Glycoconjugates of the surface of the spermatozoa of Drosophila melanogaster: a qualitative and quantitative study

Lectin binding sites on the plasma membranes of Orthoptera Tettigonioidea spermatodesms

In many Vertebrate and invertebrate, the interaction mechanisms among gametes are based on a high affinity and specificity of recognition and link between specific saccharidic residues and receptors present on the surface of gametes. Literature data also suggest that Insects could use this strategy. In particular, Orthoptera Tettigoniidae spermatodesms and sperms undergo radical changes passing through the male to the female genital tracts that may be interpreted as well as a capacitation process. These changes could also concern the presence and distribution of surface glycoconjugates. Our study aims to highlight the presence and distribution of saccharide residues on the spermatozoa surface in five species of Orthoptera Tettigoniidae using a battery of lectins Fluorescein Isothiocyanate Conjugated and Gold Conjugated. The results of this investigation have shown that on the surface of the male gametes are present saccharide residues whose nature and distribution are species-specific, during their transfer to the female genital tract, they significantly undergo a change. These results let us hypothesize that also for this group of Insects, the glycoconjugates play a significant role in the process of interaction between gametes.

Overview on spermatogenesis and sperm structure of Hexapoda

The main characteristics of the sperm structure of Hexapoda are reported in the review. Data are dealing with the process of spermatogenesis, including the aberrant models giving rise to a reduced number of sperm cells. The sperm heteromorphism and the giant sperm exceeding the usual sperm size for length and width are considered. The characteristics of several components of a typical insect sperm are described: the plasma membrane and its glycocalyx, the nucleus, the centriole region and the centriole adjunct, the accessory bodies, the mitochondrial derivatives and the flagellar axoneme. Finally, a detailed description of the main sperm features of each hexapodan group is given with emphasis on the flagellar components considered to have great importance in phylogenetic considerations. This study may be also useful to those requiring an introduction to hexapod reproduction.

Drosophila spermiogenesis: Big things come from little packages

Drosophila melanogaster spermatids undergo dramatic morphological changes as they differentiate from small round cells approximately 12 μm in diameter into highly polarized, 1.8 mm long, motile sperm capable of participating in fertilization. During spermiogenesis, syncytial cysts of 64 haploid spermatids undergo synchronous differentiation. Numerous changes occur at a subcellular level, including remodeling of existing organelles (mitochondria, nuclei), formation of new organelles (flagellar axonemes, acrosomes), polarization of elongating cysts and plasma membrane addition. At the end of spermatid morphogenesis, organelles, mitochondrial DNA and cytoplasmic components not needed in mature sperm are stripped away in a caspase-dependent process called individualization that results in formation of individual sperm. Here, we review the stages of Drosophila spermiogenesis and examine our current understanding of the cellular and molecular mechanisms involved in shaping male germ cell-specific organelles and forming mature, fertile sperm.

Lectin-binding sites on ejaculated stallion sperm during breeding and non-breeding periods

Stallion sperm from semen collected in Southern Italy during the breeding (June-July) and non-breeding (December-January) periods were analyzed by means of twelve lectins to evaluate the glycoconjugate pattern and to verify whether there are any seasonal differences in the glycosylation pattern of the sperm glycocalyx. The acrosomal cap showed reactivity for Maackia amurensis (MAL II), Sambucus nigra (SNA), Arachis hypogaea (PNA), Glycine max (SBA), Helix pomatia (HPA), Canavalia ensiformis (Con A) Triticum vulgaris (WGA), and Griffonia simplicifolia isolectin II (GSA II) in breeding and non-breeding ejaculated sperm, suggesting the presence of oligosaccharides terminating with Neu5Ac alpha 2,3Gal beta 1,4GlcNAc, Neu5Ac alpha 2,6Gal/GalNAc, with Gal beta 1,3GalNAc, alpha/beta GalNAc and glycans with terminal/internal alpha Man and GlcNAc. During the non-breeding period, the acrosomal cap expressed oligosaccharides terminating with Gal beta 1,4GlcNAc (Ricinus communis(120) affinity) (RCA(120)) and L-Fuc alpha 1,2Gal beta 1,4GlcNAc beta (Ulex europaeus affinity) (UEA I). The equatorial segment placed between the acrosomal cap and post-acrosomal region did not display glycans terminating with GalNAc, GlcNAc, and alpha L-Fuc. The post-acrosomal region of sperm collected in the breeding and non-breeding periods bound Con A, MAL II, SNA, and SBA, thus showing the presence of N-linked oligosaccharides from high-Man content, terminating with Neu5Ac alpha 2,3Gal beta 1,4GlcNAc, Neu5Ac alpha 2,6Gal/GalNAc and GalNAc. In winter, the post-acrosomal region also expressed oligosaccharides terminating with alpha GalNAc, GlcNAc, and L-Fuc alpha 1,2Gal beta 1,4GlcNAc beta (HPA, GSA II, and UEA I staining). The tail of sperm from semen collected during the breeding and non-breeding periods showed a lectin binding pattern similar to the post-acrosomal region, except for the absence of HPA staining in sperm collected during the winter season. These results indicate that the surface of stallion sperm contains different glycocalyx domains and that the glycosylation pattern undergoes changes during the breeding and non-breeding periods.

