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.

https://www.tandfonline.com/doi/pdf/10.4161/spmg.21798

Drosophila spermiogenesis: Big things come from little packages

β-N-Acetylhexosaminidase: What's in a name…?

In some animals, such as fish, insects, and cephalopods, the thick egg coat has a narrow canal—a micropyle—through which spermatozoa enter the eggs. In fish, there is no indication that spermatozoa are attracted by eggs from a distance, but once spermatozoa come near the outer opening of the micropyle, they exhibit directed movement toward it, suggesting that a substance exists in this defined region to attract spermatozoa. Since Coomassie Blue (CB) binds preferentially to the micropyle region in flounder, herring, steelhead, and other fish, it probably stains this sperm guidance substance. This substance—a glycoprotein based on lectin staining—is bound tightly to the surface of the chorion, but can be removed readily by protease treatment. Although fertilization in fish (flounder) is possible after removal of this substance, its absence makes fertilization inefficient, as reflected by a drastic reduction in fertilization rate. The sperm “attraction” to the micropyle opening is species specific a...

https://bioone.org/journals/biology-of-reproduction/volume-88/issue-2/biolreprod.112.105072/Sperm-Attractant-in-the-Micropyle-Region-of-Fish-and-Insect/10.1095/biolreprod.112.105072.pdf

Sperm Attractant in the Micropyle Region of Fish and Insect Eggs

Chitin is an abundant extracellular amino-sugar polymer that in association with other external biomacromolecules (carbohydrates, proteins) is an essential structural component in forming cell walls in fungi as well as exoskeletons and peritrophic membranes in arthropods. Chitin synthesis and degradation in insects are cyclical dynamic events, and since being crucial for facilitating growth and development, are strictly coordinated and regulated. Chitin formation and hydrolysis are complex, multi-faceted, interconnected and highly harmonized intracellular and extracellular cascades of biochemical and biophysical transformations. The list of processes, many of which are still poorly understood, include transcriptional, translational and post-translational modifications relative to the catalytic machinery; cellular movement of clustered catalytic units to and their eventual fixed spatial integration into plasma membranes; chitin polymerization and translocation of polymers across the cell membrane barrier; coalescence of nascent external chitin chains forming crystallites that subsequently associate with assorted proteins to form fibrillar supramacromolecular structures. Cloned and sequenced genes encoding the anabolic chitin synthase, and the catabolic chitinase, β- N -acetylglucosaminidase and chitin deacetylase combined with purification and characterization of the expressed enzymes as well as crystallographic and inhibition studies were instrumental in elucidating the intricate mechanisms of catalysis relative to chitin polymerization and degradation. The powerful tools of RNAi knockout methodologies were harnessed for functional analysis of a variety of chitin-related genes. Chitin research carries practical aspect as the physiologically crucial synthesis and hydrolysis of the polymer have been regarded as suitable, attractive and largely selective targets for interference and for producing effective pharmaceuticals and safe biopesticides.

Chitin Biochemistry: Synthesis, Hydrolysis and Inhibition

Structural Determinants of an Insect β-N-Acetyl-d-hexosaminidase Specialized as a Chitinolytic Enzyme

Sperm surface beta-N-acetylhexosaminidases are among the molecules mediating early gamete interactions in invertebrates and vertebrates, including man. The plasma membrane of Drosophila spermatozoa contains two beta-N-acetylhexosaminidases, DmHEXA and DmHEXB, which are required for egg fertilization. Here, we demonstrate that three putative Drosophila melanogaster genes predicted to code for beta-N-acetylhexosaminidases, Hexo1, Hexo2, and fdl, are all expressed in the male germ line. fdl codes for a homolog of the alpha-subunit of the mammalian lysosomal beta-N-acetylhexosaminidase Hex A. Hexo1 and Hexo2 encode two homologs of the beta-subunit of all known beta-N-acetylhexosaminidases, which we have named beta(1) and beta(2), respectively. Immunoblot analysis of sperm proteins indicated that the gene products associate in different heterodimeric combinations forming DmHEXA, with an alphabeta(2) structure, and DmHEXB, with a beta(1)beta(2) structure. Immunofluorescence demonstrated that all the gene products localized to the sperm plasma membrane. Although none of the genes was testis-specific, fdl was highly and preferentially expressed in the testis, whereas Hexo1 and Hexo2 showed broader tissue expression. Enzyme assays carried out on testis and on a variety of somatic tissues corroborated the results of gene expression analysis. These findings for the first time show the in vivo expression in insects of genes encoding beta-N-acetylhexosaminidases, the only molecules so far identified as involved in sperm/egg recognition in this class, whereas in mammals, the organisms where these enzymes have been best studied, only two types of polypeptide chains forming dimeric functional beta-N-acetylhexosaminidases are present in Drosophila three different gene products are available that might generate numerous dimeric isoforms.

/pdf/identification-and-expression-analysis-of-drosophila-26py0owfvu.pdf

F. Cattaneo

Papers

Identification and expression analysis of Drosophila melanogaster genes encoding β-hexosaminidases of the sperm plasma membrane