intact even after gastrulation started. This observation suggests that FAD is not released from the acrosomal matrix during the fertilization process or early development and supports an idea that FAD is involved in the formation of the acrosomal matrix. The intrinsic fluorescence of the A. remigis acrosome will be a useful marker for following spermatogenesis and fertilization. J. Cell. Physiol. 226: 999–1006, 2011. © 2010 Wiley‐Liss, Inc.     

Cellular distribution of secretory pathway markers in the haploid synergid cells of Arabidopsis thaliana

In flowering plants, cell–cell communication plays a key role in reproductive success, as both pollination and fertilization require pathways that regulate interactions between many different cell types. Some of the most critical of these interactions are those between the pollen tube (PT) and the embryo sac, which ensure the delivery of sperm cells required for double fertilization. Synergid cells function to attract the PT through secretion of small peptides and in PT reception via membrane‐bound proteins associated with the endomembrane system and the cell surface. While many synergid‐expressed components regulating PT attraction and reception have been identified, few tools exist to study the localization of membrane‐bound proteins and the components of the endomembrane system in this cell type. In this study, we describe the localization and distribution of seven fluorescent markers that labelled components of the secretory pathway in synergid cells of Arabidopsis thaliana. These markers were used in co‐localization experiments to investigate the subcellular distribution of the two PT reception components LORELEI, a GPI‐anchored surface protein, and NORTIA, a MILDEW RESISTANCE LOCUS O protein, both found within the endomembrane system of the synergid cell. These secretory markers are useful tools for both reproductive and cell biologists, enabling the analysis of membrane‐associated trafficking within a haploid cell actively involved in polar transport.     

Fine structure of the spermatozoon of Marthasterias glacialis (Linnaeus) (Echinodermata; Asteroidea), with special reference to acrosomal morphology

The sperm of Marthasterias glacialis (Linnaeus) was studied by light and electron microscopy. It is a long uniflagellated cell of the “primitive” type. The head has a spherical shape and contains a nucleus with a spheroid acrosome lying in a cup-shaped anterior fossa. The acrosome is formed by an acrosomal vesicle surrounded by the periacrosomal material. The basal specializations of the acrosomal vesicle show a clear differentiation of its constituents resembling the structure of membrane. The midpiece contains a very large annular mitochondrion which encircles two perpendicular centrioles. The distal centriole is in close association with a pericentriolar radial complex. The tail, containing a common microtubular axoneme, is projected to a variable position.     

Sperm storage by spermatodoses in the spermatheca of Trioza alacris (Flor, 1861) hemiptera,psylloidea, triozidae: A structural and ultrastructural study

Female insects generally store sperm received during mating in specific organs of their reproductive tract, i.e., the spermathecae, which keep the sperm alive for a long time until fertilization occurs. We investigated spermatheca morphology and ultrastructure in the psylloidean insect Trioza alacris (Flor, 1861 ) in which spheroidal sperm packets that we refer to as ‘spermatodoses’ are found after mating. The ectoderm‐derived epithelium of the sac‐shaped spermatheca that has a proximal neck, consists of large secretory and flat cuticle‐forming cells. Secretory cells are characterized by a wide extracellular cavity, bordered by microvilli, in which electron‐dense secretion accumulates before discharge into the spermathecal lumen. The cuticle‐forming cells produce the cuticular intima of the organ and a peculiar specialized apical structure, through which secretion flows into the lumen. At mating, the male transfers bundles of sperm cells embedded in seminal fluid into the spermathecal neck. Sperm cells proceed towards the spermathecal sac lumen, where they are progressively compacted and surrounded with an envelope that also encloses secretions of both male and female origin. We describe the formation of these sperm containing structures and document the contribution of the female secretion to spermatodose or female‐determined spermatophore construction. We also discuss the choice of the term ‘spermatodose’ for T. alacris and suggest it be used to refer to sperm masses constructed in the female reproductive organs, at least when they involve the contribution of female secretion. © 2011 Wiley Periodicals, Inc.     

The fine structure of the sperm of a holothurian and an ophiuroid

The fine structure of the mature sperm of the holothurian, Cucumaria miniata, and the ophiuroid, Ophiopholis aculeata, is described with particular reference to their acrosomal and centriolar satellite complexes, and compared to the sperm of other echinoderms. In Cucumaria, the acrosome is in the form of a diffuse acrosomal vesicle. It is unusual in that it apparently lacks an acrosomal membrane. A membrane separating the acrosomal vesicle from the periacrosomal material may not be equivalent to a typical inner acrosomal membrane. In Ophiopholis, the acrosome is dense, with some internal substructure, and is enclosed by a complete acrosomal membrane. In both species, the acrosome is partially surrounded by an amorphous periacrosomal mass. There is a notable absence of a subacrosomal depression and associated structures as found in other echinoderm sperm. The centriolar satellite complex (CSC) is essentially identical in both species. A reconstruction of the CSC is presented. The CSC consists of nine satellites radiating angularly from the distal centriole, each bifurcating at a dense node before inserting on a marginal ring containing circumferential microtubules. The ring is probably a cytoskeletal element. Immediately below the satellites are nine Y-shaped connectives. connecting each of the axonemal alpha doublets to the flagellar membrane.