Spatial and temporal regulation of glycosylation during Drosophila eye development

Glycosylation plays an essential role during development, in processes such as morphogen distribution, cell-to-cell communication, and extracellular matrix formation. Glycosylation is regulated during development in both a spatial and temporal manner. This study presents a detailed description of glycan distribution from late pupal to adult stages in Drosophila ommatidia by using nine different lectins. The lectins ConA, LCA, and DSA, which recognize high-mannose or complex types of N-linked glycans stain both apical and basolateral membranes of photoreceptor cells, whereas SBA, DBA, and ABA lectins, which bind to mucin-type O-glycans, label the inter-rhabdomeral space. The O-linked GlcNAc moiety is strongly labeled by WGA on the nuclear membrane. The localization of these glycans does not change throughout late pupal development. In contrast, the abundance of O-linked glycans, bisected oligosaccharides, and GlcNAc-containing glycans detected by PNA, PHA-E4, and WGA, respectively, is reduced in rhabdomeres and other subcellular domains during late pupal development. Some of these glycans have also been detected in the Golgi and/or putative secretory vesicles, suggesting their dynamic transport during development. These glycans, whose expression is dynamically regulated in a spatial and temporal manner, may therefore play critical roles in ommatidial development.

The Class I PITP Giotto Is Required for Drosophila Cytokinesis

Phosphatidylinositol transfer proteins (PITPs) are highly conserved polypeptides that bind phosphatidylinositol or phosphatidylcholine monomers, facilitating their transfer from one membrane compartment to another . Although PITPs have been implicated in a variety of cellular functions, including lipid-mediated signaling and membrane trafficking, the precise biological roles of most PITPs remain to be elucidated . Here we show for the first time that a class I PITP is involved in cytokinesis. We found that giotto (gio), a Drosophila gene that encodes a class I PITP, serves an essential function required for both mitotic and meiotic cytokinesis. Neuroblasts and spermatocytes from gio mutants both assemble regular actomyosin rings. However, these rings fail to constrict to completion, leading to cytokinesis failures. Moreover, gio mutations cause an abnormal accumulation of Golgi-derived vesicles at the equator of spermatocyte telophases, suggesting that Gio is implicated in membrane-vesicle fusion. Consistent with these results, we found that Gio is enriched at the cleavage furrow, the ER, and the spindle envelope. We propose that Gio mediates transfer of lipid monomers from the ER to the equatorial membrane, causing a specific local enrichment in phosphatidylinositol. This change in membrane composition would ultimately facilitate vesicle fusion, allowing membrane addition to the furrow and/or targeted delivery of proteins required for cytokinesis.

Intraflagellar Transport Is Required in Drosophila to Differentiate Sensory Cilia but Not Sperm

BACKGROUND

Intraflagellar transport (IFT) uses kinesin II to carry a multiprotein particle to the tips of eukaryotic cilia and flagella and a nonaxonemal dynein to return it to the cell body. IFT particle proteins and motors are conserved in ciliated eukaryotes, and IFT-deficient mutants in algae, nematodes, and mammals fail to extend or maintain cilia and flagella, including sensory cilia. In Drosophila, the only ciliated cells are sensory neurons and sperm. no mechanoreceptor potential (nomp) mutations have been isolated that affect the differentiation and function of ciliated sense organs. The nompB gene is here shown to encode an IFT protein. Its mutant phenotypes reveal the consequences of an IFT defect in an insect.

RESULTS

Mechanosensory and olfactory neurons in nompB mutants have missing or defective cilia. nompB encodes the Drosophila homolog of the IFT complex B protein IFT88/Polaris/OSM-5. nompB is expressed in the ciliated sensory neurons, and a functional, tagged NOMPB protein is located in sensory cilia and around basal bodies. Surprisingly, nompB mutant males produce normally elongated, motile sperm. Neuronally restricted expression and male germline mosaic experiments show that nompB-deficient sperm are fully functional in transfer, competition, and fertilization.

CONCLUSIONS

NOMPB, the Drosophila homolog of IFT88, is required for the assembly of sensory cilia but not for the extension or function of the sperm flagellum. Assembly of this extremely long axoneme is therefore independent of IFT.

Membrane specializations in the spermatozoa of collembolan insects

Here we describe the membrane specializations displayed by "dormant" collembolan spermatozoa, during the period when they are temporarily stored in the male genital ducts before being laid in the soil as a spermatophore, which is then picked up by the female. In the male deferent ducts and in the spermatophore, these "dormant" spermatozoa are rolled up into flattened ellipsoids that surround a central extracellular cavity filled with dense material. In this condition, the plasma membranes that surround the central extracellular cavity contain two types of membrane specializations. One consists of parallel rows of intramembrane particles on the E-face of the membrane facing the outside of the spermatozoa. The other consists of small orthogonal plaques of intramembrane particles intermingled with these rows. These plaques associate with the P-face of the membrane, and are therefore likely to represent preferential sites for receiving and transmuting environmental signals, especially whatever signal(s) induce these spermatozoa to transform into filiform and motile cells upon reaching the female spermatheca.

Circadian rhythm of glycoprotein secretion in the vas deferens of the moth, Spodoptera littoralis

BACKGROUND

Reproductive systems of male moths contain circadian clocks, which time the release of sperm bundles from the testis to the upper vas deferens (UVD) and their subsequent transfer from the UVD to the seminal vesicles. Sperm bundles are released from the testis in the evening and are retained in the vas deferens lumen overnight before being transferred to the seminal vesicles. The biological significance of periodic sperm retention in the UVD lumen is not understood. In this study we asked whether there are circadian rhythms in the UVD that are correlated with sperm retention.

RESULTS

We investigated the carbohydrate-rich material present in the UVD wall and lumen during the daily cycle of sperm release using the periodic acid-Shiff reaction (PAS). Males raised in 16:8 light-dark cycles (LD) showed a clear rhythm in the levels of PAS-positive granules in the apical portion of the UVD epithelium. The peak of granule accumulation occurred in the middle of the night and coincided with the maximum presence of sperm bundles in the UVD lumen. These rhythms persisted in constant darkness (DD), indicating that they have circadian nature. They were abolished, however, in constant light (LL) resulting in random patterns of PAS-positive material in the UVD wall. Gel-separation of the UVD homogenates from LD moths followed by detection of carbohydrates on blots revealed daily rhythms in the abundance of specific glycoproteins in the wall and lumen of the UVD.

CONCLUSION

Secretory activity of the vas deferens epithelium is regulated by the circadian clock. Daily rhythms in accumulation and secretion of several glycoproteins are co-ordinated with periodic retention of sperm in the vas deferens lumen.

Nuclear changes and acrosome formation during spermiogenesis in Euchistus heros (Hemiptera: Pentatomidae)

Ultrastructural and cytochemical studies were carried out on nuclear changes and acrosome formation during the spermiogenesis of the phytophagous bug Euchistus heros. The development of the nucleus involves changes in the shape and in degree of chromatin condensation: initially it is dispersed and with a low-electron density, then assumes a fibrillar arrangement and finally compacts in an electron-dense material. The acrosome is formed by the Golgi complex and presents unusual morphological features during its development. The reaction product of acid phosphatase, glucose-6-phosphatase and thiamine pyrophosphatase activities were detected during various stages of acrosome development. In contrast, residues of alpha-N-acetylgalactosamine and basic proteins were only reported in the intermediate and late stages of the differentiation process, respectively.

Inhibition of bovine sperm-oocyte fusion by the carbohydrate GalNAc

The TEC-2 epitope is a carbohydrate located on the plasma membrane (oolemma) of the oocyte and appears to be involved in bovine sperm-oolemma fusion. The carbohydrates N-acetylgalactosamine (GalNAc) and galactose are part of the TEC-2 epitope and this study investigated the involvement of these carbohydrates during bovine fertilization. Gametes were exposed to the carbohydrates GalNAc, galactose, and fructose, and the lectins DBA and Con A to determine whether there was an effect on fertilization. The DBA lectin recognizes the carbohydrate GalNAc, whereas Con A recognizes the carbohydrates glucose and mannose. Oocytes pretreated with the DBA lectin prior to fertilization showed a reduction in cleavage corresponding to an increase in lectin concentrations. There was a significant increase in sperm-oolemma binding although fusion was inhibited. Oocytes exposed to GalNAc prior to sperm insemination had no effect on fertilization, however, sperm pretreatment with the carbohydrate caused inhibition of fertilization, with a reduction in cleavage rates as the GalNAc concentration increased. There was also a significant decrease in sperm-oolemma fusion and a significant increase in sperm-oolemma binding. When gametes were exposed to GalNAc at the time of fertilization a similar response to that seen with sperm pretreatment was observed. The carbohydrates galactose and fructose and the lectin Con A did not affect fertilization. In conclusion, the carbohydrate GalNAc, which is associated with the TEC-2 epitope, has a specific role during bovine sperm-oolemma fusion. This study also suggests that there is a carbohydrate-binding molecule on the sperm that binds GalNAc.

Plasma membrane association and preliminary characterization of Drosophila sperm surface glycosidases

Previous studies have identified beta-N-acetylglucosaminidase (GlcNAc'ase) and (alpha-mannosidase activities on the Drosophila melanogaster sperm surface which may have a role in fertilization. The aim of this study was to investigate their linkage to the sperm plasma membrane. We verified that glycosidases are not peripherally adsorbed to the cell surface by evaluating their resistance to release by KI, by buffered salt solutions of high ionic strength or alkaline buffers. Glycosidases were released from the sperm surface by detergents and, only to a minor extent, by mild proteolysis. Differential detergent solubilization pointed out that Triton X-114 was the most effective releasing agent for GlcNAc'ase and CHAPS for mannosidase. No activity was released from the membrane by a phosphatidylinositol-specific phospholipase C (PI-PLC). The released forms were quite hydrophilic in phase separation experiments with Triton X-114. This finding indicates the presence of a hydrophobic domain limited to a single transmembrane helix or/and the presence of an extensive glycosylation. The use of a Con-A binding assay demonstrated that both the enzymes are glycosylated. The molecular weight of the released glycosidases estimated by gel filtration was 158 kDa for GlcNAc'ase and 317 kDa for mannosidase. These results suggest that Drosophila melanogaster GlcNAc'ase and mannosidase are mannosylated integral membrane proteins that would function as exoenzymes with their active sites accessible in the extracellular space.

Paternal effects in Drosophila: implications for mechanisms of early development

The study of paternal effects on development provides a means to identify sperm-supplied products required for fertilization and the initiation of embryogenesis. This review describes paternal effects on animal development and discusses their implications for the role of the sperm in egg activation, centrosome activity, and biparental inheritance in different animal species. Paternal effects observed in Caenorhabditis elegans and in mammals are briefly reviewed. Emphasis is placed on paternal effects in Drosophila melanogaster. Genetic and cytologic evidence for paternal imprinting on chromosome behavior and gene expression in Drosophila are summarized. These effects are compared to chromosome imprinting that leads to paternal chromosome loss in sciarid and coccid insects and mammalian gametic imprinting that results in differential expression of paternal and maternal loci. The phenotypes caused by several early-acting maternal effect mutations identify specific maternal factors that affect the behavior of paternal components during fertilization and the early embryonic mitotic divisions. In addition, maternal effect defects suggest that two types of regulatory mechanisms coordinate parental components and synchronize their progression through mitosis. Some activities are coordinated by independent responses of parental components to shared regulatory factors, while others require communication between paternal and maternal components. Analyses of the paternal effects mutations sneaky, K81, paternal loss, and Horka have identified paternal products that play a role in mediating the initial response of the sperm to the egg cytoplasm, participation of the male pronucleus in the first mitosis, and stable inheritance of the paternal chromosomes in the early embryo.

Glycosidases are present on the surface of Drosophila melanogaster spermatozoa

We investigated the presence of enzymes on the surface of Drosophila melanogaster spermatozoa that might bind the carbohydrate residues of the egg shell. Spectrophotometric and fluorimetric studies were used on whole spermatozoa to assay galactosyltransferase and glycosidase activities. No galactosyltransferase is present on the sperm surface, whereas two glycosidases, beta-N-acetylglucosaminidase (GlcNAc'ase) and alpha-mannosidase (Man'ase), have been evidenced. They have an optimal pH of 6-6.5 and 4, respectively. The same glycosidases were detected as soluble forms probably secreted by the seminal vesicle epithelium. We suggest that these enzymes might be involved in the recognition of alpha-mannose and beta-N-acetylglucosamine residues present on the egg shell at the site of sperm entry.

Assessment of the acrosome reaction in Bufo arenarum spermatozoa by immunostaining: comparison with other methods

The acrosome reaction in Bufo arenarum spermatozoa has been visualised only by electron microscopy. Different staining procedures for spermatozoa are described in the present study. By light microscopy the acrosomal status cannot be determined. In some reacted sperm, stained with Coomassie blue, a filament that could be the "perforatorium' was observed, as seen by electron microscopy. Several fluorescent lectins were used, but only FITC-PNA binds to acrosomal proteins. However, the fluorescence observed was weak. Indirect immunofluorescence, with antibodies raised against acrosomal matrix, showed different staining patterns between acrosome-reacted and intact spermatozoa. The technique is specific for evaluating acrosomal status in a large population of spermatozoa. Moreover, immunostaining, in contrast with lectin staining, can be carried out in the presence of glycoconjugates such as oocyte extracellular matrix without interference.